Chromosome numbers (somatic and/or gametic) were determined in 50 populations of M. bimucronata (DC.) O. Kuntze collected in the species area of distribution in Rio Grande do Sul, south Brazil. All populations were diploid (2n = 2x = 26, n = 13). Polysomatic (mostly tetraploid) cells were detected in the seedlings root-tip cells in 39 out of the 41 populations examined, ranging from 3.0 to 28.2 % among populations, but were absent in the root-tips of grown plants. Polysomaty was as well absent in pollen-mother cells. In M. bimucronata pollen-mother cells are joined two-by-two before the onset of meiosis, remaining attached during all the meiotic division until the formation of pollen grain polyads, composed of two sets of four pollen grains each, that are dispersed in this way, which, according to previous suggestions would be an adaptation to ensure high seed set after a single pollination event.
maricá; intraspecific variability; polyads
