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Karyotype evolution in cycads has been described in 113 species covering all the 10 genera. Cycads are a conservative group in this regard as the genera with low basic numbers i.e. Dioon, Macrozamia, Lepidozamia, Encephalartos, Bowenia (2n = 18) and Ceratozamia and Stangeria (2n = 16) have relatively symmetrical karyotypes while those with higher numbers i.e. Cycas (2n = 22) and Microcycas (2n = 26) have more asymmetric karyotypes. The situation in Zamia is more complicated with different species showing a range of chromosome numbers of 2n = 16–28 while some species even show intraspecific variation. The increase or decrease in number as seen in some Zamia species has occurred mainly by chromosomal fission/fusion. Some variability is however, seen in chromosome banding as well as the position of rDNA loci. The phylogenetic relationships between the genera have been discussed on the basis of karyotype evolution.

The literature containing which chemical elements are found in cycad leaves was reviewed to determine the range in values of concentrations reported for essential and beneficial elements. We found 46 of the 358 described cycad species had at least one element reported to date. The only genus that was missing from the data was Microcycas. Many of the species reports contained concentrations of one to several macronutrients and no other elements. The cycad leaves contained greater nitrogen and phosphorus concentrations than the reported means for plants throughout the world. Magnesium was identified as the macronutrient that has been least studied. Only 14 of the species were represented by data from in situ locations, with most of the data obtained from managed plants in botanic gardens. Leaf element concentrations were influenced by biotic factors such as plant size, leaf age, and leaflet position on the rachis. Leaf element concentrations were influenced by environmental factors such as incident light and soil nutrient concentrations within the root zone. These influential factors were missing from many of the reports, rendering the results ambiguous and comparisons among studies difficult. Future research should include the addition of more taxa, more in situ locations, the influence of season, and the influence of herbivory to more fully understand leaf nutrition for cycads.

Cycadales is an extant group of seed plants occurring in subtropical and tropical regions comprising putatively three families and 10 genera. At least one complete plastid genome sequence has been reported for all of the 10 genera except Microcycas, making it an ideal plant group to conduct comprehensive plastome comparisons at the genus level. This article reports for the first time the plastid genome of Microcycas calocoma. The plastid genome has a length of 165,688 bp with 134 annotated genes including 86 protein-coding genes, 47 non-coding RNA genes (39 tRNA and eight rRNA) and one pseudogene. Using global sequence variation analysis, the results showed that all cycad genomes share highly similar genomic profiles indicating significant slow evolution and little variation. However, identity matrices coinciding with the inverted repeat regions showed fewer similarities indicating that higher polymorphic events occur at those sites. Conserved non-coding regions also appear to be more divergent whereas variations in the exons were less discernible indicating that the latter comprises more conserved sequences. Phylogenetic analysis using 81 concatenated protein-coding genes of chloroplast (cp) genomes, obtained using maximum likelihood and Bayesian inference with high support values (>70% ML and = 1.0 BPP), confirms that Microcycas is closest to Zamia and forms a monophyletic clade with Ceratozamia and Stangeria. While Stangeria joined the Neotropical cycads Ceratozamia, Zamia and Microcyas, Bowenia grouped with the Southern Hemisphere cycads Encephalartos, Lepidozamia and Macrozamia. All Cycas species formed a distinct clade separated from the other genera. Dioon, on the other hand, was outlying from the rest of Zamiaceae encompassing two major clades—the Southern Hemisphere cycads and the Neotropical cycads. Analysis of the whole cp genomes in phylogeny also supports that the previously recognized family—Stangeriaceae—which contained Bowenia and Stangeria, is not monophyletic. Thus, the cp genome topology obtained in our study is congruent with other molecular phylogenies recognizing only a two-family classification (Cycadaceae and Zamiaceae) within extant Cycadales.

