Subgenus Phyllodineae Research Articles

Macroecology meets invasion ecology: performance of Australian acacias and eucalypts around the world revealed by features of their native ranges

Native geographical range extent has frequently emerged as a correlate of invasiveness, especially for plant species. We tested whether dimensions of the native range (measured by the area-of-occupancy and its scaling patterns) of 720 Australian eucalypts (genera Angophora, Eucalyptus and Corymbia) could explain introduction and invasion success. We also compared our results with a previous study on 979 Australian acacias (previously grouped in Acacia subgenus Phyllodineae) to investigate whether features of their native ranges explained the much higher invasion success in this group compared to eucalypts. From nine databases we found records that 373 eucalypts have been introduced to areas outside their native ranges; 82 of these have become naturalised, and eight are invasive. A similar proportion of Australian acacias have been introduced, but almost three times as many are invasive (384 species introduced, 71 of which are naturalized and 23 invasive). Eucalypts with large native ranges are more likely to have been introduced and subsequently naturalise, as is the case with acacias. Unlike acacias, however, the native range size of invasive eucalypts was not significantly greater than naturalised (but not invasive) species. Intriguingly, the human preference for introducing species with larger ranges was much greater for acacias than for eucalypts as the geometric mean range sizes of introduced, naturalised and invasive acacias are 2.04, 1.88 and 3.59 times those of eucalypts at the same stage. Moreover, the percolation exponent (i.e. the slope of occupancy scaling) becomes more extreme towards the end of the introduction–naturalization–invasion continuum, decreasing for acacias but increasing for eucalypts, with acacias, except for non-introduced species, having a lower exponent than eucalypts. The selection preference of acacias during introduction is thus for species that can rapidly expand their range; in contrast, slow-spreading eucalypts have been selected for dissemination. In other words, humans appear to have selected for highly invasive acacias but against introducing highly invasive eucalypts.

Invasiveness in introduced Australian acacias: the role of species traits and genome size

AbstractAim To assess associations between invasiveness, genome size and species traits in Australian Acacia species introduced outside their native range.Location Global.Methods Holoploid genome size was determined by flow cytometry for 92 species in Acacia subgenus Phyllodineae native to Australia. These data were used to test whether genome size was significantly different for invasive (n = 21; species known to be established and spreading in foreign environments) and non‐invasive (n = 71; species that have been introduced to foreign environments but which are not known to be spreading) species. Data for five functional traits [seed mass, specific leaf area (SLA), relative growth rate (RGR), maximum height and dispersal mode] and three characteristics of native range (size, temperature range and precipitation range) were used to test for univariate and multivariate relationships between (1) invasiveness and traits and (2) genome size and traits.Results Genome size ranged from 1.20 to 2.13 pg/2C and was not significantly smaller in invasive compared with non‐invasive acacias. However, invasive acacias were found to be taller and possess a larger native range size and a wider range of annual precipitation when compared with non‐invasive acacias. Multivariate analyses revealed significant differences between invasive and non‐invasive acacias (PERMANOVA; P < 0.01) driven largely by differences in native range characteristics. We detected a positive relationship between genome size and SLA (P = 0.02) and elaiosome dispersal mode (P < 0.01) in analyses across species, but these findings were not supported by evolutionary divergence analyses.Main conclusions Genome size variation does not underpin variation in traits associated with the invasive/non‐invasive dichotomy in introduced acacias, probably because of the very small DNA values in the Acacia species studied. Acacias introduced into new environments are most likely to become invasive if they are tall shrubs or trees and are widely distributed in their native range.

