Inflorescence structure and development in the Zingiberales: Thalia geniculata (Marantaceae)

The inflorescence of Thalia geniculata is among the most complex in a family characterized by complex inflorescences. The main axis of the inflorescence bears primary bracts which subtend either enriching branches, in the enriching zone, or pairs of flowers, in the florescence. The enriching branches repeat the structure of the inflorescence as a whole, with the addition of two specialized bracts: a prophyll and an interphyll. The paired flowers of the Marantaceae are mirror images of each other. The first bract of the inflorescence is formed in the plane of distichy of the leaves. Subsequent bracts are formed slightly to one side of the apex, giving a one-sided distichous arrangement. On an enriching branch the sterile prophyll is formed adaxially, followed by a fertile, abaxial interphyll. The first bract following the interphyll lies in a plane approximately perpendicular to the plane of the prophyll and interphyll. With the second bract the alternating divergence angles of approximately 115 and 145° begin to be established. The paired flowers of the florescence are subtended by a single, adaxial prophyll. Unlike many other Marantaceae no interphyll or bracteoles are formed below the flowers