Diversity and distribution of extrafloral nectaries in a region with three converging South American biomes

MARAZZI, BRIGITTE; VIVIANA GRISELDA SOLIS NEFFA

Boise, Idaho

Congreso; Botany Conference; 2014

American Society of Botany

Plants in over a hundred families and even some ferns bear extrafloral nectaries (EFNs). These secretory structures occur on virtually any above-ground plant part, except flower organs participating in pollination. The secreted nectar represents a valuable, sometimes critical, food resource for ants and many other arthropods. In return for the nectar, the ants (and other aggressive arthropods) often protect the plants from herbivory. EFN diversity and the ecologically important interactions that they mediate have been studied especially in tropical forests and savanna-like habitats (where they rather represent a large proportion of the vascular flora), but also in North American and Asian temperate regions (where they represent only a minor fraction), whereas they remain largely unknown from subtropical ecosystems. Therefore, here we investigate patterns in the phylogenetic and geographic distribution of EFN-bearing plants in a region of subtropical South America characterized by the convergence of three main biomes: Chaco, Espinal and Paranaense. Specifically, we assess the total diversity of EFN-plants and their proportion relative to the rest of the vascular plants and compare results for individual biomes to identify which one displays the highest EFN diversity. The region of biome convergence corresponds geographically to the Argentinean province of Corrientes. Therefore, we compiled a list of vascular plant species with EFNs by comparing a floristic list of Corrientes (made of herbarium specimens extracted from the Flora of Argentina database) with reports from the literature and the online world list of EFN-plants and with our observations of herbarium material and living specimens. We assigned EFN-species to the three biomes according to their geographic distribution. Approximately 38% of the 162 vascular plant families in our checklist of Corrientes potentially include species with EFNs. These are distributed in 116 angiosperm and two fern genera, totaling 636 species. As found in other studied ecosystems, Leguminosae (Fabaceae) are on top with 34 genera and (potentially) some 137 species. Other families with noteworthy EFNs include the Bignoniaceae (15 genera/~26 spp.) and Euphorbiaceae (15 genera/~51 spp.), while in Cactaceae, there are more EFN-genera than currently thought (7 genera/~13 spp.). The Chaco biome appears to include most of the EFN-bearing plants. This might be explained by the fact that legumes are a dominant component of the Chaco and that this biome is known for its diversity and abundance of ants. Our study sets the stage for needed research on ant-EFNs interactions in South American subtropical ecosystem.