Mimosoid Clade Research Articles

Senegalia ajaya (Mimosoid clade, Caesalpinioideae, Fabaceae), a new species from Birbhum District, West Bengal, India

A new species of Senegalia, S. ajaya (Mimosoid clade, Caesalpinioideae, Fabaceae) is described and illustrated from Birbhum district of West Bengal, India. This species is closely related to Senegalia caesia but can be distinguished from S. caesia by its distinctive characters such as: climbing shrub habit; internode bearing 6-lines of prickles; tendrils on the branches; rachilla prickles on the underside; two types of paraphyllidia at pinnae bases; asymmetrically rounded leaflet base; mid vein extended straight to the apiculate apex.

Taxonomic revision of the genus Punjuba (Leguminosae, Caesalpinioideae)

Punjuba is a Neotropical genus of the mimosoid clade (Leguminosae). The genus was recently restablished and is recognized by presenting shrubs and trees, with lax racemes or spiciform racemes, leaves with 1–3 pairs of pinnae and 2–7 pairs of leaflets in each pinna, thin and lateraly compressed legumes, curved to spiral, and seeds lacking pleurogram. Recent advances on legumes systematics have been producing great challenges on the circumscription of genera, especially on the mimosoid clade. Molecular phylogenetic studies confirm that Punjuba is monophyletic, and a revision of the genus and species circumscriptions are needed. Here we present a taxonomic revision of Punjuba, providing an identification key for all species currently recognized in the genus, morphological descriptions, and distribution maps. We recognize six species in the genus: P. callejasii, P. centiflora, P. killipii, P. lehmannii, P. racemiflora and P. foreroana, being the last one described here as a new species. Abarema josephi is proposed as a new synonym of P. lehmannii. Morphological characters including the inflorescence, indumentum, leaves and leaflets, besides quantitative characters, were applied as diagnostic to recognize the species.

The genomes of seven economic Caesalpinioideae trees provide insights into polyploidization history and secondary metabolite biosynthesis

The Caesalpinioideae subfamily contains many well-known trees that are important for economic sustainability and human health, but a lack of genomic resources has hindered their breeding and utilization. Here, we present chromosome-level reference genomes for the two food and industrial trees Gleditsia sinensis (921 Mb) and Biancaea sappan (872 Mb), the three shade and ornamental trees Albizia julibrissin (705 Mb), Delonix regia (580 Mb), and Acacia confusa (566 Mb), and the two pioneer and hedgerow trees Leucaena leucocephala (1338 Mb) and Mimosa bimucronata (641 Mb). Phylogenetic inference shows that the mimosoid clade has a much higher evolutionary rate than the other clades of Caesalpinioideae. Macrosynteny comparison suggests that the fusion and breakage of an unstable chromosome are responsible for the difference in basic chromosome number (13 or 14) for Caesalpinioideae. After an ancient whole-genome duplication (WGD) shared by all Caesalpinioideae species (CWGD, ∼72.0 million years ago [MYA]), there were two recent successive WGD events, LWGD-1 (16.2–19.5 MYA) and LWGD-2 (7.1–9.5 MYA), in L. leucocephala. Thereafter, ∼40% gene loss and genome-size contraction have occurred during the diploidization process in L. leucocephala. To investigate secondary metabolites, we identified all gene copies involved in mimosine metabolism in these species and found that the abundance of mimosine biosynthesis genes in L. leucocephala largely explains its high mimosine production. We also identified the set of all potential genes involved in triterpenoid saponin biosynthesis in G. sinensis, which is more complete than that based on previous transcriptome-derived unigenes. Our results and genomic resources will facilitate biological studies of Caesalpinioideae and promote the utilization of valuable secondary metabolites.

Comparative floral development in Mimosa (Fabaceae: Caesalpinioideae) brings new insights into merism lability in the mimosoid clade.

