About Chloracantha spinosa (Benth.) G.L.Nesom
Chloracantha is a monotypic genus of flowering plants in the aster family, holding only the single species Chloracantha spinosa, whose scientific name is Chloracantha spinosa (Benth.) G.L.Nesom. This species is distributed across the southwestern and south-central United States, occurring in California, Nevada, Arizona, Utah, New Mexico, Texas, Oklahoma, and Louisiana. It is also found across most of Mexico and much of Central America. Its English common names are spiny chloracantha, spiny aster, devilweed aster, and Mexican devilweed. In Spanish, it is known by the common names espina de agua, espinaza, and espinosilla.
Chloracantha spinosa is a perennial herb or subshrub. Its green stems appear more herbaceous than woody, but it behaves more like a subshrub: its tough stems live for multiple years and rapidly develop vascular cambia. The stems are hairless, and sometimes have a waxy texture. Some of its lateral branches may be sharply angled, reduced in size, and become thorns. Its alternately arranged leaves persist for only a short time before falling off. Large colonies of bare stems spread from robust rhizomes. Stems usually reach a maximum height of around 1.5 meters, but may sometimes grow well over 2 meters tall.
The plant produces loose arrays of many flower heads, each roughly half a centimeter long and wide. Each flower head is lined with layers of hairless phyllaries. It holds up to 33 coiling white ray florets, plus many yellow disc florets. The fruit produced is a cypsela with a pappus made of many barbed bristles.
This species grows in both dry habitats and moist locations such as streambanks and seeps, and it can tolerate some types of saline habitat. Four varieties are recognized: Chloracantha spinosa var. spinosa; Chloracantha spinosa var. jaliscensis (McVaugh) S.D. Sundb., found in Jalisco and Nayarit; Chloracantha spinosa var. spinosissima (Brandegee) S.D.Sundb., found in Baja California; and Chloracantha spinosa var. strictospinosa S.D.Sundb., found in Chiapas, Michoacán, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua, and Panama.
