1. The chromosome number and karyotype of Smilacina racemosa vars. racemosa and amplexicaulis, S. stellata vars. stellata and sessilifolia, and S. paniculata are reported.
2. S. racemosa var. racemosa in eastern North America contains tetraploid (2n=36), octoploid (2n=72), and 16-ploid (2n=ca. 144) chromosomal races, with the octoploid the most common. No obvious gross morphological variations seem to be correlated with the different polyploid types.
3. Previous reports for the tetraploid (2n=36) nature of the western North American S. racemosa var. amplexicaulis and S. stellata var. sessilisfolia, as well as the eastern var. stellata, were verified.
4. Costa Rican material of the widespread Central American S. paniculata proved to be likewise tetraploid (2n=36). The same basic karyotype formula (K(n)=3V+7J+8v) was found for all the North and Central American taxa studied and coincides with that reported by other authors for several Asiatic species of Smilacina.
5. The distribution of Smilacina in the three widely separated main survival areas of the ancient Arcto-Tertiary Geoflora generally, and the close ecological relationships to temperate montane subtropical forests with prominent Arcto-Tertiary influence especially, suggests that this genus has had a common evolutionary history not only with this Geoflora, but in particular with such cloud forest habitats. Though the great similarity of some species suggests recent long-range dispersal, the great variety of species in Central America would point to a Tertiary, and not a Pleistocene origin of the disjunct Arcto-Tertiary elements there. Since the basic karyotype of all Smilacina species (with a slight exception in the highly specialized S. trifolia) is apparently remarkably uniform throughout the genus, its particular configurations must therefore date back to at least the middle Tertiary, when interchange between Old World and New World Arcto-Tertiary floristic areas was still possible. Thus, despite tremendous migrations, gross morphological changes and speciation, this basic Smilacina karyotype has remained unchanged for extremely long periods (perhaps 50 million years?).