FLORAL ONTOGENY IN LEGUME GENERA PETALOSTYLIS, LABICHEA, AND DIALIUM (CAESALPINIOIDEAE, CASSIEAE), A SERIES IN FLORAL REDUCTION

Floral ontogeny of taxa of two subtribes (Labicheinae, Dialiinae) of c aesalpinioid tribe Cassieae, characterized by reduced number of floral organs, was compared. All three taxa studied are distichous; Petalost ylis labicheoides flowers are solitary in leaf axils, Labichea lanceol ata has few-flowered racemes, and Dialium guieense has numerous-flower ed cymes. The first sepal primordium in each is initiated abaxially an d nonmedianly. Order of organogenesis in Petalostylis is: five sepals bidirectionally, five petals and carpel simultaneously, then five stam ens bidirectionally, starting abaxially. The order in Labichea is: fiv e sepals helically (one lagging in time). five petals unidirectionally starting abaxially, the carpel and petals concurrently. then two stam ens successively, starting laterally. Order in Dialium is: five sepals bidirectionally, the single Fetal abaxially, and lastly the carpel an d two stamens concurrently. Specializations include (1) reduction of t he five sepals to four by fusion in Petalostylis and Labichea: (2) red uction of petal number to one in Dialium: (3) reduction of stamen numb er to two in Labichea and Dialium, and reduction of functional stamens to three in Petalostylis; and (4) an elaborate, late-developing style in Petalostylis. Floral asymmetry, another specialization, characteri zes Labichea, expressed by dissimilar stamens, while the other genera have zygomorphic flowers. Floral ontogenies are compared with other ta xa of Cassieae.