Funding for this work was provided by a University of Washington Royalty Research Fund Grant (R.B.), National Science Foundation Graduate Research Fellowship DGE‐1256082 (M.A.K.), and German Research Foundation (DFG) Fellowship GE2558/3‐1 (M.M.G). Cyanobiont collection was funded by grant no. 265‐605 of the Australian Biodiversity and Resources Programme (M.M.G). Molecular nitrogen (N2) constitutes the majority of Earth's modern atmosphere, contributing ~0.79 bar of partial pressure (pN2). However, fluctuations in pN2 may have occurred on 107–109 year timescales in Earth's past, perhaps altering the isotopic composition of atmospheric nitrogen. Here, we explore an archive that may record the isotopic composition of atmospheric N2 in deep time: the foliage of cycads. Cycads are ancient gymnosperms that host symbiotic N2‐fixing cyanobacteria in modified root structures known as coralloid roots. All extant species of cycads are known to host symbionts, suggesting that this N2‐fixing capacity is perhaps ancestral, reaching back to the early history of cycads in the late Paleozoic. Therefore, if the process of microbial N2 fixation records the δ15N value of atmospheric N2 in cycad foliage, the fossil record of cycads may provide an archive of atmospheric δ15N values. To explore this potential proxy, we conducted a survey of wild cycads growing in a range of modern environments to determine whether cycad foliage reliably records the isotopic composition of atmospheric N2. We find that neither biological nor environmental factors significantly influence the δ15N values of cycad foliage, suggesting that they provide a reasonably robust record of the δ15N of atmospheric N2. Application of this proxy to the record of carbonaceous cycad fossils may not only help to constrain changes in atmospheric nitrogen isotope ratios since the late Paleozoic, but also could shed light on the antiquity of the N2‐fixing symbiosis between cycads and cyanobacteria. Postprint

The presence of small depressions on stone tools found in various parts of Australia has frequently been assumed to be the consequence of bipolar knapping. In contrast, Pardoe et al. (2019) and Attenbrow and Kononenko (2019) proposed that these attributes derive from their use for nut cracking. To test this hypothesis, we conducted experiments using the hammer and anvil technique to crack Macrozamia seeds and macadamia nuts for prolonged periods. The use-wear traces that developed on the experimental tools were found to compare favourably with those on a sample of 11 ground-edged hatchets from the Central Coast, New South Wales. Our results suggest that the consumption of seeds and nuts in pre-contact Aboriginal diets in south eastern Australia might have been more significant than currently recognised and should be investigated further.

The cycads pose classic problems in evolutionary biogeography, owing to their far-flung extant distributions and the sparse fossil records of living genera. A noteworthy example is Tribe Encephalarteae of Family Zamiaceae, today consisting of Encephalartos (Africa) and the Australian genera Lepidozamia and Macrozamia. Numerous petrified trunks of Encephalarteae described from the Cretaceous of Patagonia, Antarctica, and India indicate far larger past distributions across Gondwana and subsequent extinctions. The only fossils close to the current range are Paleogene leaf fragments from Australia assigned to Lepidozamia and Macrozamia. Here, we report a large frond piece and several isolated leaflets of a compressed cycad, along with an associated spiny petiole, from the late-Gondwanan, 52.2 Ma Laguna del Hunco flora of Patagonia, Argentina. Austrozamia stockeyi gen. et sp. nov., has the novel combination of an Encephalartos-type leaf and Lepidozamia-type cuticle. The Australian Lepidozamia fossils, widely used for molecular clock calibrations, could also represent an extinct genus. Austrozamia stockeyi demonstrates survival of the Encephalarteae in Patagonia and presumably across Gondwana until its terminal phase, adding a striking new component to the growing list of South American plant extinctions associated with Antarctic separation and related climate changes.

The association of an armoured scale insect (a diaspidid) with dieback of a population of a native cycad (Macrozamia communis L.A.S.Johnson) was investigated on the south coast of New South Wales. The diaspidid was found to be undescribed but morphologically similar to oleander scale – here we call it Aspidiotus cf. nerii. It is probably native to Australasia and its current known distribution is within Murramarang National Park (MNP). Aspidiotus cf. nerii has been abundant on symptomatic M. communis at MNP over at least the past decade and has spread to new parts of the park. In population studies of infested and uninfested areas we found that, although both areas had populations with reverse J curves showing dominance of seedlings, mortality of seedlings and caulescent plants was significantly higher in infested sites. Infested areas had been burnt less frequently than uninfested areas. Fire does not appear to eradicate the diaspidid but may reduce its effects enough for plants to recover. We recommend further research into the use of fire as a management tool. Although other factors may be contributing to the severity of the dieback, we suggest there is sufficient evidence for the diaspidid to be regarded as the primary cause of dieback in M. communis in MNP, regardless of its origin. Given the occurrence of similar diaspidids on cultivated plants in botanic gardens, translocation of threatened Macrozamia species using plants grown in nurseries should be undertaken with extreme caution.

