A Geography of Pokeweed

Abstract

The plants we call weeds stand apart from their truly wild and truly tame fellows because of their special ability to establish themselves in artificial habitats. In spite of indifference or active repression by man, they have been able to thrive and multiply with the advance of civilization. By the very fact of their existence such plants suggest problems of special botanical and ethnological interest. There is the problem of the peculiar characteristics which have allowed the weeds to exploit disturbed places. There are also the questions of how the ancestors of modern weeds fitted into the ancient natural plant associations of pre-human times, how much these plants have evolved, and how far they have migrated since they first allied themselves with man. General answers to such questions will require understanding of the stories of many individual species. Since only fragments of direct historical evidence on most weed species can be found in published records or herbarium collections, their stories must be reconstructed largely from indirect evidence. One of the most powerful lines of indirect evidence may be found in geographic distributions. The present geographic patterns of the weeds, like those of any phenomena irregularly distributed over the earth's surface, offer strong though sometimes complex and cryptic clues to their past stories. This paper represents an attempt to describe and understand the distribution patterns of a single species, Phytolacca amnericana L. (P. decandra L.; includes P. rigida Small), commonly called pokeweed or simply poke. Poke is in some ways an especially attractive subject for such a case study. The species is relatively clear-cut taxonomically and is the sole representative of its genus through almost its entire range. Thus a wealth of previous records can be used in studying its distribution, with slight danger of accepting mistaken identifications. The gross range is considered first, followed by examination of the microdistribution. Finally, an effort is made to reconstruct some of the story of how poke became a successful weed.