Seed ontogeny of Serjania communis and Urvillea ulmacea and its relationship to transitional characters in Paullinieae (Sapindoideae, Sapindaceae)

Structural aspects of the seeds of Serjania communis Camb. and Urvillea ulmacea Kunth were described aiming to increase the knowledge about these organs in Sapindaceae. Ovules and seeds were collected at different stages of development and morphological and anatomical studies were performed according to standard techniques. Ovules are anatropous, tending or bowing to campilotropous, bitegmic, and pachychalazal; they also develop a pachychalazal, bitegmic, exotestal, and exalbuminous seed. Seeds are small, lenticular in S. communis and ellipsoid in U. ulmacea, and become campilotropous by means of the development of an invagination originating from the meristematic activity on the rapheal region. The exotesta consists of macrosclereids arranged in palisades. The other layers of the testa and the tegmen collapse up. In U. ulmacea, a cordiform aril is observed in the funicle and, as registered in the literature, it is similar to that found in Serjania inflata Poepp. & Endl. In other Serjania species there is no aril, but these two genera are considered phylogenetically close by many authors. Seed development in the studied species is similar and resembles other species of Paullinieae. Our results associated with those found in the literature seem to reinforce the transitional character of seed structures associated with fruit type in the tribe, as the reduction or absence of aril in indehiscent fruit of Serjania. However, seed ontogenetic studies must be extended to more species so as to allow reliable mapping of a larger number of characteristics of seeds on tribe phylogenies.