Thelypodium is a genus of flowering plants in the mustard family (Brassicaceae), placed in the order Brassicales. The genus comprises 16 to 17 accepted species — all native to western and west-central North America, extending into northern Mexico. Plants in this genus are commonly known as "thelypodies."
Members of Thelypodium are biennials, perennials, or rarely annuals, growing from simple to several erect stems, though occasionally decumbent. They are glabrous or pubescent. Leaves are both basal and cauline: basal leaves are often rosulate with petiolate blades whose margins may be entire, dentate, lyrate, or pinnately lobed; cauline leaves are petiolate or sessile, with bases ranging from cuneate to auriculate, sagittate, or amplexicaul. Racemes are usually dense to lax and elongate considerably in fruit. Flowers are small to medium-sized, with sepals typically erect or ascending and petals coloured white, lavender, or purple — spatulate to obovate or oblanceolate to linear in shape, sometimes with crisped margins. The anthers are notably often linear-oblong and circinately coiled after dehiscence, an unusual trait within the family. Stamens are subequal or tetradynamous, frequently exserted beyond the petals. Fruits are stipitate (borne on a gynophore), linear, and either smooth or torulose (constricted between seeds), with each valve bearing a prominent midvein; the chromosome base number is x = 13.
The genus name derives from Greek thelys ("female") and podion ("little foot"), a reference to the gynophore — the stalk that elevates the pistil above the receptacle — a feature that helps distinguish Thelypodium from other Brassicaceae genera. The genus was formally described by Endlicher in 1839; earlier synonyms include Pachypodium Nuttall (1838, a name already occupied by a succulent genus) and the segregate Stanleyella Rydberg. Some authors treat Stanleyella as a distinct genus on the basis of its spreading sepals, flattened fruits with veinless septa, and clavate rather than cylindrical styles; others subsume it within Thelypodium.
Notable species include T. integrifolium (entireleaved thelypody), one of the more widespread members; T. laciniatum (cutleaf thelypody), distinguished by solid stems and horizontal pedicels; T. milleflorum (manyflower thelypody), recognisable by its hollow stems and strongly curved pedicels; and T. stenopetalum (slenderpetal thelypody), a narrow-endemic of southern California with thread-like petals and conservation concern.
Etymology
The name Thelypodium derives from the Greek thelys ("female") and podion ("little foot"), alluding to the gynophore — a short stalk that carries the pistil above the receptacle. This feature, unusual in the mustard family, was the defining character cited by Endlicher when he formally described the genus in 1839.
Distribution
All 16 species of Thelypodium are native to western and west-central North America, with the range extending into northern Mexico. The genus is treated exclusively in the Flora of North America (FNA Vol. 7) as a western North American element, with no species native to eastern North America or other continents.
Taxonomy Notes
Thelypodium is somewhat heterogeneous. The segregate genus Stanleyella Rydberg — comprising species with spreading sepals, flattened fruits, veinless fruit septa, and clavate to subconical styles — has been proposed for formal recognition by some authors (notably Payson 1923), while others (Al-Shehbaz 1973; Rollins 1993) subsume it within Thelypodium. Key diagnostic features of Thelypodium s.str. include erect sepals and petals, terete (cylindrical) fruits with prominently veined septa, and cylindrical styles. The chromosome base number is x = 13.
