CHROMATOGRAPHIC DOCUMENTATION OF INTERSPECIFIC HYBRIDIZATION IN VERNONIA: COMPOSITAE

Chromatographic analysis of the flavonoid compounds in leaf extracts support field anid morphological studies which lead to the interpretation of Vernonia guadaltupensis, Heller as a natural hybrid between F. tindheimneri Enigelm. and Gray and V. interior Small. Of 16 major flavonoids found in leaf extracts of the parental species, 8 were found only in V. lindheimneri, 3 were found only in V. interior; 5 were common to both. All 16 were found in leaf extracts of V. guadalupensis. VERNONIA GUADALUPENSIS was described by Heller (1901) from material collected at Kerrville oni the Guadalupe River in Kerr County, Texas. Gleason (1922), in his revision of North American Vernonia, treated the plant as a valid species, but in a later publication (Gleason, 1923) he pointed it out as a suspected hybrid. Shinners (1950), after examination of herbarium specimens, stated that V. guadalupensis was "without much doubt" a hybrid between V. lindheimeri Engelim. and Gray and V. baldwinii Torr. (V. interior Small sensu Gleason, 1922). A total of 36 clones of Vernonia gtuadalupensis at seven different sites have been examined (Table 1). At six of these sites the plant was found growing adjacent to V. lindheimeri and at one it was growingof next to V. interior. In spite of extensive searclhing I have never found V. guadalupensis without V. lindheimneri or V. interior growinig nearby. Pure stands of the latter two, on the other hand, can readily be found. Vetnonia lindheirneri grows in shallow rocky limestone soil of Central Texas and throughout most of its range it is geographically sympatric with V. interior which has a much broader distribution (Fig. 1). The two are edaphicallv different; V. interior grows in less xeric sites in deeper, richer soil along stream banks, hillsides and roadsides. The two habitats frequently come together in the limestone hills of the Edwards Plateau where the action of streams has exposed the underlying limestone; it is here that V. guadalupensis is most frequently found. Both V. lindheimeri and V. interior also grow along roadsides, the former in the shallow rocky limestone of deeper road cuts and the latter in the 'Received for publication May 27, 1966. Supported by National Science Foundation Grants GE 3069 (Research Participation for College Teachers Program to the Department of Botany, University of Texas) and GE 6939. The writer is grateful to R. E. Alston*, B. L. Turner, and their associates at The University of Texas for assistance during the course of this work. * Deceased February 17, 1967. more poorly drained richer soils. V. gtadalitpensis has also been found with one or the other of the putative parental species along roadsides. At three riverside localities (Table 1, collectionls 550, 551, 571, 573, 574) plants of all three types were growing within 50 yards of one another. Vernonia interior and V. lindheimneri were preponiderantly more numerous. than V. guadahtpensis at two of these sites. Three clones of V. giadalaupensis adjacent to a single clone of V. livdheimneri were found about 30 yards from a large population of V. interior at the third (collection 550). At three of the other four locationis V. lindheimeri was preponderant; at the last (collection 547) a single clone of V. gtadalutpensis was found among numerous clones of V. interior. The missing putative parent was niot seen within 1 to 6 miles of collection 547 aind the Blalnco County collections; however, these were, roadside locales and no attempt was made to seek out the missing plant off the road. All three plants, which are perennials with underground rhizomes, are morphologically quite distinct. Vernonia lindheimeri, the shortest plant with short internodes, is characterized by its narrow revolute leaves and a hoary indument which wv)hitens the lower surface of the leaves, the outer surface of the involucral scales, the younger portionis of the stems and the branches of the inflorescence. V. interior, the tallest plant with lonig internodes, is characterized by its broad, flat, sharply serrate leaves and a thin tomenitum usually present on the lower surface of the leaves. V. guadalupensis shows varying degrees of intermediateness in all these charaeters (Fig. 2). A remarkable feature has been noted in the foliar trichomes of the three plants, adding additional support to the interpretation of Vernonia guadalupensis as a hybrid. V. lindheimeri has short-stalked T-shaped trichomes which cover the lower surface of the leaves. V. interior has T-shaped hairs with a uniseriate stalk 6-13 cells long occurring on the lower surface of its