中國玄參科植物地理之替代現象

Vicariism in the Geography of the Scrophulariaceae in China

In the distribution of plant, a frequently notes phenomenon is the occurrence of closely related species in geographically neighboring areas. Sometimes the separation is horizontal or geographical; while at other times the difference is mainly altitudinal, a lowland species being substituted by a morphologically similar species at higher elevations. Such vicarious forms are usually morphologically so closely related that their intimate genetic kinship is evident. Phylogenetically, they are descendents from a common ancestral type. This concept of vicariism or geographical displacement is not necessarily limited to species. It is equally applicable to subspecific categories. When a large series of specimens of a single species are made available, these being collected from various localities of the range of the species, geographical variations are often detectable.