Australian Journal of Botany最新文献

Reproductive success in dioecious plant species may be limited by severe pollen limitation owing to their separate sexes and pollination barriers.

Dodonaea viscosa subsp. angustifolia (Jacq.) (Sapindaceae) is a dioecious and wind-pollinated species that has a long flowering period. This study sought to determine the relationship between its reproductive behaviour and pollen availability during different flowering phases.

Extra-stigmatic pollen germination and reproductive performance during different phases of flowering were investigated and correlated with pistil elongation under natural conditions.

The species offers whole stigmatic and stylar surfaces for pollen to land and germinate under natural conditions. During pollen-limiting conditions, the length of the pistil increases significantly to enhance pollen capture. Depending on where on the pistil pollen lands, the timing of pollen tube arrival at the ovary varies.

Dodonaea viscosa subsp. angustifolia is the first reported wild species in the Sapindaceae where pistil elongation is regulated by pollination conditions and extra-stigmatic pollen germination ensures reproduction during phases of differing pollen availability. Our results indicated that the flexibility of female function and reproductive behaviour in Dodonaea viscosa subsp. angustifolia adds to the evolutionary possibilities to overcome pollination constraints.

This unique strategy for increasing female fitness through pollen presentation in D. viscosa subsp. angustifolia could be explored in other subspecies of D. viscosa on the Australian subcontinent.

Most tissues of Myrtaceae plants have oil glands. The anthers of many species have an oil-containing apical gland that is larger than those in other tissues of the plant.

Representative species in the family were examined for the diversity of gland form and their oil contents.

Representative anthers were sectioned for light microscopy and scanning electron microscopy study and anthers from selected species were analysed for oil content.

The most common gland form is globular and narrowly attached to the apex of the connective, but in members of certain tribes, the gland is completely enclosed in the connective. The greatest morphological diversity is in the Chamelaucieae. Anther glands vary from plesiomorphic globular forms to glands that are larger than the anther thecae and almost completely fill the connective.

There are three possible functions for the glands, including the following: (1) protecting the anthers from herbivores, (2) mixing with the pollen to aid adhesion to stylar hairs on many Chamelaucineae, and (3) rewarding pollinators that use the oil–pollen mixture as food.

It is generally considered that the oils in various tissues of the Myrtaceae deter herbivores. In Myrtaceae with abundant anthers, the glands could deter flower visitors from consuming the anthers. Gland oil of the Eucalyptus and Leptospermum species examined contained α pinene as did the leaves of all species examined. The gland oil composition in Chamelaucium uncinatum and Verticordia grandis that have pollen presenters was different from that in the leaves and also different from that in the anthers of the two Verticordia species where bees collect the pollen–oil mixture for food.

Epiphytes are typically associated with wet forests and are seldom documented in drylands. This absence is presumed to reflect moisture limitations to their establishment and survival.

In response to a large body of epiphyte observations made by a pastoralist in collaboration with local Indigenous people, we investigated and documented an unusually high concentration of woody epiphytes from semi-arid eastern Australia and describe this in relation to ecological and cultural factors.

We searched for, recorded and measured epiphytic trees and shrubs in semi-arid eucalypt woodlands of northern New South Wales and southern Queensland. Factors influencing their distribution were examined.

Eucalypts growing along the Barwon River palaeochannels host 21 species of shrubs and trees. Over 95% of the 712 woody epiphytes documented were alive, and some appeared decades old; 70% were growing in trees that had been modified by humans, and at least half of the host sites were directly anthropogenically created. Epiphytes are widely, but typically sparsely, distributed in other semi-arid eucalypt woodlands, with a further 311 found during regional surveys.

The large trees of the Barwon palaeochannels, their extensive human modification to create favourable sites for epiphyte establishment, and the diversity of understorey shrubs providing a propagule source have combined to create this epiphyte-rich woodland. Their association with Culturally Modified Trees and the relatively low density of epiphytes elsewhere suggest that Aboriginal people have played a direct role in creating this landscape, to which they remain deeply connected.

Epiphytes may be more widespread in drylands than previously recognised. We hope that this study stimulates further research on their distribution, characteristics, and ecological and cultural associations.

