Molecular and Morphological Analysis Supports the Separation ofRobrichiaas a Genus Distinct fromEnterolobium(Leguminosae: Caesalpinioideae: Mimosoid Clade)

Abstract

Abstract— As currently circumscribed, the legume genus Enterolobium comprises 11 species in two sections: E. sect. Enterolobium and E. sect. Robrichia, with an overall distribution from Mexico to Argentina and a centre of diversity in Amazonia. In the absence of the characteristic indehiscent fruits, Enterolobium is difficult to distinguish from other genera in the ingoid clade, including Albizia sensu lato, Samanea, and Cathormion. Previous phylogenetic studies which have included Enterolobium have sampled few species of the genus, leaving questions about its monophyly and interspecific relationships. Here we evaluate the circumscription of Enterolobium and its two infrageneric taxa, their phylogenetic placement in the ingoid clade, and interspecific relationships within the two sections of the genus. Our study includes all Enterolobium species, and analyses of nuclear (ITS and ETS) and plastid (trnD-T and trnL-F) molecular regions, and morphology. Bayesian inference, maximum parsimony, and maximum likelihood analyses show that Enterolobium, as presently circumscribed, is not monophyletic. The genus is divided into two well-supported independent clades, corresponding to the two previously recognized sections; one of them is sister to the genus Leucochloron and is here raised to generic rank as the genus Robrichia, with three species, Robrichia glaziovii, Robrichia oldemanii and Robrichia schomburgkii. The genus Enterolobium consequently now comprises eight species and is more closely related to a clade composed of Albizia and Falcataria. This new arrangement is reinforced by morphological synapomorphies recovered by ancestral character state reconstructions. Indumentum type, the number of pinnae pairs per bipinnate leaf and leaflet pairs per pinna, inflorescence type, and fruit shape characterize Robrichia, while the recognition of Enterolobium remains based on fruit traits. We also provide the formal lectotypifications for E. contortisiliquum, E. cyclocarpum, E. gummiferum, E. maximum, E. monjollo, and R. schomburgkii.

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

“…For example, the polyphyly of the genus Enterolobium Mart. (de Souza et al 2022a;Figs 10-11) was unexpected because the two clades of Enterolobium species share the distinctive indehiscent thickened and curled 'ear pod' fruit type. Similarly, it also seems clear that septate lomentiform fruits with valves readily cracking between the seeds and breaking up into one-seeded articles have also evolved multiple times (Fig.…”

“…Luz & E.R. Souza (de Souza et al 2022a)), bringing the current tally of Caesalpinioideae genera to 152, of which 90 are mimosoids.…”

A new generic circumscription of Hydrochorea (Leguminosae, Caesalpinioideae, mimosoid clade) with an amphi-Atlantic distribution

“…Recent advances in molecular systematics of ingoid legumes also demonstrated the pod morphology to be less informative than previously thought (Souza et al 2013;Iganci et al 2016;Koenen et al 2020b;Soares et al 2021;Souza et al 2022). Barneby and Grimes (1996) stated that Balizia and Hydrochorea closely resemble Albizia but are distinguished by indeterminate inflorescence-axes and vegetative branches arising from sylleptic and proleptic buds, pinnate leaflet venation, and truncate ovaries.…”

Osodendron gen. nov. (Leguminosae, Caesalpinioideae), a new genus of mimosoid legumes of tropical Africa

“…Notes. Osodendron is closely related to the Central and South American Robrichia, which was originally described as a section of Enterolobium by Barneby and Grimes (1996) and later segregated as a new genus by Souza et al (2022). In the phylogeny of Ringelberg et al (2022), the sampled species of both genera form sister-lineages.…”

“…The species of Robrichia are characterised by contorted ("ear-shaped") indehiscent pods (Fig. 1G, H; Souza et al 2022: Fig. 2D, E, J) which led them to be previously classified in Enterolobium Mart., while the related African species have twisted to coiled articulated lomentiform pods (C. altissimum,Figs 1A,2G,H), straight to slightly curved woody pods (S. dinklagei,Figs 1C,3F) or intermediate straight to slightly curved articulated pods (S. leptophylla/C.…”