Packera hesperia is a flowering plant in the aster family, Asteraceae. Commonly known as western ragwort and as serpentine groundsel, it is endemic to the Siskiyou Mountains, where it grows on serpentine soils. Conservation groups have identified this species as vulnerable, in part due to its limited geographic distribution.
Packera hesperia is an perennial with fibrous roots and a single herbaceous stem 7âÂÂ15 cm tall, which can be either smooth or sparsely covered by woolly hairs. The basal leaves are 1âÂÂ3 cm long and 0.5âÂÂ2 cm wide, petiolate with tapering bases, and have either smooth or toothed margins. Cauline leaves are much smaller, have smooth edges, and clasp the stem.
At the end of the stem, there is a corymb bearing 1âÂÂ4 flowering heads held on densely-woolly penduncles. Both the phyllaries (whorls of green bracts forming a cup-like structure that holds the flower) and the calyculi (bracts subtending the phyllaries) are green with red tinges or tips. The phyllaries are densely-woolly near their bases.
Flowering occurs from mid-April to mid-June. The flower is composite, with 8âÂÂ13 yellow ray florets 6âÂÂ10 mm long and 30âÂÂ50 disc florets. The cypselae (dry fruit holding a single seed) are 1.5âÂÂ2 mm long. The pappi, which act as parachutes for the seeds during wind dispersal, are 5âÂÂ6 mm long.
Thomas J. Howell collected the type specimen of Packera hesperia in southern Oregon, and Edward Greene formally described the taxon as Senecio hesperius in 1891. The epithet hesperius (now hesperia) comes from the Greek for "western," referring to the plant's geographic distribution. In 1976, ÃÂskell and Doris Löve segregated a new genus, Packera, out of Senecio based on chromosome number (x=22 or 23) and morphological features. Together with William Alfred Weber, ÃÂskell Löve recombined this species from S. hesperius to P. hesperius in 1981. Its chromosome number is 2n=46.
Packera hesperia is endemic to the Siskiyou Mountains, where it grows at elevations of 500âÂÂ2500 m. There are at least 5,000 individuals in Josephine and Curry Counties in southwestern Oregon, spread across at least 45 populations. In California, there are 4 known populations, all in Del Norte County. It grows in open woodlands on serpentine soils. Associated species commonly found growing with P. hesperia include the serpentine endemics Pinus jeffreyi and Arctostaphylos viscida.
While Packera hesperia enjoys neither state nor federal protections, NatureServe recognizes the species as vulnerable globally. The Oregon Biodiversity Information Center considers P. hesperia vulnerable (S3) in Oregon, and the CNPS Inventory of Rare and Endangered Plants of California lists it as critically imperiled (S1) in California. Compounded by its limited geographic distribution, threats to this species include fire management regimes, mining, and to a lesser extent logging, grazing, and damage by off-road vehicles.