If so, the production of sterile ovules by otherwise fertile microsporangiate strobli may reflect the ancestral condition (i.e., a functional bisporangiate
compound cone) rather than a teratology.
But the extensive evidence for parasitic insects in extinct seed plants making a switch to become pollinators has also to account for a switch from unisporangiate to bisporangiate strobili.
Bisporangiate strobili: the presumed ancestral Angiosperm character.
Styphelioideae are supported as monophyletic by the presence of bisporangiate anthers (char.
#55), bisporangiate, usually monothecal anthers (char.
Stamens (2-)5-10(-16), free from the corolla or adnate, sometimes connate, included or exserted, the filaments straight to variously curved, unicellular-pubescent or glabrous; anthers tetrasporangiate or bisporangiate, inverting (late, or more commonly early) in development, with 2 or 4 apparently terminal or dorsal appendages (awns, spurs) or these sometimes on the filaments, opening by pores or short to long slits, sometimes through narrowed tubules, an endothecium usually lacking.
However, in the Secamonoideae with functionally bisporangiate
anthers, it is the two inner (ventral) ones that are reduced (Civeyrel, 1995, 1996), whereas in the Asclepiadoideae it is the two outer (dorsal) ones that have become obsolete.
Androecium: stamens [1 (Usteria)-]4-5(-16), isomerous, alternipetalous, adnate to corolla: anthers bisporangiate
or tetrasporangiate, dithecal and introrse; dehiscing via longitudinal slits; usually isostylous, occasionally heterostylous (Gelsemieae); usually free, rarely connivent (Gardneria).