A member of the mustard family, the Western Wallflower ( Erysimum capitatium ) is a brightly colored yellow flower which is quite common across the western United States, including Arizona, Utah and Nevada.. In European countries, the wallflower earned its name from a habit of growing on… you guess it, walls. More specifically stone, masonry or wooden fences. The name was transposed to the American species despite the fact the plants have no preference for walls.
Scientific Taxonomy and Categorization
- Kingdom: Plantae
- Clades: Tracheophytes, Angiosperms, Eudicots, Rosids
- Order: Brassicales
- Family: Brassicaceae (mustard or cabbage family)
- Genus: Erysimum
- Species: Erysimum capitatum (Douglas ex Hook.) Greene (binomial name)
The species belongs to the tribe Erysimeae within Brassicaceae. It is a dicot angiosperm (eudicot) herb. Flora of North America recognizes two main varieties: E. c. var. capitatum (often called western or sanddune wallflower) and E. c. var. purshii (Pursh’s wallflower). Numerous synonyms exist due to high morphological variability and past taxonomic confusion with E. asperum (prairie rocket). Chromosome number is 2n = 36. The plant is categorized as a biennial or short-lived perennial herb (sometimes behaving as a winter annual in southern deserts), with a taproot and variable growth form depending on elevation and habitat.
Detailed Plant Description
Erysimum capitatum is a highly variable, taprooted herb that produces one to several erect, leafy stems (0.5–12 dm / 1.5–12 ft tall) arising from a basal rosette. Stems are often branched distally, coarse, and covered in stiff, appressed, forked or branched (malpighiaceous/dolabriform) hairs. The plant leaks a pungent, watery juice when damaged.
Basal leaves are simple, alternate, spatulate to narrowly oblanceolate or linear (2–27 cm long × 3–30 mm wide), with prominent midribs and margins ranging from entire to dentate or denticulate. Stem leaves are smaller, sessile, and angled upward. Leaves are typically deep green and hairy (rayed hairs vary by variety: mostly 3–7-rayed in var. capitatum; 2–3-rayed in var. purshii). Plants develop short to elongate caudices clothed in old leaf bases.
Growth habit and life cycle show plasticity: low-elevation plants are often taller, less branched biennials and more drought-resistant; high-elevation (alpine) plants are dwarf, multi-stemmed perennials. The species is early-seral, thriving in disturbed sites, and exhibits semelparity (single reproductive event) in dry lowlands versus iteroparity (multiple events) in moist high-elevation habitats.
Detailed Flower Description
Flowers are perfect, arranged in congested terminal racemes that elongate in fruit. Each flower is 2.5–3.8 cm wide with four distinct, rounded petals arranged in a cross shape (typical of Brassicaceae). Petals are usually bright yellow to orange (occasionally lavender, maroon, red, white, or purple in certain populations or high elevations); var. capitatum tends toward orange-yellow, var. purshii toward yellow. Flowers have four sepals, six stamens (tetradynamous: four long, two short), a stout style (up to 3 mm), and a superior ovary. They are fragrant and bloom primarily April–August (as early as January in southern ranges or to September).
Fruits are linear, narrow siliques (3.5–15 cm long × 1.3–3.3 mm wide), upright or nearly parallel to the stem, four-sided or slightly flattened, with prominent midveins. Each valve contains 40–80 seeds; siliques dehisce at maturity. Seeds are small, oblong (~1.5 mm), lightweight, and winged in var. capitatum. Pollination is required for full seed set; visitors include bees, flies, butterflies, and beetles.
Habitat
The western wallflower occupies diverse dry, open sites from valley bottoms to alpine summits. It prefers well-drained, sandy, gravelly, or rocky soils with low organic matter and fertility. Substrates include sandstone, granite, basalt, limestone, serpentine, dunes, and talus. It occurs in desert grasslands/shrublands, chaparral, pinyon-juniper woodlands, aspen groves, montane meadows, forest openings, sagebrush flats, and alpine tundra. Elevation range is sea level to 13,120 ft (4,000 m), with var. capitatum generally lower (0–5,600 ft) and var. purshii higher (3,280–13,120 ft). It tolerates full sun, drought, and disturbance (roadsides, burns, grazed areas).
Range and Distribution
Erysimum capitatum is one of the most widespread native North American wallflowers. Its range spans western North America from Alaska and Yukon Territory south through British Columbia, Washington, Oregon, California, Idaho, Montana, Wyoming, Utah, Colorado, Nevada, Arizona, New Mexico, and into northern Mexico (Chihuahua, Sonora, etc.). It extends eastward across the Great Plains to the Great Lakes region (Illinois, Indiana, Missouri, etc.) with scattered disjunct populations as far as Ohio and Tennessee. Var. capitatum has the broadest distribution; some California varieties (e.g., var. angustatum) are narrowly endemic and endangered. It has been introduced in parts of New England. Overall, it is considered secure (NatureServe).
This adaptable species plays ecological roles as a nectar source for pollinators (including butterflies), larval host plant, and early colonizer of disturbed or post-fire sites. It also provides forage for wildlife such as elk, deer, bighorn sheep, and small mammals.
Other Names
- Coast wallflower
- Douglas’ wallflower
- Sanddune wallflower
- Prairie rocket
