XVI International Botanical Congess
In SE Colorado, shales of the Niobrara Formation are rich in rare and endemic species. In light of increasing habitat loss, we examined site physical, chemical and biological characteristics. We found no unusual geochemistry, rarity is probably due to water competition and not edaphic factors. Most of the species are at least facultatively autogamous, low reproductive success appears to be due to herbivory and climatic stress, not pollinator limitation. Many of the endemic species show a characteristic growth form with woody caudices or extensive rhizomes which penetrate bedrock interstices, this facilitates tolerance of disturbance or inclement climatic periods, and opportunistic response to sporadic water abundance. The shale barrens should be considered regional targets for conservation due to their biological significance.