Insights on the systematics and morphology of Humiriaceae (Malpighiales): androecial and extrafloral nectary variation, two new combinations, and a new Sacoglottis from Guyana

Humiriaceae have had little recent comparative morphological study except for their distinctive fruits. We surveyed the diversity of stamen structures in the family with consideration of dehiscence patterns and the evolutionary transitions between tetra- and disporangiate anthers. Novel interpretations of floral morphology support new combinations (Duckesialiesneri K.Wurdack & C.E.Zartman, comb. nov. and Vantaneaspiritu-sancti K.Wurdack & C.E.Zartman, comb. nov.) for two species formerly in Humiriastrum. We investigated all eleven species of Sacoglottis for diagnostic features that may contribute to better species delimitations, and describe Sacoglottisperryi K.Wurdack & C.E.Zartman, sp. nov. as an endemic of the Pakaraima Mountains in western Guyana. Finally, our survey across Humiriaceae for extrafloral nectaries (EFNs) revealed their presence on leaves of all extant species as adaxial basilaminar and/or abaxial embedded glands, in addition to the frequent occurrence of marginal glandular setae. The significance of inter-generic variation in gland position and anther morphology within the family are discussed.