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The diaspores of Lepidosperma Labill. (Cyperaceae) have thickened perianth members persistent at the base of the fruit, which are generally assumed to form a unique type of elaiosome but this assumption has not been tested rigorously. We tested whether the perianth provides a lipid-rich food reward and improves diaspore removal by ants in three species of Lepidosperma. We measured (i) the lipid and fatty acid composition of the fruit and perianth of two species of Lepidosperma, and of the seed and aril of two species of Acacia (known myrmecochores), (ii) the relative attractiveness to ants of the perianth in three species of Lepidosperma, and (iii) the relative attractiveness to ants of the diaspores of the same species of Lepidosperma compared with the two species of Acacia. We found that (i) Lepidosperma diaspores show traits consistent with myrmecochory, particularly the high lipid content (∼12–60%) and fatty acid profile of perianth material, (ii) isolated perianth members were removed in greater numbers over all times than were diaspores only (i.e. with perianth removed) in two species of Lepidosperma (n = 100, P = 0.035 and 0.047), whereas the difference was equivocal in the third species (n = 100, P > 0.05), and (iii) Lepidosperma and Acacia diaspores were removed in similar numbers over time (n = 100, P > 0.5). Seven species of diaspore-removing ant were observed, with Rhytidoponera metallica accounting for ∼50% of observed removals. We conclude that the perianth members of Lepidosperma are an elaiosome that provides a lipid-rich food reward.

In order to study the relationships between mistletoes and their host species, comprehensive collections of both mistletoes and hosts are needed. The effect of sampling effort on the estimation of mistletoe host range was demonstrated in a comparison of an inventory of host mistletoe interactions published by Downey in 1998 and a 2019 inventory presented here, which is based on data from collections in the Australian Virtual Herbarium and information in the literature. New hosts were recorded for 93% of the 90 Australian mistletoes. There were 338 previously known hosts recorded to be parasitised by additional mistletoe species, and 317 new host species that were not previously known as mistletoe hosts (25 being alien species). These were from 78 new host genera and 13 new host families. The total number of host species was 1186 within 327 genera from 92 host families. A total of 63% of all Australian mistletoes parasitise species of either Eucalyptus or Acacia or both these genera. The large rise in host species recorded in less than two decades between inventories suggests that current knowledge of hosts is still incomplete, such that further new hosts will be discovered in future. Some mistletoe species show a strong preference to one host family or genus but due to insufficient collecting it is premature to conclude that any of the three species known from a single host are host specific.

In arid Australia, fires in different seasons often result in markedly different recruitment rates of woody plants, and this can have important and long-lasting impacts on post-fire community structure and composition. The current study investigated ecological mechanisms behind this effect in four widespread arid Acacia species: Acacia aptaneura, Maslin & J.E.Reid Acacia kempeana F.Muell., Acacia maitlandii F.Muell. and Acacia melleodora Pedley. Specifically, the study examined whether increased recruitment after summer compared with winter burning relates to (1) higher soil temperatures during summer fires having increased capacity to overcome dormancy of seeds with heat-stimulated germination; (2) warmer soil temperature conditions after summer fires providing more favourable incubation temperatures for germination; and/or (3) summer fires coinciding with seasonal fluxes in seedbank densities, which may occur in response to granivory and/or rapid rates of seed deterioration after dispersal. Results supported hypotheses (1) and (2), as germination of all species responded positively to heat shock and warmer incubation temperatures. Some support was also demonstrated for hypothesis (3), as seedbank densities were shown to fluctuate seasonally, most likely in response to strong granivory. This multi-species study provides insights into mechanisms behind enhanced shrub recruitment after arid zone summer fires; and reinforces the notion that season of burn can be a strong determinant of regeneration trajectories of woody plants after fire.

Acacia s. str. (Mimosoideae, Fabaceae) is the largest plant genus in Australia (~1000 species). Its seeds have physical dormancy from a hard, water-impermeable testa. Heat from fire (natural systems) and hot water (nursery production) can break this dormancy. It is often reported that these treatments ‘soften’ or ‘crack’ the seed coat, but in practice they only affect a minute part of the seed coat, the lens. We examined lens structure in a wide range of Acacia species to determine what diversity of testa and lens structure was present, if there were differing responses to a hot water dormancy breaking treatment and if there were structural differences between soft- and hard-seeded species. Seed morphology, testa and lens structure were examined before and after hot water treatment (~90°C for one minute), in 51 species of Australian Acacia from all seven sections, from all states and territories of Australia and from a wide range of environments. Five of the species had been noted to produce non-dormant seed (‘soft-seeded’ species). Average seed mass per species ranged from 3.1 to 257.9 mg (overall average 24.2 mg, median 13.8 mg). Almost all species had a relatively thick seed coat (average 132.2 µm) with well-developed palisade cells (average 41.5 µm long) and a lens which ‘popped’ in response to hot water treatment. For 44 species ranging in average seed mass from 3.1 to 43.9 mg (×14 range), the unpopped lens area only ranged ×3 (11480–36040 µm2). The lens was small (in 88% of species the average length of the unpopped lens was

Knowledge of xylem vessel length is important for several reasons, including the accurate calculation and comparison of hydraulic conductivity studies in excised stems. Vessel length data and distributions are also relevant in some anatomical, ecological, evolutionary, pathological and compatible hydraulic studies. However, determining vessel length is tedious, so is often either avoided or undertaken arbitrarily in hydraulic conductivity studies. We examined four injection media (paints and inks) under transmission electron microscopy to ascertain which was most suitable for determining vessel length. Hunt’s Speedball India ink, with evenly distributed, uniform spherical carbon particles of 33 nm, would avoid premature vessel blockage and, therefore, coupled with the fact that it is non-toxic, is the preferred medium to determine vessel length in Acacia amoena Wendl. terminal stems. The longest vessel was 10 cm, which accounted for 0.4% of vessels. Vessel length distributions were then determined and compared using the same dataset and four established methods. All four methods produced distributions which indicated that the most common vessel length class was short (0–2 cm), and no method was significantly different from the other; however, for ease of calculation, the Christman et al. (2009) method is recommended. Whether vessel length or distribution is necessary for hydraulic-conductivity studies will depend on whether or not merely indicative rates of flow are required, but to provide comparative information for global datasets, then they are needed.

