Phylogeny of the Coneflowers and Relatives (Heliantheae: Asteraceae) Based on Nuclear rDNA Internal Transcribed Spacer (ITS) Sequences and Chlorplast DNA Restriction Site Data

The internal transcribed spacer (ITS) region of 18S–26S nuclear ribosomal DNA (rDNA) was sequenced in 65 taxa representing most coneflowers (i.e., species in Dracopis, Echinacea, Ratibida, and Rudbeckia) and other taxa representing 21 outgroup genera of tribe Heliantheae. Results of parsimony analysis of the rDNA dataset by itself and in combination with the cpDNA dataset uphold the hypothesis from an earlier cpDNA restriction site study that Echinacea is not closely related to the other three genera of coneflowers. The data support placement of Echinacea in subtribe Zinniinae. The remaining three coneflower genera represent a monophyletic lineage corresponding to subtribe Rudbeckiinae sensu H. Robinson. The rDNA data support two sublineages in Rudbeckia congruent with the two traditionally recognized subgenera, subg. Macrocline and subg. Rudbeckia. In subg. Macrocline, two geographic areas of diversification are indicated: southeastern and western United States. The widespread species R. laciniata is placed strongly with the western lineage of subg. Macrocline. The rDNA data support transfer of Dracopis to Rudbeckia subg. Macrocline, a relationship also supported by multiple morphological characters. The rDNA data do not confidently resolve the sister group of Rudbeckiinae from among the members of Heliantheae investigated. Multiple hypotheses are suggested for the outgroup taxa, such as expanding subtribe Zinniinae to include Echinacea and Trichocoryne, a genus previously regarded as belonging to subtribe Hymenopappinae (Heleneae or Heliantheae sensu lat.). Our findings further support expansion of subtribe Engelmanniinae to include Balsamorhiza, Borrichia, and Wyethia even though these taxa lack ray floret complexes and have fertile disc ovaries. We suggest that bioprospectors might usefully search among taxa of Zinniinae for bioactive substances similar to the immune stimulants of Echinacea. Traditionally, the genera Dracopis Cass., Echinacea Moench, Ratibida Raf., and Rudbeckia L. have been known as coneflowers. They are among the best known wildflowers in North America. Black-eyed Susan (Rudbeckia hirta), brown-eyed Susan (R. triloba), prairie coneflowers (Ratibida spp.), and purple coneflowers (Echinacea spp.) are common in the central prairies of the United States and along woodland margins of the eastern states. In addition, some species in Rudbeckia subg. Macrocline (Torr. & A. Gray) P. B. Cox & Urbatsch occur in the western United States. With few exceptions, the coneflowers display large, showy capitula characterized by prominently elongated or spherical receptacles and colorful, spreading to reflexed ray corollas. Various species are cultivated for their ornamental qualities and some have become naturalized in areas beyond their native ranges. Other species are rare and their existence is threatened by habitat modifications associated with agricultural practices and urbanization. Echinacea laevigata and E. tennesseensis are listed as endangered by the Division of Endangered Species (U.S. Fish and Wildlife Service). Rudbeckia auriculata and R. heliopsidis are considered to be threatened or endangered in the southeast United