Review of chromosome cytology in Moraea (Iridaceae: Irideae): what chromosomes reveal about the evolution of the genus

Abstract

A review of the chromosome cytology of the African and Eurasian geophytic genus Moraea Mill. (currently 214 spp.); including 51 new counts, many for taxa poorly known cytologically or not counted before, that shows that 167 species, representing 78% of the total, have been counted from one or more populations. The inferred ancestral base number is x = 10. Polyploidy is relatively rare; available counts indicate that both Eurasian species are tetraploid, but that, among the sub-Saharan species, just nine species (less than 5%) are exclusively polyploid and an additional 15 (7%) have diploid and polyploid populations. Chromosome rearrangement leading to reduced base numbers has occurred in subg. Polyanthes (x = 10), in which four sections have a base number of x = 6. Three subgenera, Grandiflorae, Homeria and Vieusseuxia, also have x = 6, but have different karyotypes. Several species and one subspecies are dysploid, all but one with haploid numbers lower than in related species, and are neodysploids. Except for M. virgata subsp. karooica, dysploidy is interpreted as descending. Fourteen species have diploid and polyploid populations, notably M. crispa (subg. Polyanthes) and M. cookii (subg. Homeria), in which the distribution of populations with 2n = 12, 24 and 36 is correlated with geography. Seven species have euploid and dysploid populations at the diploid level and M. inclinata has populations with 2n = 12 and 22. Differences in chromosome number within species are not normally reflected in external morphology. Compared to most other genera of Iridaceae in sub-Saharan Africa, chromosome number and karyotype are unusually variable so that sampling of multiple populations of species is required to establish these characters. Although many species remain to be examined cytologically, those uncounted are mostly in the species-rich subg. Grandiflorae and subg. Vieusseuxia, both of which exhibit little variation in chromosome number and karyotype. Chromosome rearrangement and polyploidy appear to have been important in the early evolution of the genus as well as in recent speciation.