Obligate pollination mutualisms are rare and few have been investigated deeply. This paper focuses on one such mutualism involving thrips in the genus Cycadothrips that pollinate cycads in the genus Macrozamia. Both represent old lineages relative to insects and plants generally, are endemic to Australia, and are mutually co-dependent. The phylogenetic analyses presented here demonstrate that the pollinator is much more diverse than previously considered, with each pollinator lineage being extremely specific to between one and three host species where these latter share part of their distribution. The new species diversity we demonstrate in Cycadothrips all presently falls under the species name C. chadwicki, and these different lineages diversified during two periods. An older divergence, beginning 7.3 Mya (4.4–11.1, 95% HPD), resulted in three major lineages, and then further diversification within each of these three lineages took place at most 1.1 Mya (0.6–1.8, 95% HPD). These divergence estimates correspond to times when aridification was increasing in Australia, suggesting that population fragmentation following climatic change has played a significant role in the evolutionary history of Cycadothrips and Macrozamia. This means that co-diversification of the host and pollinator in allopatry appears to be the dominant process affecting species diversity. Host switching is also clearly evident in the discrepancy between the divergence times of the C. chadwicki lineage and C. albrechti, about 10.8 Mya (6.0–17.1, 95% HPD), and their hosts, at about 1.1 Mya (0.2–3.4 Mya, 95% HPD), in that the pollinator split pre-dates the origin of the associated host species of each. These results add to the body of evidence that the evolutionary processes important in obligate pollinator mutualisms are more varied than previously assumed.

The geographical distribution and life history of insects and their host plants determines when, and if, they will interact. The vast majority of herbivorous insects are host-plant specialists and their narrow host range limits their distribution and may also restrict gene flow between their populations. Generalist insect herbivores, by contrast, might be expected to have much higher gene flow across populations because the distribution of multiple host plant species is likely to be much more contiguous. Species distributions shift continually, so with enough time the populations of a specialist insect species should experience more events that fracture their distribution because of the changing distribution of their relatively fewer hosts. The changing distribution of insects and their host plants is thus important for mediating host-plant interactions and will also influence how and when adaptation to a host plant, or subset of host plants, occurs. To investigate the influence of geography and host breadth on gene flow, and thus speciation, I explore the evolutionary history and population genetic structure of two herbivorous insects with different host plant relationships, the generalist bug Nezara viridula (Pentatomidae, Hemiptera), a global pest species, and the specialist thrips Cycadothrips chadwicki (Aeolothripidae, Thysanoptera), the pollinator in a brood-site mutualism with Macrozamia cycads. The results from these systems were then integrated with other similar data sets from phytophagous insects to understand better how gene flow and host specificity relate to one another, and to examine the role each has played (and may still play) in the evolution of insect-plant interactions more generally. The pest bug N. viridula has two globally distributed mitochondrial lineages, the Asian (mtDNA lineage A) and the European (mtDNA lineage E), and the species status of these lineages has not been resolved. In Australia, I found that both of these N. viridula mitochondrial lineages were present. Microsatellite data show two genetically and geographically distinct populations, but these did not correspond directly to the two mitochondrial lineages. Together, mtDNA and microsatellite data shown that secondary contact has occurred in eastern Australia between the two lineages and has resulted in introgression of mtDNA lineage A into predominantly mtDNA lineage E populations in a narrow area, but without widespread introgression across the nuclear genome. Past research on this insect suggested that these lineages represented a single species because these mtDNA haplotypes were found together in single populations. The evidence presented here indicates that mating between lineages can occur, but that an analysis of mtDNA alone is not enough to understand the evolutionary history of these insects. Further, spatial and temporal genetics analyses of eastern Australian populations of N. viridula show that they do not differ genetically across different host plants. Most host plants this insect feeds on in Australia have a narrower distribution than that of N. viridula and so gene flow is maintained between populations of N. viridula even in areas where most of its host plants are unavailable. Even substantial changes in the distribution of a number of potential host plants may not impact the population genetic structure of this insect significantly. The Australian endemic thrips C. chadwicki is shown here to be a complex of at least five species, with some having diverged from one another about six Mya and others less than one Mya. Each thrips species is associated with a different subset of Macrozamia cycad species, with each found only on one or two Macrozamia species. One of these Cycadothrips species, C. chadwicki sp. 4, is found in southern Queensland where it is associated with M. lucida and M. macleayi. Population genetics analysis of this thrips across its geographic distribution shows high amounts of gene flow between populations, but also some weak spatial genetic structure. For C. chadwicki, more generally, these results support the presence of a species complex as no gene flow occurs over even short geographic distances between putative species in the C. chadwicki complex, even though a high amount of gene flow is observed within the single species C. chadwicki sp. 4. Geography appears important for speciation in Cycadothrips and Macrozamia, and so the conditions that lead to speciation may be the product of rare events that isolate both thrips and cycad populations. How much gene flow occurs between populations of Macrozamia, relative to the amount of gene flow among the associated Cycadothrips populations, requires further resolution. The evolutionary history and population genetic structure of N. viridula and C. chadwicki fit with the general predictions of this study. An analysis of the population genetics literature involving phytophagous insects suggests that these results are consistent also for other herbivorous insect species, with relatively specialised phytophagous insects having lower amounts of gene flow between their populations. The approach developed in this thesis, as well as the insights from the study of N. viridula and C. chadwicki, will help understand the role that host breadth and geography play in the evolution of herbivorous insects.