Phytostabilisation with native plant species has been advocated as a cost-effective approach to rehabilitate mine tailings containing phytotoxic metal-bearing minerals. For this purpose, five Acacia species (natural colonisers) native to north-west Queensland region of Australia were investigated for metal uptake and root exudation characteristics in response to growth for 3 weeks in three different mine tailings (Cu and Cu-Pb-Zn) differing in their degree of weathering. Root tissues of the plant species grown in the three types of tailings accumulated up to 0.9 mg Cd kg–1, 10 mg Co kg–1, 177 mg Cu kg–1, 38 mg Pb kg–1 and 4800 mg Zn kg–1 (DW basis) – being suitable for phytostabilisation purposes. However, elevated levels of root exudates in rhizosphere tailings enhanced the bioavailability of metals, leading to the accumulation of high levels of some metals in Acacia shoots (e.g. shoot concentrations of 140 mg Zn kg–1 in Acacia acradenia F.Muell. and 230 mg Zn kg–1 in Acacia hilliana Maiden). Positive correlations (P

Short duration dry heat shock similar to the heat of fire is known to be effective in alleviating physical dormancy in seeds, but are we underestimating the impact of the cumulative heat dose of summer soil temperatures on dormancy loss in hard-seeded species in the context of a changing climate? This study investigated short and long duration dry heat treatments in seeds of four Acacia species (Fabaceae) from South-West Western Australia. Seeds were treated at 90, 100, 110 and 120°C for 10 and 180 min (‘fire’) and at fluctuating temperatures of 30/20, 55/20, 65/20°C for 14, 28, 56 and 112 days (‘summer’). The non-dormant seed fraction of each species was low, but seeds were highly viable after scarification. The results indicate the presence of species-specific temperature thresholds for dormancy loss with duration of heating slightly less important than temperature for dormancy break. Seeds remained highly viable after all long duration treatments but short duration heat shock treatments above 110°C resulted in increased seed mortality. Although cumulative periods of lower fluctuating temperatures were less effective in breaking physical dormancy than the heat of fire in three of the four species, more than 40% of seeds of Acacia nigricans (Labill.) R.Br. lost dormancy after 28 days at 65/20°C. These potentially disturbing findings suggest that long hot summer conditions may compromise soil seed bank longevity over time and may be detrimental to the bet-hedging ability afforded by a hard seed coat in some species in the face of climate warming forecasts for the region.

Mineral-sands mining in the semiarid and arid zone of south-eastern Australia is now a widespread disturbance that may adversely affect large areas of remnant vegetation, including mallee (Eucalyptus spp.) with hummock grass or spinifex (Triodia scariosa) understorey. No broad-scale restoration projects have been undertaken to revegetate mallee Eucalyptus species with spinifex. We report on the survivorship and relative importance (spatial coverage) of hand-planted tubestock 10 years after establishment in 2001, which included mallee Eucalyptus, Triodia scariosa, Acacia spp. and Hakea spp. These taxa are the dominant plants in a semiarid dune–swale system on a former mineral-sands mine licence area in semiarid, north-western Victoria. Mean survivorship of tubestock was 0.58 ± 0.04. Spinifex (Triodia scariosa), needlewood (Hakea) and several mallee species (Eucalyptus spp.) survived substantially better than the average of all tubestock-planted species, although Acacia spp. had low survivorships. Although the plantings were undertaken in the early stages of the most severe drought in the instrumental record (the ‘Millennium drought’), several taxa survived well and species such as spinifex established and developed ground coverage greater than the benchmark values for the ecological vegetation class of the location. We conclude that hand-planting of tubestock can achieve restoration objectives for this component of spinifex–mallee vegetation, even under extremely arduous conditions associated with long-term drought. We also herald the importance of taking a long-term view to the assessment of revegetation success, in this case 10 years.

Dry eucalypt forests are believed to be highly fire tolerant, but their response to fire is not well quantified. We measured the effect of high-severity fires in dry eucalypt forest in the Tasmanian Midlands, the driest region on the island. We compared stand structures and fuel loads in long-unburnt (>15 years since fire) and recently burnt (

As part of a program to breed sterile triploid varieties of tropical Acacia, a series of inter-and intra-specific crosses were made among clones of neo-tetraploid A. mangium (AM-4x) and diploid A. mangium (AM-2x) and A. auriculiformis (AA-2x). The present paper reports variation in seed-crop development from anthesis to harvest, in comparison with that after open pollination of the respective parent trees. Abscission of spikes and pods within spikes commenced soon after anthesis and was more rapid in inter-cytotype crosses than in open-pollinated controls. Less than 12% of spikes were retained to maturity in either cytotype, emphasising the likely importance of resource competition during development. Inter-cytotype crosses showed higher levels of abnormal ovule development at 7 weeks after pollination and more undeveloped seeds in those pods which did develop to maturity. No inter-cytotype combination produced more than one viable seed per pod on average, and all needed to be germinated in vitro to survive. A directional effect was apparent in the inter-cytotype crosses within AM but this was not obvious when the cross was inter-specific. The study contributes new knowledge of the post-anthesis timeline for ovule, pod and spike abscission and discusses the likely genetic and environmental causes of observed differences between inter-and intra-cytotype crosses as well as the implications for breeding.

