The Origin and Geographical Affinities of the Flora of California

Abstract

Before undertaking to discuss the origin and geographical affinities of the flora of California it might be advisable to roughly outline the factors governing the geographical distribution of plants, in order that you may more clearly see the point of view from which I propose to attack the question. For the sake of brevity we may group these factors under three main propositions: (i) Plants will endure only where the environment is favorable for growth and reproduction. (2) Different kinds of plants require different environments; not all plants thrive under the same temperature, moisture and soil condition. (3) The individuals of a species, and in a broader sense the members of a genus, have common ancestors with a common place of origin from whence the descendants have migrated. It is this last proposition that chiefly concerns us in the present discussion. If it be true that closely related plants have common ancestors and a common place of origin the logical deduction is that the members of a natural group will be found in the same general region in places accessible, or at one time accessible from the point of origin. To illustrate this point let us examine into the distribution of the genus Tumion. Those of you familiar with the conifers of the state no doubt know the California Nutmeg, Tumion californica. It is not a true nutmeg, indeed it is in no way related to the nutmeg of commerce, but is a gymnosperm belonging to the Yew family. It is the ruminating endosperm that suggests the name. The genus Tuinion comprises four species all similar and evidently closely related. Each species is restricted to a comparatively small area and remote from the others. One is in California, one in Florida, one in Japan and one in China. Now if our theory of a common origin of closely related plants is sound, these four species go back to a common stock and place of origin. How then have they reached these widely separated regions? For the answer we must turn to geology and paleo-botany. In North America we find