STANDLEY TREES AND SHRUBS OF MEXICO. 



species and one for the determination of families. Tlie last is 

 adapted from a key to the families of tropical American plants pub- 

 lished recently by Mr. Henry Pittier.^ It is very difficult, if not im- 

 possible, to prepare a key to the families of tropical plants which 

 will enable one always to refer a plant to its family, because many 

 of the plants are still imperfectly known, and because there are in 

 some families many exceptions to the typical plan of organization 

 of the group. With complete material of a given plant, however 

 it is hoped that the present key will usually be adequate for indicat- 

 ing its family position. 



It has been intended to give references to the names of all woody 

 plants published or reported from Mexico, disregarding, however, 

 certain obviously incorrect names which have not received notice in 

 more recent or important works. Casual references are made in 

 addition to the more common cultivated exotic species. Published 

 names not illustrated by material examined by the writer or not 

 identifiable from the descriptions accompanying them have been 

 listed as " doubtful species " at the end of their respective genera. 

 The plan has been to list as a valid species or as a synonym each 

 specific name based upon Mexican material, but it has not been 

 deemed necessai-y to list all the combinations under various genera, 

 unless their citation seemed to serve some useful purpose. The writer 

 has not attempted to classify all the names of Mociilo and Sesse, 

 which occur in their Plantae Novae Hispaniae and Flora Mexicana, 

 for these names have justly received little attention from taxonomists. 

 and their determination would require an amount of labor quite 

 inconsistent with any advantage that would result. Some of these 

 names, however, have been referred to in their proper places. A 

 very few of Mocifio and Sesse's names are valid, but it is only by 

 accident that such is the case. 



BANGES OF THE SPECIES. 



The range in Mexico ascribed to each species is based chiefly upon 

 material in the National Herbarium, but reliable published reports 

 have been taken into account when they indicated noteworthy ex- 

 tensions of range. It is probable that in many cases the species have 

 wider ranges than is indicated, but the limits of distribution can 

 not be determined definitely until more extensive explorations have 

 been carried out. Much more comprehensive collections are needed 

 from all parts of Mexico, but especially from the states of Tabasco, 

 Michoacan, Guerrero, Oaxaca, and Chiapas. Those available from 



* Clave analitica de las familias de plantas fanerogamas de Venezuela y 

 partes adyacentes de la America Tropical. Pp. 1-108. Caracas, 1917. 



