Chloracantha is a monotypic genus of flowering plants in the aster family (Asteraceae, order Asterales), containing the single species Chloracantha spinosa. It is a perennial herb or subshrub native to the southwestern and south-central United States, Mexico, and Central America. Common names include spiny chloracantha, spiny aster, devilweed aster, and Mexican devilweed.
The plant produces green, hairless, sometimes waxy stems that are more herbaceous than woody but persist for several years, behaving like a subshrub. Some lateral branches become sharply angled and reduced to thorns. Its alternately arranged leaves are short-lived and fall away early, leaving bare thorny stems that spread vigorously from robust rhizomes into large colonies. Stems typically reach about 1.5 metres in height but can exceed 2 metres.
Flower heads are borne in loose arrays, each roughly half a centimetre long and wide, lined with layers of hairless phyllaries. Each head contains up to 33 coiling white ray florets surrounding many yellow disc florets. The fruit is a cypsela equipped with a pappus of many barbed bristles.
The genus is distributed from California east to Louisiana and south through Mexico into Central America, with four recognized varieties occupying distinct regions. It grows in dry habitats as well as moist sites like streambanks and seeps, and tolerates saline conditions.
Distribution
Chloracantha is native to the southwestern and south-central United States (California, Nevada, Arizona, Utah, New Mexico, Texas, Oklahoma, Louisiana), most of Mexico, and much of Central America. Its four recognized varieties have more specific ranges: var. spinosissima is restricted to Baja California, var. jaliscensis to Jalisco and Nayarit, and var. strictospinosa extends from Chiapas and Michoacán through Central America to Panama.
Ecology
Chloracantha spinosa grows in both dry habitats and moist sites such as streambanks and seeps. It tolerates saline habitat types, forming large colonies from robust rhizomes. Its short-lived leaves and persistent green thorny stems give it a distinctive appearance among the vegetation of arid and semi-arid regions.
Taxonomy Notes
Chloracantha is a monotypic genus in the family Asteraceae (order Asterales). Its sole species, Chloracantha spinosa, was originally described under different genera before being segregated into its own monotypic genus. Four varieties are recognized under the single species: var. spinosa (the type), var. jaliscensis, var. spinosissima, and var. strictospinosa.
There is a taxonomic disagreement in the literature: some authorities (e.g., G.L. Nesom) elevate Chloracantha spinosissima to full species rank, while others (e.g., S.D. Sundberg) treat it as a variety of C. spinosa. Wikipedia and major regional floras follow the single-species-with-varieties treatment. GBIF reflects the split, with some backbone checklists accepting the two-species treatment and others accepting only the single species.