Macroecology meets invasion ecology: linking the native distributions of Australian acacias to invasiveness

AbstractAim Species’ native ranges reflect the net outcome of interactions between life‐history strategies and biotic and abiotic influences over evolutionary time‐scales. Differences in native ranges might be indicative both of relative historical performance and adaptability to new conditions. Consequently, the native ranges of successful invaders might have distinctive biogeographical characteristics. We test this hypothesis by (1) quantifying macroecological patterns of the entire assemblage of native taxa in Acacia subgenus Phyllodineae in Australia, (2) testing whether highly invasive taxa represent random samples from the patterns observed for the assemblage as a whole and (3) exploring the link between native geographical range and the position of species along the introduction‐naturalization‐invasion continuum.Location Australia and worldwide.Methods Three distributional metrics representing particular biogeographical characteristics of species’ native ranges – the logarithms of range size, percolation intercept and percolation exponent – were calculated by fitting a revised alpha hull to records from Australia’s Virtual Herbarium. Randomization and cascaded tests were used to compare these metrics for species at different stages of invasion.Results The macroecological patterns of the three distributional metrics displayed lognormal‐like frequency distributions. Most invasive species had significantly lower percolation exponents and larger native ranges than expected from random draws from the entire assemblage of Australian acacias, but percolation intercepts were not significantly different. This can be explained by a selection bias at the early stages of invasion.Main conclusions The outcome of the natural experiment of transplanting many Australian acacias into novel environments is not random. While invasive species have a particular macroecological pattern, this can be explained by the observation that species with large native ranges and low percolation exponents (i.e. high population increase rate) are most likely to have been introduced and naturalized. Whether this pattern is an artefact of human selection or reflects a human bias towards selecting invasive species remains to be seen.

Jack‐of‐all‐trades and master of many? How does associated rhizobial diversity influence the colonization success of Australian Acacia species?

AbstractAim To evaluate the role of rhizobial diversity, and symbiotic promiscuity, on the invasive ability of Australian acacias (Acacia species in subgenus Phyllodineae native to Australia).Location Global.Methods A bibliographic review of the rhizobial diversity associated with Australian Acacia species was performed to assess symbiotic promiscuity for invasive and non‐invasive species. The rhizobial diversity associated with Acacia dealbata and A. saligna in Australia and Portugal and with A. pycnantha in Australia and South Africa was assessed by 16S rDNA and intergenic spacer sequencing of bacteria isolated from field‐collected nodules.Results All studied Australian acacias are nodulated by strains in the genus Bradyrhizobium, which appears to be the dominant group of acacia symbionts in native and non‐native soils. Both literature and experimental data from this study suggest that Australian bradyrhizobia might have been co‐introduced with acacias to new geographical regions. The studied Acacia species can also harbour other root‐nodulating alpha and betaproteobacteria genera, although these are less abundant than Bradyrhizobium.Main conclusions There is no clear difference in the diversity of rhizobial species associated with invasive and non‐invasive Australian acacias. All studied invasive acacias nodulate in both native and non‐native regions, harbouring predominantly Bradyrhizobium strains but showing some degree of symbiotic promiscuity. The co‐introduction of compatible root‐nodulating bacteria from Australia might explain the establishment of invasive populations, but novel associations with rhizobia from the invaded soils are also possible. Invasive legumes might use both strategies but species with low symbiotic promiscuity would become invasive only if compatible bacteria are co‐introduced in the new regions. The progress of invasion and the impacts on the invaded ecosystems might also differ depending on the nodulation strategy.

Human‐mediated introductions of Australian acacias – a global experiment in biogeography

AbstractAim Australian acacias (1012 recognized species native to Australia, which were previously grouped in Acacia subgenus Phyllodineae) have been moved extensively around the world by humans over the past 250 years. This has created the opportunity to explore how evolutionary, ecological, historical and sociological factors interact to affect the distribution, usage, invasiveness and perceptions of a globally important group of plants. This editorial provides the background for the 20 papers in this special issue of Diversity and Distributions that focusses on the global cross‐disciplinary experiment of introduced Australian acacias.Location Australia and global.Methods The papers of the special issue are discussed in the context of a unified framework for biological invasions. Distributions of species were mapped across Australia, their representation in bioclimatic zones examined and the potential global distribution of the group modelled. By collating a variety of different lists, we determined which Australian acacias have reached different stages in the introduction‐naturalization‐invasion continuum in different parts of the world. Paradigms and key research questions relating to barriers to invasion, stages of invasion and management perceptions are sketched.Results According to our global database of Australian acacia records, 386 species have been moved outside Australia by human agency, 71 species are naturalized or weedy, and 23 are unequivocally invasive. Climatic models suggest that about a third of the world’s land surface is climatically suitable for Australian acacias. Many species are commercially important crops or are useful for other purposes and have been extensively planted, and many different human perceptions of Australian acacias exist in different parts of the world. The papers in the special issue cover all the barriers, stages and processes that define biological invasions and touch on many aspects: history and the human dimension; aspects of the species pool; species traits; biotic interactions; climate and niche; and management.Main conclusions Australian acacias are an excellent model group for examining interactions between evolutionary, ecological and socio‐economic drivers of species introductions. New insights have emerged on the biological, ecological and evolutionary correlates of naturalization and invasion, but human usage factors permeate all explanatory models. Understanding and managing introduced Australian acacias requires a fundamental and integrative appreciation of both intrinsic (e.g. species traits) and extrinsic (e.g. human usage and perceptions) aspects.

