Notes on the Flora of Mexico: World Distribution of the Woody Dicotyledonous Families and the Origin of the Modern Vegetation

Abstract

(With one Figure in the Text) Mexico has one of the richest floras in North America. From the tropical rainforests of Tabasco to the alpine meadows of Popocatepetl and Ixtaccihuatl, there are thousands of species representing hundreds of genera and scores of families. Because of their size and abundance the woody dicotyledons are the most conspicuous among the Mexican flowering plants. They represent about 140 families; the exact number varies with the degree to which the more inclusive venerable families are split in response to modern thinking on plant systematics. The foundation for a list of dicotyledonous families represented in Mexico by woody species was well laid by Standley (1920-6). Few additional families have been listed since by other botanists. The known world distributions of families with woody species indigenous to Mexico may give us a clue as to the origins of the rich flora native to that country. Although further explorations may change them slightly, it is possible to derive a general distribution pattern for most of these families by combining the information from Gunderson (1950), Good (1947) and Hutchinson (1926). It must be remembered that whereas we are restricting the discussion here to woody plants in Mexico, these families as discussed by the above authors often include herbaceous species. There is no family with woody members which is strictly endemic to Mexico. There are four, however, which extend little beyond her frontiers. The Crossosomataceae extends from north-west Mexico into California. The Fouquieriaceae is found from north central Mexico to Arizona, New Mexico and Texas. The Koeberliniaceae is limited to the last state outside of Mexico. The Pterostemonaceae (by some considered a part of Hydrangeaceae) seems to extend southward only to Central America. Six additional dicotyledonous families with woody Mexican species appear to be endemic to the warmer parts of the Americas. The Brunelliaceae (represented in Mexico only by Brunellia comocladifolia), Caricaceae and Marcgraviaceae are strictly tropical in distribution. The Julianaceae extends from Mexico to Peru; the Cyrillaceae, from Virginia to Brazil; and the Lacistemonaceae from Mexico and Central America to the northeastern half of South America. The last two families are represented by one species each in Mexico (respectively Cyrilla racemijfora and Lacistema aggregatum). Another group of families with woody Mexican members are those which are mainly