Flower and Inflorescence Development in Montrichardia arborescens (L.) Schott (Araceae)

The spadix of Montrichardia arborescens contains unisexual flowers without a perianth. The pistillate flowers occur in the basal portion, and the staminate flowers are in the apical portion of the inflorescence axis. In some spadices the zone between male flowers and female flowers contains vestigial flowers. A morphological gradient seems to be apparent in the intermediary zone: the portion of the bisexual flower facing the staminate zone possesses staminate characters (stamens), and the portion facing the pistillate zone possesses pistillate characters (aborted gynoecium). The floral primordia appear in successive alternating rows producing parastichies (helices) around the spadix. The number of opposed contact parastichies can vary depending on the form of the inflorescence and on the number of flowers produced. Pistillate and staminate flowers are inserted in the same contact parastichies along the inflorescence, with no discontinuity among the female zone, the bisexual zone, and the male zone. On the same parastichies, one can observe a continuum from the lower to the upper part of the young inflorescences.