Floral organogeny and development are described in Cadia purpurea, a legume with radial symmetry, unstable petal aestivation, and free organs, all unusual features among papilionoids. Flowers are usually solitary or, rarely, in few-flowered racemes. No bracteoles are formed. The order of organ initiation is unidirectional in each whorl, and the carpel initiates directly after petal initiation.The petal primordia remain small until all other floral organs have initiated, enlarged, and differentiated. Petal aestivation is variable, unlike the great majority of papilionoid flowers. Petal margins of Cadia grow straight outward rather than some petal margins curving inward inside the adjacent petal as is the case in other papilionoids. When adjacent growing petal margins of Cadia meet, chance determines which petal becomes positioned inside the other. Hence, the pattern of petal aestivation is random.Key words: aestivation; Cadia; Fabaceae; floral development; flower; Leguminosae; Papilionoideae; radial symmetry; Sophoreae.Cadia belongs to papilionoid tribe Sophoreae, long considered one of the most basal but heterogeneous tribes of papilionoid legumes (Polhill, 1981(Polhill, , 1994. The tribe has recently been shown to be nonmonophyletic (Herendeen, 1995;Doyle et al., 2000;Ireland, Pennington, and Preston, 2000) and is currently in the process of dismemberment, with certain woody taxa of sophoroids appearing to be more closely related to some elements of tribes Swartzieae, Dalbergieae, and others (Ireland, Pennington, and Preston, 2000;Pennington et al., 2000Pennington et al., , 2001. Recent molecular-based analyses (Doyle et al., 2000;Pennington et al., 2000Pennington et al., , 2001 place Cadia as sister to Calpurnia (tribe Podalyrieae) but embedded within a clade containing other sophoroid taxa. Cadia, a genus of small shrubs from Arabia, Madagascar, and eastern Africa, has long been of interest because of its radial floral symmetry and atypically unstable petal aestivation (van der Maesen, 1970;Tucker, 1984Tucker, , 1987, in contrast to the prevailingly uniform, descending cochleate aestivation of nearly all other Papilionoideae.The tribe Sophoreae sensu Polhill (1981Polhill ( , 1994 includes the putatively least specialized and most plesiomorphic taxa of the large subfamily Papilionoideae of legumes. As originally conceived by Bentham (1841) the tribe was considered transitional between papilionoids and the subfamily Caesalpinioideae. The emphasis on the heterogeneity in Sophoreae (Polhill, 1981) prompted examination of the pollen structure (Ferguson, Schrire, and Shepperson, 1994), endothecial characters (Manning and Stirton, 1994), and wood (Gasson, 1994). Because of the recent surge in interest in taxa of Sophoreae sensu lato (s.l.), the floral ontogeny of Cadia purpurea Ait. is presented, together with updated comments on its putatively plesiomorphic character states.
MATERIALS AND METHODSYoung inflorescences and flower buds of all sizes were collected and preserved in formalin-acetic acid-70% ethyl alcohol ...