A Systematic Study and Monograph of the Turk's-Cap Lilies of Eastern North America (with the Introduction of Some New Cultivars)

Adams, Richard

ABSTRACT: The turk's-cap lilies of eastern North America have been considered taxonomically difficult as to delimitation of taxa, identification of evolutionary processes involved in speciation, and interpretation of the species' phylogeny. The present study has made use of herbarium study (including study of morphology and distribution), field study (pollination ecology and analysis of edaphic factors), and laboratory analyses (numerical phenetics and allozyme chemistry) to help elucidate these problems. The determination of isolating mechanisms, phenetic similarity, and genetic distance have resulted in the following interpretation: Lilium canadense subsp. editorurn, centralized in New York and Pennsylvania, is the least specialized taxon, being pollinated both by hummingbirds and sweatbees, and is closest to the ancestor of the group. Lilium canadense subsp. canadense, which is distributed close to the limit of the range of the ruby-throated hummingbird, has become specialized for pollination by sweatbees and also may be better adapted to the more nutrient-depleated spodosolic soils of New England. Lilium grayi is adapted to high-altitude environments of the Appalachians, where bees are rare, and has floral color and structure specialized for hummingbird pollination; it introgresses (complicating determinations) with L. canadense subsp. editorum over an altitudinal gradient. The preceeding three taxa have flowers with only slightly recurving tepals and are thus subject to nectar-thievery by butterflies. Lilium michiganense seems adapted to the drier, alkaline soils of the midwestern prairies and can be pollinated by sweatbees, the hummingbird, and—because its tepals recurve—by butterflies. It introgresses with L. canadense subsp. editorum where the major soil masses merge. Lilium superbum, of the northern Appalachians and Atlantic coastal plain, is adapted to butterfly-, sweatbee-, and hummingbird-pollination and appears to be a physiologically more adaptable, more widespread, more vigorous species. Lilium michauxii, of the southern Appalachians and Gulf coastal plain, is closest to L. superbum but is adapted to drier soils through specializations such as short height and thick leaves which reduce transpiration, and large, fragrant flowers which increase pollination efficiency. Lilium iridollae is close to L. michauxii and L. superbum and grows in moist environments along the Gulf coast.