†Background and aims Despite a recent new classification, a stable phylogeny for the cycads has been elusive, particularly regarding resolution of Bowenia, Stangeria and Dioon. In this study, five single-copy nuclear genes (SCNGs) are applied to the phylogeny of the order Cycadales. The specific aim is to evaluate several gene tree ‐ species tree reconciliation approaches for developing an accurate phylogeny of the order, to contrast them with concatenated parsimony analysis and to resolve the erstwhile problematic phylogenetic position of these three genera. †Methods DNA sequences of five SCNGs were obtained for 20 cycad species representing all ten genera of Cycadales. These were analysed with parsimony, maximum likelihood (ML) and three Bayesian methods of gene tree ‐species tree reconciliation, using Cycas as the outgroup. A calibrated date estimation was developed with Bayesian methods, and biogeographic analysis was also conducted. †Key Results Concatenated parsimony, ML and three species tree inference methods resolve exactly the same tree topology with high support at most nodes. Dioon and Bowenia are the first and second branches of Cycadales after Cycas, respectively, followed by an encephalartoid clade (Macrozamia ‐Lepidozamia‐Encephalartos), which is sister to a zamioid clade, of which Ceratozamia is the first branch, and in which Stangeria is sister to Microcycas and Zamia. †Conclusions A single, well-supported phylogenetic hypothesis of the generic relationships of the Cycadales is presented. However, massive extinction events inferred from the fossil record that eliminated broader ancestral distributions within Zamiaceae compromise accurate optimization of ancestral biogeographical areas for that hypothesis. While major lineages of Cycadales are ancient, crown ages of all modern genera are no older than 12 million years, supporting a recent hypothesis of mostly Miocene radiations. This phylogeny can contribute to an accurate infrafamilial classification of Zamiaceae.

Several cycad species in the genus Macrozamia are threatened by habitat loss, fragmentation and pollinator loss including at least 11 that rely on the thrips Cycadothrips chadwicki for pollination and therefore their continued survival. We developed 18 highly polymorphic microsatellite markers (mean alleles per locus = 11.1) by 454 shotgun sequencing and present primer options for an additional 14,219 loci.

Changes in the potential habitat of five allopatric species of threatened Macrozamia cycads under scenarios of increased ambient temperature were examined. A lack of seed dispersal, poor recruitment, low seedling survival, obligate pollinator mutualisms and continued habitat loss have led to extant populations being largely restricted to refugia. Models predict that the area of suitable habitat will further contract and move upslope, resulting in a reduced incidence within protected areas with increasing annual mean temperature. Areas of potential habitat for all five species are also predicted to become increasingly isolated from one another, further reducing the exchange between metapopulations and subpopulations, exacerbating existing threatening processes.

