Results of a literature review and of original research by the authors were used in a detailed autecological comparison of the narrow-endemic Solidago shortii and its widespread congener S. altissima. The purpose of the study was to identify differences in the biology of these two species that might contribute to an explanation for the great differences in their geographical distribution. The most ecologically-relevant aspects of the biology of S. shortii and S. altissima compared were morphology, response to disturbance, life history, reproductive biology, ecophysiology, and biotic interactions. Although S. shortii and S. altissima are quite similar in many aspects of their biology, there are some important differences. Thus, S. altissima is a better competitor than S. shortii via its greater height, larger leaf area, and more extensive clonal growth, whereas S. shortii is a better drought-stress tolerator than S. altissima via allocation of a higher percentage of biomass to roots, higher root/shoot ratio, and greater capacity to maintain leaf turgor (i.e., not wilt as readily) under xeric conditions. Of the many aspects of the biology of these two taxa compared in this study, relative competitive ability would seem to be the single most important one related to differences in their geographical distribution. The capacity of S. altissima to form a larger and longer-lived soil seed bank than S. shortii also may be a contributing factor.

Key words: comparative biology, conservation biology, endangered species, rarity, Solidago altissima, Solidago shortii