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Although Utricularia cornuta Michx. and U. juncea Vahl, sympatric in the southeastern United States, have been considered conspecific by various authors, the present biosystematic approach shows them to be separate species. The taxa are seasonally isolated. While both have the same chromosome number (n 9), strong internal isolation is apparent since artificial hybrids cannot be produced by standard methods. In Utricularia cornuta the mean values of characters studied quantitatively are much higher than those of U. juncea though the extremes of the ranges may overlap. Utricularia juncea has both cleistogamous flowers and chasmogamous flowers while U. cornuta has only chasmogamous flowers. The flowers are self-fertile and apparently are usually, if not always, self-pollinated, even though they are highly adapted to specialized insect pollinators. THE LENTIBULARIACEAE has been considered to consist of as few as five (Kamienski, 1895) to as many as sixteen genera (Barnhart, 1915). Approximately 310 species have been described. Two genera, Pinguicula and Utricularia, occur in North America. Here, species of Ultricularia, about twenty in number, are found as freely floating or anchored aquatics, epiphytes in wet mosses, or terrestrial plants of wet to moist, sandy soils. Much general comparative information regarding the characteristics of the bladders on leaves, stolons, and rhizomes of species of Utricularia has been summarized by Goebel (1889, 1891), Meierhofer (1902), Luetzelburg (1910), Withycombe (1924), and Lloyd (1929, 1932, 1942). Taxonomic treatments of the genus Utricularia include the works of Kamienski (1895, 1904), Bentham (1869), Sylven (1909), Barnhart (1913, 1915, 1933), and Taylor (1963a, 1963b, 1964, 1967). Pollen morphology of the genus has been observed by Thanikaimoni (1966) and Huynh (1968). The North American species of Utricularia, however, are poorly characterized in most standard references, especially with respect to quantitative details. The species are diagnosed but scarcely described, and biosystematic studies are lacking. Since some observed morphological variation in vegetative structures of the species of Utricularia can be correlated with differences in habitats, individual plants are often difficult to identify from published descriptions. 'Received for publication 16 March 1971. Based on a Master's thesis submitted to the faculty of the University of North Carolina, Chapel Hill. The author wishes to express sincere appreciation to Dr. C. R. Bell who directed this research program. The author is similarly indebted to Dr. A. E. Radford, Dr. C. R. Parks, and Dr. N. G. Miller for their interest and helpful suggestions during the preparation of this thesis. When variation between some species of Utricularia is slight, the taxa are often reduced to varietal rank. This is true of U. juncea M. Vahl which is considered conspecific with U. cornuta Michx. by Steyermark (1957). More recently, Taylor (1967) treats U. cornuta and U. juncea as distinct species because the taxa have different geographic distributions and somewhat dissimilar pollen with intermediate forms infrequent. Since both species are closely related, they should be examined for possible evidence which would contribute to satisfactory taxonomic treatment. My own observations on U. cornuta and U. juncea were done to clarify this problem. Utricularia juncea is found in both North and South America, but U. cornuta appears to be limited to eastern North America where north of 40? latitude only this species is found. In the southeastern United States, both taxa occur on the Coastal Plain. Utricularia cornuta and U. juncea have been studied intensively in the field in North Carolina and Florida, and plants have also been brought to the greenhouse and grown under conditions of high moisture and light intensity. Observations in the greenhouse have been carried out for two years. All populations of the two taxa investigated are listed in Table 1. CHROMOSOME NUMBERS-The chromosomes of Utricularia are very small and difficult to study; chromosome numbers have been reported for only a few taxa. With the exception of U. biflora Lam., n = 14 (Kondo, in press) known New World species of Utricularia have a basic chromosome number of nine (Lewis, Stripling, and Ross, 1962; Kondo, 1966, 1969, 1971a, in press). Flower buds of Utricularia cornuta and U. juncea were collected in the field or from plants |
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