Adoption, use and perception of Australian acacias around the world

AbstractAim To examine the different uses and perceptions of introduced Australian acacias (wattles; Acacia subgenus Phyllodineae) by rural households and communities.Location Eighteen landscape‐scale case studies around the world, in Vietnam, India, Réunion, Madagascar, South Africa, Congo, Niger, Ethiopia, Israel, France, Portugal, Brazil, Chile, Dominican Republic and Hawai‘i.Methods Qualitative comparison of case studies, based on questionnaire sent to network of acacia researchers. Information based on individual knowledge of local experts, published and unpublished sources.Results We propose a conceptual model to explain current uses and perceptions of introduced acacias. It highlights historically and geographically contingent processes, including economic development, environmental discourses, political context, and local or regional needs. Four main groupings of case studies were united by similar patterns: (1) poor communities benefiting from targeted agroforestry projects; (2) places where residents, generally poor, take advantage of a valuable resource already present in their landscape via plantation and/or invasion; (3) regions of small and mid‐scale tree farmers participating in the forestry industry; and (4) a number of high‐income communities dealing with the legacies of former or niche use of introduced acacia in a context of increased concern over biodiversity and ecosystem services.Main conclusions Economic conditions play a key role shaping acacia use. Poorer communities rely strongly on acacias (often in, or escaped from, formal plantations) for household needs and, sometimes, for income. Middle‐income regions more typically host private farm investments in acacia woodlots for commercialization. Efforts at control of invasive acacias must take care to not adversely impact poor dependent communities.

Predicting invasiveness of Australian acacias on the basis of their native climatic affinities, life history traits and human use

AbstractAim Many Australian Acacia species have been widely planted around the world. Some taxa are among the most aggressive of invasive alien plants and cause severe ecosystem degradation. We aimed to predict invasiveness of taxa in a large set of Australian Acacia species on the basis of easy‐to‐assess predictors.Location Global.Methods We considered three groups of predictors: (1) climatic affinities of species in their native ranges; (2) life history traits; and (3) human usage factors. Logistic multiple regressions were applied to construct predictive models for 85 Australian acacias (species in Acacia subgenus Phyllodineae) that are known to have been transported outside of their native range (17 known to be invasive and 68 non‐invasive). The best model was then applied to predict the probability of an additional 34 Acacia species with unknown invasive status.Results Water availability in the native range and human uses were significant predictors of invasiveness in all models. Life history index (proportional to plant height, leaf area and seed mass) and climatic amplitude were also positive predictors of invasiveness when human use was not considered. The best model, based on human uses and water availability, correctly classified 92% of the species. Results suggest that Acacia species that evolved under low climatic stress have a greater chance of becoming invasive.Main conclusions Species that are useful to humans are more likely to be disseminated to and within new regions, thus increasing the risk of invasion. Combining ecological, evolutionary and human‐use criteria is useful for quantifying the risk of Australian acacias becoming invasive. Acacia species can attain invasive status by virtue of intrinsic traits and/or through increased use by humans. Therefore, we predict that the invasion risk of species coming from native areas with high water availability will rise sharply if the interest in exploiting these species increases.