A mathematical model based on conservation of energy has been developed and used to simulate the temperature responses of cones of the Australian cycads Macrozamia lucida and Macrozamia. macleayi during their daily thermogenic cycle. These cones generate diel midday thermogenic temperature increases as large as 12 °C above ambient during their approximately two week pollination period. The cone temperature response model is shown to accurately predict the cones' temperatures over multiple days as based on simulations of experimental results from 28 thermogenic events from 3 different cones, each simulated for either 9 or 10 sequential days. The verified model is then used as the foundation of a new, parameter estimation based technique (termed inverse calorimetry) that estimates the cones' daily metabolic heating rates from temperature measurements alone. The inverse calorimetry technique's predictions of the major features of the cones' thermogenic metabolism compare favorably with the estimates from conventional respirometry (indirect calorimetry). Because the new technique uses only temperature measurements, and does not require measurements of oxygen consumption, it provides a simple, inexpensive and portable complement to conventional respirometry for estimating metabolic heating rates. It thus provides an additional tool to facilitate field and laboratory investigations of the bio-physics of thermogenic plants.

The nitrogen-fixing bacterium, Nostoc, is a commonly occurring cyanobacterium often found in symbiotic associations. We investigated the potential of cycad cyanobacterial endosymbionts to synthesize microcystin/nodularin. Endosymbiont DNA was screened for the aminotransferase domain of the toxin biosynthesis gene clusters. Five endosymbionts carrying the gene were screened for bioactivity. Extracts of two isolates inhibited protein phosphatase 2A and were further analyzed using electrospray ionization mass spectrometry (ESI-MS)/MS. Nostoc sp. 'Macrozamia riedlei 65.1' and Nostoc sp. 'Macrozamia serpentina 73.1' both contained nodularin. High performance liquid chromatography (HPLC) HESI-MS/MS analysis confirmed the presence of nodularin at 9.55±2.4 ng μg-1 chlorophyll a in Nostoc sp. 'Macrozamia riedlei 65.1' and 12.5±8.4 ng μg-1 Chl a in Nostoc sp. 'Macrozamia serpentina 73.1' extracts. Further scans indicated the presence of the rare isoform [L-Har(2)] nodularin, which contains L-homoarginine instead of L-arginine. Nodularin was also present at 1.34±0.74 ng ml(-1) (approximately 3 pmol per g plant ww) in the methanol root extracts of M. riedlei MZ65, while the presence of [L-Har(2)] nodularin in the roots of M. serpentina MZ73 was suggested by HPLC HESI-MS/MS analysis. The ndaA-B and ndaF genomic regions were sequenced to confirm the presence of the hybrid polyketide/non-ribosomal gene cluster. A seven amino-acid insertion into the NdaA-C1 domain of N. spumigena NSOR10 protein was observed in all endosymbiont-derived sequences, suggesting the transfer of the nda cluster from N. spumigena to terrestrial Nostoc species. This study demonstrates the synthesis of nodularin and [L-Har(2)] nodularin in a non-Nodularia species and the production of cyanobacterial hepatotoxin by a symbiont in planta.

Does the diversity of cyanobacteria in the cycad rhizosphere relate to the cyanobiont species found in the coralloid roots of these ancient plants? The aim of this study was to identify the diversity of soil cyanobacteria occurring in the immediate vicinity of 22 colonized coralloid roots belonging to members of the cycad genera: Macrozamia, Lepidozamia, Bowenia and Cycas. The majority of coralloid roots were sampled at depths > 10 cm below the soil surface. A total of 32 cyanobacterial isolates were cultured and their 16S rRNA gene partially sequenced. Phylogenetic analysis revealed nine operational taxonomic units of soil cyanobacteria comprising 30 Nostoc spp., a Tolypothrix sp. and a Leptolyngbya sp. Microscopy indicated that all isolates were unialgal and confirmed their genus identity. Rhizospheric diversity was compared to existing data on cyanobionts isolated at the same time from the cycad coralloid root. The same isolate was present in both the cycad coralloid root and rhizosphere at only six sites. Phylogenetic evidence indicates that most rhizosphere isolates were distinct from root cyanobionts. This weak relationship between the soil cyanobacteria and cycad cyanobionts might indicate that changes in the soil community composition are due to environmental factors.

