The distribution of anthochlor floral pigments in North American Coreopsis (Compositae): taxonomic and phyletic interpretations

Anthochlors (chalcones and aurones) occur in floral tissues of all members of North American Coreopsis. The genus in North America consists of 46 species distributed in 11 sections, and a total of five chalcone aglycones are found in it. The chalcone butein occurs in all sections, and is the only anthochlor constituent in the closely related woody Mexican sections Electra and Anathysana. These two sections are viewed as primitive. The morphologically distinct but putatively unspecialized woody Mexican section Pseudo-Agarista sequesters both okanin and butein; the same two anthochlors also characterize two additional sections of herbaceous perennials, Silphidium and Tuckermannia. Sections Euleptosyne and Pugiopappus, comprised of annuals restricted primarily to California, exhibit the rare chalcone stillopsidin in addition to butein and okanin. The remaining four sections, Palmatae, Coreopsis, Calliopsis and Eublepharis are among the more specialized in North America, and are sometimes considered to represent a distinct phyletic line or two related lines. All or some of the members of these sections sequester the very rare chalcone lanceolatin in floral tissues in addition to okanin. Butein is also present in some or all species in each section, and isoliquiritigenin occurs rarely in two sections. Those sections considered more specialized have additional anthochlors relative to primitive sections, and any compound found in a more primitive section also occurs in a more advanced one. Thus, the trend in floral anthochlors in North American Coreopsis is toward increased number of compounds rather than reduction. THE CHALCONES AND AURONES represent classes of flavonoid pigments which are widely and sporadically distributed in the angiosperms, but they characterize the subtribe Coreopsidinae (Compositae: Heliantheae) (Crawford and Stuessy, 1981). These flavonoids, often known collectively as anthochlors, are important floral pigments involved in pollination (Dement and Raven, 1974; Scogin, 1976; Scogin and Zakar, 1976; Scogin, Young and Jones, 1977; Harborne and Smith, 1978, for example), but also may occur in leaves (Crawford, 1970a, b, for example) where their function is much less obvious. The genus Coreopsis in North America is recognized as consisting of 11 sections and 46 species (Smith, 1975, 1976). One of us (Smith, 1975) summarized morphological features for the sections, listed chromosome numbers known at that time, and presented an hypothesis of phyletic relationship among the sections in North America. In a later paper, Smith (1976) ' Received for publication 8 January 1982; accepted 6 April 1982. Supported by NSF grants DEB 77-21727 and DEB 8011655 to DJC and DEB 80-11712 to EBS. discussed relationships among eastern North American taxa, including results of crossing studies. In addition, geographic distributions of taxa as well as keys for identification were given. The value of leaf flavonoids (i.e., primarily flavones and flavonols) in taxonomic studies of Coreopsis at the species and infraspecific levels has been demonstrated (Crawford 1 970a, b; Crawford and Smith, 1980; Crawford, Smith and Mueller, 1980; Smith and Crawford, 1981, as examples). Data reported in the papers cited above as well as our unpublished information suggest that distribution of the flavones and flavonols predominant in leaves of North American Coreopsis may be too variable for inferring relationships at the sectional level. In an earlier paper one of us (Crawford, 1976) indicated that the distribution of chalcones and aurones in Mexican Coreopsis is concordant with other information in suggesting relationships at the sectional level. The primary purpose of the present study was todetermine the distribution of anthochlors in floral tissues of North American Coreopsis. More specific questions addressed include the following: 1) Do species within sec-