Subgenus Acacia 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.

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.

Neotropical mutualism between Acacia and Pseudomyrmex: Phylogeny and divergence times

The interaction between Acacia and Pseudomyrmex is a textbook example of mutualism between ants and plants, nevertheless aspects of its evolutionary biology have not been formally explored. In this paper we analyze primarily the phylogenies of both New World Acacia and of their associated species of ants, and the geographic origin of this mutualism. Until now, there has been no molecular analysis of this relationship in terms of its origin and age. We analyzed three chloroplast markers (matK, psaB-rps14, and trnL-trnF) on a total of 70 taxa of legumes from the subfamily Mimosoideae, and two nuclear regions (long-wavelength rhodopsine and wingless) on a total of 43 taxa of ants from subfamily Pseudomyrmecinae. The monophyly of subgenus Acacia and within the New World lineages that of the myrmecophilous Acacia group was established. In addition, our results supported the monophyly of the genus Pseudomyrmex and of the associated acacia-ants P. ferrugineus group. Using Bayesian methods and calibration data, the estimated divergence times for the groups involved in the mutualism are: 5.44+/-1.93 My for the myrmecophilous acacias and 4.58+/-0.82 My for their associated ant species, implying that their relationship originated in Mesoamerica between the late Miocene to the middle Pliocene, with eventual diversification of both groups in Mexico.

Taxonomic Revision of the Vachellia acuifera Species Group (Fabaceae: Mimosoideae) in the Carribean

Twelve Caribbean species of Vachellia (formerlyAcacia subgenus Acacia) are formally monographed with taxonomic, habitat, geographic distribution descriptions, and lists of representative specimens examined. The species treated here are all part of the informal Vachellia acuifera group, which is characterized by generally enlarged stipular spines borne in clusters on the stems, 1–3 pairs of pinnae per leaf, and 20–50 stamens. Ordination analyses of vegetative characters show that these species form discrete groups in two- and three-dimensional plots. Vachellia baessleria Clarke, Seigler, & Ebinger, endemic to Guantánamo and Las Tunas, Cuba, is newly described. Vachellia acuifera is wide ranging, occurring from the Bahamas to Cuba. The other species are highly restricted in their distribution and ecological setting. Four of the species are only known from Hispaniola (V. barahonensis, V. caurina, V. cucuyo, and V. oviedoensis) and six only from Cuba (V. baessleria, V. belairioides, V. bucheri, V. daemon, V. roigii, and V. zapatensis). Another species, V. anagadensis, is only found on the island of Anegada in the British Virgin Islands.

A phylogenetic analysis of the Acacieae and Ingeae (Mimosoideae: Fabaceae) based on trnK, matK, psbA-trnH, and trnL/trnF sequence data

A phylogenetic analysis of exemplars of Acacieae, Ingeae, and some Mimoseae, based on trnK, matK, psbA-trnH, and trnL/trnF sequence data, is presented. The results support other recent studies in showing that neither the Ingeae nor Acacieae is monophyletic. Some subgenera of Acacia, specifically subgenera Acacia and Phyllodineae, are monophyletic, but subg. Acacia is in a basal polychotomy with various members of Mimoseae and a large clade with the other members of Ingeae and Acacieae. Acacia subg. Phyllodineae is sister group to members of the Ingeae. Both the Ingeae and Acacia subg. Aculeiferum are paraphyletic.

New peltogynoids from Acacia nilotica

The genus Acacia (Leguminosae, subfamily Mimosoideae) includes some 1400 species of trees and shrubs widespread throughout the warm arid and semi-arid regions of the world. Acacia nilotica (L.) Delile belongs to the subgenus Acacia. It naturally occurs in tropical Africa, from Senegal and Egypt southwards to Mozambique and Natal, and also in Asia, from Arabia to India and Burma. A. nilotica is a more or less shrubby tree 5–20m high. This species is widely used in traditional medicine in Africa. Repeated column chromatography over silica gel of the CHCl3 soluble part of the EtOH extract obtained from the stem bark of Acacia nilotica, resulted in the isolation of the two novel peltogynans, acanilol I (1) and II (2), together with the known triterpene lupenone. The structures of the novel compounds were established on the basis of mass spectrometry and NMR experiments [1].