The reproductive biology of exotic species affects their capacity to become naturalised and invasive in non-native areas. Selfing is a common trait in many invasive plants probably because it provides reproductive assurance under low availability of pollination vectors and sexual partners. Nonetheless, the predominantly self-incompatible Australian Acacia species are among the most aggressive plants worldwide. To address whether there have been changes in selfing ability and natural reproductive success of A. longifolia during invasion, we compared one population in the invaded area (Portugal) with one population in the native range (Australia). We specifically assessed floral traits, fruit set and offspring traits for selfing and open-pollination treatments. Within each pollination treatment, no differences were found between areas, suggesting that the level of self-compatibility has not changed during invasion. However, the number of aborted seeds and seed size were significantly different between pollination treatments in Australia but not in Portugal. There were significant differences in the number of seeds per pod and in seed weight between ranges. A lower number of aborted seeds, a higher number of fully developed seeds and a greater seed size were found in the invaded area for both pollination treatments. In spite of the low selfing ability of A. longifolia in the invaded area, there was an increase in the quantity and size of the seeds produced in the new region, even for self-pollinated fruits, which might contribute to A. longifolia invasiveness.

Invasion of grass weeds is a major threat for ecosystems. Mission grass (Cenchrus pedicellatus and C. polystachios) vigorously competes with native vegetation and has become a serious problem in northern Australian savanna. A lower density of mission grass has been observed under the canopy of stands of native Acacia holosericea. We used a series of laboratory and shade house experiments to assess the potential for allelopathy and the role of litter on germination, emergence and seedling growth of these two species of mission grass. Different concentrations of aqueous leaf extract of A. holosericea were used to assess allelopathic effects on germination. Various depths and types of litter were used to investigate the allelopathic and physical effects of litter on emergence and growth of mission grass seedlings in the shade house. Results indicate that extracts did not affect germination of either species of mission grass but root growth of seedlings was affected. Emergence of seedlings in the shade house was affected by physical litter treatments but not by allelopathy. After emergence no negative effects on seedling growth were detected. Overall we found that there was no allelopathic effect on germination and that the negative effect on emergence was due to the physical properties of the litter. This effect on emergence increased with increasing depth of litter. Allelopathy slightly inhibited root growth but once seedlings emerged, litter tended to facilitate growth. This has implications for the ecological management of mission grass on disturbed lands, using strategies such as manipulation of litter cover through Acacia establishment.

Acacia s.s. comprises approximately 1020 species (i.e. just under one-third of all mimosoid legumes) and is almost entirely restricted to, although widespread, on the Australian continent. We investigated variation in the wood anatomy of 12 species from temperate New South Wales in a study concentrating on four recognised taxonomic sections (Botrycephalae, Juliflorae, Phyllodineae and Plurinerves), to elucidate which characteristics are consistent within the sections, having removed climatic effect as much as possible. The sections had great utility in species identification, whereas none of the wood characters reflected the hypothesised phylogeny of the genus. The main consistent difference among species was in ray width (uniseriate versus 1–3 cells wide). All species had distinct growth rings. The vessels had alternate vestured pitting and simple perforation plates. Fibres were generally thick-walled, and many fibres had a gelatinous inner wall (tension wood fibres) and were inconsistently distributed. Axial parenchyma was mainly paratracheal, ranging from vasicentric to confluent and varied greatly in abundance. Prismatic crystals were usually present in chambered fibres and axial parenchyma strands, and also varied in abundance. The variation in these qualitative characters obscures taxonomic differences, but may allow inferences to be made about environmental adaptation.

The ubiquitous and highly diverse element Australian Acacia makes an ideal candidate for investigating a range of questions about the evolution of the flora of continental Australia. In the past, such efforts have been hampered by a lack of well-supported phylogenies and by the relatively poor macrofossil record, which probably reflects the depositional environment in which Acacia species are predominantly found. However, the broader subfamily Mimosoideae offers several reliably age-constrained fossils that can be used as calibrations in divergence-dating analyses of DNA sequence data. In addition, the microfossil pollen record of Acacia is relatively rich and provides a good age constraint for the entire Acacia clade. By using multiple reliable fossil constraints, we applied a combination of primary calibration points to produce a comprehensive study of divergence dates in Acacia s.s. and related mimosoid legumes. Previous dating studies included very limited samples of the diversity of Australian Acacia and experienced difficulties in identifying appropriate age calibrations for the lineage, leading to considerable variation in their results. We used novel calibration schemes and multiple nuclear and chloroplast DNA sequence markers to produce the first estimates of divergence dates for major lineages within the Australian Acacia s.s. clade and for related lineages across the Mimosoideae subfamily. We estimate average crown divergence dates for Vachellia at 13–17 Ma, Senegalia at 31.0–33.4 Ma and Acacia s.s. at 21.0–23.9 Ma. The timing of radiations within these lineages is consistent with the hypothesis that Miocene aridification in Africa, the Americas and Australia was a driver for the diversificationss of lineages in Acacia s.l.

Acacia, with over 1000 species, is the largest plant genus in Australia and is distributed throughout most of the continent. This work investigates seed mass and seedling phyllotaxy development in 287 species of this genus to better understand these important ecological and taxonomic traits. Seed mass varied over 100-fold with an average mass of 17.9 (range 2.1–308) mg per seed. Two common forms of seedling phyllotaxy were seen. The most common seedling development type displayed a pinnate first leaf with an alternate, bipinnate second leaf (pinnate : bipinnate). In the less common form, the first two leaves were pinnate and opposite each other (pinnate : pinnate). When compared with the phylogenetic tree of Acacia, the pinnate : pinnate state is more commonly resolved in taxa found at the basal nodes of the tree, but not exclusively. Overall, species with heavier seeds have more seedling leaflet pairs and pinnules. However, it was also found that the pinnate : bipinnate seedlings had more first leaf leaflet pairs than the pinnate : pinnate form. The pinnate : pinnate plants had an identical number of leaflet pairs on their first and second leaves. The number of leaflet pairs on the first leaf was highly correlated with the number of pinnules on a leaflet of the second leaf on the pinnate : bipinnate form. We discuss the phyllotactic variation within the Acacia phylogenetic context and possible developmental processes.

