BIOSYSTEMATICS OF RUELLIA TUBEROSA L. (ACANTHACEAE)

Ruellia tuberosa is a wide-ranging tropical, perennial herb that has been designated the type species for the large genus Ruellia. To clarify interspecific relationships, the R. tuberosa species complex, including R. nudiflora, R. malacosperma, and R. lorentziana, and R. tuberosa, has been proposed as the redefined and restricted genus Ruellia. All other Ruellia species would be transferred to segregate genera. Biosystematic investigations that included artificial hybridization experiments, herbarium comparisons, chromatographic analyses, and cytological studies demonstrated that R. tuberosa is genetically related to a number of North American temperate taxa and to certain other tropical species. The narrow definition of Ruellia cannot be supported from the biosystematic evidence at hand. Morphological comparisons suggest that R. tuberosa may be a primitive component in a broadened generic concept. RUELLIA, as generally understood, is a large and variable genus of mostly tropical perennial herbs and shrubs ranging in size from a few centimeters to large, bushy plants. It is the second largest genus of Acanthaceae with about 250 named species widely distributed in both the Old and New World tropics, but with relatively few species occurring in the temperate regions of North America. The broad, inclusive circumscription of Ruellia by Lindau (1895, p. 308-311) has usually been followed by taxonomists although the genus historically has been subjected to numerous attempts to split it up into segregate genera (Long, 1973). Characters that tend to define the genus are the conspicuous tubular or broadly campanulate corollas of chasmogamous flowers and inconspicuous tubular cleistogamous flowers; epipetalous didymous or didynamous stamens with filaments fused at the base; oblong, symmetrical anthers, and cylindrical capsules. The concept of the genus was established by Linnaeus (1754, p. 702) based on an illustration of R. tuberosa by Plumier (1703, p. 12). Later the species was selected as the lectotype for the genus (Britton and Brown, 1913, p. 241). Although many species have been assigned to Ruellia by various authors, Bremekamp and NannengaBremekamp (1948) proposed that Ruellia be restricted to just those species having cylindrical estipitate capsules that contain large numbers of Received for publication 31 July 1975. 'Research supported by N.S.F. grants GB-35231 and BMS 72-02209 A03. Dr. Richard Mansell, Dept. of Biology, University of South Florida, supervised the identification of phenolic compounds. Ms. Suzanne Todd was research assistant in the investigation. Contribution No. 95 from the Botanical Laboratories, University of South Florida, Tampa, Florida. seeds. This concept would result in a genus being composed of only five tropical and subtropical American species, namely R. tuberosa (Fig. 1), R. intermedia Leonard, R. nudiflora (Engelm. & Gray) Urban, R. lorentziana Griseb. and R. malacosperma Greenm. The generic definition would be essentially the same species group that Leonard (1927) described as "R. tuberosa and a few of its close relatives." Ruellia sensu stricto is characterized by lax axillary cymes, pedicellate blue or lavender flowers, 5-lobed calyx, subcampanulate or infundibuliform corolla throat, included stamens, and cylindrical, many-seeded capsules. The numerous other species that have been assigned to Ruellia sensu Lindau and other authors would be transferred to segregate genera such as Arrhostoxylum Nees, Stephanophysum Pohl, Dipteracanthus Nees, Leptosiphonium F. v. Muell., Nothoruellia Bremek. & Nannenga-Bremek., Pararuellia Bremek. & Nannenga-Bremek., and Ulleria Bremek. (Bremekamp and Nannenga-Bremekamp, 1948; Bremekamp, 1969). The taxonomic effects of all these changes would be to throw the original generic concept of Linnaeus into doubt, and to reestablish a number of more or less distinguishable taxa as genera strictly on the basis of morphological variance. In order to establish the relative taxonomic position of R. tuberosa with other species of the genus sensu lato, as well as to test the genetic relationships of the species related to R. tuberosa, biosystematic investigations were made that included field studies, chromosomal and cytological analyses of meiosis, hybridization experiments, and chromatographic comparisons of corolla pigments. These studies have enabled us to gain some insight into the complex relationships of tropical and temperate American species that were largely unsuspected from purely morphological