Tahoe yellow cress is the only species in the Sierra Nevada that is restricted to a single lake and no one really knows why. It is impossible to know exactly how Tahoe yellow cress came to be. Its ancestor, probably from the Columbia River drainage, became stranded many hundreds of thousands of years ago in the ancient basin of the Truckee River beside an immense, glacial-fed lake. Perhaps seeds were carried to this basin by accident, or maybe the ancestral plant descended from a more widespread species that inhabited the region during a distant geological period. In either case, its arrival long preceded human occupation of the continent and its evolution was guided by endless cycles of rising and falling waters.
Imagine the potentially suitable habitat created by lake recession during the distant past. During low lake periods, millions of Tahoe yellow cress-like ancestors could have colonized vast, open areas near the retreating lakeshore. With the return of high waters, most established sites would be inundated and individuals lost except for those upslope and those which were carried to new shores as floating seeds or rootstocks. Such catastrophic changes in population size are known to have significant and rapid effects on gene pool composition and could thus affect the rate and direction of evolutionary change. Tahoe yellow cress would, as a species, reflect eons of these lake-driven fluctuations in its distribution and abundance. With such a long history of rapid, unpredictable change, it is remarkable that this plant has persisted. Extreme climate change, extraordinary high waters, even landslides and lake tsunamis could have led to the extinction of Tahoe yellow cress. This diminutive, unassuming plant has proven itself tenacious in its quest for existence; not only weathering the severe forces of Lake Tahoe for hundreds of thousands of years, but incorporating those forces into a unique physical and physiological form.