The aim of this study is to identify and map the spatial distribution of species richness and endemism of the genus Acacia in Australia. A database of 171 758 geo-referenced herbarium records representing 1020 Acacia species was assembled and aggregated to a 0.25° grid cell resolution. A neighbourhood analysis of one-cell radius was applied to each of the grid cells to map the spatial patterns of species richness and endemism. The primary centres of species richness are in accordance with previous results, occurring in the South-West Botanical Province in Western Australia, the MacPherson-Macleay overlap and the Central Coast of the Sydney Sandstone region. We identify 21 centres of endemism, of which six were previously unrecognised. The primary centres of endemism are located in South-West Western Australia, the Kimberley District and the Wet Tropics in Queensland. The South-West Botanical Province in Western Australia contained the greatest number of regions with the highest number of endemic species of Acacia. A randomisation test showed that our 21 centres of endemism were significantly different from random. The majority of centres of Acacia endemism were incongruent with the centres of species richness, with only three grid cells in the top 1% for both measures. We also confirm that South-West Western Australia is a region of very high species richness and endemism, in accordance with its status as a global hotspot of biodiversity.

The mulga complex (Acacia aneura F. Muell ex Benth and closely related species) consists of woody trees and shrubs, and is distributed across 20% of the Australian continent. A. aneura is renowned for a wide variety of phyllode shapes and growth forms, which may co-occur at any one site. We examined the intra- and inter-specific variation in growth form and phyllode shape in four species of the mulga complex, including A. aneura, across topographic gradients in semiarid north-west Australia. We measured 792 trees across 28 sites stratified into six discrete landscape positions; upper slope, lower slope, low open woodland, banded woodland, low woodland, and drainage line. Dominance of phyllode shapes was strongly related to landscape position. A. aneura with terete phyllodes were dominant on the hill slopes, whereas broad phyllodes were most common on A. aneura in all valley woodlands. Trends in growth form were less distinct, although single-stemmed forms were more common on hills, whereas the valleys had more multi-stemmed forms. The quantification of growth form and phyllode shape variability within the mulga complex provides a basis for the quantitative determination of functional links between morphology and environmental conditions at both the site and landscape level.

The persistence of relatively fire-sensitive mulga (Acacia aneura F.Muell. ex Benth., Mimosaceae) shrublands within a landscape matrix of highly flammable spinifex (Triodia spp. R.Br., Poaceae) hummock grassland is a central question in the ecology of semiarid Australia. It is also a special case of questions about the coexistence of grasses and woody plants that have general application in semiarid rangelands and tropical savannas. With the use of field surveys and a 24-year fire history, we examined their coexistence on a sandplain in the Tanami Desert, Northern Territory, Australia. Mulga and spinifex each formed discrete monodominant stands with generally abrupt boundaries that did not correspond to obvious edaphic or topographic discontinuities. Spinifex hummock grasslands burnt almost three times as often as mulga shrublands and tended to occur on lighter soils with less biological crusting and more physical soil crusting. A combination of fire and soil variables described the environmental partitioning better than did either alone. Biological crusting increased with time since fire in both vegetation types. The demographic structure of mulga stands reflected their fire history, the more frequently burnt stands comprising almost entirely small plants. One fifth of mulga plants

Acacia melanoxylon (Mimosoideae or Mimosaceae) is a high quality timber tree with an extensive natural distribution in Australia and a wide genetic and phenotypic diversity. Seeds from three widely differing provenances in Tasmania were tested to determine whether they had different responses to various dormancy-breaking treatments. All provenances had limited germination (

Nutrient cycling in mixed-species plant communities may be enhanced in comparison to what might be expected from the component species. In this study, we investigated (1) whether the admixing of nitrogen-rich litter from Acacia mearnsii can accelerate the decomposition of Eucalyptus globulus leaf litter and (2) whether eucalypt litter originating from mixed stands with acacias decomposes faster than litter from pure eucalypt stands. To address the first question, pure and mixed litter was incubated in the laboratory for 110 days at 25°C in the following proportions: 100%E, 75%E : 25%A, 50%E : 50%A, 25%E : 75%A and 100%A, where %E and %A refers to the proportion of eucalypt and acacia in the microcosms, respectively. Since mass loss and N loss of litter in the 50 : 50 mixture was higher than for pure eucalypt but not higher than for acacia, it appears that acacia litter accelerated decomposition of eucalypt litter but not vice versa. Decomposition rates increased with N concentration in the combined litters up to 1.1% N, above that point it remained constant. To address the second question, eucalypt litter from pure and mixed stands was incubated in microcosms. The loss of mass, N and P after 110 days was not different for eucalypt litter originating from mixed (75E : 25A, 50E : 50A, 25E : 75A) and pure (100E) plantations. Together, these studies suggest that admixture of A. mearnsii to E. globulus has the potential to accelerate decomposition and N cycling, and that the species interactions are most pronounced in the 50 : 50 mixture. Mixing of the two species in plantations has so far had no influence on the decomposability of eucalypt litter.

