Erigeron lemmonii A. Gray, restricted to Scheelite Canyon in the Huachuca Range, Arizona, has previously been proposed for federal listing as an endangered species but basic cytological and reproductive information has been wanting. The first chromosome count for the species is 2n = 18, which is the common diploid number in Erigeron. Analyses of eight plants from five disparate sites within the population show that pollen averages 85.8% staining in cotton blue in lactophenol. Microscopic observation using differential interference contrast optics shows that E. lemmonii combines about equally monosporic and bisporic megagametophyte development within a single capitulum. Despite variability in developmental route, the egg apparatus among mature megagametophytes appears to be nearly uniform in structure. In greenhouse culture, isolated plants fail to set seed indicating that plants are probably self-incompatible. Controlled crosses yield seed, but variation in seed set intimates the possible presence of genetic barriers within the population.
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Vol. 61 • No. 1