Aluminium accumulation in leaves of Rubiaceae: Systematic and phylogeneticimplications

Aluminium (Al) accumulators are plants which accumulate more than 1000 ppm Al in their tissues. In addition to earlier analyses on leaves of Rubiaceae , 251 specimens were tested to verify the systematic importance of this cha racter. The distribution of Al accumulators in the family shows that the fe ature is more or less restricted to a widely circumscribed subfamily Rubioi deae including Craterispermeae, Knoxieae, Urophylleae and Pauridiantheae. O ther Rubioideae representing strong Al accumulators are the genus Coccocyps elum, Coussareeae, Prismatomerideae, and most Psychotrieae. It is hypothesi zed that the ability to accumulate high levels of Al evolved in an ancestor of the Rubioideae s.l. since the feature is concentrated in basal taxa of this subfamily. Moreover, recent phylogenetic insights in the subfamilial c lassification of the Rubiaceae based on macromolecular data are confirmed, ill accumulation is reported in only two genera outside Rubioideae s.l., vi z. Coptosapelta and Alberta. Al accumulators generally are woody, relativel y primitive taxa which occur in tropical forests with relatively high rainf all. In more derived Rubioideae such as Anthospermeae, Hedyotideae, Paederi eae, Rubieae and Spermacoceae the tendency to herbaceousness is possibly as sociated with the absence of Al accumulation. It is likely that this lack i s related to their adaptation to more xeric, alkaline soils and their more temperate distribution. (C) 2000 Annals of Botany Company.