Synopsis of the Hypericum denticulatum Complex (Hypericaceae)


James R. Allison

Additional Authors:


March 2011


hypericum, st. john’s wort, atlantic costal plain

ABSTRACT Among herbaceous species of Hypericum with surficially glandular-punctate leaves and quadrate, narrowly winged stems, the five taxa of the ‘‘Hypericum denticulatum complex’’ of southeastern United States have in common petals that are strongly inequilateral, orange-yellow, ca. 1 cm long and 0.5 cm wide; stamens numerous (50–80); and styles comparatively long (2–4 mm). Three of the species are obligate wetland plants: H. denticulatum, H. harperi, and H. erythreae. The last-named, until now wrongly synonymized, is a species of the Atlantic Coastal Plain of southeastern Georgia and, historically, southern South Carolina. It resembles the mostly more northern H. denticulatum in having appressed or ascending leaves that are shorter than their internodes and in growing in boggy habitats, but is a taller plant that also differs by its notably sparse leaves that are distinctly reduced upward and on average proportionately narrower. The remaining two species are obligate upland plants: H. virgatum and H. radfordiorum sp. nov., the latter endemic to granite outcrops in or near the Brushy Mountains (inner Piedmont of North Carolina). It is like H. virgatum in having upper leaf surfaces much less conspicuously glandular-punctate than the lower, but in H. radfordiorum the leaves average longer and more acuminate, the stems are distinctly glandular-punctate, and many of the upper leaf axils bear flowering branches with leaves longer than their internodes.