sist mainly of unlclonal populations. The apparent lack of production of viable seeds in the wild is consistent with speculation that Z. celata is self-Incompatible and with our evidence that most populations consist of single clones. Viable seeds have been produced ex situ from accessions of population HIGH which coflowered with accessions of population LASF. Unusual reproductive patterns have been reported within Ziziphus, which consists of 86 mostly tropical species. Investigations of these species have been triggered, in most cases, by the observation of low fruit set (Ackerman 1961). Several Ziziphus species are protandrous and heterodichogamous (Galil and Zeroni 1967; Lyrene 1983; Vashishtha and Pareek 1979; Zietsman and Botha 1992). In this reproductive system pollen is shed before the stigma becomes receptive, and the phenologies of flowers within a tree are coordinated. The presence of two flowering types ("early" and "late") within populations permits cross-pollination and fertilization to occur. Although Ziziphus fruits have been formed from self-pollinations, these fruits abort early in development or contain no viable seeds (Ackerman 1961; Zeitsman and Botha 1992). For Z. celata the small area occupied, the clumping of stems, and the overall appearance of two populations (FREED and SULL) permit the conclusion that these sites each consist of a single individual that has resprouted and spread vegetatively after mowing. However, shrubs in two of the populations (LASF and MLS) are scattered over some distance, with several individuals in each population found 45-60 m distant from others. It is improbable that these sprouts were generated from a single root system. One explanation for these observations is that our allozyme analyses did not detect existing clonal diversity within these sites. Another possibility is that occasional asexual reproduction via parthenogenesis (the development of seed without fertilization) has permitted the spread of genotypes at these sites. Parthenogenesis has been observed in some Ziziphus (jujube) cultivars (Lyrene 1983); If variation exists within Z celata for parthenogenesis, the absence of pollen, or the absence of compatible pollen, would likely favor this mode of reproduction. Conservation Implications Our genetic results and the in situ and ex situ observations of seed set provide con-

curring evidence that most Z. celata populations consist of single self-incompatible multilocus genotypes. The lack of compatible pollen, as well as the lack of suitable habitat, may seriously affect the persistence of this species in the wild. The enhancement of seedling recruitment in situ could be fostered by the introduction of unique multilocus genotypes into existing uniclonal populations. The possibility of the introduction of genotypic variants is substantiated by our observation that the 10 seedlings produced ex situ at Bok Tower Gardens had unique multilocus genotypes. This result suggests that genotypic diversity within the species can be easily reconstituted and provides hope for the reestablishment and long-term persistence of natural Z. celata populations. From the Departments of Botany and Genetics, University of Georgia, Athens, GA 30602 (Godt and Hamrick) and Bok Tower Gardens, Lake Wales, Florida (Race). We thank David Price and Robert Godt for helping with collections and University of Georgia undergraduates Sunltha Vege and Kassie DelHierro for laboratory assistance. This study was funded by the U.S. Fish and Wildlife Service (P.O. 41910-546930). The Journal of Heredity 1997:88(6)

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