An important outcome of plant thermogenesis is increased emissions of volatiles that mediate pollinator behaviour. We investigated whether the large increase in emissions, mainly the monoterpene s-myrcene (>90%), during daily thermogenic events of Macrozamia macleayi and lucida cycad cones are due solely to the influence of high cone temperatures or are, instead, a result of increased respiratory rates during thermogenesis. We concurrently measured temperature, oxygen consumption and s-myrcene emission profiles during thermogenesis of pollen cones under typical environmental temperatures and during experimental manipulations of cone temperatures and aerobic conditions, all in the dark. The exponential rise in s-myrcene emissions never occurred without a prior, large increase in respiration, whereas an increase in cone temperature alone did not increase emissions. When respiration during thermogenesis was interrupted by anoxic conditions, s-myrcene emissions decreased. The increased emission rates are not a result of increased cone temperature per se (through increased enzyme activity or volatilization of stored volatiles) but are dependent on biosynthetic pathways associated with increased respiration during thermogenesis that provide the carbon, energy (ATP) and reducing compounds (NADPH) required for s-myrcene production through the methylerythritol phosphate (MEP) pathway. These findings establish the significant contribution of respiration to volatile production during thermogenesis.

Phylogenetic relationships among the three families and 12 living genera of cycads were reconstructed by distance and parsimony criteria using three markers: the chloroplast matK gene, the chloroplast trnK intron and the nuclear ITS/5.8S rDNA sequence. All datasets indicate that Cycadaceae (including only the genus Cycas) is remotely related to other cycads, in which Dioon was resolved as the basal-most clade, followed by Bowenia and a clade containing the remaining nine genera. Encephalartos and Lepidozamia are closer to each other than to Macrozamia. The African genus Stangeria is embedded within the New World subfamily Zamiodeae. Therefore, Bowenia is an unlikely sister to Stangeria, contrary to the view that they form the Stangeriaceae. The generic status of Dyerocycas and Chigua is unsupportable as they are paraphyletic with Cycas and the Zamia, respectively. Nonsense mutations in the matK gene and indels in the other two datasets lend evidence to reinforce the above conclusions. According to the phylogenies, the past geography of the genera of cycads and the evolution of character states are hypothesized and discussed. Within the suborder Zamiieae, Stangeria, and the tribe Zamieae evolved significantly faster than other genera. The matK gene and ITS/5.8S region contain more useful information than the trnK intron in addressing phylogeny. Redelimitations of Zamiaceae, Stangeriaceae, subfamily Encephalartoideae and subtribe Macrozamiineae are necessary.

Complementary field and laboratory tests confirmed and quantified the pollination abilities of Tranes sp. weevils and Cycadothrips chadwicki thrips, specialist insects of their respective cycad hosts, Macrozamia machinii and M. lucida. No agamospermous seeds were produced when both wind and insects were excluded from female cones; and the exclusion of wind-vectored pollen alone did not eliminate seed set, because insects were able to reach the cone. Based on enclosure pollination tests, each weevil pollinates an average 26.2 ovules per cone and each thrips 2.4 ovules per cone. These pollinators visited similar numbers of ovules per cone in fluorescent dye tests that traced insect movement through cones. Fluorescent dye granules deposited by Cycadothrips were concentrated around the micropyle of each visited ovule, the site of pollen droplet release, where pollen must be deposited to achieve pollination. In contrast, Tranes weevils left dye scattered on different areas of each visited ovule, indicating that chance plays a greater role in this system. Each weevil and 25 thrips delivered 6.2 and 5.2 pollen grains, respectively, on average, to each visited ovule per cone, based on examination of dissected pollen canals. In sum, the pollination potential of 25 Cycadothrips approximates that of one Tranes weevil.

