Geoffrey E. Burrows

The classification of acacias has gone through recent upheaval. The latest phylogenies indicate that Acacia sensu stricto is only relatively distantly related to the species with which it was once grouped. Its sister group is the monospecific Paraserianthes . This study concerns P. lophantha subsp. lophantha , a species from SW Western Australia that is widely invasive. Both genera have seeds with physical dormancy (PY) and a lens-type water gap. Seed structure, particularly that of the lens, was assessed in Paraserianthes and compared with Acacia . Seed batch viability was almost 100%, all seeds had PY and average seed mass was 73 mg. The seed coat and the embryo made almost equal contributions to seed mass, indicating a substantial seed coat. Average testa (410 µm) and palisade layer (163 µm) thicknesses were greater than in most investigated Acacia species. Unpopped lenses were small (0.11 mm ² , about 0.15% of the seed surface area). With a 1 min boiling water treatment, the lens detached from the seeds. The palisade cells of the lens were about 100% larger in area after detaching, which indicates that they previously were under considerable tension. With other PY-breaking treatments, the lens formed a mound or a slight change in colour occurred. The seeds of Paraserianthes lophantha had the same basic construction as most Acacia seeds, although they were relatively large and heavy, the testa made up a large proportion of the seed and the palisade cells were long. Different lens morphologies, associated with different dormancy-breaking treatments, have rarely been described.

Context: Most gymnosperms are dioecious (no self-pollination). It was not known if Wollemia nobilis (monoecious) could produce viable seeds via self-pollination. Aims: In the nearly 30 years since its scientific discovery Wollemia nobilis (Araucariaceae) has been the focus of considerable scientific attention. While this includes several aspects of sexual reproduction, many features of ovulate cone morphology and seed biology have not been investigated. Methods: Various aspects of ovulate cone morphology were quantified, as were seed morphology and germination (e.g. seed moisture content and rate of imbibition), in material from an isolated tree of Wollemia nobilis. Seeds of Agathis microstachya and Araucaria cunninghamii were also examined to allow comparisons across the Araucariaceae. Key results: In Wollemia nobilis most seeds were empty (no formation of a megagametophyte and embryo (M + E)). Empty and filled seeds were morphologically very similar. On average, the fresh weights (FW) of empty and filled seeds were 6.2 and 33.1 mg, respectively. On average, the FW of the M + E was 25.8 mg (78% of seed mass, the other 22% was testa). The average moisture content (FW basis) of the testa and the M + E were 9.6% and 7.0%, respectively. The M + E imbibed water relatively slowly and imbibed, on average, to ~110% increase in FW after 48 h. In Agathis robusta and Wollemia nobilis the seeds separated freely from the cone scales. In Araucaria cunninghamii the M + E was an integral part of the bract/scale complex. Conclusions: The seeds examined in this study came from an isolated, almost certainly self-fertilised tree. The seeds were of approximately the same dimensions as those from the wild populations of Wollemia nobilis, while average filled seed FW was greater and less variable. The filled seeds had a high viability and an excised M + E could germinate rapidly. This study shows that Wollemia nobilis can produce large, viable seeds via self-fertilisation. Successful self-fertilisation may be a factor in the low genetic diversity detected in the wild population. Implications: Based on evidence from a single tree it would appear that Wollemia nobilis can produce large, viable, vigorous seeds via self-fertilisation. This has implications for the population structure of this species.

Summary: Plant cuticles protect the interior tissues from ambient hazards, including desiccation, UV light, physical wear, herbivores and pathogens. Consequently, cuticle properties are shaped by evolutionary selection. We compiled a global dataset of leaf cuticle thickness (CT) and accompanying leaf traits for 1212 species, mostly angiosperms, from 293 sites representing all vegetated continents. We developed and tested 11 hypotheses concerning ecological drivers of interspecific variation in CT. CT showed clear patterning according to latitude, biome, taxonomic family, site climate and other leaf traits. Species with thick leaves and/or high leaf mass per area tended to have thicker cuticles, as did evergreen relative to deciduous woody species, and species from sites that during the growing season were warmer, had fewer frost days and lower wind speeds, and occurred at lower latitudes. CT–environment relationships were notably stronger among nonwoody than woody species. Heavy investment in cuticle may be disadvantaged at sites with high winds and frequent frosts for ‘economic’ or biomechanical reasons, or because of reduced herbivore pressure. Alternatively, cuticles may become more heavily abraded under such conditions. Robust quantification of CT–trait–environment relationships provides new insights into the multiple roles of cuticles, with additional potential use in paleo‐ecological reconstruction.

