GENETIC DIVERGENCE AND ISOZYME NUMBER VARIATION AMONG FOUR VARIETIES OF ALLIUM DOUGLASII (ALLIACEAE)

Allium douglasii comprises four, allopatric varieties confined to the northwestern United States: var. columbianum, var. constrictum, var. douglasii, and var. nevii. Although no apparent karyotypic differences distinguish the four taxa, evidence from starch gel electrophoresis indicates that they are very distinct at genes coding for enzymes. The mean genetic identity for pairwise comparisons of populations of all four varieties is 0.84. This value is lower than identity values generally observed for subspecific taxa, and may be indicative of a long period of geographic separation and subsequent lack of gene flow among the varieties. However, a higher genetic identity of 0.93 was observed between var. constrictum and var. columbianum relative to other varietal comparisons. In addition, var. constrictum exhibited two biochemical autapomorphies: 1) loss of expression for the gene coding for Tpi-3, and 2) duplication or reactivation of an ADH gene. These data indicate that var. constrictum may be a recent derivative of var. columbianum. The distribution of genetic variation within and among populations of the putative progenitor/derivative pair also supports this hypothesis. ALLIUM L. is a genus of 550 species (Dahlgren, Clifford, and Yeo,1985) distributed in the northern hemisphere. In North America, the genus consists of approximately 70 species divided into nine well-defined species alliances (Ownbey and Aase, 1955). The Allium falcifolium alliance is the largest and comprises 31 taxa including A. macrum S. Wats., A. robinsonii Hend., and the four members of the Allium douglasii Hook. complex (Mingrone, 1968). Allium douglasii comprises four varieties (vars. douglasii, columbianum Ownbey & Mingrone, constrictum Ownbey & Mingrone, and nevii (S. Wats.) Ownbey & Mingrone) confined to the northwestern U.S. (Mingrone, 1968). All four varieties are diploid (2n = 14, perennial herbs, and allopatric (Fig. 1). Although all four taxa are restricted in range (Fig. 1), var. constrictum is particularly limited in distribution, known only from Douglas, Grant, and Lincoln Counties in northcentral Washington. The four taxa also differ significantly in ecological preferences. Variety douglashi occurs in winter wet, moderately deep, rocky, I Received for publication 4 November 1986; revision accepted 10 February 1987. This study was supported in part by NSF Grant BSR 8315088 to DES, a NSF dissertation improvement grant to LHR and DES, and by a Northwest Scientific Association award to PMP, LHR, and CRA. We thank Pam Soltis, Dan Crawford, and an anonymous reviewer for helpful comments on the manuscript. sandy, clay loam soils, whereas var. columbianum is generally found in spring wet, clay loams and stony meadows. Variety nevii occurs in wet meadows, along streams, and vernal flats in deep clay loam soils, and var. constrictum is restricted to shallow lithosolic soils, often dry and sandy. The remaining two species, A. macrum and A. robinsonii, are closely related to A. douglasii (Mingrone, 1968) and were utilized as outgroups in this study. Allium macrum is the most closely related species to A. douglashi (Mingrone, 1968) and ranges from central Washington south to Klamath County, Oregon. Allium robinsonii is more restricted in range, occurring along the Columbia River in Washington and Oregon. We employed allozyme, karyotype, and isozyme number variation to 1) measure genetic divergence among the four varieties of Allium douglasii, 2) analyze intraspecific relationships within Allium douglasii, and 3) examine the origin of Allium douglashi var. constrictum. MATERIALS AND METHODS-Plant collections-Leaves for isozyme studies (30-60 per population), floral buds for chromosome counts, and bulbs for generating root tips to be used in karyotype comparisons were gathered from populations in northwestern U.S. (Table 1). Plant material was collected from a total of 26 populations (numbers in parentheses indicate number of populations analyzed):