Biosystematics of Erythronium propullans gray and sympatric populations of Erythronium albidum Nuttall (Liliaceae)

Abstract

A biosystematic comparison of Erythronium propullans and sympatric populations of E. albidum was conducted to clarify the relationships of these two species. E. propullans is endemic to southeastern Minnesota, while E. albidum is common and widespread throughout the eastern United States, including southeastern Minnesota. The morphology, geography, cytology, ecology, and reproductive biology of each species were investigated. Populations of E. albidum and E. propullans within Rice and Goodhue Counties, Minnesota, were utilized in the study. A morphological analysis of six characters indicated that E. albidum and E. propullans are morphologically distinct species, and that three size classes of plants exist: E. propullans, depicted as a dwarfed E. albidum, an intermediate size class, and E. albidum. The intermediate size class suggested that E. albidum and E. propullans hybridize to form fertile offspring. The rarity of the hybrid further suggested that some reproductive isolation between the two species exists. The pollen-ovule ratio, protandry, and the dimorphic stamens of E. propullans and E. albidum suggest that both species are facultatively outcrossing. Breeding experiments demonstrated that E. albidum is facultatively outcrossing and able to produce seed when crossed with E. propullans. Self-fertilization in E. albidum required a physical mechanism to transfer pollen from the anther to the stigma. E. propullans, however, produced seed only when crossed with E. albidum. Pollen was found to be effectively transferred either between clones of E. albidum or E. propullans by Andrena carlini Ck11., a solitary oligolectic bee whose pollination behavior was well suited to the flowers of both species. Visits by this insect were primarily to E. albidum flowers. The reproductive evidence questions the validity of the specific ranking given to Erythronium propullans as suggested by its morphology. The restricted range, the relative sterility, and the ploidy level of E. propullans suggest it is a relatively young species of recent origin derived from E. albidum. The inability of E. propullans to reproduce with itself, and a natural low level of seed production in this species, further suggested that populations are maintained exclusively by vegetative reproduction. The lack of input of genetic variability by sexual processes indicates that E. propullans will not adapt to drastically changing environments. Unless critical habitat is preserved, the populations are likely to be extirpated in the near future, resulting in the extinction of E. propullans.