Morphology and Structure of Staminate Inflorescences and Flowers of Leitneria floridana (Simaroubaceae) : Revisited

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Leitneria floridana, a dioecious shrub indigenous to North America, was recently transferred from its own family Leitneriaceae (usually placed in 'Amentiferae') to the family Simaroubaceae (Sapindales). Its staminate inflorescence is catkin-like, bearing 40-50 large bracts arranged in a 5/8 phyllotaxis on the axis. In each bract axil, a varying number of stamens (usually 10) are produced. They have been considered to represent a (one- to) three-flowered cymule instead of a single flower. In reviewing the limited evidence for the presence of the cymule and the revised familial position of the species, I re-examined the structure of the staminate inflorescences by analyzing serial microtome sections. The results confirmed that the staminate inflorescence of Leitneria is a reduced form of a thyrse consisting of many cymules, and that each cymule consists of one central and two lateral flowers (florets). Each flower has four stamens arranged in a cross-like configuration, in contrast to the previously considered diagonal configuration. One or more stamens, however, may be lacking in each flower, particularly in the lateral flowers, resulting in a varying number of stamens in the bract axil.
2013-02-21