FLORAL MORPHOLOGY AND EMBRYO SAC DEVELOPMENT IN BURRETIODENDRON KYDIIFOLIUM HSU,Y.C. ET ZHUGE,R. (TILIACEAE) AND THEIR SYSTEMATIC SIGNIFICANCE

Floral morphology and development of megaspore and megagametophyte in Burretiodendron kydiifolium are described. The ovule is anatropous, cr assinucellate and bitegmic. The archesporium is multicellular and usua lly two cells develop to megasporocytes. The tetrad is linear or very rarely T-shaped. The chalazal megaspore functions and develops into a Polygonum-type of embryo sac. The antipodals degenerate very early and the fertilizable embryo sac consists of only one egg cell, two synerg ids and two polar nuclei. In a fertilizable embryo sac the micropyle i s formed by both outer and inner integuments, which are three to four and five cells thick, respectively. The epidermal cells of the nucellu s divide to form a nucellar cap. A group of special cells with large n uclei and less staining are observed below the sporogeneous cells. Com parison of the embryological features of Burretiodendron s.s. with tho se of Tiliaceae indicates that this genus differs greatly from other m embers of Tiliaceae and no close relationship is established among Bur retiodendron and other tiliaceous taxa. Most embryological features of Burretiodendron are shared by the genus Pterospermum of Sterculiaceae although they differ considerably in gross morphology. (C) 1998 The L innean Society of London.