Floral ontogeny of Lecointea, Zollernia, Exostyles, and Harleyodendron (Leguminosae: Papilionoideae: Swartzieae s.l)

Abstract

Floral initiation and development were examined using scanning electron microscopy in Exostyles venusta, Harleyodendron unifoliolatum, Lecointea hatschbachii, and Zollernia ilicifolia. Common features include (1) unidirectional sepal initiation, (2) simultaneous petal initiation, (3) unidirectional initiation of each stamen whorl (except in the antesepalous whorl in Lecointea and Exostyles), (4) overlap in time of initiation of the two stamen whorls, and (5) initiation of the carpel concurrently with petals. Significant developmental features include (1) the first sepal median abaxial in all except Lecointea where it is non-median abaxial; (2) intraspecific variation in petal aestivation in Exostyles, Harleyodendron, and Lecointea; (3) initiation of antepetalous stamens before the antesepalous ones in Zollernia, Exostyles, and Lecointea; and (4) ovule initiation before the carpel margins are fused in Exostyles. The stamen sequence has not been found in any other legumes. The following late developmental events distinguish the four genera from each other: copious hairs hold the anthers together as a domelike structure at anthesis in Harleyodendron; zygomorphy in Zollernia results from differing petal reflexion; late hypanthium in Exostyles, Lecointea, and Holocalyx (no hypanthium in Harleyodendron or Zollernia); and reflexed sepal lobes in Exostyles, Harleyodendron, and Zollernia but not in Holocalyx and Lecointea. The genera studied here are ontogenetically more similar to taxa of Sophoreae than to other Swartzieae that have been investigated. None of the taxa studied here has a ring meristem, the structure that characterizes the remaining swartzioid taxa studied elsewhere.