Notes on the floral anatomy of Annona haematantha Miq.: an unexpected and specialized annonaceous corolla

The South-American species Annona haematantha Miq. exhibits a very puzzling corolla, which was previously interpreted as two stacked corolla tubes. An anatomical study was undertaken in order to solve this question. The outer and inner petals are fused at their base in a wide tube not appressed to the reproductive organs. The inner petals are adaxially modified into prominent glands on the proximal 3/4 of their length. The receptacular vasculature, as well as androecial and gynoecial structures are otherwise wholly in accordance with the floral anatomy of other known Annona L. species. Such a localized adaptation suggests a peculiar pollination process and widens the range of nutritious tissue patterns recorded in Annonaceae flowers. The pollination system probably involves night-flowering, thermo-genesis, scent emission, and intervention of scarab beetles.