The genus Mimosa L. (Leguminosae; Caesalpinioideae; mimosoid clade), comprising more than 500 species, is an intriguing genus because, like other members of the mimosoid clade, it presents an enormous variation in floral characteristics and high merism lability. Thus, this study aimed to elucidate the floral development and identify which ontogenetic pathways give rise to merism variation and andromonoecy in Mimosa caesalpiniifolia, M. pudica, M. bimucronata, and M. candollei. Floral buds at various stages of development and flowers were collected, fixed, and processed for surface analysis (SEM). The development of the buds is synchronous in the inflorescences. Sepals appear simultaneously as individualized primordia in M. caesalpiniifolia and in reversed unidirectional order in M. bimucronata, with union and formation of an early ring-like calyx. Petal primordia appear in unidirectional order, with a noticeably elliptical shape in M. caesalpiniifolia. The wide merism variation in Mimosa results from the absence of organs from inception in the perianth and androecium whorls: in dimerous, trimerous, or tetramerous flowers, the additional organs primordia to compose the expected pentamerous flowers are not initiated. The haplostemonous androecium of M. pudica results from the absence of antepetalous stamens from inception. In the case of intraspecific variations (instabilities), there is no initiation and subsequent abortion of organs in the events of reduction in merosity. In addition, extra primordia are initiated in supernumerary cases. On the other hand, staminate flowers originate from the abortion of the carpel. Mimosa proved to be an excellent model for studying merism variation. The lability is associated with actinomorphic and rather congested flowers in the inflorescences. Our data, in association with others of previous studies, suggest that the high lability in merism appeared in clades that diverged later in the mimosoid clade. Thus, phylogenetic reconstruction studies are needed for more robust evolutionary inferences. The present investigation of ontogenetic processes was relevant to expand our understanding of floral evolution in the genus Mimosa and shed light on the unstable merism in the mimosoid clade.

A new fossil wood of Detarioideae from the Boa Vista Basin, Upper Oligocene (Northeast Brazil): Comparisons with living and fossil Leguminosae Subfamilies. Paleoclimate and biogeography inferences for the Leguminosae story

A new genus and species of Leguminosae wood has been discovered and described from the Upper Oligocene in Northeast Brazil. The well-preserved tissues and unique diagnostic characters allowed for its assignment to Goniorrhachisinoxylon sergioarchangelskii nov. gen. et sp. (Detarioideae). Leguminosae woods have a rich fossil record, and in order to establish this new genus and species, detailed comparisons were made among the living subfamilies Cercidoideae, Detarioideae, Duparquetioideae, Dialioideae, and Caesalpinioideae, and a revision of the generic diagnoses of caesalpiniod fossil woods (except the Mimosoid clade) was conducted. By examining the presence of some wood characters and using modern related forms, it was inferred that seasonal (possibly monsoonal) palaeoclimatic conditions existed in Northeast Brazil at the end of the Oligocene. This new record from the Boa Vista Basin can contribute to our understanding of the origin and distribution of some members of the Leguminosae.

Circumscription of Abarema (Leguminosae, Caesalpinioideae, Mimosoid clade)

The genus Abarema (Caesalpinioideae, Mimosoid clade), as traditionally circumscribed, emerged as polyphyletic in recent phylogenetic studies. The type species of the genus, Abarema cochliacarpos, is positioned within the Inga clade, separate from the remaining species previously included in the genus (now combined to Punjuba and Jupunba genera). Here we present the new circumscription of Abarema. The two species included in the genus occur in the Atlantic Forest and Caatinga biomes in Brazil. We provide a morphological description of Abarema and its two species, an identification key, conservation status and a geographic distribution map.

An updated description of Parkia barnebyana (Leguminosae: Caesalpinioideae, mimosoid clade) from Amazonian Venezuela and Brazil, and comparison with other species in sect. Parkia with erect capitula