Gall inducers take a leap: host-range differences explain speciation opportunity (Thysanoptera: Phlaeothripidae)

Phytophagous insects that specialise on broadly distributed plant groups are exposed to host-species diversity gradients. The gall-inducing thrips genus Kladothrips (Froggatt) that specialise on Australian Acacia Mill. (Mimosoideae: Leguminosae, subgenus Phyllodineae DC.) is expected to exhibit variation in host range that is dependent on host ecology. Host Acacia species distributions show structuring between the arid Eremean and non-arid biomes of the monsoonal tropics and temperate south-western and south-eastern Australia. We investigate two aspects of host use in: (1) the Kladothrips rugosus species complex that specialises on hosts whose distributions overlap among sibling lineages on different Acacia species; and (2) Kladothrips nicolsoni that specialises on a species that is relatively isolated from hosts of sibling lineages. First, several approaches that use DNA sequence data are combined to infer putative species among K. rugosus lineages collected from multiple Acacia species using: phylogenetic inference; statistical parsimony; amova; maximum likelihood genetic distance relationships; and generalised mixed Yule coalescent likelihood test of lineage delimitation. Second, haplotype network analysis is used to estimate population structuring of K. nicolsoni that specialises on a geographically isolated Acacia host species. Analyses indicated below species-level relationships among lineages that each induces galls on different Acacia host species. In contrast, haplotype network analysis for a gall-thrips species that is largely allopatric with hosts of sibling species indicates isolation by distance and range expansion effects. Greater host-species richness enhances gall-thrips opportunity to host shift resulting in founder effects that lead to disruptive selection. Restricted gene flow among gall-thrips populations specialising on a relatively isolated host species implies genetic drift via allopatric mechanisms. The results suggest gall-thrips speciation is driven by the combined influence of ecologically based selection with genetic drift that is largely determined by variation in host-species richness between arid and non-arid Australia.

Molecular phylogeny of three groups of acacias (Acacia subgenus Phyllodineae) in arid Australia based on the internal and external transcribed spacer regions of nrDNA

The phylogeny of three groups of arid Australian acacias ‐ the Acacia victoriae, A. murrayana and A. pyrifolia groups ‐ was constructed based on parsimony analysis of sequence data from the internal and external transcribed spacers (ITS and ETS) of the nuclear ribosomal DNA. Forty ingroup taxa were sequenced, including multiple accessions for some taxa and two species (A platycarpa and A. longispinea) that had been identified in other analyses as relatives of these acacias. Acacia anthochaera was used as the functional outgroup. The ITS and ETS regions proved to be sufficiently variable to resolve relationships at both the specific and intra‐specific level. Two main clades were resolved. One clade confirmed the monophyly of the Acacia murrayana group, and relationships of species were strongly supported. All taxa in this clade have a similar pattern of seedling leaf development. In the second clade, the A. pyrifolia group is nested within the A. victoriae group and all taxa have spinose stipules. Acacia platycarpa and A. longispinea are related to this clade. Phyllode nerve number (uninerved or plurinerved) proved to be homoplasious. Acacia victoriae is a widespread and very variable species. The molecular data identified two major groups: a group of populations occurring across northern Australia and a group of populations from the Western, Central and Eastern deserts. Further analysis of population variation is required to assess the taxonomic status of various forms in this species complex. The geographic distributions of sister taxa suggest predominantly allopatric speciation. The degree of molecular divergence and position of the clades within subgenus Phyllodineae suggest that the lineages are not of recent origin, but have a history that relates to increased aridity in the Australian Eremean region during the Cenozoic.

Water relations of phyllodinous and non‐phyllodinous Acacias, with particular reference to osmotic adjustment