The plant pathogen Phytophthora cinnamomi causes severe declines in susceptible vegetation, including loss of plant species, vegetation structure and fauna abundance. Grasstrees (Xanthorrhoea spp.) are keystone species that provide optimal habitat for vertebrates and invertebrates and are highly susceptible to the pathogen. Although effects in the Otway Ranges have been assessed at specific sites, there is less knowledge across the landscape on the extent of loss of Xanthorrhoea australis (austral grasstree).

The aims were thus to assess impacts at three Heathy Woodland sites and to determine the magnitude of loss of X. australis and susceptible species losses.

Floristic composition, species cover or abundance, and basal area of X. australis were recorded in quadrats within treatments (uninfested, infested, post-infested vegetation). Analyses included floristics (PRIMER v7), significant effects (ANOSIM), species contribution to similarity/dissimilarity (SIMPER). Species richness and susceptible species cover were analysed using two-way crossed ANOVAs to detect the influence of site, treatment, and interactions.

Species composition of uninfested vegetation was significantly different to infested and post-infested vegetation, with susceptible species more abundant in uninfested areas. Post-infested vegetation had the lowest percentage cover of susceptible species. The mean percentage cover of X. australis in uninfested vegetation (43%) was 10-fold greater than in infested areas (4.3%) and extremely low in post-infested vegetation (0.9%).

Susceptible species were subject to density declines and extirpation, and the loss of X. australis resulted in major structural vegetation changes.

These results have severe implications for heathy woodland communities and reliant fauna. Limiting the spread of P. cinnamomi and protecting grasstrees is critical for their security.

The nature of Australia’s high mountains is changing. Recent, repeated landscape-scale fires have burnt much of the subalpine forests dominated by snow gum (Eucalyptus pauciflora). Long-unburnt snow gum forests are important for ecosystem services, have socio-cultural benefits, and conservation values, but they are now exceedingly rare, comprising <1% of snow gum forests in the Victorian Alps. We identify where long-unburnt snow gum stands persist in the Victorian Alps and outline why management intervention is necessary to protect unburnt refuges and, more broadly, to allow mature/adult stands (such as occur on the Baw Baw Plateau) to develop into future old forests.

Species fire responses were investigated in a mixed sclerophyll–rainforest ecosystem in the Nightcap Range, North Coast, New South Wales.

To examine rates of seedling recruitment and resprouting in functional and phytogeographic components of wet sclerophyll forest (WSRf), and adjacent open forest (OF) and rock outcrop shrubland (RO).

Species resprouting and seedling recruitment traits (fire responses) were recorded in 45 stem plots and 225 seedling subplots in WSRf, OF and RO. Species fire responses were classified, community fire-response spectra compiled and rates of seedling recruitment and resprouting in WSRf examined in relation to primary fire response, growth-form, habitat and broad functional and phytogeographic species groupings. Species size-regenerative class distribution was used to analyse population structure, fire impact, regeneration and recruitment in resprouter species that comprised most of the mesic-Gondwanan element of the WSRf flora.

WSRf, OF and RO habitats had distinctively different fire-response spectra. In WSRf, there was a high proportion of mesophyll resprouter species of Gondwanan origin with nil or very low seedling recruitment, a distinct component of mesophyll seeders of Indo-Malayan origin, as well as sclerophyll seeders and resprouters that also comprised most of the OF and RO floras. Resprouters comprised 75% of the WSRf flora, 50% OF and 10% pavement shrubland. Continuous size-class distributions indicated recruitment between fire events in the majority of mesophyll resprouters in WSRf. Lower total seedling density appeared to reflect inherent species traits and less canopy disturbance by fire. Large sclerophyll species forming the unburnt canopy of WSRf had very low seedling recruitment.

Different habitats (WSRf, OF and RO) and functional and phytogeographic clades in WSRf display distinctive patterns of resprouting and seedling-recruitment fire response. Fire responses of species that maintain species population and community composition are governed by fire regime, habitat variables and inherent species traits.

The distinctive fire-response spectrum of WSRf appears to be a direct consequence of the overlap of ‘new’ and ‘old’ floras in this broad vegetation type.

The parasitic interaction between the galling insect Palaeomystella oligophaga (Lepidoptera) and the host plant tissues of Macairea radula (Melastomataceae) leads to the formation of globoid galls. These galls have storage and typical nutritive tissues (outer and inner compartments, respectively), whose functions may be related to differential cell wall component distributions and to the stage of development of the gall inducer.

We evaluated whether the cell wall composition of the gall compartments (storage and nutritive tissues) changes according to the developmental stage of the gall inducer P. oligophaga.