SummaryAn updated description, including characters of the capitulum and fertile flowers, is provided for Parkia barnebyana. Originally recorded from southern Venezuela, this small canopy tree from igapó (blackwater flooded forest) is now also known by two collections from north-western Brazil. The capitula are yellow and held erect, with the fertile flowers uppermost; they are borne on short, robust, upright peduncles that arise from long compound inflorescence axes projecting directly above the crown. The structure and shape of the capitula place this species in pantropical sect. Parkia and its pod morphology suggests that it lies outside the largely Amazonian nitida-group; both conclusions are supported by a recent phylogenetic analysis. The indehiscent pods remain in the tree at maturity and most seeds are apparently removed by arboreal dispersers and vertebrate seed predators. Two other neotropical species in sect. Parkia, P. cachimboensis and P. decussata, are known to have erect, yellow or largely yellow capitula and in both, a well-developed fringe of staminodia projecting from the basal flowers is absent. Both these species are chiropterophilous and although we predict that P. barnebyana is also likely to be bat-pollinated, we have made no observations. A fourth neotropical species, P. nana, also with yellow flowers, is reported to have erect capitula but they do have staminodial fringes; its pollination has not been studied. Within sect. Parkia, erect capitula occur only in the Neotropics, probably because of the head-down position in which quite large generalist phyllostomid bats land on them to access nectar. Erect capitula appear to have evolved more than once within neotropical sect. Parkia and at least sometimes from ancestors with pendent capitula, but further phylogenetic data are needed to confirm this.

Four new species of Mimosa sect. Batocaulon ser. Cordistipulae (Leguminosae) from Bahia, Brazil

Four new species of Mimosa series Cordistipulae (Leguminosae: Caesalpinioideae: Mimosoid clade) are described from Bahia state, Brazil: M. crassifolia, M. bahiana and M. confusa from rupestrian grasslands (campo rupestre vegetation) of the Chapada Diamantina mountain range, and M. melosa from inland dry scrub on sand dunes of the São Francisco River. We provide illustrations, comments on the geographical distribution, preliminary conservation assessments, and morphological affinities.

Sympetaly in the mimosoid clade (Leguminosae, Caesalpinioideae): An unusual trait in the rosid group

Sympetaly is a notable feature within the mimosoid clade (Leguminosae: Caesalpinioideae), specially as it is uncommon in rosids. The way the petals are organized, forming a tubular corolla by the union of the petals directly affects the perception of pollinators. This study examines whether the petal union leading to a sympetalous corolla in the mimosoid clade is widespread and whether there is variation in type and extent. For this purpose, floral buds and flowers of 16 species from 13 genera were collected, fixed, and processed for analysis by light and scanning electron microscopy. Most species studied display a pentamerous sympetalous corolla with free lobes. The petal primordia are individualized and emerge simultaneously on the floral apex, alternating with the sepal primordia. Petals remain free at the beginning of the intermediate stages of development, and subsequently, the petals curve and approach each other, and their margins touch. Epidermal papillae are found on the petals’ apical margin interconnecting the lobes, which enclose the inner organs of the floral bud. The structure of the sympetalous corolla is variable regarding the type and extent of the union. Four different types of sympetaly were found and classified as follows: 1. full connation - petals fully united along their length; 2. connation-coherence - petals genuinely united in the basal portion and coherent in the median and apical portion; 3. full coherence - petals intertwined with papillae throughout; and 4. partial coherence - free petals at the base and intertwined with papillae in the middle and apical portion. Thus, sympetaly of mimosoid legumes results from postgenital union of the petals at the apical, median, and basal regions during their development by tissue union (connation), intertwining of epidermal papillae (coherence), or both processes. The mucilage cells found along the petals guarantee the stabilization and flexibility of the tubes, in addition to contributing to the protection of the internal organs of the flower. Although more studies on floral development are needed to understand the evolution of this unusual trait, connation appears to be a derived trait within mimosoids.

A genome resource for Acacia, Australia's largest plant genus.

