Hecastocleis shockleyi (Hecastocleideae),the desert enigma: close encounters
with one of Compositae's most solitary lineages

Colin  Hoag

Department of Anthropology, Smith College, Hillyer Hall 309, 10 Elm Street, Northampton, MA 01063, USA

https://orcid.org/0000-0003-3666-4266

DOI: http://dx.doi.org/10.53875/capitulum.04.1.03

ABSTRACT:  The desert subshrub Hecastocleis shockleyi is the sole member of tribe Hecastocleideae and sub-family Hecastocleidoideae, a species that raises questions about the biogeographic history of the Compositae. It features a unique floral morphology, with single-flowered capitula aggregated together in a terminal inflorescence that is subtended by spiny, papery bracts. Additionally, its corolla and style branches resemble those of basal members of the family. Molecular phylogentic data support H. sockleyi as an early diverging lineage sister to all other members of the large radiation of subfamilies Carduoideae and Asteroideae, yet it is found only in the southwest U.S., far from other early diverging lineages found in South America. In spite of this mysterious biogeography, which links the family’s early radiations to its eventual global spread, little is known about the ecology and genetic diversity of the species. This report briefly summarizes three field trips in 2023, 2024, and 2025 that aimed to address this gap in our understanding of this charismatic and important Compositae.

Keywords:  Asteraceae, biogeography, dispersal, Great Basin, Mojave, natural history, phenology, pollination.