Subgenus Acacia Research Articles

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.

Geographical patterns in neotropical Acacia (Leguminosae: Mimosoideae)

Native neotropical species of Acacia, totalling 230 species, are represented by two subgenera, Acacia and Aculeiferum. The number of taxa per country and their distribution are presented. For subgenus Aculeiferum, the species of section Filicinae are the richest in Mexico, while species of section Monacanthea are the most diverse in Brazil, Bolivia and Mexico. The species of subgenus Acacia have three main areas of diversity, with Mesoamerica being the most important region for the myrmecophyllous species and Mexico, the United States and Cuba for the non-myrmecophyllous species.

Impact of bush fire on germination of some West African acacias

Bush fire is a widespread and recurrent feature of the African dry savannas and contributes largely to changes in the composition of vegetation communities. However, the impact on seed regeneration in local species has received little attention. This study evaluates the effects of managed bush fire on seed viability and germination capacity for 10 species of West African acacia (sensu lato), taking into consideration fire intensity (related to the quantity of combustible biomass) and seed location (in, on or above the soil) at the time of the fire. The results indicate that the behavior of different species is related to their taxonomic position. Acacia species belonging to the sub-genus Aculeiferum are characterized by their lack of integument inhibition. The consequences of the passage of fire, depending on the intensity of heat shock, are limited to seed survival: they either retain viability or die. Seeds from the sub-genera Acacia and Faidherbia albida have a hard integument that needs to be scarified in order for germination to ensue. In our study, we show that on the whole, heat shocks cannot scarify the integument of the seeds without resultant lethal damage to their embryos. This is true regardless of seed status (naked or protected by seed pods), seed location (in, on or under the soil) and fire intensity. The only species to manifest an improvement in germination capacity, under certain selective experimental fire conditions, and in relation to the non-scarified control are A. raddiana, A. seyal and A. sieberiana. Nevertheless, germination remains substantially inferior to that obtained after scarification by removal of a small piece of integument. It thus seems conceivable to conclude that, contrary to what takes place in Mediterranean climate ecosystems and the wet tropics, fire does not encourage the in situ germination of different Acacia species. This finding implies that in dry savanna areas, it is not possible to regard fire as an accessory to reforestation or natural regeneration of these species.

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.

Implications of Chloroplast DNA Restriction Site Variation for Systematics of Acacia (Fabaceae: Mimosoideae)

Abstract Comparative restriction site mapping of the chloroplast genome of 26 accessions of Acacia plus outgroups (Caesalpinia, Albizia, and Ebenopsis) was carried out to analyze phylogenetic relationships among the subgenera of Acacia and, in particular, within Acacia subgenus Acacia. One or more taxa from each of seven New World species-groups plus two African species of Acacia subgenus Acacia were included in the analysis to generate hypotheses of the evolution and radiation of this group. Restriction maps constructed from data from 11 restriction enzymes yielded 212 informative restriction sites out of a total of 900. Parsimony analysis resulted in a total of 12 most parsimonious trees of 663 steps each. The strict consensus tree and bootstrap and decay indices indicate strong support for monophyly of Acacia subgenus Acacia and provisional support for the paraphyly of Acacia overall. Moderately to strongly supported clades within Acacia subgenus Acacia indicate that the mesically adapted A. macracanth...

Phylogenetic analysis of Australian Acacia (Leguminosae: Mimosoideae) by using sequence variations of an intron and two intergenic spacers of chloroplast DNA

Three regions of chloroplast DNA are assessed for their utility for phylogenetic analysis of Acacia subgenus Phyllodineae: psbA–trnH intergenic spacer, the trnL intron and the trnL–trnF intergenic spacer. There are large differences in the lengths of the psbA–trnH spacer (155–440 bp) and trnL–trnF intergenic spacer (101–422 bp) regions, and large multi-residue indels were coded as multistate characters. Overall information content in these regions is relatively low, but the total evidence tree has 12 nodes resolved, five with jackknife support. By using Parkia timoriana as the outgroup, Acacia subgenus Acacia (A. farnesiana) is basal and Acacia subgenus Aculeiferum (A. senegal) is the sister taxon to subgenus Phyllodineae. Although based on a small sample size, within subgenus Phyllodineae, the results of this study have shown that section Alatae is not monophyletic, section Lycopodiifoliae is monophyletic and Botrycephalae is related to members of section Phyllodineae with racemose inflorescences.

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Forty legume species, of which most were tree species of potential multipurpose value, were grown for 120 days in individual containers in an outdoor nursery, in a slightly acidic soil (pH 6.0) taken from a subhumid field site where test plantings were planned. Twenty-four species were also grown in a neutral soil (pH 7.2), taken from an arid zone field site. Dry weight of shoots, roots and nodules, as well as N2 content (DW) and nodule types were compared for all species and four provenances of the locally dominant Acacia caven. A nitrogen fixation and uptake (NFU) ratio was calculated as N2/nodules (DW). In both soil types, members of sub-family Mimosoideae nodulated more and grew faster than the Caesalpinioideae or Papilionoideae tested. Within the Mimosoideae, Acacia species, especially of sub-genus Acacia (= series Gummiferae Benth.), grew faster and accumulated more nitrogen than several Prosopis species or any other genus. In acidic soil, the local provenance of Acacia caven performed as well or better than three introduced provenances. Weedy species nodulated more consistently than non-weedy ones. Within the range tested, soil pH did not appear to affect relative performance of species and provenances tested. NFU ratios did, however, vary in the different soils. On the basis of these nursery tests, several weedy candidate species were excluded from field trials, in favor of similarly performing candidates with less potential of becoming invasive weeds.

