CAPITULUM: The International Compositae Alliance Newsletter

What in the whorled: The rediscovery of Helianthus verticillatus Small (Heliantheae) over 100 years later

Erika R. Moore

https://orcid.org/0000-0002-1182-9274

DOI: https://doi.org/10.53875/capitulum.01.1.07

Keywords: clonality, conservation, endangered species, whorled sunflower

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Abstract

Helianthus verticillatus is a narrowly distributed, federally endangered perennial sunflower endemic to the southeastern United States, notable for a mixed reproductive strategy combining sexual reproduction with extensive rhizomatous clonality. The species is morphologically distinctive among regional congeners, particularly by its 3–4 whorled lower leaves that are nearly sessile to short-petiolate, a prominent midvein, and yellow disk-floret corollas, and it occupies wet prairie habitats, open floodplains, and wet forest-edge depressions where plants often occur as large clonal clumps. Described in the late 19th century from Tennessee material, H. verticillatus went unrecorded in nature for more than a century before being rediscovered in 1994; subsequent surveys revealed additional populations in Alabama (1997), Tennessee (1998, 2006), Mississippi (2017), and Virginia (2019), yielding six known extant occurrences spanning five states. Although historically suspected to represent a hybrid entity, later morphological and genetic studies support recognition of H. verticillatus as a distinct species and indicate unexpectedly high genetic diversity at both population and species levels, suggesting a formerly broader distribution. Conservation concerns center on habitat modification and degradation of remnant prairie systems and potentially restricted gene flow among isolated populations, consistent with reliance on bee pollinators, some of which may forage only short distances. Despite federal listing (2014), a formal recovery plan is lacking; given its showy inflorescences and ecological role in threatened habitats, targeted management to protect sites and sustain pollination and recruitment is critical for long-term persistence.