Morphological characterization of polyads from Marlimorimia, Pityrocarpa, and Parapiptadenia supports the recent circumscription of the Stryphnodendron clade (Caesalpinoideae: Mimoseae)

Abstract

Recent phylogenetic hypotheses have been used as evidence to reorganize the former genus Pseudopiptadenia into a new circumscription of Pityrocarpa and the recently described Marlimorimia, while confirming the monophyly of Parapiptadenia. In this study, we provide an additional line of evidence for these taxonomic changes by contributing new descriptions and evaluating whether pollen morphology supports the current generic circumscriptions. To achieve that, we analyzed acetolyzed palynological material using light microscopy (LM) and scanning electron microscopy (SEM), describing their morphology and evaluating the distribution of pollen traits across taxa. Continuous pollen characters, particularly polyad size, do not support the recognition of Marlimorimia as a distinct genus but corroborate the monophyly of Parapiptadenia. In contrast, discrete characters, especially the number of pollen grains per polyad, support the recognition of Marlimorimia and highlight the relevance of pollen traits for evaluating generic boundaries within the Stryphnodendron clade. Our results indicate that the generic circumscriptions are consistent with palynological data, with polyad size emerging as the most distinctive trait among the analyzed groups. This study reinforces the value of pollen morphology as complementary evidence for evaluating generic boundaries within the Stryphnodendron clade.