Land clearing in Queensland is often practised to enhance pasture production, and hence, increase financial returns from beef production. The benefits of clearing have been quantified in terms of short-term gains in pasture yield but have not adequately accounted for possible medium- or longer-term impediments that may be attributed to clearing. Therefore, impacts of clearing and the subsequent sowing of exotic grasses such as Cenchrus ciliaris L. on pasture composition and production were studied. To achieve this, paired sites were selected representing cleared and uncleared pastures across three different times since clearing (i.e. 5, 11–13 and 33 years since clearing) for the three dominant tree communities of central Queensland (i.e. Eucalyptus populnea F.Muell. (poplar box), E. melanophloia F.Muell. (silver-leaved ironbark) and Acacia harpophylla F.Muell. ex. Benth. (brigalow)). The results demonstrated that species diversity declined with clearing and sowing of exotic pastures. Species diversity and pasture production were negatively related. Although pasture yield was 2–3 times greater 13 years after clearing of E. populnea and A. harpohylla, the gains in pasture yield were not consistent over time, yields being only 1.5 times greater after 33 years of clearing. In E. melanophloia, an increase in the yield of only 1.5–1.8 times occurred 5 years after clearing compared with uncleared pastures, whereas 33 years after clearing, yield was 3/4 of that in uncleared pastures. The initial gains in pasture yield were accompanied by a loss of plant diversity that may affect ecosystem functions such as nutrient cycling or soil mineralisation, and the longer-term production gains.

In a glasshouse experiment, we used the shrub Grevillea speciosa to examine the reliability of estimating the depth of seed burial based on the distance from the soil surface to the junction of the swollen hypocotyl with the radicle. We then examined the applicability of the technique in the field by using post-fire seedling emergence. We found that the mean length of the swollen hypocotyl in seedlings was a good predictor of the depth of seed burial (R2 = 0.97). Most variation occurred for seeds buried near the surface at 2-cm depth, where the swollen hypocotyl overestimated the depth of seed burial by about 1 cm. There was a decline in the ability of seeds to successfully emerge from soil depths below 2 cm, with seedlings of G. speciosa able to emerge from soil depths up to 8 cm in the glasshouse. This corresponds with the estimated maximum emergence depth based on seed mass. In the field, seedlings were estimated to have emerged from depths of 1–7 cm after an intense wildfire. There was an approximately normal distribution of seedling emergence depths; however, the mode of this distribution varied among locations. The technique gave comparable results to a similar technique developed for Acacia spp., allowing consideration of a greater range of species and post-fire locations. Use of the technique has the potential to provide insights into the impacts of fires below ground, including the nature of post-fire germination, residual soil seed banks, the depth-related action of fire-induced germination cues and small-scale spatial variation.

Five Acacia species native to Western Australia were assessed for their potential to protect the highly susceptible species Banksia grandis Wield from infection by the plant pathogen Phytophthora cinnamomi Rands. In a rehabilitated bauxite pit at Jarrahdale 55 km south-east of Perth and in a glasshouse trial, B. grandis planted either alone or with A. pulchella R.Br., A. urophylla Benth., A. extensa Lindl., A. lateriticola Maslin or A. drummondii Lindl., was soil inoculated with P. cinnamomi. It could only be shown that A. pulchella significantly protected B. grandis from P. cinnamomi infection in the rehabilitated bauxite pit trial up to 1 year after inoculation. This confirms the potential of this species for biological control of the pathogen in infested plant communities. The observed protection was not the result of a decrease in soil temperature or moisture. Protection was not emulated in a glasshouse trial where optimum environmental conditions favoured P. cinnamomi. Despite a delay in infection of B. grandis planted with Acacia spp., none of the five species definitively protected B. grandis from P. cinnamomi. However, in the glasshouse trial, A. pulchella, A. extensa, A. lateriticola and A. drummondii did significantly reduce the soil inoculum of P. cinnamomi, indicating a possible biological control effect on the pathogen. The mechanisms of biological control are discussed and the implications for management of rehabilitated bauxite mined areas and forests severely affected by P. cinnamomi are considered.

The leaf properties and construction costs (CC) are reported for eight indigenous heath (kerangas) forest species and three invasive (exotic) species of Acacia. Both groups of species co-occur and colonise disturbed lowland tropical heath rainforest habitats in Brunei, Borneo Island. Across species, CC mass-based increased with nitrogen (N) and heat of combustion (H C ), and decreased with ash content. CC area-based showed similar trends (although weaker in strength) in addition to significant positive correlation with leaf mass per unit area (LMA). Within the native species, the CCs of the shrub and small tree species were lower and significantly different from those of medium-sized tree species. Given the invasive success of the three acacias, it is hypothesised that these species may require less energy for biomass construction than do the native species. Within similar life growth form, no difference in CC mass-based was detected between the native trees and the invasive acacias. For CC area-based, the invasive Acacia species had a higher value. These findings failed to uphold our hypothesis. LMA and leaf N and phosphorus (P), but not potassium (K), were higher in the invasive acacias. The higher N and LMA could have been the cause of higher CC area-based in the invasive acacias. From the ordination of 11 species on the basis of leaf properties, the invasive and native species are more likely to be found in different groupings—although some native species seem more affiliated with the invasive than with their own guild, especially Alphitonia and Macaranga. BT04 Lea io iv ic e O. O. Os et al

With over 960 species, Acacia is the largest genus of plants in Australia with all but nine of these species classified as subgenus Phyllodineae. DNA sequences for the chloroplast trnK region were sequenced for over 100 species to test sectional classification and survey species relationships within this subgenus. Only one of the seven recognised sections was found to be monophyletic; however, the close relationship of sect. Botrycephalae to certain racemose, uninerved species of sect. Phyllodineae is confirmed. Support is found for an expanded version of Vassal's Pulchelloidea, with the addition of sect. Lycopodiifoliae and several members of sect. Phyllodineae. These species, while morphologically distinct in adult foliage, possess similar seedling characteristics. The multinerved species are unresolved, indicating a rapid morphological radiation with little chloroplast sequence divergence among these species. The low levels of sequence divergence, large numbers of morphological species groups and the adaptive radiation of the group are discussed.