In a recent paper in Southern Forests, Jaganathan and co-workers indicated that the low constant-temperature drying method (LCTDM) (103°C for 17 h) is satisfactory for determining moisture content (MC) in seeds with physical dormancy (PY). Would this recommendation apply to Acacia, a large genus (1000+ species) with a seed coat so strong that seeds in the soil can maintain high viability for many decades? MC was assessed, using the LCTDM, in six Australian Acacia species by comparing intact seeds with those cut in half. Halved seeds of all species lost moisture rapidly and their mass had largely stabilised after about 2–3 h. Intact seeds had a wide variation in moisture-loss patterns. In some species, the testa was morphologically unchanged after 24 h at 103°C and this was associated with a relatively slow moisture loss. In other species, the testa had completely shattered after 8 h, leading to a rapid moisture loss. If the LCTDM is used to determine MC in Acacia species, it is advisable to employ a technique that substantially disrupts the testa.

Acacia implexa, Eucalyptus rossii and Exocarpos cupressiformis are native plants of Australia, which were used by the First Peoples for medicinal purposes. In this study, 70% aqueous ethanol crude extracts were prepared from A. implexa bark and leaves, E. rossii leaves and E. cupressiformis leaves, and partitioned via sequential extraction with n-hexane, dichloromethane (DCM), ethyl acetate and ethanol. The crude extracts and fractions were screened for antioxidant activity using a novel, high-throughput lipid-based antioxidant assay, as well as the aqueous ABTS (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) assay and the Folin–Ciocalteu test for total phenols. In the lipid-based assay, non-polar n-hexane and DCM fractions showed higher antioxidant activity against the formation of peroxides and thiobarbituric acid reactive substances (TBARS) than the other fractions, whereas the non-polar fractions were not effective in aqueous assays. This illustrates that the high potential of the lipid-soluble n-hexane and DCM fractions as antioxidants would have been missed if only aqueous-based assays were used. In addition, the potent antioxidant compounds were putatively annotated using liquid chromatography quadrupole time-of-flight mass spectrometry (LC-qTOF-MS). Gallic acid, (+)-catechin, (−)-epicatechin and tannins were found in most crude extracts.

Gymnosperms are generally regarded as poor resprouters, especially when compared to angiosperms and particularly following major disturbance. However, is it this clear-cut? This review investigates two main aspects of gymnosperm resprouting: (i) various papers have provided exceptions to the above generalization—how frequent are these exceptions and are there any taxonomic trends?; and (ii) assuming gymnosperms are poor resprouters are there any anatomical or physiological reasons why this is the case? Five of six non-coniferous gymnosperm genera and 24 of 80 conifer genera had at least one species with a well-developed resprouting capability. This was a wider range than would be expected from the usual observation ‘gymnosperms are poor resprouters’. All conifer families had at least three resprouting genera, except the monospecific Sciadopityaceae. Apart from the aboveground stem, buds were also recorded arising from more specialised structures (e.g., lignotubers, tubers, burls and underground stems). In some larger genera it appeared that only a relatively small proportion of species were resprouters and often only when young. The poor resprouting performance of mature plants may stem from a high proportion of apparently ‘blank’ leaf axils. Axillary meristems have been recorded in a wide range of conifer species, but they often did not form an apical dome, leaf primordia or vascular connections. Buds or meristems that did form often abscised at an early stage. While this review has confirmed that conifers do not resprout to the same degree as angiosperms, it was found that a wide diversity of gymnosperm genera can recover vegetatively after substantial disturbance. Further structural studies are needed, especially of: (i) apparently blank leaf axils and the initial development of axillary meristems; (ii) specialised regeneration structures; and (iii) why high variability can occur in the resprouting capacity within species of a single genus and within genera of the same family.