Photoperiod Evidence in the Introduction of Xanthium Strumarium to Tahiti and Hawaii from Mexico

Abstract

Successful invasion of islands in the Pacific by Xanthium probably resulted from the chance introduction of a morpho-physiological form adapted to subtropical coastal habitats in North America. This hypothesis was tested by comparing naturalized plants from Tahiti in the Society Islands and Oahu in the Hawaiian Islands with collections from various coastal sites in Mexico. Plants from Tampico and Ciudad Mante, Tamaulipas; Veracruz (Antigua), Veracruz; and Salina Cruz, Oaxaca have morphological and physiological similarity to the Pacific introductions; however, each collection has certain niche relations that are slightly different from each other. All of the collections are in the same morphological complex and have apparent critical nights of 10.75–11 hr for reproduction. This morpho-physiological form is probably indigenous to Mexico, and it is widely distributed on the northeastern coastal plain of Tamaulipas.