INTROGRESSION IN CENTRAL AMERICAN PHYTOLACCA (PHYTOLACCACEAE)

A numerical analysis of morphological variation in Central American Phytolacca distinguishes P. rivinoides Kunth & Bouché from the P. iscosandra complex, which includes elements that have been recognized as P. icosandra L., P. octranda L., P. purpurascens A. Br. & Bouché, P. rugosa A. Br. & Bouché, and P. costaricensis Suesseng. A third and rarely collected taxon, P. meziana H. Walt., is also distinguished. New chromosome counts of 2n = 36 are recorded for P. rivinoides and two representatives of the P. icosandra complex. Nearly half the morphological variation in the sample is summarized by a multivariate axis that separates P. rivinoides from the P. icosandra complex. This axis correlates with a cline in elevation; P. rivinoides occurs between sea level and 2,200 m, and P. rugosa occurs between 1,000 and 3,400 m. It is hypothesized that introgression of the P. rivinoides genome into that of P. rugosa has generated the P. icosandra complex; elements of this complex then migrated northward through Mexico and may have been progenitors of the North American P. americana L.