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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. International Association for Plant Taxonomy (IAPT) is collaborating with JSTOR to digitize, preserve and extend access to Taxon. Summary A formal infrageneric classification for the genus Helianthus is presented. The classification was derived using phenetic, cladistic and biosystematic procedures. The 49 species of Helianthus are placed into four sections and seven series. (Fig. 1) based primarily on underground characteristics and crossing results. Although an infrageneric classification of Helianthus has recently been proposed (Heiser et al., 1969), it has never been formalized. An infrageneric classification would be a useful reference for investigations of plant breeding and phytochemistry stimulated by the developing prominence of the domesticated sunflower (H. annuus) as an oilcrop. Comparison of the results of different methods of classification is of interest because hybridization, introgression and polyploidy have played an important evolutionary role within the genus (Heiser et al., 1969). Previous investigators have subdivided Helianthus in various ways. DeCandolle (1836) placed the species into four groups in his key. Torrey and Gray (1842) divided the genus into six sections, although Gray (1884) later used only two groups. Watson (1929) divided the genus into two artificial sections based on the color of disc corollas (a trait that is variable within some species). Heiser et al. (1969) placed the species into three sections and seven seriesThe present study uses methods of phenetics, cladistics and biosystematics to produce an infrageneric classification of Helianthus. The treatment of species by Heiser et al. (1969) will be used with the following exceptions. The South American species previously recognized as subgenus Viguieropsis (Heiser, 1957) have been removed by Robinson (1979) to a new genus, Helianthopsis, and hence are excluded from the current study. Other excluded species are H. similis and H. ludens, which are better placed in Viguiera. One additional species formerly included in Viguiera has been transferred to Helianthus: H. porteri (Yates and Heiser, 1979). Materials and MethodsMeasurements were obtained for 42 characters (Table 1) for each species. Data were obtained from publications and graduate theses at Indiana University (Heiser et al.

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