Physaria is a genus of flowering plants in the family Brassicaceae (the mustard family), placed in the order Brassicales. Commonly known as twinpods or bladderpods, the genus comprises roughly 100–130 species of densely hairy annual and perennial herbs native to the Americas, with the greatest diversity concentrated in western North America.
Plants in the genus typically grow prostrate or decumbent, spreading along the ground in patches or clumps. They are covered in stellate (star-shaped) hairs that give the foliage a silvery or gray-green appearance. Inflorescences bear clusters of small, bright yellow flowers characteristic of the mustard family. The most distinctive feature is the fruit: a silicle that is deeply notched at the apex, splitting into two inflated, bladder-like lobes — the characteristic that gives rise to both the common names "twinpod" and "bladderpod" and the genus name itself (from Greek physa, meaning bladder or bellows).
Many species of Physaria were formerly classified in the separate genus Lesquerella, which was sunk into Physaria following a comprehensive molecular revision. The genus has also attracted scientific interest as a model system for studying the allocation of resources between annual and perennial life-history strategies.
Several species have economic significance. Physaria fendleri, in particular, is a source of bladderpod oil, a seed oil with industrial applications as a potential substitute for castor oil, containing unusual hydroxy fatty acids.
Etymology
The genus name Physaria derives from the Greek physa (φῦσα), meaning "bladder" or "bellows," referring to the inflated, bladder-like lobes of the fruit. The common names "bladderpod" and "twinpod" describe the same characteristic: the deeply notched silicle that divides into two puffed, paired sections at maturity.
Distribution
Physaria is native to the Americas, with the majority of species endemic to western North America — particularly the Rocky Mountain region, Great Basin, and adjacent arid and semi-arid habitats of the western United States and Canada. A smaller number of species extend into Mexico and South America.
Taxonomy
Many Physaria species were formerly placed in the genus Lesquerella, which was merged into Physaria after molecular phylogenetic studies demonstrated that maintaining both genera would render Physaria paraphyletic. The consolidated genus is placed in the family Brassicaceae, order Brassicales. GBIF records 127 accepted descendants. Authorship of the genus name is not resolved in the current GBIF dataset.
