ALUMINIUM ACCUMULATION IN RUBIACEAE: AN ADDITIONAL CHARACTER FOR THE DELIMITATION OF THE SUBFAMILY RUBIOIDEAE?

Abstract

The chrome azurol-S test, which is a chemical spot-test for Al accumulation in wood, was applied to 443 wood samples of members of the Rubiaceae. A positive reaction was found in 103 specimens. Comparison of the results with earlier analyses of leaves of Rubiaceae shows that Al accumulation occurs more frequently in leaves than in wood. The strongest Al accumulators occur in the neotropical genera Psychotria subg. Heteropsychotria, Coussarea, Faramea, and Rudgea. The distribution of Al accumulators is discussed in view of recent tribal and subfamilial classification of the Rubiaceae. The major conclusion is that Al accumulation is almost limited to the subfamily Rubioideae. Within the Rubioideae, however, not all tribes show the character, especially the predominantly herbaceous Anthospermeae, Paederieae, Rubieae, and Spermacoceae. Al accumulation in the Urophylleae, Pauridiantheae, Craterispermeae, and Knoxieae supports earlier associations of these tribes with the Rubioideae.