An investigation was made into the effects of long‐ and short‐term water stress on the growth and water relations of species of Acacia belonging to four major sections of the subgenus Phyllodineae; the bipinnate‐leaved Botrycephalae and the phyllodinous Juliflorae, Phyllodineae and Plurinerves. The germplasm was collected from sites within a narrow rainfall band [700–800 mm mean annual rainfall (m.a.r.)]. Shoot and root mass were significantly decreased in three of the four sections by water stress. The exception was the Juliflorae that showed a conservative growth strategy. A high root/shoot ratio is associated with tolerance to arid or semiarid environments, however, the highest root/shoot ratio was found for the temperate Botrycephalae. Measurements were made of the capacity for active and partial osmoregulation. All sections showed a biphasic response to drought stress for natural logarithm plots of relative water content (RWC) vs. osmotic potential in one or both experiments. This pattern of response has previously only been reported in a few plant species. Osmotic adjustment (OA) ranged from 1.6 MPa for the Botrycephalae to 3.4 MPa for Juliflorae at RWC of 60%. Active osmoregulation in the second phase was lower for the Botrycephalae and Phyllodineae than for the Juliflorae and Plurinerves. Although the germplasm was collected within a narrow and relatively high m.a.r. band, the sections with arid and semiarid relatives (Juliflorae and Plurinerves) still retained a higher degree of xeromorphic character and drought tolerance as determined by the growth responses and the higher capacity for OA.

Biogeography of the Acacia victoriae, pyrifolia and murrayana species groups in arid Australia

A molecular phylogeny of all extant species (21) in two clades of phyllodinous acacias , including the Acacia victoriae, A. pyrifolia and A. murrayana groups, is the basis of a paralogy-free subtree analysis of historical relationships of geographic areas in arid and semi-arid Australia. These clades are in a relatively basal position within Acacia subgenus Phyllodineae. Sister taxa generally show vicariant (allopatric) patterns. The summary area cladogram indicates that the earliest regions to differentiate were Arnhem and the North-West semi-arid region (including Dampierland, Ord-Victoria Plains and Tanami), relative to the other regions occupied by these acacias. In arid central Australia, the Central and MacDonnell Ranges are most closely related to the South-West Interzone (Coolgardie bioregion). The Eastern Desert, Western Desert and Pilbara are related as a group, which does not support the idea that these two deserts have been colonized independently from different centres on the margin of the continent. The widespread and genetically variable A. victoriae species complex also showed regional differentiation, one pattern being the relationship of the Northern subtropical regions, from the southern Kimberley east to the Gulf Uplands and Cape York. It is argued for these acacias that the underlying differentiation of areas of endemism in the Eremean zone of Australia is relatively old, with increasing aridity during the Cenozoic, not withstanding that present-day species pairs and intra-specific variation might relate to more recent shifts in vegetation and arid cycles.

An investigation of phyllode variation in Acacia verniciflua and A. leprosa (Mimosaceae), and implications for taxonomy

Acacia verniciflua A.Cunn. and A. leprosa Sieber ex DC. are believed to be closely related, although strict interpretation of the current sectional classification of subgenus Phyllodineae places them in separate sections based on main nerve number. Six populations, comprised of the common and the southern variants of A. verniciflua and the large phyllode variant of A. leprosa, were sampled to test the value of nerve number as a taxonomic character and the current delimitation of these geographically variable species. Morphometrics, microscopy and the AFLP technique were used to compare and contrast populations. Phyllode nerve development was investigated and the abaxial nerve was found to be homologous with the mid-rib of a simple leaf. Three taxa were differentiated, two that are consistently two-nerved and one taxon that is variably one-nerved, two-nerved or both within a single plant. The first two-nerved taxon, characterised by smaller phyllodes, matches the type specimen of A. verniciflua. The second two-nerved taxon, characterised by large phyllodes, is apparently endemic to Mt William. The third taxon, with variable main nerve number, also has large phyllodes, and combines large phyllode variant A. leprosa (Wilhelmina Falls) and southern variant A. verniciflua (Kinglake) individuals. The number of main nerves per face in phyllodes is not a useful taxonomic character for sectional classification of Acacia. Although it has clearly proved functional in some instances, the character appears too variable to reliably define natural monophyletic groups. Anatomical features such as cell number of resinous glands and staining patterns proved to be informative.

