Western Wallflower is an erect native biennial or short-lived perennial, with stems usually not branched below the inflorescence. Height varies as the inflorescence elongates as flowers open at the top of the stem, eventually elongating to 3 feet or more. Stems are not woody.
The leaves are both basal and stem. Basal leaves are more elliptical in shape, 4 to 6x longer than wide and sometimes wither by the time fruit is forming. The stem leaves are linear to lanceolate, up to 4 inches long, with pointed tips, usually without stalks, and the reduce in size in the upper stem. Margins are entire to sparsely toothed. Leaf surfaces have tiny Y shaped hairs, giving a grayish tint to the color. These same hairs are on the stem and seed pods.
The inflorescence is a dense showy raceme, or group of racemes in a branched inflorescence, which elongate as flowers open from the bottom to the top and seed pods form from the mature lower flowers.
The individual flowers are about 1/2 inch wide and have long stalks; the corolla has 4 yellow spreading petals that are obovate to more circular in shape, 13 or more mm wide, with rounded tips and bases slightly clawed. There are 3 pairs of stamens, with one pair shorter (tetradynamous). These have nectar glands around their base, and have linear anthers. The style has a blunt tip, just slightly two-lobed. The 4 sepals of the flower calyx are linear to oblong in shape, 7 - 14 mm long with pointed tips. One pair of the sepals has a narrowed base compared to the other pair. Flowers are slightly fragrant.
Seed: Fertile flowers a long thin pod called a silique. These are 4-angled, longitudinally 4-striped and covered with the small dense hairs like the stem and leaves. The pods are not twisted, usually straight, pointing outward or upward, but not curving upward, and up to 5 inches long. When mature the pod splits along its sections (valves) to release the ovoid small brown to black seeds that are up to 2.3 mm long by 1.2 mm wide. The inside of the valves is without hair.
Habitat: Western Wallflower develops a taproot, grows in full sun in soils that are mesic to dry, such as open prairies, pastures, sand hills, and bluffs, with considerable range in elevation - up to 6,500 feet.
Names: The genus Erysimum is a Greek word that refers to the Bittercress plant (another member of the mustard family). The base is the Greek word, eryso, meaning 'to cure' or to 'ward off'; thus referring to the curative aspects of certain plants of this genus. The species asperum means 'rough', referring to the dense forked hair on the plant. The term 'wallflower' is generally thought to refer to several of the old world plants that resemble this species and were frequently found growing on old walls.
The author names for the plant classification are two-fold. The first to classify, in 1818 and assigning the name Cheiranthus asper, was ‘Nutt.’ who was Thomas Nuttall (1786-1859) English botanist who lived and worked in America from 1808 to 1841. On his many expeditions he collected many species that had been originally collected by Lewis and Clark but lost by them on their return journey. He also collaborated with French botanist Francois Andre Michaux (1770-1855) in Michaux’s 3 volume North American Sylva. Nutthall's work was amended in 1821 by ‘DC’ who was Augustin Pyramus de Candolle (1778-1841), Swiss botanist, who influenced Charles Darwin. He studied plants, began a systematic catalogue and has 2 genera named for him.
Comparisons: Two other species of Erysimum are found in Minnesota: E. cheiranthoides, the Wormseed Wallflower which was introduced from Europe, and E. inconspicuum, the Small-flowered Wallflower. E. inconspicuum has a flower stigma strongly 2-lobed, smaller seeds, pod valves not striped, not hairy inside, and petals less rounded - more broad in the upper portions and up to 9 mm wide. E. cheiranthoides has petals slightly larger than inconspicuum, up to 10 mm wide, but smaller than asparum and compared to asparum the bases are more narrowly clawed, the sepals are only 1.8-3.2 mm long and the valves of the seed pod inside are densely hairy. Another yellow flowered Mustard Family plant found in Minnesota is the introduced and invasive Yellow Rocket, Barbarea vulgaris.
Above: The inflorescence is an erect raceme at the top of each stem branch with new flowers opening at the apex and long thin seed pods forming beneath. The pods are held spreading outward or ascending with the blunt tip of style at the end. Drawing from Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. 3 vols. Charles Scribner's Sons, New York.
Below: 1st photo - The apex of the raceme hold numerous buds not yet open, while the raceme itself elongates upward as the flowers open. 2nd photo - Seed pod are strongly 4-angled, striped, and dense with the fine Y shaped hairs.
Below: Flower petals can be almost circular to obovate as seen here, at least 13 mm wide. The stamens are in 3 pairs with one pair shorter. The style is long and has a blunt but slightly 2-lobed stigma.
Below: The fine dense hair can be seen here on the flower stalks, the style and the seed pod in the background. The 4 sepals of the flowerhead are linear, yellow-green, with acute tips. Note the difference in the base on the sepals facing the camera.
Below: This view of the developing Upland Garden at Eloise Butler was taken by Martha Crone in May 1948, 3 years after she planted numerous Western Wallflower plants. It may be probable that the scattered yellow flowers visible are some of those plants.
Notes: Western Wallflower was added to Eloise Butler in 1945 when Martha Crone was developing the new upland prairie area that had been added to the Garden in 1944. On July 16 she put in 30 plants without specifying her source. Between Sept. 15 and Sept. 27 she put in 421 additional plants. On July 20 and 27th and on Sept. 30, she also planted seeds. Martha also referred to this plant as "Yellow Phlox", but today that common name should only apply to Phlox Drummondii. Western Wallflower was listed on her 1951 census of Garden plants and it is probable that the numerous yellow flowered plants visible in her May 1948 Kodachrome of the upland hillside are this plant.
Western Wallflower is native to Minnesota and is still reported by the Minnesota DNR to be found in a handful of counties including Anoka and Ramsey. In North America Western Wallflower is found in the Rocky Mountains and east into the plains as far east as Minnesota, Iowa, Illinois and Missouri. The lower Canadian Provinces all report it, except the Maritime.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"