Acacia (Leguminosae, Caesalpinioideae, mimosoid clade) is the largest and most widespread genus of plants in the Australian flora, occupying and dominating a diverse range of environments, with an equally diverse range of forms. For a genus of its size and importance, Acacia currently has surprisingly few genomic resources. Acacia pycnantha, the golden wattle, is a woody shrub or tree occurring in south-eastern Australia and is the country's floral emblem. To assemble a genome for A. pycnantha, we generated long-read sequences using Oxford Nanopore Technology, 10x Genomics Chromium linked reads, and short-read Illumina sequences, and produced an assembly spanning 814 Mb, with a scaffold N50 of 2.8 Mb, and 98.3% of complete Embryophyta BUSCOs. Genome annotation predicted 47,624 protein-coding genes, with 62.3% of the genome predicted to comprise transposable elements. Evolutionary analyses indicated a shared genome duplication event in the Caesalpinioideae, and conflict in the relationships between Cercis (subfamily Cercidoideae) and subfamilies Caesalpinioideae and Papilionoideae (pea-flowered legumes). Comparative genomics identified a suite of expanded and contracted gene families in A. pycnantha, and these were annotated with both GO terms and KEGG functional categories. One expanded gene family of particular interest is involved in flowering time and may be associated with the characteristic synchronous flowering of Acacia. This genome assembly and annotation will be a valuable resource for all studies involving Acacia, including the evolution, conservation, breeding, invasiveness, and physiology of the genus, and for comparative studies of legumes.

Phylogenomic analysis of 997 nuclear genes reveals the need for extensive generic re-delimitation in Caesalpinioideae (Leguminosae).

Subfamily Caesalpinioideae with ca. 4,600 species in 152 genera is the second-largest subfamily of legumes (Leguminosae) and forms an ecologically and economically important group of trees, shrubs and lianas with a pantropical distribution. Despite major advances in the last few decades towards aligning genera with clades across Caesalpinioideae, generic delimitation remains in a state of considerable flux, especially across the mimosoid clade. We test the monophyly of genera across Caesalpinioideae via phylogenomic analysis of 997 nuclear genes sequenced via targeted enrichment (Hybseq) for 420 species and 147 of the 152 genera currently recognised in the subfamily. We show that 22 genera are non-monophyletic or nested in other genera and that non-monophyly is concentrated in the mimosoid clade where ca. 25% of the 90 genera are found to be non-monophyletic. We suggest two main reasons for this pervasive generic non-monophyly: (i) extensive morphological homoplasy that we document here for a handful of important traits and, particularly, the repeated evolution of distinctive fruit types that were historically emphasised in delimiting genera and (ii) this is an artefact of the lack of pantropical taxonomic syntheses and sampling in previous phylogenies and the consequent failure to identify clades that span the Old World and New World or conversely amphi-Atlantic genera that are non-monophyletic, both of which are critical for delimiting genera across this large pantropical clade. Finally, we discuss taxon delimitation in the phylogenomic era and especially how assessing patterns of gene tree conflict can provide additional insights into generic delimitation. This new phylogenomic framework provides the foundations for a series of papers reclassifying genera that are presented here in Advances in Legume Systematics (ALS) 14 Part 1, for establishing a new higher-level phylogenetic tribal and clade-based classification of Caesalpinioideae that is the focus of ALS14 Part 2 and for downstream analyses of evolutionary diversification and biogeography of this important group of legumes which are presented elsewhere.

Mezcala - a new segregate genus of mimosoid legume (Leguminosae, Caesalpinioideae, mimosoid clade) narrowly endemic to the Balsas Depression in Mexico.

Recent results have demonstrated that the genus Desmanthus is non-monophyletic because the genus Kanaloa is nested within it, with a single species, Desmanthusbalsensis placed as sister to the clade comprising Kanaloa plus the remaining species of Desmanthus. Here we transfer D.balsensis to a new segregate genus Mezcala, discuss the morphological features supporting this new genus, present a key to distinguish Mezcala from closely related genera in the Leucaena subclade, and provide a distribution map of M.balsensis.

Boliviadendron, a new segregate genus of mimosoid legume (Leguminosae, Caesalpinioideae, mimosoid clade) narrowly endemic to the interior Andean valleys of Bolivia.

Phylogenetic analyses of DNA sequence data sampling all species of Leucochloron alongside representatives of genera of the Inga and Albizia clades of the larger ingoid clade of mimosoid legumes (sensu Koenen et al. 2020) confirm the non-monophyly of the genus Leucochloron. We show that Leucochloronbolivianum is placed in the Albizia clade, while the remaining four species of Leucochloron are placed in the Inga clade, in line with previous results. To rectify this non-monophyly, L.bolivianum is segregated as the new genus, Boliviadendron, with a single species, Boliviadendronbolivianum, narrowly endemic to the interior Andean valleys of Bolivia. We illustrate this new segregate genus, present a map of its distribution and discuss the striking lack of morphological distinctions between Boliviadendron and Leucochloron, as well as the phylogenetic and morphological affinities of Boliviadendron to the genera Enterolobium and Albizia.

