INTRODUCTION Astragalus L. (Fabaceae: tribe Galegeae), with about 3000 species worldwide, is the largest genus of flow- ering plants. The high variation of morphological characters has made the taxonomic division of the genus uncertain and problematic (Liston and Wheeler, 1994; Sanderson and Liston, 1995; Sanderson and Wojciechowski, 1996; Wojciechowski et al., 1999; Zarre, 2000). Several previous systemat- ic studies attempted to classify this huge genus into formal taxonomic groups, that is, subgenera and sec- tions (Bunge, 1868; Podlech, 1982), but only a few groups found support from molecular systematics (Wojciechowski et al., 1999; Kazempour Osaloo et al., 2003, 2005). Detailed cladistic investigations indicat- ed the homoplastic nature of most gross morphologi- cal characters in delimitation of subgenera and sec- tions in Astragalus. Embryological studies have provided useful characters in assessing subgeneric classifications in Papilionoideae (Rembert, 1969; Palser, 1975; Lersten, 1983; Prakash, 1987; Cameron and Prakash, 1994; Soverna et al., 2003) as well as in the genus Astragalus (Akhalkatsi et al., 1988; Gvaladze and Akhalkatsi, 1996; Riahi et al., 2003). However, the methods of such investigations in Astragalus are time-consuming and difficult to carry out due to prob- lems in cultivating the plants under greenhouse con- ditions or in gardens (Riahi et al., 2003). In this work we made a detailed embryological study of A. cemerinus G. Beck (sect. Microphysa) and A. ruscifolius Boiss. (sect. Dissitiflori), two endemic species of Astragalus in Iran, with the aim of providing valuable characters useful in assessing relationships within this genus. MATERIALS AND METHODS Flowers and young pods of A. cemerinus and A. rus- cifolius were collected in May 2004 from mountains (~1580 m a.s.l.) above Mashhad Ardahal in Esfahan Province, Iran. At least 60 developing seeds and * e-mail: zarre@khayam.ut.ac.ir SEED DEVELOPMENT IN ASTRAGALUS CEMERINUS AND A. RUSCIFOLIUS (FABACEAE), AND ITS SYSTEMATIC IMPLICATIONS MEHRSHID RIAHI AND SHAHIN ZARRE * Department of Plant Sciences, University of Tehran, PO Box: 14155–6455, Tehran, Iran Received February 17, 2009; revision accepted May 15, 2009 This study focuses on seed development in Astragalus cemerinus and A. ruscifolius, two endemic species of Astragalus in Iran. In both species the ovules are campylotropous, bitegmic and crassinucellate. Two polar nuclei fuse before fertilization, forming the diploid secondary nucleus. Division of the primary endosperm nucle- us gives rise to coenocytic endosperm; however, part of it becomes cellular at the late globular stage. The first division of the zygote is transverse and the embryo proper forms after several divisions of the terminal cell. The mature suspensor consists of a mass of cells equal in size to the globular embryo proper, with several inflated cells towards its base. This massive suspensor seems to be plesiomorphic, as compared with the biseriate sus- pensor known only in section Incani. Abnormalities in the embryo proper as well as in the suspensor are observed at the globular stage. In both A. cemerinus and A. ruscifolius, fusion of the polar nuclei occurs in the median regions of the central cell and before fertilization occurs, as is the rule in most of the Papilionoideae, but in species of section Incani as in a few other species of the family, the polar nuclei approach the egg apparatus before fertilization and do not fuse until fertilization. The embryological characters of A. cemerinus and A. rus- cifolius are compared with those of other species of Astragalus, and the taxonomic application of these charac- ters as well as their phylogenetic significance are discussed. Key words: Abnormal embryology, Astragalus cemerinus, Astragalus ruscifolius, megagameto- phyte, embryo proper, suspensor, phylogeny. ACTA BIOLOGICA CRACOVIENSIA Series Botanica 51/1: 111–117, 2009 PL ISSN 0001-5296 © Polish Academy of Sciences and Jagiellonian University, Cracow 2009