Search

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.

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 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. Fil: Wilf, Peter. State University of Pennsylvania; Estados Unidos Fil: Stevenson, Dennis Wm.. New York Botanical Garden; Estados Unidos Fil: Cúneo, Néstor Rubén. Museo Paleontológico Egidio Feruglio; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

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.

Studies of cycad pollination globally have revealed obligate pollination mutualisms with insects, typically hostspecific beetles. Some cycads in the genus Cycas have floating seeds allowing oceanic dispersal, and have colonized remote islands such as Fiji, Guam, and Madagascar. This seems to contradict the expected requirement that specific beetle pollinators be present in order for cycads to establish in remote localities. We therefore postulated that these ‘island’ cycads are wind pollinated. We tested for adaptations associated with wind pollination in a laboratory study of pollen aerodynamics. The pollen from a range of (non-cycad) wind-pollinated plants was not relatively ‘buoyant’: the settling velocities of wind-pollinated species exceeded those of insect-pollinated cycads and some animal-pollinated angiosperms. We attributed this result to settling velocity being, in part, correlated with pollen size, as cycad pollen was consistently smaller. A better predictor for pollination vector was the tendency of pollen to aggregate during a vertical fall. Pollen of wind-pollinated plants separated into single grains, whereas cycad pollen and pollen of animal-pollinated angiosperms adhered in large aggregations, the settling velocity of which increased rapidly with aggregate size. The pollen of cycads known to be insect pollinated was similar in morphology, settling speed, and clumping behaviour to pollen of ‘island’ cycads of unknown pollination biology. Based on these aerodynamics, we predict that cycad species on oceanic islands have insect pollinators. More broadly, we propose that pollen aggregation during a vertical fall provides a sound test for wind versus animal pollination when the pollination vector is unknown.

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.

Amongst the 100 described species worldwide of the genus Scirtothrips, the South African Citrus Thrips, S. aurantii Faure, has been considered unique because the males possess a comb of stout setae on the hind femora (Hoddle & Mound, 2003). A new species that shares this character state is described here from Cedrus (Pinaceae) in Kenya, although no information is available for either species concerning the functional significance of this comb. The host association of this new species is interesting, because Scirtothrips species are generally considered to be associated with the young leaves of dicot plants, on which some are important pests (Mound & Palmer, 1981). Despite this, several relatively unrelated species within the genus have radiated onto various unrelated Gymnospermae. Two are associated with Juniperus (S. brevipennis in eastern North America, and S. juniperinus in Central Asia), one with Libocedrus (S. solaris in California), and one with Taxodium (S. taxodii in eastern North America), and in Australia two species are associated with the young fronds of cycads (S. litotetes on Lepidozamia and S. tenor on Cycas). Moreover, two species are known from different tree ferns (S. pteridis in Costa Rica, and S. frondis in Australia). Scirtothrips is thus yet another example of radiation within a genus of Thysanoptera that involves exploitation of unrelated plants (Mound, 2005), such as Cranothrips Bagnall (Pereyra & Mound, 2009) and Echinothrips Moulton (Mound & Marullo, 1996), rather than fidelity to any particular plant lineage. For full nomenclatural details of all taxa mentioned here see Mound (2010).

The ontogenesis of chloroplasts during leaf development in Lepidozamia peroffskyana Regel is described; this cycad lives in the ground layer of the evergreen subtropical closed forest of south-eastern Australia. Characteristic features in young plastids are long bands of multilayered thylakoids, resembling photosynthetic structures of some green algae and ferns. 'Optional' structures, namely prothylakoid bodies and crystalline inclusions, are present in the pre-grana stages, in relation to the slow rate of leaf development. Mature chloroplasts are characterised by a great number of randomly oriented high grana stacks, a lack of starch, a high ratio of appressed to exposed thylakoids, and a low ratio of Chl a to Chl b; these shade features appear coherent with the natural habitat of Lepidozamia. However, since similar structures have been reported in mature chloroplasts of other cycads living in exposed sites, the existence of a genetically superimposed structural pattern is hypothesised, reflecting a primitive adaptation to weak light conditions of this group of ancient seed plants.

Thermogenesis occurs in the strobili of 42 of 43 species in the 10 genera of cycads, indicating a wide-spread phenomenon in this group. Heat production generally follows a circadian rhythm, and its strength and duration are positively correlated with strobili size. Male strobili contain high concentrations of starch that may supply the energy for thermogenesis. Strobili of all examined species release odors that are sweet, resiny, or musty. Heat production in the strobili may help to volatilize odors that attract insects for pollination.

The descriptions of Pterostoma R.S.Hill, a new cycad genus with two species (P. zamiodes R.S.Hill and P. anastomosans R.S.Hill) and Lepidozamia foveolata R.S.Hill add significantly to our knowledge of the floristic components of the Australian Tertiary. Along with other reports of Tertiary cycads, the discovery of these new species supports the theory that cycads had a greater geographical range and diversity in Australia during the Tertiary than at present. The evolutionary position of Pterostoma in relation to other fossil and extant cycads is considered and it is concluded that Pterostoma represents an extinct line. The possibility that fossil cycads could be of value in biostratigraphy and in estimating palaeoclimate is discussed.