Phylogenetic relationships in the genus Aspalathus L. (Fabaceae; Papilionoideae; Crotalarieae) based on molecular and morphological evidence

Abstract

• The Cape Crotalarieae clade comprise six genera, whereby Aspalathus is largest. • Infrageneric phylogenetic relationships remain uncertain in Aspalathus . • We expand sampling and use four DNA markers to improve phylogenetic resolution in Aspalathus . • Aspalathus is not monophyletic, with two major clades in backbone polytomy with other Cape Crotalarieae. • The two major clades in Aspalathus differ in their morphology and ecology. The genus Aspalathus , comprising approximately 300 species predominantly endemic to South Africa's Core Cape Subregion, is the largest genus within the legume (Leguminosae /Fabaceae) family in the subregion. Despite its ecological and economic significance, phylogenetic reconstructions within Aspalathus have been hindered by poor resolution, largely due to limited variation in commonly used molecular markers. This study expands sampling within Aspalathus and employs four DNA markers—ETS, ITS, mat K, and trn S -trn G—to improve phylogenetic resolution and clarify relationships within the genus. Our results indicate that Aspalathus , as currently circumscribed, may not be monophyletic, with two major clades sharing a common ancestor with other Cape Crotalarieae genera. A polytomy at the backbone of the phylogeny suggests unresolved evolutionary relationships, potentially influenced by limited marker variation. Character inference highlights morphological and ecological differences between the two major clades, particularly in leaf lamina morphology, supporting previous hypotheses of taxonomic divergence within the genus. These findings refine the phylogenetic framework for Aspalathus , but further studies, like those using the angiosperm353 target capture sequencing approach, are needed to improve resolution. Additionally, broader sampling of related taxa will be essential for accurately determining the position of Aspalathus within the tribe Crotalarieae.