Dilemmas in generic delimitation of Senegalia and allies (Caesalpinioideae, mimosoid clade): how to reconcile phylogenomic evidence with morphology and taxonomy?

Senegalia comprises 219 species distributed in tropical and subtropical regions of North and South America, Africa, Asia and Australia. Two sections are currently recognised within Senegalia and these are most readily distinguished by the differences in disposition of their cauline prickles, i.e. sect. Senegalia with prickles at or near leaf nodes and sect. Monacanthea with mostly internodal prickles. Previous phylogenetic studies, based primarily on small numbers of plastid DNA loci, found Senegalia to be monophyletic with two large subclades corresponding to the sections. Here, we present new phylogenomic evidence from 997 single-copy nuclear gene sequences for a small, but representative set of species. These new analyses show that Senegalia is non-monophyletic, but instead, forms a grade that is paraphyletic with respect to the remainder of the ingoid clade (i.e. Ingeae + Acacia s.s. + Acaciella), comprising two well-supported subclades most likely representing the same clades as found in previous phylogenetic studies of the genus and, interspersed between these, a third, moderately supported clade, comprising the genera Mariosousa, Pseudosenegalia and Parasenegalia. In marked contrast to the nuclear phylogeny, the two Senegalia clades are sister groups in the plastid phylogeny, based on analyses of 72 chloroplast genes, rendering the genus monophyletic, based on plastid data alone. We discuss this new evidence that Senegalia is non-monophyletic in relation to the marked cytonuclear discordance, high gene tree conflict and lack of resolution across this senegalioid grade and review the consistency of the key morphological characters distinguishing the two sections of Senegalia. We conclude that it is likely that Senegalia will need to be split into two (or possibly more) genera: a re-circumscribed Senegalia s.s. that corresponds to the existing Senegaliasect.Senegalia plus the S.ataxacantha group (Senegaliasect.Monacanthea s.s.; future studies may show that this group warrants generic status) and a new genus corresponding to the remainder of sect. Monacanthea (here designated as Senegaliasect.Monacanthea p.p.). However, re-delimiting Senegalia now would be premature given that the key morphological characters are not fully congruent with the two sections and pending denser phylogenetic sampling of taxa. A judiciously selected list of critical taxa is presented to facilitate future phylogenomic studies. Finally, we discuss the identity of Albizialeonardii, which is also placed in this senegalioid grade in these new phylogenomic analyses and place it in synonymy with Parasenegaliavogeliana.

Re-establishment of the genus Pseudalbizzia (Leguminosae, Caesalpinioideae, mimosoid clade): the New World species formerly placed in Albizia.

Following recent mimosoid phylogenetic and phylogenomic studies demonstrating the non-monophyly of the genus Albizia, we present a new molecular phylogeny focused on the neotropical species in the genus, with much denser taxon sampling than previous studies. Our aims were to test the monophyly of the neotropical section Arthrosamanea, resolve species relationships, and gain insights into the evolution of fruit morphology. We perform a Bayesian phylogenetic analysis of sequences of nuclear internal and external transcribed spacer regions and trace the evolution of fruit dehiscence and lomentiform pods. Our results find further support for the non-monophyly of the genus Albizia, and confirm the previously proposed segregation of Hesperalbizia, Hydrochorea, Balizia and Pseudosamanea. All species that were sampled from section Arthrosamanea form a clade that is sister to a clade composed of Jupunba, Punjuba, Balizia and Hydrochorea. We find that lomentiform fruits are independently derived from indehiscent septate fruits in both Hydrochorea and section Arthrosamanea. Our results show that morphological adaptations to hydrochory, associated with shifts into seasonally flooded habitats, have occurred several times independently in different geographic areas and different lineages within the ingoid clade. This suggests that environmental conditions have likely played a key role in the evolution of fruit types in Albizia and related genera. We resurrect the name Pseudalbizzia to accommodate the species of section Arthrosamanea, except for two species that were not sampled here but have been shown in other studies to be more closely related to other ingoid genera and we restrict the name Albizia s.s. to the species from Africa, Madagascar, Asia, Australia, and the Pacific. Twenty-one new nomenclatural combinations in Pseudalbizzia are proposed, including 16 species and 5 infraspecific varietal names. In addition to the type species Pseudalbizziaberteroana, the genus has 17 species distributed across tropical regions of the Americas, including the Caribbean. Finally, a new infrageneric classification into five sections is proposed and a distribution map of the species of Pseudalbizzia is presented.