Impact of Protected Areas and Land Use on Regeneration of Acacia Woodland’s in Eastern Burkina Faso

Regeneration success, persistence strategies (seedlings vs. coppicing), and population trend of Acacia spp. were tested under two land-use regimes in eastern Burkina Faso: (i) protected areas shielded to livestock grazing pressure, to logging, and using early annual fire as a management system; (ii) areas with high human impact (heavily and extensive livestock grazing, harvesting for wood and for medicinal plants). Generally, a good regeneration rate of Acacia species was observed in protected areas and a poor regeneration rate in areas with high human impact. Nevertheless, some species affiliated to the subgenus Aculeiferum as A. dudgeoni and A. polyacantha showed a good regeneration under both land use regimes. Juvenile plants less than 25 cm height of A. dudgeoni and A. gourmaensis increased by 116 to 50 % in areas with human impact as compared to their populations in protected areas. With SCD slopes varying from –0.40 to -0.70, the protected Acacia woodland displayed a stable population structure due to abundance of recruitment, and coppicing persistence (more common in the subgenus Aculeiferum) favoured by early annual fire. Consequently, the protected areas are favourable for Acacia woodland regeneration. Conversely, SCD slopes are positive or close to zero in areas of anthropogenic regime and showed a declining population, especially more marked with the subgenus Acacia due to permanent seed and seedling removal by livestock grazing. Nevertheless, the number of seedlings of some species was higher in areas under human pressure than in protected areas, especially for the subgenus Aculeiferum, improving the genetic variability and thus the long-term maintenance of the population

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.

A new combination in Senegalia and typification of six New World Acacia names

Recent and past morphological and genetic studies suggest that the genus Acacia s.l. is better treated as a number of segregate genera. The generic segregates more or less follow the boundaries of the former Acacia subgenera. It is thus an appropriate time to transfer Acacia kelloggiana A.M. Carter & Rudd from Acacia subgenus Aculeiferum to Senegalia Rafinesque. Studies of New World members of Acacia subgenus Aculeiferum have also revealed the necessity to select neotypes or lectotypes for some names of species now placed in the genus Senegalia.

Characterization and properties of Acacia senegal (L.) Willd. var. senegal with enhanced properties (Acacia ( sen) SUPER GUM™): Part 1—Controlled maturation of Acacia senegal var. senegal to increase viscoelasticity, produce a hydrogel form and convert a poor into a good emulsifier

The Acacia gum ( Acacia senegal var. senegal), which is a food additive approved by Codex Alimentarius, is defined within the Acacia subgenus (family Leguminosae). The structural characteristics associated with a “poor” and “good” emulsifying A. senegal var. senegal exudate gum are identified and it is shown that it is possible to maturate the “poor” emulsifier in a process comparable to that which occurs to the exudate gum as the age of the tree increases from 1 to 15 years and when the gum is stored naturally after collection. Thus, the molecular parameters of the “good” gum can be matched, and the emulsification effectiveness can attain the level of the “good” emulsifier. The process can be further continued to produce a series of gums of precisely structured molecular dimensions with improved properties and if the maturation is continued can yield a hydrogel form of Acacia. The new forms of A. senegal which are described here, and which have not previously been available are designated Acacia ( sen) SUPER GUM™ which are constant in properties and with precisely structured molecular dimensions, unlike the naturally occurring gum. The viscosity can be increased up to 20 times compared to the starting material. The controlling factor is the agglomeration of the proteinaceous components within the molecularly disperse system that is A. senegal gum to increase the amount of arabinogalactan protein (AGP) emulsifying component up to more than double the amount present originally. This results in a dramatic increase in the interfacial surface properties and coverage of the oil droplet in oil in water emulsion. No other chemical change is initiated by the maturation process.

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.

The importance of species identity in the biocontrol process: identifying the subspecies of Acacia nilotica (Leguminosae: Mimosoideae) by genetic distance and the implications for biological control