Acacia mangium seedlings were grown and nodulated with selected elite strains of Bradyrhizobium spp. under aeroponic conditions. The aeroponics system is well known for furnishing a very rich air environment around the roots and has been shown in our earlier work to induce rapid growth and enhance performance of Acacia seedlings under greenhouse conditions. This paper reports that the positive effects on growth, such as increased height and leaf area, induced by aeroponic culture with the Bradyrhizobium strains, Tel 2 from Malaysia and Aust 13c from Australia, continued to be sustained for 4 months after plants were transferred to field conditions. Random sampling and analyses of Bradyrhizobia by polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) also showed that Aust 13c continued to persist in root nodules of inocualated plants in the field, with inoculated plants having significantly higher nitrogen and phosphorus concentrations as well as higher photosynthetic rates than non-inoculated controls. The A. mangium plants were only 8 months old from germination but had already reached mean heights of approximately 2.4 m. The results suggest that aeroponic growth and nodulation should be further investigated for their potential to promote growth of A. mangium, especially on difficult soils.

Acacia axillaris Benth. had been recommended for downgrading from a conservation status of vulnerable to one of rare in response to changed knowledge of its distribution. Ecological investigations of its phytosociology, stand structure, germination requirements, soil seed store and response to fire and disturbance indicate, however, that it is susceptible to elimination by fire regimes that allow the survival of most of its co-occurring species and most other Australian species of Acacia. The species is also vulnerable to land clearance and weed competition in the lowland part of its range, which is largely on private land.A. axillaris may be a refugial species, better suited to glacial Tasmania than to interglacial Tasmania. On ecological evidence, the species should retain its conservation status of vulnerable to extinction.

Preferential clearance of productive Acacia-dominated ecosystems was determined using digital land-system mapping and a 1994–1995 native vegetation remnant coverage from central Queensland. The previously mapped land systems are composed of complexes of land units, covering a range of productive potentials that are not individually mapped but defined according to their proportions within the land systems. Some land units were grouped into 11 ‘Acacia ecosystems’ composed of unique combinations of geology and vegetation dominated by brigalow (Acacia harpophylla F.Muell. ex Benth.), gidgee (A. cambagei R.T.Baker) or blackwood (A. argyrodendron Domin). Calculation of the remnant area of these Acacia ecosystems, assuming equal proportions of vegetation clearance of the land unit components within the land-system complexes (equal proportion calculation), was compared with a more accurate calculation based on interpretation of aerial photography (aerial-photograph calculation) data. The aerial photograph calculation of remnant area was 44% of the equal proportion calculation for brigalow on Tertiary clay and the ratio between these calculations was greater than 100% for only one Acacia ecosystem of relatively low production potential. The proportion of the remnant Acacia ecosystems relative to less productive ecosystems on tenures assigned to production (leasehold and freehold) was consistently lower than on other tenures. The use of mapping consisting of composite ecosystems with various production potentials for area-based assessment of vegetation clearance will overestimate the remnant areas of the relatively productive types unless a procedure such as that outlined here is used to correct for preferential clearance. This study provides near-complete and accurate data on the 1994–1995 status of Acacia ecosystems in central Queensland. Relative to their original area, values ranged from 6.8% for brigalow on Tertiary clay to 37.6% for gidgee–blackwood on alluvium.

Four species of tropical tree (Acacia auriculiformis Cunn. ex Benth., A. mangium Willd., A. crassicarpa Cunn. ex Benth. and Eucalyptus pellita F.Muell.) were studied at a site on Melville Island, off the north coast of the Northern Territory of Australia, in the wet–dry tropics. Rates of light-saturated assimilation were measured every 2 months, in the morning and afternoon, concurrently with gs (stomatal conductance) and microclimate (air temperature, relative humidity and photosynthetic photon flux density). Phyllodes were also sampled for subsequent nitrogen determination. Pre-dawn and diurnal phyllode water potentials were measured at the end of the wet and dry seasons. Tree height and canopy area were recorded at the end of 50 months of growth. Assimilation was found to decline substantially in the afternoon compared with the morning in the dry season but not the wet season. This was not due to diurnal declines in phyllode water potential but was attributed partially to decreased gs resulting from increased leaf-to-air vapour pressure difference. However, an interpretation of the Ci/Ca (ratio of intenal to ambient CO2 concentrations) data suggested that additional factors, other than gs, may be involved in causing the afternoon decline in assimilation rate. There was a linear relationship between pre-dawn water potential and Amax (maximum assimilation) and an inverse relationship between Amax and tree height, a result attributed to differences between species in allocation of carbon within the tree.

Somatic chromosome numbers were reported for 47 accessions of Acacia (Tourn.) Miller, representing 23 species including A. albida (syn. Faidherbia albida), together with 19 accessions (11 species) of Prosopis (L.) Burkart. Microphotographs of somatic metaphases of 12 accessions and six representative idiograms are shown. Somatic numbers of different accessions of a species can be different. Somatic numbers of accessions of subgenus Acacia were predominantly 52; a few had 2n = 78 or 104. However, A. sieberana had 2n = 26 and A. nubica 2n = 56. Except for A. polycantha, which had 2n = 52, somatic numbers of subgenus Aculeiferum were invariably 26. Of the six species of subgenus Heterophyllum studied, five had 26 somatic chromosomes and one (A. holoceraceae) had 52. All the four accessions of A. albida had 2n = 26. Out of the 19 Prosopis accessions investigated, five had 56 somatic chromosomes and 14 accessions had 28. In Acacia, subgeneric and specific differentiations are probably caused by structural changes in the chromosomes, whereas differences in the degree of euploidy appear to create infraspecies. Subgenus Aculeiferum is a possible progenitor of all other taxa of Acacia and Prosopis. The study suggests that Prosopis has diverged later in geological times from a diploid ancestor (2n = 26) of Aculeiferum through centric fission of the second-largest chromosome pair.

