Relative Salt Tolerance of Cakile Edentula (Brassicaceae) From Lacustrine and Marine Beaches

Seeds of Cakile edentula ssp. edentula var. edentula (hereafter edentula ) were collected from the Pacific Ocean shore of Washington, and Cakile edentula ssp. edentula var. lacustris (hereafter lacustris ) seeds were collected from the Lake Huron shore of Ontario. Germination rates of the two varieties showed equal tolerance of substrate salinities ranging from 0–10,000 ppm. Early root growth of edentula seedlings was significantly stimulated by 1,000 ppm salts, but otherwise both varieties showed equal tolerance to 10,000 ppm. Edentula plants exposed for 4 wk to salt spray intensities of 0, 20, and 90 mg dm –2 d –1 , applied in a growth chamber environment, showed no significant changes in shoot or root biomass, plant morphology, or reproductive effort. Lacustris plants exhibited significant declines in stem length and reproductive effort with increasing levels of salt spray. Our results suggest that lacustris and edentula have diverged physiologically over the past 9,000 years, and field observations from the literature corroborate our conclusion that this divergence in salt tolerance has ecological significance.