PHYLOGENETIC STUDY OF HEDYOTIS (RUBIACEAE) IN NORTH AMERICA

Abstract

Lewis, Walter H. (Stephen F. Austin State Coll., Nacogdoches, Texas.) Phylogenetic study of Hedyotis (Rubiaceae) in North America. Amer. Jour. Bot. 49(8): 855–865. Illus. 1962.—Chromosome numbers for 39 taxa of Hedyotis separable into the subgenera Edrisia (Raf.) Lewis and Oldenlandia (L.) T. & G. are reported. The occurrence of basic numbers of x = 6, 7, 8, 9(10), 11, and 13, including infraspecific aneuploidy in H. nigricans (Lam.) Fosb., illustrates the importance of aneuploidy in the speciation of Hedyotis in contrast to most rubiaceous genera. In the North American subg. Edrisia, 25 species are ranked according to primitive and advanced expressions for 13 characters. It is postulated on the basis of these, ecologic, geographic, and chromosomal data that the x = 11 group gave rise to the x = 13 line by the gain of chromosomes and to the x = (10)9, 8, and 7 groups by reduction. Those species with a basic number of 6 are thought to have an Asian origin. Although aneuploidy has been dominant in the evolution of subg. Edrisia, only 12% of the species are polyploids. The development of polyploid races in 3 species, H. caerulea (L.) Hook., H. polypremoides (Gray) Shinners, and H. purpurea (L.) T. & G., however, suggests a greater role of polyploidy in the current evolution of Hedyotis.