VARIATION AND TAXONOMY OF PHYTOLACCA-AMERICANA AND P-RIGIDA IN THE SOUTHEASTERN UNITED-STATES

Phytolacca americana L. is a common native weed of the eastern United States, ranging from Quebec and Ontario south to northeastern Mexico. Previous authors have disagreed as to the status of a second taxon, P. rigida Small, which is distinguished from P. americana by erect, rather than drooping racemes and pedicels that are shorter than the berries. In addition, P. rigida is restricted to Florida and the Atlantic and Gulf coasts. Artificial cross-pollinations between plants of the two taxa yielded viable seeds, but interpretation of this result is equivocal because of the strongly autogamous nature of the plants. Flavonoid profiles of the two taxa were found to be indistinguishable, consisting of six glycosides of the flavonols quercetin and kaempferol. No taxonomically useful differences were detected in salinity tolerance or seed germination. The region between the Upper Coastal Plain and Quaternary deposits of the Lower Coastal Plain appears to form an ecological barrier between the two taxa. Analyses of 14 morphological characters in 36 populations from the Coastal Plain of the southeastern United States showed that P. rigida is distinct from P. americana in several characters. It is not, however, sufficiently distinct to deserve recognition as a separate species. Therefore, a new combination is proposed: Phytolacca americana var. rigida.