The gynostegium of Hoya spartioides (Apocynaceae – Asclepiadoideae): A striking case of incongruence between molecular and phenotypic evolution

In molecular phylogenies Hoya spartioides, formerly regarded as the only species in a separate genus Absolmsia, is nested in the genus Hoya. It appears as sister to H. curtisii within a larger clade including H. lacunosa, H. imbricata, and H. caudata. In contrast to this close molecular relationship the floral morphology of H. spartioides differs considerably not only from that of its sister, H. curtisii, but from all other species of Hoya investigated so far. Of special interest are the differences in functional morphology of the pollinating apparatus, which in spite of its high degree of synorganization has undergone considerable evolutionary change in H. spartioides. Some of the new traits are even unique within the subfamily Asclepiadoideae as a whole. The large phenotypic distance between H. spartioides and H. curtisii is not reflected in corresponding differences in the tested marker genes, which raises the question of how the flower of H. spartioides has evolved.