Aluminium accumulation in leaves of 127 species in Melastomataceae, with comments on the order Myrtales.

The distribution and systematic significance of aluminium accumulation is surveyed based on semi-quantitative tests of 166 species, representing all tribes and subfamilies of the Melastomataceae as well as a few members of related families within the Myrtales. The character is strongly present in nearly all members of the Memecylaceae and in most primitive taxa of the Melastomataceae, while non-accumulating taxa are widespread in the more derived tribes of the Melastomataceae. The variable distribution of Al accumulation in advanced clades of the latter family is probably associated with the tendency to herbaceousness, although it is unclear whether the more herbaceous representatives have developed more specialized Al-response mechanisms that may exclude high Al levels from the shoot. It is hypothesized that Al accumulation is symplesiomorphic for Melastomataceae and Memecylaceae, and that the feature characterizes the most primitive families in the Myrtales. Indeed, Al accumulation is also characteristic of Crypteroniaceae, Rhynchocalycaceae and Vochysiaceae. Crypteroniaceae and Rhynchocalycaceae probably take a basal position in a sister clade of the Memecylaceae and Melastomataceae, while Al accumulation suggests a basal position for Vochysiaceae in the Myrtaceae clade.