Comparative ecophysiology of a rare and a widespread species of Echinacea (Asteraceae)

Among various potential causes of rarity, one explanation could be that a rare species has more narrow physiological tolerances to important environmental variables than does a widespread species. To test this hypothesis photosynthetic performance as a function of irradiance and temperature was compared for the rare cedar glade endemic Echinacea tennesseensis and its widespread prairie congener E. angustifolia following various light and soil moisture preconditioning regimes. Although the species differed in some morphological characteristics such as specific leaf area, both species demonstrated similar photosynthetic light-response curves on a leaf area basis, with low to moderate photosynthetic capacity. Thus no photosynthetic differences were found that could account for the contrasting geographic distributions of the endemic species and its widespread congener.