Summary 1 While cycads are often considered to be wind-pollinated, it is now clear that insects are pollen vectors in many species. This study addresses the role of thermogenesis in pollination biology of the dioecious cycad Macrozamia machinii P.I. Forster & D.L. Jones. 2 The patterns of thermogenesis in intact male and female cones were assessed with thermometry and respirometry throughout the pollination period in the field. 3 Thermogenic episodes in male cones occurred from about 17.00–00.00 h on successive evenings, in association with dehiscence of sporangia and presence of their pollinating weevils (Tranes sp.). 4 Temperatures of the 167 g male cones rose ≈6 °C above ambient, and mean rate of oxygen consumption peaked at 7·7 µmol s−1 (3·6 W). Regulation of male cone temperature was not evident, and thermogenesis of female cones was insignificant. 5 Male cones probably heat to augment scent production and enhance weevil activity, including mating and egg-laying, but female cones may benefit from reduced visitation and freedom from damage by weevil larvae. Male cones may be sacrificial in providing the reward to the pollinators while the female cones are safeguarded.

A treatment of the 'gymnosperms' native to the Northern Territory is provided. Fourteen species are recognised in four genera: Podocarpus (one species), Callitris (two species), Cycas (10 species), and Macrozamia (one species). Cycas brrunea is not recognised as occurring in the Northern Territory. The subspecies of Cycas arnhemica are reduced to synonymy under this species and Cycas canalis subsp. carinata is reduced to synonymy under Cycas canalis. Only two subspecies, Cycas maconochiei subsp. maconochiei and Cycas maconochiei subsp. viridis, are recognised for Cycas maconochiei. Identification keys to the genera, species, and infraspecific taxa in the Northern Territory are provided. Descriptions, notes, illustrations and distribution maps are also provided.

Cone traits (volatile components and thermogenesis) of three cycad species in the genus Macrozamia were examined for differences related to their specific insect pollinators, the weevil, Tranes spp., or the thrips, Cycadothrips chadwicki. Linalool (>80% of emissions) dominated cone volatile components of M. machinii (Tranes-pollinated) and beta-myrcene was a minor component (

Specialist beetles (Insecta, Coleoptera) have generally been considered to be the sole pollinators of cycads that have been studied. The possible pollination role of members of the thrips genus Cycadothrips (Thysanoptera, Aeolothripidae) found on male and female cones of some species of the Australian cycad genus Macrozamia (Zamiaceae), however, has never been experimentally investigated. This study, which included behavioral observations, visitation rates, pollen loads and exclusion experiments of insect visitors to Macrozamia communis cones in New South Wales, indicated that both Cycadothrips chadwicki Mound and Tranes lyterioides (Pascoe) (Coleoptera, Curculionidae) affect pollination. This is the first demonstration that specialist pollinators of two different insect orders pollinate a cycad. Cycadothrips adults and larvae fed on pollen, and Tranes weevil adults fed mainly on male sporophyll tissue and some pollen. Larvae of both insects developed in male cones; thrips larvae fed on pollen and weevil ...

Macrozamia macdonnellii (Zamiaceae) grows at a few isolated sites in central Australia. Male cones support large populations of a host‐specific thrips, Cycadothrips albrechti n.sp. (Thysanoptera, Aeolothripidae). This insect breeds only in these male cones, from which the adults swarm in late afternoon as the temperature falls and humidity rises. A small sticky trap at one female cone caught 3844 adults on a single afternoon; large numbers of thrips were observed entering this cone. Each thrips carried an average of 15 pollen grains, and pollen delivery into the cone was thus estimated to average more than 5500 grains per ovule. No other potential pollinators were found on these cycads, and it is concluded that C. albrechti is the sole pollinator of M. macdonnellii. Since Cycadothrips constitutes a basal clade within the Thysanoptera, the possibility is considered that thrips were involved in pollen transfer before the radiation of flowering plants.

Cetricycas antarcticus gen. et sp. nov. occurs in the Late Coniacian to Campanian Lachman Crags Member of the Santa Marta Formation, Marambio Group, James Ross Island, Antarctica. The petrified trunk comprises a thick pith containing thin and thick walled parenchymous cells, vascular traces surrounded by a thin layer of loose secondary wood. Medullary bundles arise inside the wood zone and pass outwards through multiseriate medullary rays. The trunk anatomy indicates assignment to the Cycadales, and the presence of medullary bundles indicates the affinities with a clade comprising Lepidozamia, Macrozamia, and Encephalartos. This clade is presently confined to Australia and Africa, but fossil representatives extend the geographic range to India, South America and now Antarctica.

