A SURVEY OF ALUMINIUM ACCUMULATION IN EUMACHIA (RUBIACEAE)

Abstract

A useful character for spotting specimens of the pantropical Rubiaceae genus Eumachia is the leaves drying green. The physiological reasons for this are unresolved. We investigated whether the phenomenon is related to the accumulation of aluminium. Samples of foliage from herbarium specimens of nine species of Eumachia (Rubiaceae), including collections from Asia-Pacific, Africa and the Americas, were analysed for elemental concentrations. For comparison, specimens of the closely related genera Psychotria and Palicourea from similar geographical regions were also analysed. Two species, Palicourea violacea (Panama) and Psychotria pallens (Brazil) were found to be aluminium hyperaccumulators (≥ 1% Al by dry weight), with a third species, Eumachia collina (from New Caledonia), falling just short of the threshold with 0.99% Al. Aluminium accumulation (≥ 0.4% Al by dry weight) occurs but is infrequent among species of Eumachia and appears less
common than in the close relative Palicourea. Aluminium accumulation also appears patchy in Psychotria sensu stricto. It seems unlikely that herbarium greenness in Eumachia is directly related to aluminium accumulation.