It is well known that physical leaf traits influence leaf functions, and that these traits vary across environmental gradients. Stomata can influence leaf function, with changes in density and size affecting potential water loss, CO2 uptake, and also leaf cooling. Plasticity in stomatal traits occurs in response to environmental factors; however, identifying which factors have the greatest influence is often difficult. We investigated variation in leaf size, stomatal density and size, and potential water loss from open stomata (gwmax), in the Australian native shrub Dodonaea viscosa subsp. angustissima, across a range of environmental factors including temperature, rainfall and CO2. We used herbarium specimens collected across a latitudinal gradient, and also sampled along an elevation gradient in southern Australia. There were significant relationships between mean summer maximum temperature and stomatal density, and gwmax. We found no significant relationships between rainfall or CO2 and the leaf traits we studied. Increased stomatal density at warmer locations may result in an increase in the potential for transpiration, as a means for evaporative cooling. Alternatively, it may enable increased CO2 and nutrient uptake during the short, winter-growing season.

Eucalypts have influenced the fire ecology of the Australian landscape more than any other plant group. They are the iconic plant taxon in the Australian vegetation today, but their origin, early evolution and migration remain poorly understood, mostly because of a remarkably sparse and underworked fossil record. However, a recent major macrofossil find in southern South America, coupled with increasing sophistication of molecular phylogenetic and palynological research allow for a more comprehensive summary of the likely early history of this group of genera. It is likely that the origin was close to the Cretaceous–Paleogene boundary, somewhere in the Weddellian Biogeographic Province (which includes southern South America, western Antarctica and south-eastern Australia), in an area with high natural fire frequency. Evidence for the early record of eucalypts in Australia and their eventual spread across the continent, leading to their current dominance of the Australian plant biomass is growing and is consistent with a drying climate and increasing fire frequency following a very wet period during the Paleogene. The causes of the extinction of eucalypts from South America and probably New Zealand are considered, but remain obscure.

Premise Within closed‐canopy forests, vertical gradients of light and atmospheric CO2 drive variations in leaf carbon isotope ratios, leaf mass per area (LMA), and the micromorphology of leaf epidermal cells. Variations in traits observed in preserved or fossilized leaves could enable inferences of past forest canopy closure and leaf function and thereby habitat of individual taxa. However, as yet no calibration study has examined how isotopic, micro‐ and macromorphological traits, in combination, reflect position within a modern closed‐canopy forest or how these could be applied to the fossil record. Methods Leaves were sampled from throughout the vertical profile of the tropical forest canopy using the 48.5 m crane at the Daintree Rainforest Observatory, Queensland, Australia. Carbon isotope ratios, LMA, petiole metric (i.e., petiole‐width2/leaf area, a proposed proxy for LMA that can be measured from fossil leaves), and leaf micromorphology (i.e., undulation index and cell area) were compared within species across a range of canopy positions, as quantified by leaf area index (LAI). Results Individually, cell area, δ13C, and petiole metric all correlated with both LAI and LMA, but the use of a combined model provided significantly greater predictive power. Conclusions Using the observed relationships with leaf carbon isotope ratio and morphology to estimate the range of LAI in fossil floras can provide a measure of canopy closure in ancient forests. Similarly, estimates of LAI and LMA for individual taxa can provide comparative measures of light environment and growth strategy of fossil taxa from within a flora.

Intra-species variation in specific leaf area (SLA) and leaf area (LA) provides mechanistic insight into the persistence and function of plants, including their likely success under climate change and their suitability for revegetation. We measured SLA and LA in 101 Australian populations of the perennial shrub Dodonaea viscosa (L.) Jacq. subsp. angustissima (narrow-leaf hop-bush) (Sapindaceae). Populations were located across about a 1000 km north-south gradient, with climate grading from arid desert to mesic Mediterranean. We also measured leaves from 11 populations across an elevational gradient (300-800 m asl), where aridity and temperature decrease with elevation. We used regression and principal component analyses to relate leaf traits to the abiotic environment. SLA displayed clinal variation, increasing from north to south and correlated with latitude and the first principal component of joint environmental variables. Both SLA and LA correlated positively with most climatic and edaphic variables. Across latitude, LA showed more variability than SLA. Changes in leaf density and thickness may have caused the relative stability of SLA. Only LA decreased with elevation. The absence of a SLA response to elevation could be a consequence of abiotic conditions that favour low SLA at both ends of the elevational gradient. We demonstrated that the widely distributed narrow-leaf hop-bush shows considerable variability in LA and SLA, which allows it to persist in a broad environmental envelope. As this shrub is widely used for revegetation in Australia, South America and the Asia-Pacific region, our results are consistent with the notion that seed used to revegetate mesic environments could be sourced from more arid areas to increase seed suitability to future climate change.

Premise of research. This study describes a new fossil species of Bowenia and reconsiders known fossil species and their evolutionary significance. Methodology. The fossils we describe here were collected for this study or were available from previous collections made over several decades. The fossils were identified by direct comparisons with extant and fossil species. Pivotal results. A reexamination of known and newly discovered Bowenia macrofossils confirms the presence of at least three fossil species in Australia. A new species, Bowenia johnsonii, is described from the southernmost location, the Early Eocene Lowana Road site in southwest Tasmania. When compared with the two extant species, the three fossil species demonstrate two distinct pinnule morphologies: relatively small with distinct serrations in Bowenia eocenica and Bowenia papillosa and larger pinnules with minute serrations in B. johnsonii. When considered together, the stomata of the extant species are denser and larger than those of the fossil taxa. Conclusions. The cycad genus Bowenia has a restricted extant distribution along the east coast of Queensland but is known more widely within Australia from fossils. The fossil record of Bowenia is important in documenting the past distribution of this genus, and aspects of its pinnule morphology provide insights into its environmental interactions. The possible relationship of the fossil Bowenia species with the Aptian Argentinian genus Eobowenia is considered, along with some fragmentary Australian fossils of probable Bowenia.