• floral organogenesis;
  • floral construction;
  • teratology;
  • Alismatales;
  • Echinodorus.

The primary trimerous pattern of the flower of Echinodorus amazonicus Rataj is clearly exhibited in the earliest developmental stages. After the inception of three sepals, theree alternisepalous petal-stamen complexes arise, each of which, at successively higher levels of the primordia, consists of a petal, a pair of stamens, and a single stamen. In alternation with these three petal-stamen complexes three groups of three pistil (carpel) primordia are formed. Subsequent pistil primordia are formed rapidly in alternation with the preceding ones. Teratological buds were observed in which one pistil primordium appeared to be replaced by a normal stamen primordium. General features of the flowers of the Alismatales are summarized in developmental fashion which includes the mature flower as a final stage. With the exception of Limnocharis and probably Wisneria, all alismatalean flowers appear to be characterized by antipetalous stamen (or staminodial) paris. In members studied thus far, the basic trimery differs radically from that found in certain taxa of the Magnoliidae.