Starch gel electrophoresis was employed to estimate the levels of genetic variation among five entities of the Macrozamia heteromera (Zamiaceae) group which can be recognised on morphological grounds. A total of 168 specimens were assayed for 12 enzyme systems coded by 16 loci. Low levels of genetic variation were observed with 10 of the 17 loci (58%) being monomorphic. Mean percent polymorphic loci ( P =26%), number of alleles per locus ( A =1.3) and expected heterozygosity ( H e =0.06) were all low. Although notably morphologically different, the species are very similar genetically. The overall G st value of 0.10 and the high genetic identity value of (range 0.92–0.97) suggest that these species are either recently evolved or they are depauperate in genetic variation due to inbreeding.

Allozyme variation in 12 enzyme systems coded by 17 loci was investigated in six populations of Macrozamia, including two populations of M. parcifolia, three populations of M. pauli-guilielmi and one population of M. crassifolia from Queensland (Australia) in order to measure the levels of genetic variation. This was required to establish whether the allozyme data supports recent taxonomic treatment. Seven loci were found to be monomorphic. All species were genetically depauperate, with low levels of genetic diversity (P=17.6–35.3%, A=1.2–1.4, H e =0.02–0.11) compared with two (only) existing reports, and plants in general. Genetic differentiation among populations was high (GST=0.47). UPGMA cluster analysis using Nei unbiased genetic distance showed M. parcifolia and M. pauli-guilielmi to be more similar genetically to each other than either is to M. crassifolia. This is concordant with groupings based on morphological characters, thus supporting the objectives of the investigation.

The ovulate cone Microzamia gibba (A.E. Reuss) Corda, from the Bohemian Cenomanian (Czech Republic, Central Europe) is described. The genus Microzamia Corda is newly emended and compared with the fossil genera Beania Carruthers, Zamiostrobus Endlicher and the extant genera Zamia L., Chigua Stevenson, Macrozamia Miquel, Ceratozamia Brongniart and Encephalartos Lehmann. The genus Cycadeostrobus Carruthers might be synonymous with Microzamia. The typification of Microzamia gibba is discussed resulting in the designation of a neotype. It is demonstrated that the stony layers of Beania gracilis and M. gibba have a similar anatomy. A reconstruction of the ovulate cone M. gibba is proposed, showing large cataphylls on the cone peduncle. The ovulate cones occur in association with the leaves Jirusia jirusii (Bayer) Domin.

BACKGROUND AND AIMS Ontogenetic patterns of odour emissions and heating associated with plant reproductive structures may have profound effects on insect behaviour, and consequently on pollination. In some cycads, notably Macrozamia, temporal changes in emission of specific odour compounds and temperature have been interpreted as a 'push-pull' interaction in which pollinators are either attracted or repelled according to the concentration of the emitted volatiles. To establish which mechanisms occur in the large Encephalartos cycad clade, the temporal patterns of volatile emissions, heating and pollinator activity of cones of Encephalartos villosus in the Eastern Cape (EC) and KwaZulu Natal (KZN) of South Africa were investigated. METHODS AND KEY RESULTS Gas chromatography-mass spectrometry (GC-MS) analyses of Encephalartos villosus cone volatiles showed that emissions, dominated by eucalyptol and 2-isopropyl-3-methoxypyrazine in EC populations and (3E)-1,3-octadiene and (3E,5Z)-1,3,5-octatriene in the KZN populations, varied across developmental stages but did not vary significantly on a daily cycle. Heating in male cones was higher at dehiscence than during pre- and post-dehiscence, and reached a maximum at about 1830 h when temperatures were between 7·0 and 12·0 °C above ambient. Daily heating of female cones was less pronounced and reached a maximum at about 1345 h when it was on average between 0·9 and 3·0 °C above ambient. Insect abundance on male cones was higher at dehiscence than at the other stages and significantly higher in the afternoon than in the morning and evening. CONCLUSIONS There are pronounced developmental changes in volatile emissions and heating in E. villosus cones, as well as strong daily changes in thermogenesis. Daily patterns of volatile emissions and pollinator abundance in E. villosus are different from those observed in some Macrozamia cycads and not consistent with the push-pull pattern as periods of peak odour emission do not coincide with mass exodus of insects from male cones.