Pterocaulon is a genus of perennial herbaceous flowering plants in the sunflower family (Asteraceae), order Asterales. The roughly 20 species are distributed across North America, South America, and Australasia, with additional representatives in Southeast Asia, the Philippines, and New Guinea. A common name for North American species is blackroot.
Plants in this genus are characteristically covered in dense woolly or cottony hairs (tomentum), giving them a silvery or whitish appearance. Leaves are simple and have decurrent bases — they extend downward along the stem, creating distinctive wing-like ridges that run along the sides of the stems, a feature that gives the genus its name. Inflorescences are typically dense, spike-like clusters of small composite flower heads.
The genus spans a wide ecological range, from the southeastern United States (P. pycnostachyum in the Carolinas, Georgia, and Florida) to the grasslands and scrublands of South America (P. alopecuroides, P. virgatum) and the open woodlands and disturbed habitats of Australia (P. sphacelatum, P. serrulatum).
Etymology
The name Pterocaulon derives from the Greek pteron (wing) and kaulos (stem), meaning "winged stem." This refers to the decurrent leaf bases that form conspicuous wing-like ridges running down the length of the stem — a defining morphological feature of the genus.
Distribution
Pterocaulon occurs in North America (southeastern United States, West Indies including Puerto Rico and Virgin Islands), throughout much of South America (Brazil, Argentina, Paraguay, Uruguay, Bolivia, and neighboring countries), and in Australasia (Australia — principally Western Australia, Northern Territory, and Queensland). One species, P. redolens, extends into Indochina, Hainan, the Philippines, Maluku, and New Guinea, giving the genus a broadly pantropical and warm-temperate distribution.
