LISTADO FLORÍSTICO DE LA CUENCA DEL RÍO BALSAS, MÉXICO

Abstract

The Balsas river basin is one of the largest and
most important in Mexico. Comprising
approximately 112,320 km2, it forms an eastwest-oriented depression in central-south
Mexico and occupies portions of the states of
Guerrero, Jalisco, México, Michoacán,
Oaxaca, Puebla, and Tlaxcala, and all of
Morelos. The basin is physiographically
delimited by the Transverse Volcanic Belt to
the north and the Sierra Madre del Sur to the
south, and lies between 17°00' and 20°00' N
latitude and 97°30' and 103°15' W longitude.
The prevailing climate is warm and semiarid,
with the aridity increasing eastward, where
most of the xerophytic elements are thus
concentrated. Due to its position between two
major mountain chains and the resultant
variations in elevation within the area, various
and diverse vegetation types occur in the
region, ranging from xerophyllous scrubs to
tropical forests to oak-pine forests and even
alpine grasslands above treeline. The great
diversity of environmental conditions that
characterize the Balsas river basin, as well as
the biotic relationships to the neighboring
areas, which belong to quite separate floristic
regions, confer a great floristic diversity to
the area.
The existing information on the vegetation and
flora of the basin is not extensive, and we
therefore can consider this to be one of the
more poorly known regions of Mexico from
the botanical point of view.
The principal objective of this work is to
present a preliminary list of the phanerogamic
flora of the balsas river Basin, based on the
species that have been collected in or cited
from the area. The list is alphabetical by
family, genus, and species within the major
groups of pteridophytes, gymnosperms, and
angiosperms.
The list includes 202 families, 1,246 genera
and 4,442 species. The largest families are:
Compositae with 136 genera and 573 species,
Leguminosae with 90 genera and 486 species,
Gramineae with 84 genera and 253 species and
Orchidaceae with 51 genera and 197 species.
The best collected states within the basin at
present are Guerrero, Michoacán and Morelos.