Seed‐feeding species of Bruchophagus Ashmead (Hymenoptera: Eurytomidae) associated with native Australian acacias that are invasive in South Africa, with the description of two new species

Abstract A search for phytophagous eurytomid wasps of the genus Bruchophagus Ashmead that develop in the seeds of certain native Australian acacias in Australia and New Zealand has yielded three species. Although these three species are probably restricted to members of the subgenus Phyllodineae, to which the vast majority of Australian Acacia species belong, they are not host specific at the species level. Interest in these phytophagous wasps stems from an ongoing search for suitable natural enemies to limit the invasiveness of certain Australian acacias in South Africa. The three species are B. acaciae (Cameron), B. orarius sp. n and B. interior sp. n. A key for their separation, and comments on their relationship with other eurytomids that are associated with the genus Acacia, are also provided.

Phytochemistry of Acacia— sensu lato

Little is known about the chemistry of most species of the genus Acacia, although the genus is quite large and widespread in the warm subarid and arid portions of the world. As presently defined, Acacia is a cosmopolitan genus containing in excess of 1350 species. Taxonomic relationships and identification of Acacia species are difficult; new studies of the genus confirm that Acacia is an agglomeration of at least five discrete groups. The major elements of this ‘genus’ are the groups now recognized as the subgenus Acacia, the genus Faidherbia, the subgenus ‘ Aculeiferum’, relatives of Acacia coulteri, Bentham’s series Filicinae, the subgenus Phyllodineae, and possibly others, each with somewhat distinct chemistry. A number of secondary metabolites have been reported from various Acacia species including amines and alkaloids, cyanogenic glycosides, cyclitols, fatty acids and seed oils, fluoroacetate, gums, non-protein amino acids, terpenes (including essential oils, diterpenes, phytosterol and triterpene genins and saponins), hydrolyzable tannins, flavonoids and condensed tannins. The most evident and best known are polysaccharides (gums) and complex phenolic substances (condensed tannins).

Molecular phylogenetics of the Australian acacias of subg. Phyllodineae (Fabaceae: Mimosoideae) based on the trnK intron

With over 960 species, Acacia is the largest genus of plants in Australia with all but nine of these species classified as subgenus Phyllodineae. DNA sequences for the chloroplast trnK region were sequenced for over 100 species to test sectional classification and survey species relationships within this subgenus. Only one of the seven recognised sections was found to be monophyletic; however, the close relationship of sect. Botrycephalae to certain racemose, uninerved species of sect. Phyllodineae is confirmed. Support is found for an expanded version of Vassal's Pulchelloidea, with the addition of sect. Lycopodiifoliae and several members of sect. Phyllodineae. These species, while morphologically distinct in adult foliage, possess similar seedling characteristics. The multinerved species are unresolved, indicating a rapid morphological radiation with little chloroplast sequence divergence among these species. The low levels of sequence divergence, large numbers of morphological species groups and the adaptive radiation of the group are discussed.

Molecular phylogeny of Acacia subgenus Phyllodineae (Mimosoideae : Leguminosae) based on DNA sequences of the internal transcribed spacer region

The largest monophyletic group within Acacia is subgenus Phyllodineae, with more than 950 predominately Australian species, the majority characterised by adult foliage consisting of phyllodes. Molecular sequence data from the internal transcribed spacers (ITS) of the nuclear ribosomal DNA repeat were used to investigate the monophyly of seven sections within the subgenus. A nested PCR approach was used to amplify the ITS region. Fifty-one species representative of all sections were sequenced together with one outgroup taxon Lysiloma divaricata (Ingeae).Phylogenetic parsimony analysis suggested that there are two main clades within Phyllodineae but that only one section, Lycopodiifoliae, is apparently monophyletic. In one of the main clades, Lycopodifoliae is related to some taxa in sections Alatae and Pulchellae and some members of section Phyllodineae. In the second main clade, sections Juliflorae, Plurinerves and Botrycephalae cluster with other members of section Phyllodineae. The two sections that are characterised by bipinnate foliage, Botrycephalae and Pulchellae, are nested within phyllodinous clades, indicating that at least two separate reversals to bipinnate leaves have occurred. Botrycephalae is paraphyletic with respect to taxa from section Phyllodineae that have single-nerved phyllodes and racemose inflorescences.

