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

Abstract

The genus Osodendron is here newly described to accommodate three species and one subspecies of African mimosoid legumes. These taxa have previously been included by several authors in Albizia, Cathormion and/or Samanea, but they have been shown to be phylogenetically unrelated to any of these, being instead the sister-group of the recently described Neotropical genus Robrichia, which is similar in vegetative morphology and especially its very similar indumentum, but is decidedly different in pod morphology. A taxonomic treatment of the three species in the genus is presented, with species descriptions, photographs, distribution maps and an identification key. The type species Osodendron altissimum (Hook. f.) E.J.M. Koenen occurs in swamp and riverine rainforest and gallery forests, with the typical subsp. altissimum widespread across tropical Africa, while Osodendron altissimum subsp. busiraensis (G.C.C. Gilbert) E.J.M. Koenen is only known from the Busira river catchment in the western part of the Democratic Republic of Congo. Of the other two species, Osodendron dinklagei (Harms) E.J.M. Koenen is a common tree of rainforest and the forest-savannah transition including semi-deciduous and secondary forest as well as gallery forest and is restricted to Upper Guinea and the similar, but vegetatively more variable Osodendron leptophyllum (Harms) E.J.M. Koenen occupies comparable vegetation types in Lower Guinea and extends marginally into the Sudanian and Zambezian savannahs in gallery forest.

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

“…have long been uncertain and neglected (Fig. 11 ), also prompting further generic re-arrangement in this Special Issue by Koenen (2022a) . For the first time, the pantropical sampling employed here is more fully documenting these issues.…”

“…13 ), often within genera (e.g. Capuron 1970 ; Aviles et al 2022 ; Koenen 2022a ; Soares et al 2022 ) associated with hydrochory in species adapted to grow in seasonally inundated habitats and this has impacted on generic delimitation. For example, Barneby and Grimes (1996) separated their newly-segregated genera Balizia and Hydrochorea Barneby & J.W.…”

“…Nielsen 1981 , 1992 ) or just on the New World (e.g. Barneby and Grimes 1996 , 1997 ; Barneby 1998 ) have become more starkly apparent now that pantropical sampling has been achieved, revealing the non-monophyly of well-known pantropical genera, such as Albizia ( Koenen et al 2020b ; Aviles et al 2022 ) and Prosopis ( Hughes et al 2022a ), as well as previously unrecognised clades with trans-Atlantic distributions ( Soares et al 2022 ; Koenen 2022a ). Our analyses provide a glimpse of the likely extent of morphological homoplasy (Figs 13 – 15 ).…”

“…(Figs 9 and 11 ) and Albizia leonardii (Fig. 7 ), are all accounted for with new generic placements and nomenclatural combinations ( Koenen 2022b ; Soares et al 2022 ), one synonymisation ( Terra et al 2022 ) and a new segregate genus ( Koenen 2022a ), all of them being published in this Special Issue. Abarema , Hydrochorea and Balizia The recent re-circumscription of Abarema Pittier to include just two species and transfer of the remaining species to the re-instated Punjuba Britton & Rose and Jupunba Britton & Rose ( Guerra et al 2016 , 2019 ; Iganci et al 2016 ; Soares et al 2021 ), is broadly supported here (Figs 9 and 11 ), except for the anomalous placement of Jupunba macradenia (Pittier) M.V.B.…”

“…(Figs 9 and 11 ) and Albizia leonardii (Fig. 7 ), are all accounted for with new generic placements and nomenclatural combinations ( Koenen 2022b ; Soares et al 2022 ), one synonymisation ( Terra et al 2022 ) and a new segregate genus ( Koenen 2022a ), all of them being published in this Special Issue.…”