Phylogenetic analysis of Acacia (Mimosaceae) as revealed from chloroplast RFLP data

Chloroplast DNA of 22 species of Acacia (Tourn.) Miller was digested with ten restriction endonucleases, Southern-blotted and probed with cloned fragments covering the chloroplast genome of tobacco (Nicotiana tabacum L.). Phyletic and phenetic analyses of the resulting 176 polymorphic bands recorded among the 22 species were performed. The phylogram was reconstructed using heuristic search and Wagner parsimony. The resulting most parsimonious consensus phylogram displayed three major phyletic lineages, consistent with the previously established three subgenera of Acacia. The 10 species of subgenus Acacia and the 6 species of subgenus Heterophyllum formed two monophyletic sister clades. The 5 species of subgenus Aculeiferum studied and Acacia albida (Syn. Faidherbia albida) grouped together and were basal to the clades of subgenera Acacia and Heterophyllum. The phylogram indicated that subgenus Heterophyllum diverged earlier from subgenus Aculeiferum than did subgenus Acacia; however, the phenogram indicated the reverse. The study indicated that A. nilotica and A. farnesiana are sister species, though A. nilotica is Afro-Asiatic and A. farnesiana is American. The phenogram separated the three subgenera in agreement with the phylogram, but the two dendrograms differed regarding the topologies of the species and the distance of evolution between subgenera Acacia and Heterophyllum.

Cotyledon architecture and anatomy in the Acacieae (Leguminosae: Mimosoideae)

Abstract Cotyledon size, shape, venation pattern and anatomy have been investigated in Faidherbia albida and 152 species of Acacia representing the three subgenera Acacia , Aculeiferum and Heterophyllum. Cell volumes of epidermis, palisade and storage tissue, stomatal frequency, stomatal index and frequency of stomatal types have been determined for F. albida and 12 species from each subgenus. The data obtained support the recognition of the subgenera of Acacia as separate taxa but provide no indication of their status. The evidence from cotyledons also supports the separation of Faidherbia from Acacia , and the amalgamation of the Acacieae and Ingeae.

Cytoevolution of Taxa in Acacia and Prosopis (Mimosaceae)

Somatic chromosome numbers were reported for 47 accessions of Acacia (Tourn.) Miller, representing 23 species including A. albida (syn. Faidherbia albida), together with 19 accessions (11 species) of Prosopis (L.) Burkart. Microphotographs of somatic metaphases of 12 accessions and six representative idiograms are shown. Somatic numbers of different accessions of a species can be different. Somatic numbers of accessions of subgenus Acacia were predominantly 52; a few had 2n = 78 or 104. However, A. sieberana had 2n = 26 and A. nubica 2n = 56. Except for A. polycantha, which had 2n = 52, somatic numbers of subgenus Aculeiferum were invariably 26. Of the six species of subgenus Heterophyllum studied, five had 26 somatic chromosomes and one (A. holoceraceae) had 52. All the four accessions of A. albida had 2n = 26. Out of the 19 Prosopis accessions investigated, five had 56 somatic chromosomes and 14 accessions had 28. In Acacia, subgeneric and specific differentiations are probably caused by structural changes in the chromosomes, whereas differences in the degree of euploidy appear to create infraspecies. Subgenus Aculeiferum is a possible progenitor of all other taxa of Acacia and Prosopis. The study suggests that Prosopis has diverged later in geological times from a diploid ancestor (2n = 26) of Aculeiferum through centric fission of the second-largest chromosome pair.

Nueva especie mirmecófila de Acacia (Leguminosae) de la península de Yucatán, México

Se describe una especie nueva de Acacia (Subgénero Acacia) de la Península de Yucatán, México, del grupo mirmecófilo. La especie es cercana morfológicamente y en habitat a Acacia globulifera y A. hindsii. Se proporciona una clave para la determinación de las especies afines de la Península.

A chemometric study of the Acacia (gum arabic) and related natural gums

Nine physical and chemical parameters for the gums from the Acacia sub-genus ( Vulgares and Gummiferae classes) and Albizia and Combretum gums of similar composition, were subjected to chemometric analysis exploratory data analysis. The Combretum and Albizia species gums could readily be distinguished from each other and from the Acacia species gums. Whereas the Vulgares and Gummiferae subgenus could be shown to be separated, these classes merge at the boundaries, indicating that A.seyal and A.Senegal can be regarded as closely related gums in regulatory terms. The Combretum and Albizia gums also can be readily categorized, based on amino acid composition.

