Patterns of Chromosome Number Diversity and Evolution in the Melastomataceae

Abstract

The number of species of Melastomataceae for which there is chromosome information has increased over 12-fold since 1975. With 121 new counts included here, some 839 chromosome counts are now known for 575 taxa and natural interspecific hybrids in 82 genera based on a database assembled from the literature. This constitutes 47% of the genera and about 10% of the species worldwide. Interpreting chromosome number evolution in the family presents some difficulties because of data gaps for some phylogenetically critical groups, but sufficient data are now available to advance hypotheses about the original basic number for the family and to pose questions about (1) direction of chromosome number changes in clades, (2) incidence of dysploidy and polyploidy, and (3) relationships of high or unusual chromosome numbers to life history, reproductive biology, and geographic distribution. Forty haploid chromosome numbers are known for the Melastomataceae, ranging from n = 7 to n = 90, but numbers above n = 36 are uncommon and represent fewer than 20 of the counts. The common descending haploid numbers ranging from n = 12 to n = 9 are considered basic numbers for the family. We present hypotheses on the derivation of chromosome number diversity for the better-known tribes and summarize five patterns of cytoevolution for the family.