AbstractAims A molecular genetic distance study has been used in an initial survey to identify subspecies and genotypes of the weed Acacia nilotica in Australia, information needed to find suitable biocontrol agents. We use patterns of DNA sequence variation (in two DNA fragments) from each of the nine described subspecies of Acacia nilotica (L.) Delile (Leguminosae: Mimosoideae) that is to determine their genetic similarity, to verify if the Australian populations are A. nilotica ssp. indica (Benth.) Brenan, and to establish if any other subspecies are present in Australia.Location Australia and southern Africa through the Arabian peninsular to the Indo‐Pakistan subcontinent.Methods Representative specimens from the global distribution of the nine A. nilotica subspecies were sourced primarily from herbaria sheet specimens where available, and secondarily from field collections. These specimens together with related outgroups from Mimosoideae were genetically analysed using the DNA fragments trnL and internal transcribed spacer one (ITS1). We calculated a similarity index as set out in paup* using upgma (Unweighted Pair‐Group Method Arithmetic average) methods to cluster taxa to produce a genetic distance phenogram.Results Sequence results from ITS1 and trnL DNA fragments identified seven of the described subspecies of A. nilotica. Acacia nilotica ssp. cupressiformis (J. Stewart) Ali & Faruqi and A. nilotica ssp. adstringens (Schumach. & Thonn.) Roberty were not found to be genotypically distinct from A. nilotica ssp. indica and A. nilotica ssp. nilotica, respectively, based on the two DNA fragments. Subspecific ITS1 genotypes were geographically distributed similarly to previous reports that were based on morphology, with the exception that the hemispherica ITS1 genotype also occurred in Somalia. We confirmed that the Australian A. nilotica populations are mostly comprised of subspecies indica, but in addition, some individuals were found to be genetically identical to an unidentified Pakistan genotype not previously reported as occurring in Australia.Main conclusions Australian A. nilotica populations originated from India and Pakistan and we recommend further analysis to determine the complete genetic diversity profile and origins of the Australian populations. We highlight the importance of determining any hybridization between Australian populations of A. nilotica and native subgenus Acacia species. This study demonstrates the importance of genotyping weed species targeted for biocontrol and/or listed host specificity test species that may be easily misidentified. Biocontrol practitioners can justify genetic studies by considering the costs should a project fail through misidentification.

Nuclear DNA Amounts in Acacia and Prosopis (Mimosaceae) and their Evolutionary Implications

The nuclear DNA amounts of 53 accessions representing 26 species of Acacia and Prosopis, were estimated with a flow cytometer. Accessions of the same level of ploidy in each of the three subgenera of Acacia and the genus Prosopis formed four classes. The 2C-values and ploidy levels of taxa within each class were strongly correlated (r=0.968, 0.982, and 0.997 for the subgenera Acacia, Heterophyllum, and the genus Prosopis, respectively). Within species, genome size variations were mainly due to polyploidy. For subgenus Acacia, the mean 2C-value of the tetraploid accessions was 1.091 pg and for the octoploid 2.179 pg. The mean 2C-value of accessions of Aculeiferum (all are diploid) was I. 150 pg. The mean 2C-value of the diploid Heterophyllum was 1.583 and of the tetraploid 3.309 pg, whereas that of the diploid accessions of Prosopis was 0.846 pg and of the tetraploid 1.724 pg. The mean 2C-value of Acacia nubica (subgenus Acacia) was 1.680; a value closer to that of the tetraploid accessions of Prosopis. Accordingly, it is suggested that A. nubica, which also has 2n= 56, may better fit in Prosopis than in Acacia. The present results demonstrate considerable divergence in genome size among the three subgenera of Acacia and the genus Prosopis, and that speciation within subgenera may involve qualitative rather than quantitative changes in their nuclear DNA.

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).

Taxonomic significance of seed protein profiles in Acacia, with special reference to Acacia emilioana

Total seed proteins of 10 Acacia species were examined by SDS–PAGE. The protein patterns showed qualitative and quantitative differences among the taxa analysed. The main protein components of most species examined had MW's in the range of 38.5–49.0 × 103. Subgenus Aculeiferum differed from subg. Acacia in the presence of a high concentration of proteins in the range of 20–24.5 × 103. Hierarchical clustering of the 10 taxa was undertaken, based on Jaccard distances calculated from electrophoretic data. The species grouped in two main clusters, representing the two subgenera of Acacia that occur in America, namely subg. Acacia and subg. Aculeiferum. The taxonomic placement of Acacia emilioana, a species with uncertain sectional affinity within subg. Aculeiferum, is discussed.

Molecular phylogenetics of Acacia subgenera Acacia and Aculeiferum (Fabaceae : Mimosoideae), based on the chloroplast matK coding sequence and flanking trnK intron spacer regions

The genus Acacia is subdivided into the following three subgenera: subg. Acacia, subg. Aculeiferum and the predominantly Australian subg. Phyllodineae. Morphological and molecular studies have suggested that the tribe Acacieae and genus Acacia are artificial and have a close affinity to the tribe Ingeae. Sequence analysis of the chloroplast trnK intron, including the matK coding region and flanking non-coding regions, were undertaken to examine taxon relationships within Acacia subgenera Acacia and Aculeiferum. Subgenus Acacia is monophyletic while subgenus Aculeiferum is paraphyletic. Within the subgenera, major divisions are found based on biogeography, New World versus African–Asian taxa. These data suggest that characters such as inflorescence and prickle and/or stipule type are polymorphic and homoplasious in cladistic analyses within the subgenera.