Disintegration of the genus Prosopis L. (Leguminosae, Caesalpinioideae, mimosoid clade).

Robust evidence from phylogenomic analyses of 997 nuclear genes has recently shown, beyond doubt, that the genus Prosopis is polyphyletic with three separate lineages, each with affinities to other genera of mimosoids: (i) Prosopisafricana is an isolated lineage placed in the grade of Plathymenia, Newtonia and Fillaeopsis that subtends the core mimosoid clade; (ii) the remaining Old World species of Prosopis form a clade that is sister to the Indo-Nepalese monospecific genus Indopiptadenia and (iii) New World Prosopis has the Namibian / Namaqualand monospecific endemic genus Xerocladia nested within it. This means that it is now clear that maintaining the unity of the genus Prosopis sensu Burkart (1976) is no longer tenable. These three distinct lineages of Prosopis species correspond directly to Burkart's (1976) sectional classification of the genus, to previously recognised genera and to the differences in types of armature that underpin Burkart's sections. Here, we address this non-monophyly by resurrecting three segregate genera - Anonychium, Neltuma and Strombocarpa and provide 57 new name combinations where necessary, while maintaining the morphologically distinctive and geographically isolated genera Xerocladia and Indopiptadenia. The genus Prosopis itself is reduced to just three species and an emended description is presented. The impacts of these name changes for a genus of such high ecological and human use importance are discussed. These impacts are mitigated by clear differences in armature which facilitate identification and by potential benefits from the deeper biological understanding brought about by recognition of these divergent lineages at generic rank. We provide an identification key to genera and present a map showing the distributions of the segregate genera, as well as drawings and photos illustrating variation in armature and fruits.

Phylogenomic assessment prompts recognition of the Serianthes clade and confirms the monophyly of Serianthes and its relationship with Falcataria and Wallaceodendron in the wider ingoid clade (Leguminosae, Caesalpinioideae).

The Indo-Pacific legume genus Serianthes was recently placed in the Archidendron clade (sensu Koenen et al. 2020), a subclade of the mimosoid clade in subfamily Caesalpinioideae, which also includes Acacia, Archidendron, Archidendropsis, Falcataria, Pararchidendron, Paraserianthes and Wallaceodendron. Serianthes comprises ca. 18 species, five subspecies and two varieties that are characterised by bipinnately compound leaves with alternate sessile leaflets, branched axillary corymbiform panicles and woody indehiscent pods. Generic relationships, as well as species relationships within genera in the Archidendron clade, remain uncertain. While the sister relationship between Serianthes and the genus Falcataria is strongly supported by molecular data, the distinction between Serianthes and the monotypic genus Wallaceodendron has been questioned, based on their similar flower and fruit morphologies. We combined three gene-enriched hybrid capture DNA sequence datasets (generated from the 964 mimobaits v1 probe set, the expanded 997 mimobaits v2 probe set and the GoFlag angiosperm 408 probe set) and used their overlapping markers (77 loci of the target exonic and flanking regions) to test the monophyly of Serianthes and to investigate generic relationships within the Archidendron clade using 55 ingoid plus two outgroup taxa. We show that Serianthes is monophyletic, confirm the Serianthes + Falcataria sister relationship to Wallaceodendron and recognise this combined clade as the Serianthes clade within the Archidendron clade. We also evaluated the use of overlapping loci across datasets in combination with concordance analyses to test generic relationships and further investigate previously unresolved relationships across the wider ingoid clade. Concordance analysis revealed limited gene tree conflicts near the tips of the Archidendron clade, but increased discordance at the base of the clade, which could be attributed to rapid lineage divergence (radiation) and/or incomplete lineage sorting.