Phytophthora cinnamomi Rands was isolated from either dead plants or soil at 46 disease centres in Banksia woodland at national parks and reserves on the Swan Coastal Plain. Phytophthora cryptogea Pethybridge & Lafferty was also isolated from roots of dead Acacia pulchella R.Br. in one disease centre infected with P. cinnamomi. Dead plants were infected with Armillaria luteobubalina Watling & Kile in four disease centres on the Spearwood Dune System, and these centres were excluded from further analysis. Phytophthora cinnamomi diseased areas ranged from 0.01 to 30 ha in size (mean 1.6 ± s.e. 0.7 ha). The total area infested for the 46 disease centres was 71.5 ha. Impact of P. cinnamomi was high in 17% of disease centres and low in 11% of disease centres. Age of plant death was a mixture of old and recent in 85% of disease centres. Mainly old deaths occurred in only 4% of disease centres. The proportion of species dying in infested areas varied between 10-64% (mean 28 ± s.e. 2%) and was positively correlated with impact type. It was found that infestation decreased species number; on average, there were seven fewer species in infested compared to non-infested areas. Four plant species associated with moist sandy sites tended to occur more frequently in centres of high impact than by chance alone. Occurrence of P. cinnamomi was related to soil association with soils of 60% of the disease centres belonging to the Bassendean or Southern River associations of the Bassendean Dune System. Sixteen percent of disease centres occurred in the Cannington, Guildford and Serpentine River associations of the Pinjarra Plain. No disease centres of P. cinnamomi were found on soils of the Speanvood and Quindalup Dune Systems. A water table was found within 3 m of the soil surface in 48% of the centres. Disturbance was associated with all disease centres. Firebreaks were associated with 72% of disease centres. Banksia woodland remnants on the Bassendean Dune System and the Pinjarra Plain are highly vulnerable to infection by P. cinnamomi and their conservation requires control of existing infestatinns and protection from introduction af the pathogen.

Forty-seven species native to Tasmania were tested for their susceptibility to Phytophthora cinnamomi. Plants were propagated from cuttings and or seed. The plants were root inoculated by irrigating the moist growing medium with infected broth. Individuals in 36 species proved to be susceptible, four species were resistant hosts, three species resistant and four species returned inconclusive results. Epacris contained the most suceptible species and the level of susceptibility varied considerably within the Epacris, but also in Acacia and Pultenaea. Species from a number of genera contained an apparently resistant element.

Germination responses to multiple conditions related to fire, temperature and light were examined and interpreted in relation to the environment of the jarrah (Eucalyptus marginata Donn ex Sm.) forest and the mediterranean-type climate of south-western Western Australia. Eight of the 16 selected representatives required a boiling pre-treatment as a simulation of fire before subsequent germination conditions were imposed. Trial conditions included a range of constant incubation temperatures and either a constant dark or 12h light:12h dark illumination cycle. Species common to the understorey tended to have narrow optima to temperature (13-18°C) with the greatest germination being achieved in temperatures typical of winter. Eucalyptus calophylla, one of the canopy species, germinated over a wider range of temperatures than the understorey species tested. Several species (e.g. Acacia pulchella var. glaberrima, Calothamnus rupestris, Eucalyptus marginata, Trymalium ledifolium, Xanthorrhoea gracilis and X. preissii) were not affected by the different light conditions at lower incubation temperatures, but more seeds remained dormant under higher temperatures when exposed to light. Most species, however, germinated best under continuously dark conditions, which related to being buried under soil. Two species, Banksia grandis and Hakea amplexicaulis, showed much higher germination under light exposure conditions compared to continuously dark conditions. These two serotinous species are large seeded and their seed ecology favours large gap and soil surface establishment. The multiple requirements of particular combinations of fire, temperature and light are related to the ecology of these native Western Australian species.

Pollen of Acacia auriculifornzis, A. iteaphylla, A. karroo and A. mangium was stored at 25, 5, -18 or -196"C, for up to three years, and its viability tested by pollen staining, in vivo pollen tube growth or by pod set one month after hand pollination. The effectiveness of staining methods using 2,3, 5-triphenyltetrazolium chloride (TTC), 5-bromo-4-chloro-3-indole-P-galactoside (X-Gal) and fluorescein diacetate (FDA) to predict pollen viability was investigated. All of the staining methods gave variable results, but the TTC and X-Gal tests were found to be particularly unreliable. FDA staining of pollen gave the best indication of its ability to germinate on the stigma and penetrate ovules. Pollen stored for up to three days at 25OC retained the ability to penetrate ovules following hand pollination, and of that stored for three years at 5OC, 19% of the grains fluoresced with FDA. Pollen stored at -lg°C for one year retained the ability to penetrate ovules and produce pod set, and of that stored for three years 23% of the grains fluoresced with FDA. Pollen stored at -196OC for one year retained the ability to penetrate ovules and produce pod set, but thawing and refreezing of the pollen reduced viability to zero. It was concluded that the most successful and convenient method of pollen storage was vacuum drying followed by storage at -lg°C. The Australian species of Acacia investigated, A. iteaplzylla, A. auriculifornzis and A. marzgiunz, all had protogynous flowers, with stigma receptivity preceding anther dehiscence, such that flowers could be reliably hand pollinated. The African species A. karroo had protandrous flowers, with stigmas unreceptive at anthesis, but receptive at 5 days after anther dehiscence. Deposition of self pollen on the stigma prior to attainment of receptivity rendered hand pollination of this species unreliable.

