A New Introduction to the Flora of Mexico

Abstract

In December 1980 Dr Jerzy Rzedowski of the Laboratorio de Botanica Fanerogamica, Escuela Nacional de Ciencias Biologicas, Instituto Politecnico Nacional, Mexico City, collected material of a perennial herbaceous Euphorbia at San Francisco Cuautliquixco (190 41' N, 980 59' W) in the Municipality of Tecamac, along one of the main highways leading northwards from Mexico City, which he thought to be a member of the notorious esula-complex, various members of which have become such serious pests in the USA and Canada in recent years. Not being able to establish its identity in Mexico, he sent material to Kew, and rejected an initial suggestion that it might be an aberrant form of one or other of the native species E. campestris Cham. & Schlecht. or E. furcillata Kunth, remarking that they usually grow in natural or only slightly disturbed habitats, 'while this plant behaves like a recent introduction', at the same time sending further material with ripe seeds. The seeds, as is so often the case in the genus Euphorbia, proved to be the means whereby the identity of the plant could be established beyond doubt-laterally compressed pale grey seeds with a prominent pale yellow scaphoid caruncle, such as the specimen in question possessed, are characteristic of Euphorbia terracina L., which is native to the Mediterranean Region, the northern Sahara and Macaronesia. Although not a member of the esulacomplex, E. terracina nevertheless comes close to it, and this would appear to be the first record of its establishment as a member of the adventive flora of Tropical America.