The galls occupied by the gall inducer in different stages of development (i.e. larval and pupal stages, as well as empty galls) were collected and submitted to histological examination, immunocytochemical analyses using monoclonal antibodies for pectins, hemicelluloses, and glycoproteins, and histochemical analyses using phloroglucinol for lignins.

The histological results showed that nutritive tissues have smaller cells compared with storage ones when the galling insect is in the larval stage. Immunocytochemical analyses also showed the occurrence of both methyl-esterified and unesterified pectins, as well hemicelluloses in the nutritive tissue during the larval stage. The dynamic of some cell wall components changes when the gall inducer is in the pupal stage, or the galls are empty.

The changes in the composition of the cell walls, especially regarding homogalacturonans and xyloglucans, support the high metabolism and resource availability in cell walls of nutritive tissue for the gall inducer.

The cell wall composition may indicate important metabolic steps during gall formation and galling insect diet.

The radiation of eucalypts into almost every Australian environment offers valuable insights to plant ecological strategies.

We aimed to assess the degree to which functional traits across different organs are independent or reflect coordinated strategies in southern eucalypts.

We applied ordinary and phylogenetic generalised least squares regressions to 164 southern Australian taxa, examining the network of pairwise relationships between 10 functional traits representing aspects of stature, leaf economics, reproduction and post-fire regeneration. We examined coordination and modularity in this network and estimated how phylogeny affects observed trait correlations.

Stem and stature traits were generally independent of reproductive traits, with Specific Leaf Area the most connected trait, being correlated with traits from all organs. Resprouting ability was also connected to several traits. Species able to resprout basally, but not epicormically, were on average shorter, stouter, with higher stem sapwood density, thinner bark, smaller leaves and lower Specific Leaf Area than those able to resprout using both methods. Taxa resembled their relatives; phylogenetic signal was significant for all continuous traits except Relative Height, ranging from Pagel’s Lambda λ = 0.37 (Relative Bark Thickness) to λ = 0.82 (Specific Leaf Area). Phylogenetic analyses showed weakened correlations for most (but not all) trait pairs. However, most moderate relationships on the trait correlation network also displayed correlated evolution.

Stature, stem, leaf and reproductive traits and fire response of eucalypts are somewhat coordinated, principally through leaf economics. Trait combinations that confer ecological competence on eucalypt taxa in present-day conditions are likely to have been similarly favoured throughout their evolutionary history.

This supports theory of coordinated plant strategies.

To examine the potential applications of hyperaccumulator plants in the Philippines, we reviewed current data on the extent of metal hyperaccumulation in native species and partitioning of metals within the plant tissue. Twenty-eight species had reported tissue concentrations above the hyperaccumulator threshold, 11 species were endemic to the Philippines. Nickel was present in higher concentrations in the aboveground tissue than in the belowground tissue, but the reverse was found for copper, aluminium and chromium. The fact that copper accumulates belowground rather than above, and most hyperaccumulators of nickel identified were trees, has implications for the potential of phytoextraction using native Philippines flora.

The Chromolaena congesta complex is an informal group of taxa native to grasslands from south-eastern South America with numerous identification problems, currently under study using an integrative approach. Recent studies with morphological data have aided in defining some taxa, but many questions remain to be assessed, and there is much to gain from combining morphological data with other lines of evidence.

We investigated whether the species of the C. congesta complex could be circumscribed and differentiated according to climatic and distributional data and how these results compare to published morphological data.

We used a SDM approach and climatic envelope estimates of 12 taxa belonging to the C. congesta complex. To achieve that, we compiled a distributional database from herbarium specimen information and produced distribution models for each taxon by using MaxEnt and 19 bioclimatic variables.

We found that many species of the complex share similar predicted suitable distribution and climatic preferences, while also uncovering particular geographic and climatic patterns for C. ascendens and C. caaguazuensis. Our results also contributed with the circumscription of C. squarrulosa and provided data for further recognition of two taxonomic novelties.

Climatic and distributional data yielded interesting results for the taxonomy of this species complex, particularly when confronted with morphological data.

This study provided support for an apparently undescribed Chromolaena that merits recognition at species rank and the treatment of Eupatorium caaguazuense var. nervosum as a separate species from C. squarrulosa, while also supplying further evidence that morphologically diverse populations of C. squarrulosa should be treated as a single taxon.