1 COMPARATIVE EMBRYOLOGY OF SOME ASTRAGALUS SPECIES MAIA AKHALKATSI Institute of Botany of the Georgian Academy of Sciences Kojori Road 1, 380007, Tbilisi, Republic of Georgia ABSTRACT Age and spatial structure, population density and frequency influencing recruitment are estimated in populations of rare and abundant Astragalus species distributed in the same and distinct habitate. According to the obtained data rare species A.caucasicus and abundant one A.microcephalus growing in the same habitat reveal equal population density and great similarity in spatial and age distribution. But, A.microcephalus outnumbers A.caucasicus by frequency of species within area occupied by both populations. We suppose that the limiting factor for the increasing of the population of A.caucasicus may be difficulties in establishment of new seedlings in vacant ecological niches, which may be associated with interspecific competition between the two species. A.denudatus distributed in different habitat surpassed the other two species by all characteristics. The recruitment size revealed density dependent character and positive value in every investigated population. I. INTRODUCTION Astragalus caucasicus. Is included in the Red Data Book of Georgia. The negative influence on the state of this species exerts diminishing of the number of individuals in populations (Red Data Book of Georgia, 1982). Investigation of the structure of a population is particularly important for many endemic and rare plants (GARCIA & ANTOR,1995). The population structure can be described in terms of spatial distribution, age and reproductive potential of the individuals that compose it (HANZAWA & KALISZ, 1993; GARCIA & ANTOR, 1995). In the present study we evaluate the population structure of rare species A.caucasicus and compare with that of abundant Astragalus species, distributed in the same - A.microcephalus and distinct - A.denudatus habitats. The objectives of this study were to investigate interspecific variation in age spatial structure, to establish the recruitment size and to estimate the relationship among population density, frequency and recruitment in populations of three species.