Pollination ecology of acacias (Fabaceae, Mimosoideae)

We review the pollination ecology of acacias worldwide, discussing (1) the rewards provided to flower visitors, (2) the temporal patterns of flowering and reward provision and (3) the taxonomic composition of flower visitors assemblages. The flowers of most acacias (including all members of the subgenus Phyllodineae) offer only pollen to flower visitors and floral nectar is limited to a minority of species in the subgenera Acacia and Aculeiferum. The most important pollinators of acacias are social and solitary bees, although other insects and nectar-feeding birds are important in specific cases. Acacias that secrete nectar attract far more species-rich assemblages of flower visitors, although many of these are probably not important as pollinators. Most acacias in the subgenus Phyllodineae have long-lived protogynous flowers, without clear daily patterns in reward provision and visitation. In contrast, most members of the other two subgenera have flowers that last for a single day, appear to be protandrous and have clear daily patterning in reward provision and visitation. The generality of these patterns should not be assumed until the pollination ecology of many more phyllodinous acacias has been studied, particularly in arid environments. The accessibility of the floral rewards in acacia flowers makes them important examples of two general issues in plant communities—the partitioning of shared pollinators and the evolution of floral ant repellents.

Development, inheritance and cross-species amplification of microsatellite markers from Acacia mangium

Microsatellite markers were developed in Acacia mangium Willd. to provide highly variable co-dominant markers for linkage mapping and studies of the breeding system. After an enrichment procedure 40% of colonies contained microsatellites in contrast with less than 1% from a non-enriched library. The majority of microsatellite sequences were AC repeats. Co-dominant segregation of alleles in two full-sib crosses of A. mangium was demonstrated at 33 microsatellite loci. The markers were highly variable relative to restriction fragment lengths polymorphisms (RFLPs). In the two pedigrees 53% of microsatellite loci were fully informative compared with 15% of RFLPs. Based on alleles detected among four parental genotypes, the microsatellites consisting of dinucleotide repeats were more polymorphic than those with tri- and tetra-nucleotide repeats. The microsatellite markers were not as transferable across species in the genus Acacia as RFLPs. Two thirds of the primers developed in A. mangium (subgenus Phyllodineae, section Juliflorae) amplified DNA from other species within the same section but failed to amplify in species from the subgenus Acacia. The availability of multiallelic, PCR-based, co-dominant microsatellite loci makes possible efficient studies of gene flow and breeding systems in A. mangium, a species with low allozyme variation.

A plastid DNA phylogeny of the genus Acacia Miller (Acacieae, Leguminoseae)

Past classifications of the tribe Acacieae Rchb. are outlined and the confusion concerning the relationships of the three subgenera of Acacia Mill. are highlighted. A plastid DNA analysis of Acacieae shows that the genus Acacia is not monophyletic. Furthermore subgenera Acacia Vassal and Aculeiferum Vassal are sister taxa and neither appear closely related to subgenus Phyllodineae (DC.) Ser. Subgenera Acacia andAculeiferum form a clade that is basal to a well-supported clade consisting of tribe Ingeae Benth. taxa, Faidherbia albida (Del.) A. Chev. and subgenus Phyllodineae. The series of relationships suggested by the cpDNA data contradicts previous investigations of the tribe. Possible explanations of this conflict are explored, and the taxonomic implications of the plastid DNA data set are considered.

A plastid DNA phylogeny of the genus Acacia Miller (Acacieae, Leguminoseae)

Past classifications of the tribe Acacieae Rchb. are outlined and the confusion concerning the relationships of the three subgenera of Acacia Mill. are highlighted. A plastid DNA analysis of Acacieae shows that the genus Acacia is not monophyletic. Furthermore subgenera Acacia Vassal and Aculeiferum Vassal are sister taxa and neither appear closely related to subgenus Phyllodineae (DC.) Ser. Subgenera Acacia andAculeiferum form a clade that is basal to a well-supported clade consisting of tribe Ingeae Benth. taxa, Faidherbia albida (Del.) A. Chev. and subgenus Phyllodineae. The series of relationships suggested by the cpDNA data contradicts previous investigations of the tribe. Possible explanations of this conflict are explored, and the taxonomic implications of the plastid DNA data set are considered.