Morphological analysis and re‐examination of the taxonomic circumscription of Acosmium (Leguminosae, Papilionoideae, Sophoreae)

Abstract

Acosmium Schott is a Neotropical genus of ca. 17 species of trees with non-papilionoid, actinomorphic flowers. It has been included in the genistoid clade (Leguminosae, Papilionoideae) in recent phylogenetic analyses. A morphology-based cladistic analysis was performed to test the currently assumed monophyly of Acosmium, assess the validity of the infrageneric classification of Yakovlev, and detect synapomorphies and other diagnostic characters in Acosmium and related taxa. Thirty-four species representing ten genera of subfamily Papilionoideae were included in the analysis: all accepted species of the four sections of Acosmium together with species of Bowdichia, Clathrotropis, Diplotropis, Bolusanthus, Cadia, Poecilanthe, Cyclolobium, and Ormosia; two species of Luetzelburgia were selected as outgroups. The results do not support the monophyly of Acosmium; the species of this genus fall into three distinct, not closely related clades that correspond to the sections of Acosmium established by Yakovlev except for sect. Mesitis that merges into sect. Leptolobium. We propose: (1) recognizing a narrowly circumscribed genus Acosmium; (2) reinstating the generic name Leptolobium Vogel, encompassing sections Leptolobium and Mesitis; and (3) segregating A. praeclarum (Sandwith) Yakovlev into a new genus, Guianodendron. The phylogenetic relevance of some new or neglected characters, especially from bud architecture, seed, and seedling morphology is emphasized.

Systematic relevance of seedling morphology in Acosmium, Guianodendron, and Leptolobium (Leguminosae, Papilionoideae)

“…Yakovlev). Thus, seedling morphology data are in agreement with the taxonomic proposal that A. tomentellum be considered a synonym of L. nitens (Rodrigues, 2005).…”

“…Praeclara Yakovlev. In contrast, taxonomic and biosystematic studies as well as a morphological cladistic analysis (Rodrigues, 2005;Rodrigues & Tozzi, 2007a) revealed that Acosmium sensu Yakovlev (1969) did not comprise a monophyletic group. Therefore, three genera were recognized: Acosmium was restricted to three species of section Acosmium; ten species of sections Leptolobium and Mesitis were grouped together into the reinstated genus Leptolobium Vogel (Rodrigues, 2005); and Acosmium praeclarum (Sandwith) Yakovlev of section Praeclara was segregated into a new genus, Guianodendron Sch.…”

“…Mesitis Vogel to L. sect. Leptolobium, proposed on the basis of floral and seed morphology (Rodrigues, 2005;Rodrigues & Tozzi, 2007a). Leptolobium dasycarpum and L. elegans (L. sect.…”

Two new species of Leptolobium (Leguminosae, Papilionoideae) from Brazil

“…Acosmium s.str. and Leptolobium are mainly distinguished by leaflet shape and venation, inflorescence position, floral bud architecture, calyx shape, and seed and seedling morphology (Rodrigues & Tozzi, 2007a, 2008b. With respect to its phylogenetic affinities, morphological and molecular analyses provided strong evidence for a sister relationship between Leptolobium and Bowdichia Kunth (Pennington et al, 2001;Wojciechowski et al, 2004;Rodrigues & Tozzi, 2007a).…”

“…This generic name was reestablished by Rodrigues and Tozzi (2008a), based on biosystematic studies as well as a morphological cladistic analysis (Rodrigues & Tozzi, 2007a, 2008b that revealed that Acosmium Schott sensu Yakovlev (1969) did not comprise a monophyletic group. Acosmium s.str.…”