Lachesiodendron, a new monospecific genus segregated from Piptadenia (Leguminosae: Caesalpinioideae: mimosoid clade): Evidence from morphology and molecules

Abstract

AbstractThe widest historical circumscription of the mimosoid legume genus Piptadenia (Caesalpinioideae: mimosoid clade) previously embraced morphologically disparate species that are currently ascribed to nine different genera. Previous molecular phylogenetic studies have demonstrated that the neotropical dry forest Piptadenia viridiflora is not closely related to Piptadenia s.str. Here we plug gaps in the DNA sequence dataset of a recently published study to build a more comprehensive phylogeny of the Piptadenia group and revise morphological evidence to define the phylogenetic relationship of P. viridiflora. Both morphological and molecular data confirm that P. viridiflora is an isolated lineage, thus warranting the description of the new monospecific genus Lachesiodendron. The new genus is diagnosed by the combination of paired stipular spines (vs. stipules not modified into spines in Piptadenia s.str.), prickles absent (vs. present), flowers in axillary spikes not grouped in compound inflorescences (vs. spikes grouped in compound pseudoracemes or panicles), flowers with a cylindrical corolla long exserted from the calyx (vs. corolla campanulate with petals free or slightly joined at the base) and long green stamens (vs. shorter and white, pale yellow or pink stamens). In addition, Lachesiodendron has pollen aggregated into 8–celled polyads with a hamulate exine, which further contrasts with the 12–celled polyads with a psilate exine in Piptadenia s.str.