Evolution of Amphibious Vernal Pool Specialist Annuals: Putative Vernal Pool Adaptive Traits in Navarretia (Polemoniaceae)

The amphibious plants endemic to vernal pools of the California Floristic Province provide an excellent opportunity to study adaptive evolution for two reasons. First, most of these plants exhibit a major shift in habitat preference from that of their terrestrial ancestors. Second, in most cases, this shift apparently has occurred recently. Because this adaptive evolution has been dramatic and recent, obligate vernal pool species may be compared with relatives of other habitats to determine what developmental, morphological, and reproductive traits may have been important for vernal pool adaptation. A number of traits have been proposed by various authors as adaptive in vernal pool specialists. We test whether these traits are strictly correlated with the vernal pool habitat in Navarretia, a genus with closely related vernal pool specialists and terrestrial species. All vernal pool specialist taxa and their closest terrestrial relatives of the California Floristic Province were observed in their native habitats and under uniform cultivation. Adaptive hypotheses are supported for non-shattering inflorescences, outcrossing, and isoetid juvenile growth form. Contrary to prediction, spininess is reduced in the vernal pool taxa compared with their terrestrial relatives. Indehiscent fruits, small seeds, and absence of glandular hairs are perhaps advantageous traits for the vernal pool navarretias, but are not likely evolutionary adaptations in the strict sense. CITATION. Pages 76-85 in: C.W. Witham, E.T. Bauder, D. Belk, W.R. Ferren Jr., and R. Ornduff (Editors). Ecology, Conservation, and Management of Vernal Pool Ecosystems – Proceedings from a 1996 Conference. California Native Plant Society, Sacramento, CA. 1998.