Galax (Diapensiaceae): Geographic Variation in Chromosome Number

Abstract

Galax, a monotype endemic to the southern Appalachian Mountains and outlying areas, has been reported to comprise both a diploid and tetraploid cytotype (x = 6). In this study more than 850 chromosome counts of Galax urceolata from 460 locations, including numerous intra- populational counts, were made and mapped along with most of Baldwin's original counts in order to obtain a clear picture of the geographic distribution of the cytotypes. A strong correlation between guard cell size and chromosome number allowed estimation of ploidy level of herbarium collections. The diploid race occurs over most of the range of the species. Tetraploids occupy a relatively smaller portion of the range; they are abundant along the area of the Blue Ridge escarp- ment, sharply bounded on the northwest by the escarpment in northern North Carolina and by the Blue Ridge divide further south. On the Virginia coastal plain and north-central piedmont of North Carolina tetraploids occur exclusive of diploids. Along the escarpment diploids and tetra- ploids occur in complex patterns of sympatry and triploids are abundant, usually growing inter- mixed with or immediately adjacent to one of the other cytotypes. Along the escarpment there is much overlap in habitat preference, but commonly the more xeric habitats are occupied by diploids and the more mesic ones by tetraploids. No differences in habitat are apparent on the piedmont and coastal plain where the cytotypes are allopatric.