Sporogenesis and gametogenesis of Delavaya toxocarpa (Sapindaceae) and their systematic implications

Abstract

AbstractIn order to investigate the embryological characteristics of Delavaya toxocarpa Franch. and provide a basis for further understanding the phylogeny within Sapindaceae s.l., we studied the sporogenesis and gametogenesis of D. toxocarpa using the conventional paraffin section method. The results were as follows: anthers are tetrasporangium; tapetum is typically secretory type; cytokinesis in the microsporecyte meiosis is of the simultaneous type and microspore tetrads are tetrahedral; mature pollen contains two cells; the ovary is bilocular with two ovules per locule; placentation is axial; the ovule is amphitropous, bitegmic, and crassinucellate; the chalazal megaspore in a linear tetrad becomes functional; and the development of megaspore is of the polygonum type. Most similarities shared by the species observed suggest that the species and genera of Sapindaceae s.l. have phylogenetic consistency. The distinctive trait, lacking hypostase, indicates Delavaya (and Handeliodendron) might be more primitive than other genera in Sapindaceae. Moreover, some characters, such as opposite palmate compound leaf, apical thyrse, rounded seed without wing, 2 hemitropous ovules per locule, and lacking aril, indicate the close relationship between Delavaya, Aceraceae, and Hippocastanaceae. The preliminary data about the embryological and morphological characteristics in Delavaya might justify the basic systematic position of this genus in the family Sapindaceae s.s.