Six populations of apparently morphologically similar sessile-floweredTrillium(known taxonomically asT. cuneatumRaf. andT. luteum(Muhl.) Harb.) observed growing at elevations between 800 and 1700 ft in the Appalachians of western North Carolina and eastern Tennessee exhibit a wide range of variability by observation. The extent of variability was assessed by using statistical and karyotypic methods of analysis and by intraspecific cross-pollination. A correlation exists between the mean coefficient of variability and (1) the size of the population and (2) the degree of geographic isolation. The number of types of each kind of chromosome (A–E), as resolved by cold treatment, varies by one type from population to population. The homozygosity for the six populations is 85.8%, and the distribution of euchromatin is not complex. Intraspecific cross-pollination was effective among 76% of the test crosses. A review of the statistics and other morphological data indicates that the presence or absence of anthocyanins, flower scent, and the degree of geographic isolation are the three major variants among the six populations. These kinds ofTrilliumgrow sympatrically withT. grandiflorum(Michx.) Salisb.,T. simileGleason,T. erectumvar.album(Michx.) Pursh,T. flexipesRaf. (T. gleasoniFern.), andT. erectumL. The cumulative karyotype for the six stands indicates that these plants have not hybridized with any of the above species and varieties. Although these plants have been classified asT. cuneatumRaf. in some stands and asT. luteum(Muhl.) Harb. in others the data demonstrate that these six stands represent one discontinuous population of a sessile-floweredTrillium. Trillium discolorWray, although relatively rare in western North Carolina, also grows here. AlthoughT. discoloris not directly involved in this problem, its description and distinctive karyotype are included.