Can the anatomy of abnormal flowers elucidate relationships of the androecial members in the ginger (Zingiberaceae)?

Abstract

Background Interpretation of the floral structure of Zingiberaceae has long concentrated on the relationships of the androecial members. It has been suggested that the labellum is composed of two structures rather than three or five, and the glands are not only the epidermis of the ovary but are similar to nectaries. Results Serial sections were used to observe the vasculature of normal and two-staminate flowers in Alpinia intermedia ‘shengzhen’. Floral diagrams were drawn to interpret the morphological category of the floral organs and the relationships of the androecial members. Androecial vascular bundles were associated with carpellary dorsal bundles (CDBs) and parietal bundles (PBs) in a Zingiberales phylogeny setting using ancestral state reconstruction. Anatomical observations demonstrate that the fertile stamen(s) incorporate parietal strands both in normal and two-staminate flowers. The three appendages represent the three members of the outer whorl of the androecium while the labellum represents the inner whorl of the androecium in the two-staminate flower. Reconstruction of the origin of the vascular system in the androecium suggests that the outer whorl of androecium receives its vascular supply from the CDBs and the inner whorl of androecium receives from the PBs in both the basal banana group and the more derived ginger clade. Conclusions The present study adds to a growing body of literature suggesting that anatomy of abnormal flowers may not provide enough evidence for elucidating the relationships of the androecial members. Abnormal flowers are diverse in the Zingiberaceae and may derive from different types of mutations.