PLANT LIFE-FORMS AND BIOGEOGRAPHIC RELATIONS OF THE FLORA OF LAGUNILLAS (30-DEGREES-S) IN THE FOG-FREE PACIFIC COASTAL DESERT

The coastal desert of north-central Chile supports a rich but poorly k nown flora. Here, we document the importance of the annual and perenni al habits in the flora of Lagunillas (30-degrees-S), at the southern t ransition from the desert to the mediterranean climate region, and dis cuss the origin of the desert flora by examining the geographic distri bution of the taxa at the level of genus. The distribution was used to assign the species to six biogeographic elements. Annual plants repre sent 41% of the total flora (191 species) and are the most important l ife form. Excluding non-native weeds, however, decreases the importanc e of annuals to 33%. This value is higher than that for high-altitude deserts, but lower than for most other, less-equitable, lowland desert s both in North America and eastern Asia. Shrubs, geophytes, and other perennial herbs comprise 33%, 12%, and 21% of the native flora, respe ctively. The Cosmopolitan element, including weed species, accounts fo r 41% of the coastal desert flora. South American taxa include desert endemics (13%), Andean (12%), and Tropical American (10%) species. A l arge proportion (15%) of the taxa, especially shrubs, have disjunct di stributions in the arid regions of North and South America. Results su ggest that the present coastal desert flora derives primarily from rec ently diversified coastal desert and Andean taxa, most of them endemic to these areas, and secondarily from cosmopolitan weeds. The presence of a number of amphitropic xerophytes lends support to the hypothesis that arid habitats were continuous through the lowland tropics during the Glacial period.