Vegetation of Northwest Mexico vl 27 
giant bald cypress or sabino, Taxodium mucronata. Other 
important families are Lignum vitae (Guaiacum sp., known 
as palo santo and guayacan), Rutaceae (Casimiroa edulis , 
the sapote), Burseraceae (Elaphrium sp., copal), Meliaceae 
(Swietenia sp., caoba), Euphorbiaceae (Euphorbia sp., 
Croton sp., Jatropha sp., Sapium sp., etc.), Rhamnaceae 
(Zizyphys , Condalia , Karwinskia, and Ceanothus ), Bom - 
bacaceae (Ceiba sp., pochote), and Convolvvlaceae (Ipomea 
o.rborescens , palo bianco). 
The higueras, huanacaxtle, and sabino are often trees 
over a hundred feet high with an imposing spread of foliage. 
These trees, together with mora, ebano, brasil, and guamu- 
chil, are the most noteworthy species of the river valleys. 
Many of the trees and shrubs carry epiphytes and parasites. 
On the slopes and foothills, palo bianco, Agaves , pochote, 
and cardon (Pachycereus) punctuate the monotony of the 
spiny “monte” scrub. These species become lost in the 
higher ‘monte” developed towards the south by increased 
precipitation. Towards the Sierra Madre Occidental, the 
tropical association first loses the higueras, mora, huana¬ 
caxtle, and sabino, replacing them with oaks, laurels, wild 
plums and other plants of the transition to mesothermal 
climatic conditions. Tropical vegetation, however, advances 
far into the Sierra Madre along the deep barrancas that 
carry low elevations for many miles back of the coastal 
plain. 
