A Reinterpretation of the Staminate Flowers of Haptanthus

Haptanthus hazletii is an enigmatic broad-leaved angiosperm of uncertain affinities. Previous research indicated that the staminate flowers had a morphology unique within the angiosperms, consisting of a single stamen with latrorse dehiscence. Re-examination of the morphology and anatomy of the staminate flowers does not support this interpretation but shows that the two elliptic flattened structures bearing the anthers are atop a solid pedicel-like stalk and are appressed to one another. These structures can be interpreted as either tepals with adnate bilocular introrse stamens or as foliose introrse stamens, either interpretation being unlike conventional floral structures. The anatomy of the flower reveals a siphonostele in the pedicel that divides into two arcuate traces supplying the anther-bearing structures. The vascular bundle runs up between the thecae giving off small branches to them; it terminates towards the apex of the flattened structure. Each theca is surrounded internally by massive tissue with endothecial thickenings. The unusual combination of floral characters does not easily fit into any known group, although the suite of characters indicates that the genus is probably amongst the basal eudicots, perhaps near Buxaceae.