Leaf (xylem) water potentials were measured in summer and autumn on four species, Eucalyptus fasciculosa, Pultenaea daphnoides, Platylobium obtusangulum and Acacia myrtifolia growing in the understorey of sclerophyll stringybark vegetation in the Mt Lofty Ranges, South Australia. Plants regenerating in an area burnt by bushfire 2 years previously were compared with plants in an adjacent unburnt area. The Acacia was killed by fire and subsequently regenerated from seed. The other three species survived and resprouted from basal or epicormic buds. It was expected that shrubs regenerating from basal buds would be better hydrated in summer, as a large intact root system would supply a reduced canopy, and that seedlings, with smaller root systems than unburnt adults, would be more stressed. The Acacia was indeed significantly more stressed during summer in the burnt area. However the Platylobium was also more stressed than the controls, while the Pultenaea showed no significant differences between burnt and control areas. The Eucalyptus showed no differences between sites, nor between any of the three sampling times. The more negative water potentials of some of the regenerating plants are explained by greater exposure of surface soil on the burnt site, leading to more rapid drying of the surface soil in summer.

The phyllodes of Acacia harpophylla (brigalow) possess a high reflectivity (0.20) in the visible wavelengths due to the presence of a dense covering of flattened trichomes. This results in a low value for phyllode absorptivity (0.79). While dry phyllodes appear grey-blue to the eye, wet phyllodes appear green and their reflection spectra are similar to those of 'typical' foliage elements. When wet, reflectivity in the visible wavelengths is reduced (0.09) and absorptivity is increased by 14%. Examination of the wetting and drying process, both visually and by measuring the time course of reflectivity, illustrates the importance of the wettable surfaces of both the epidermis and the individual trichomes. On drying, the reflectivity increase in the near infrared (NIR, 0.41-0.59) precedes that in the visible portion of the spectrum, although changes in the visible portion of the spectrum are larger than those in the NIR.

In the Sydney region, many plants from populations on windswept headlands have a more prostrate growth habit compared with plants from populations of the same species occurring away from the coast. To determine whether these different growth habits are genetically determined, plants from four populations of each of five species (Acacia rnyrtifolia, Acacia suaveolens, Banksia ericifolia, Casuarina distyla, Hakea teretifolia) were grown under uniform glasshouse conditions. Multivariate analyses of six morphological characteristics indicate that, for four of these species, the offspring are similar to their maternal parent; we thus conclude that the habit differences are genetically fixed in these populations. The same trend is apparent for

Phyllodes of species of Acacia from the sections Julflorae, Plurinerves, Lycopodiifoliae and Phyllodineae are described in respect of the disposition of the stomates relative to the phyllode surface, size of the substomatal cavities, outline of the phyllode as seen in transverse section, and disposition of the smaller vascular bundles. The first three of these characters are shown to be related to stickiness and the third and fourth to the relative humidity or aridity of the environment. The geographical distribution of sticky species in central and eastern Australia is determined. Sticky species occur throughout the region but are commoner in the more arid interior than in the more humid coastal regions. No relationship is apparent between stickiness and membership of the sections.

Ten taxa of Acacia were selected from areas of moderate to high soil salinity (electrical conductivities of saturated soil paste extracts (ECe) between 1000 mS m--1 and 4800 mS m-1 at 50-600 mm depth) and sodicity to test the tolerance of young, symbiotic plants to increasing levels of salinity both with and without waterlogging. Nodulated plants, 3 months old, were grown in glasshouse experiments which consisted of four treatments: non-saline drained control (12 weeks); saline drained (12 weeks); non-saline waterlogged (5 weeks); and saline waterlogged (5 weeks). Acacia cyclops, A. brumalis, A. redolens (Ravensthorpe) and A. aff. lineolata had 100% survival after 12 weeks irrigation with saline solution (final ECw = 9500 mS m-1). Generally, the species tested were sensitive to waterlogging with A. patagiata, A. cyclops and A. brumalis being the most sensitive, having 19-44% mortality with no salt in the solution. The combined treatment of salt and waterlogging greatly increased the mortality of plants, with four species having > 70% dead after 5 weeks treatment (ECw = 3900 mS m-1). A. aff. lineolata and A. mutabilis subsp. ,stipulifera were highly tolerant of salt plus waterlogging, with 100% and 96% survival respectively. In salt plus waterlogged treatments, Na+ concentration in phyllodes of all taxa exceeded (0.37-2.13 mmol g-1 dry wt) that taken up by plants in freely drained salt treatments (0.03-0.42 mmol g-1 dry wt). Taxa with the slowest rates of growth tended to accumulate the highest concentrations of Na+ in the uppermost phyllodes. Provenances of A. redolens and A. patagiata collected from sites of high soil salinity (ECe > 2200 mS m-1) had less than half the Na+ concentration in uppermost phyllodes (0.22 mmol -1 dry wt) at the termination of the salt treatment, compared with provenances of the same species collected from moderately saline areas (ECe = 1100 mS m-1). This indicates that Acacia provenances collected from the most saline sites had greater potential to survive high levels of external salinity in the longer term than those from less saline sites.

Previous studies have shown that various Eucalyptus species can yield allelopathic chemicals which may be effective in suppressing understorey vegetation. However, the techniques employed in many studies do not resemble natural ecological processes. This study used germination of Lolium and growth of Lolium, Lemna, Eucalyptus and Acacia to test for allelopathy. Extraction techniques mimicked typical daily rainfall rates upon quantities of foliage, leaf litter and bark litter that are typically encountered in forests; root leachates were obtained hydroponically; stemflow was obtained following rainfall; soils were leached with water; and volatiles from leaves were studied in an enclosed chamber. Fresh intact leaves caused little growth suppression, in contrast to coarsely chopped leaves and extracted leaf essential oils which were both highly suppressive. Whole leaf litter, shed bark and, especially, stemflow yielded suppressive leachates. Evaporative concentration of leachates in soils was demonstrated, which increased their inhibitory effect. It is apparent that allelopathy must be considered in relation to rainfall and the soil water balance. Decay was shown to reduce the allelopathic effects of leaf and bark litter leachates but some inhibitory chemicals remained after 5 months. It was concluded that allelopathy is likely to be a cause of understorey suppression by Eucalyptus species especially in drier climates.