Pollinaria of Hoya (Marsdenieae, Apocynaceae): Shedding Light on Molecular Phylogenetics

First molecular phylogenies of Hoya failed to reveal many intrageneric relationships, emphasizing the need to find additional phylogenetic characters. Thirty-five species, covering the morphological and geographic variation of Hoya, were examined using light and scanning electron microscopy (SEM). Thirteen phylogenetically informative characters were scored and studied in the light of an available phylogenetic tree. Species attributed to the Acanthostemma-group share pollinaria with obliquely elongate pollinia on broad-winged caudicles, synapomorphies that also link H. anulata and H. lacunosa to this group, the latter found in a disparate position in the phylogenetic tree. The pollinaria of H. sussuela fit well with those of the other species of section Eriostemma in having pollinia with twisted caudicles, a square corpusculum, and without pellucid margins. The absence of pellucid margins on the pollinia is also characteristic of H. mitrata and H. darwinii. Australian/New Guinean species generally have obovate pollinia basally protruding outwards and thick rhomboid corpuscula, supporting a monophyletic Australian/New Guinean clade, as suggested by phylogenetic studies. Hoya australis from Australia and H. albiflora from New Guinea have identical pollinaria indicating the possibility that these taxa are conspecific, as also shown in the phylogenetic tree. Several of the examined characters of the pollinaria of Hoya are useful in inferring phylogenetic relationships, indicating the utility of pollinarium morphology in this genus.