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 known flora. Here, we document the importance of the annual and perennial habits in the flora of Lagunillas (30-degrees-S), at the southern transition from the desert to the mediterranean climate region, and discuss the origin of the desert flora by examining the geographic distribution of the taxa at the level of genus. The distribution was used to assign the species to six biogeographic elements. Annual plants represent 41% of the total flora (191 species) and are the most important life form. Excluding non-native weeds, however, decreases the importance of annuals to 33%. This value is higher than that for high-altitude deserts, but lower than for most other, less-equitable, lowland deserts both in North America and eastern Asia. Shrubs, geophytes, and other perennial herbs comprise 33%, 12%, and 21% of the native flora, respectively. The Cosmopolitan element, including weed species, accounts for 41% of the coastal desert flora. South American taxa include desert endemics (13%), Andean (12%), and Tropical American (10%) species. A large proportion (15%) of the taxa, especially shrubs, have disjunct distributions in the arid regions of North and South America. Results suggest that the present coastal desert flora derives primarily from recently 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.