A synopsis of the genus Stryphnodendron (Fabaceae, Caesalpinioideae, mimosoid clade)

Stryphnodendron is a Neotropical genus of Fabaceae (Caesalpinioideae, mimosoid clade), comprising 36 taxa occurring from Nicaragua to Southern Brazil, most of them found and endemic in Brazil, being especially frequent in savannas (Cerrado) and the Amazon Forest. This synopsis presents the designation of 16 lectotypes, eight new synonyms, a new combination with a nomenclatural status change, a species’ reestablishment, two doubtful names and three excluded species. We also present nine new species, which are described and illustrated. All the species are accompanied by comments on geographical distribution, habitat and IUCN Conservation status.

Polyads types of the mimosoid clade (Caesalpinioideae, Fabaceae): size and pollen numbers variations

The pollen morphology of 17 species and three varieties of the native mimosoid clade of forest fragments of the Cerrado (Brazilian savanna) was studied in order to expand the knowledge on the morphology of genera and species of this group, in particular on the morphology of polyads, as well as add information to pollen studies for species of Caesalpinioideae occurring in the area. The pollen grains were acetolysed, measured, described qualitatively and illustrated under light microscopy and scanning electron microscopy (not acetolysed pollen grains). Pollen metric data were examined by descriptive and multivariate analysis. The studied species showed differences on the pollen units (monads or polyads) and variations in number and distribution of pollen grains in the polyads. Three pollen types were observed: type I, pollen grains in monads (Plathymenia reticulata); type II, polyads with one tapered end (drop shape – Calliandra parviflora); type III, polyads with uniform ends with asymmetrically distributed pollen grains (Stryphnodendron species); or symmetrically (with 16 or 20 pollen grains in Acacia plumosa, Albizia niopoides, Anadenanthera species, Inga marginata, Inga vera and Senegalia species and more than 20 pollen grains in Enterolobium contortisiliquum, Inga edulis and Inga sessilis). The qualitative differences and the measuremets of the diameters of the polyads, made it possible to distinguish the taxa and to confirm the eurypalynous character of the mimosoid clade (Caesalpinioideae, Fabaceae).

Seed morphology, anatomy and histochemistry in two Mexican species of Mimosa (Leguminosae, mimosoid clade)

Mimosa species have biological and ecological importance, they exhibit advantages that make them competitive candidates for ecological restoration; considering that the seed is essential for the establishment of the species, it is required to characterize the seeds morphologically and anatomically, especially those that come from multipurpose plants like the mimosas are. The objective was to study the morphology, anatomy and histochemistry of the seeds of Mimosa aculeaticarpa and M. luisana, with the aim of better contextualising and understanding their ecological implications of the fact that the seed is the fundamental stage for the propagation and perpetuation of the species. The morpho-anatomical study was performed by light microscopy (LM) and scanning electron microscopy (SEM), histochemistry was used for detection of cuticle, lignified cell walls and starches. The seeds of M. aculeaticarpa are ovoid and those of M. luisana are spheroid to ellipsoid. In both species the seed coat shows fracture lines, in M. aculeaticarpa var. aculeaticarpa they are limited to the pleurogram, lens, hilum and micropyle regions, while in M. luisana they occupy the entire surface of the seed. Seed coat surface in M. aculeaticarpa var. aculeaticarpa is simple reticulate and each space that is enclosed by the reticulation is densely rugose, while in M. luisana it only has an irregularly rugose pattern. The micropyle is ellipsoid and protruding (M. aculeaticarpa) or punctiform and sunken (M. luisana). Anatomically, there is a cuticle; the seed coat of M. aculeaticarpa has only macrosclereids, while that of M. luisana also has a layer of osteosclereids. The anatomical characters make it possible to distinguish between the two species. The morpho-anatomical characters prevent initial germination, increase the longevity of the seeds and are the probable cause of impermeability.