Chloropyron is a small genus of annual herbaceous plants belonging to the family Orobanchaceae (broomrapes), within the order Lamiales. The plants are native to the western coast and interior of North America, where they grow in specialised habitats including salt flats, salt marshes, and alkaline soils in California, Nevada, Oregon, Utah, and Baja California, Mexico.
The plants are small and typically green or greenish-grey, often tinged red or purple due to the presence of anthocyanins. The tallest individuals reach approximately 60 cm in height. All species are hemiparasites: they produce their own energy through photosynthesis but also attach haustoria — specialised root-like structures — to the roots of neighbouring host plants to extract additional water and nutrients.
The genus was first described by the German-American polymath Hans Hermann Behr in 1855, though his work was largely overlooked at the time. The species were long placed within the genus Cordylanthus, specifically in an infrageneric group called Hemistegia established by Asa Gray in 1867. The taxonomy of the group was disputed and rearranged repeatedly through the 19th and 20th centuries. In 2009, botanists David C. Tank, John Mark Egger, and Richard G. Olmstead elevated Hemistegia to full genus rank as Chloropyron, based on molecular phylogenetic evidence.
The genus contains four accepted species: Chloropyron maritimum, Chloropyron molle, Chloropyron palmatum, and Chloropyron tecopense. Several of these species are restricted to highly specific and threatened salt-marsh habitats in California.
Etymology
The genus name Chloropyron derives from earlier taxonomic history: Roxana Stinchfield Ferris applied the name to a section of the genus Adenostegia in 1918, and it was formally adopted as the genus name when David C. Tank, John Mark Egger, and Richard G. Olmstead elevated the group to genus level in 2009. The group had originally been described by Hans Hermann Behr in 1855, though his description was largely disregarded by contemporaries.
Taxonomy
The taxonomy of Chloropyron has a complex and contested history. The species were long placed in the genus Cordylanthus, within the informal group Hemistegia defined by Asa Gray in 1867. Three separate botanists in 1891 — Edward Lee Greene, Richard Wettstein, and Otto Kuntze — independently concluded that the older name Adenostegia had priority over Cordylanthus. However, the 1905 International Botanical Congress resolved to conserve Cordylanthus to maintain stability. In 1911 Willis Linn Jepson raised Hemistegia to subgenus rank; in 2009 Tank, Egger, and Olmstead raised it further to full genus rank as Chloropyron on the basis of molecular phylogenetic analysis.
Distribution
Chloropyron is restricted to the western edge of North America. Its range spans the western United States — principally California but also Nevada, Oregon, and Utah — and extends south into Baja California, Mexico. The species are characteristic of coastal and inland salt marshes, salt flats, and alkaline soils, reflecting a narrow ecological tolerance.
Ecology
All species of Chloropyron are obligate inhabitants of saline or alkaline environments, including coastal salt marshes and interior salt flats. They are hemiparasitic annuals: while capable of photosynthesis, they supplement their nutrition by attaching haustoria to the roots of host plants. This parasitic strategy is characteristic of their family, Orobanchaceae, which contains many fully or partially parasitic members.
Conservation
Several species of Chloropyron are restricted to fragile salt-marsh and alkali-soil habitats in California that have been heavily reduced by coastal development and agriculture. Chloropyron palmatum (palmate bird's-beak) and Chloropyron maritimum subsp. maritimum (saltmarsh bird's-beak) are listed under the U.S. Endangered Species Act as endangered; Chloropyron tecopense (Tecopa bird's-beak) has an extremely limited range. The genus as a whole is considered conservation-sensitive due to its dependence on specialised, threatened wetland habitats.
