Elaiosome-bearing plants from the Iberian Peninsula and the Balearic Islands

The importance of many mutualistic interactions is poorly understood because information on their frequency and distribution at wide spatial scales is lacking. One such interaction is that between ants and plants bearing diaspores equipped with elaiosomes, which function as a reward for ants in exchange for dispersion. Our aim was to estimate the number of taxa having elaiosome-bearing diaspores in the Ibero-Balearic territory and its relationship to several factors. We estimated that at least 572 species and subspecies, almost one-third endemic, are present, which corresponds to ca. 5.1% of European angiosperms and 9% of Iberian ones. Because this number of elaiosome-bearing taxa is much higher than those given so far for the Northern Hemisphere, the Ibero-Balearic territory should be considered an important center of myrmecochory, with myrmecochorous species richness significantly positively correlated with ruggedness, latitude, and longitude. In contrast to other myrmecochorous territories (Australia and Cape Province), where numerous trees and shrubs develop on acid substrates, most myrmecochores in the Ibero-Balearic area are perennial herbs occupying basic substrates. Such perennial herbs are more frequent in the Eurosiberian floristic region, whereas annuals abound in the Mediterranean region. The enumerated taxa mainly inhabit forests, scrubs, and anthropized sites. Among them, 56.5% carry the elaiosome on seeds (especially strophiole and caruncle types). In 36.7%, the elaiosome is borne on indehiscent fruits, such as achenes in Asteraceae, where they are found either at the base of the style or the basal hilum, and at the base of nutlets (Boraginaceae and Lamiaceae).