The 5S DNA units ofAcacia species (Mimosaceae)

The DNA sequence structure of 5S DNA units inAcacia species, including representatives from the three subgenera ofAcacia, have been determined. The data was interpreted to suggest that at least three lineages of 5S DNA sequences exist inAcacia and the proposal was made that the lineages be named5S Dna-1, 5S Dna-2, and5S Dna-3. The5S Dna-1 lineage was represented by units fromA. boliviana andA. bidwilli, the5S Dna-2 lineage by units fromA. melanoxylon, A. pycnantha, A. ulicifolia, A. boliviana, A. bidwillii, andA. albida, and the5S Dna-3 lineage by units fromA. bidwillii, A. boliviana, andA. senegal. Based on this interpretation of the sequence data, the Australian species of subg.Phyllodineae grouped together as a cluster, quite separate from the subgeneraAculeiferum andAcacia. As expected from the analyses of morphological characters, the 5S DNA units fromAcacia albida (syn.Faidherbia albida) were quite separate from the otherAcacia spp.

Early growth rate and nitrogen fixation potential in forty-four legume species grown in an acid and a neutral soil from central Chile

Forty legume species, of which most were tree species of potential multipurpose value, were grown for 120 days in individual containers in an outdoor nursery, in a slightly acidic soil (pH 6.0) taken from a subhumid field site where test plantings were planned. Twenty-four species were also grown in a neutral soil (pH 7.2), taken from an arid zone field site. Dry weight of shoots, roots and nodules, as well as N 2 content (DW) and nodule types were compared for all species and four provenances of the locally dominant Acacia caven. A nitrogen fixation and uptake (NFU) ratio was calculated as N 2/nodules (DW). In both soil types, members of sub-family Mimosoideae nodulated more and grew faster than the Caesalpinioideae or Papilionoideae tested. Within the Mimosoideae, Acacia species, especially of sub-genus Acacia (= series Gummiferae Benth.), grew faster and accumulated more nitrogen than several Prosopis species or any other genus. In acidic soil, the local provenance of Acacia caven performed as well or better than three introduced provenances. Weedy species nodulated more consistently than non-weedy ones. Within the range tested, soil pH did not appear to affect relative performance of species and provenances tested. NFU ratios did, however, vary in the different soils. On the basis of these nursery tests, several weedy candidate species were excluded from field trials, in favor of similarly performing candidates with less potential of becoming invasive weeds.

Cyanogenesis in Acacia subgenus Aculeiferum

Cyanogenic glycosides are for the first time identified from members of Acacia subgenus Aculeiferum. The aromatic glycosides prunasin and sambunigrin occur in A. caffra and A. hereroensis. These African species are placed in section Aculeiferum subsection Polyacanthae. These data support other evidence derived from pollen and free amino acids in seeds that subgenus Aculeiferum is more closely related to the predominantly Australian subgenus Phyllodineae than to the pan-tropical subgenus Acacia.

Cyanogenesis in australian species of Acacia

In a survey in which approximately 96% of the Australian species of Acacia were examined, 45 species were shown to be cyanogenic. Forty-three of the 45 cyanogenic species occurred in subgenus Phyllodineae and two in subgenus Acacia. Within subgenus Phyllodineae, 37 cyanogenic species occurred in section Juliflorae, five in section Botrycephalae, and one in section Pulchellae. Cyanogenesis was not observed in the four other sections of the subgenus. The cyanogenic glycosides in subgenus Phyllodineae are prunasin and/or sambunigrin, derived from phenylalanine. The two species in subgenus Acacia contain proacacipetalin, derived from leucine. These biochemical studies are discussed in the context of the existing taxonomy of the genus.

Patterns of Distribution of Acacia in Australia

Patterns of distribution are described for the three subgenera and nine sections that make up the Australian Acacia flora. Subgenus Phyllodineae (833 species) is widespread and contains 99% of the species; subgenus Acacia (six species) and subgenus Aculeiferum (one species) are poorly represented and virtually confined to the north of the continent. The geographic patterns of species-richness are strongly influenced by sections Phyllodineae (352 species), Juliflorae (219 species) and Plurinerves (178 species). Section Phyllodineae has centres of richness south of the Tropic of Capricorn in temperate and adjacent semiarid areas of eastern, south-eastern and south-western Australia. The section is poorly represented in the tropics. The closely related sections Juliflorae and Plurinerves predominate in the north of the continent, semiarid areas of the south-west, many rocky tablelands of the Arid Zone and along the Great Dividing Range and adjacent inland riverine lowland areas in eastern Australia. The remaining four sections contribute little to the overall patterns of species-richness. The principal speciespoor areas are sandy and fluvial lowland regions of the Arid Zone. In eastern Australia, sections Botrycephalae, Juliflorae, Phyllodineae and Plurinerves show discontinuous patterns of species-richness along the Great Dividing Range. All sections have species whose ranges terminate in the area of the McPherson-Macleay Overlap region.

Cyanogenesis in Acacia pachyphloia

The cyanogenic glycoside, proacacipetalin, is reported from Acacia pachyphloia ( Acacia subgenus Acacia). This represents the first record of a glycoside with an aliphatic aglycone from a species of Acacia indigenous to Australia. This finding reinforces the taxonomic distinctions between subgenus Acacia and subgenus Phyllodineae.