Western Wallflower

Western wallflower (Erysimum capitatum) is a bright-yellow, spring-blooming plant that is native throughout western North America from Alaska to northern Mexico and from alpine meadows to desert canyons.

Western wallflower is one of our few native members of the mustard family (Brassicaceae), a family better known for its crop plants, like cabbage and broccoli, and for its troublesome invasive plants such as black mustard and wild radish.

The name “wallflower” seems inappropriate for this bold, beautiful flower. In fact, it was named after a European relative that often grows from and around old stone walls.

Description ^4,23,59

Western wallflower is a widespread and variable biennial or short-lived perennial herb. A basal rosette of linear leaves develops from a taproot the first year. The next year, this produces one or a few upright stems with ascending side branches, usually less than four feet (115 cm) tall. Leaves are linear to narrowly lanceolate or oblanceolate. The basal leaves have short petioles and the blades may reach ten inches (25 cm) long but are usually smaller. Cauline leaves lack the petioles and decrease in size upward. Leaves are dull green with a pale midvein and smooth or somewhat toothed margins. Most parts of the plant are covered with very small hairs that are attached at the midpoint rather than at one end (T-shaped); these are difficult to see with the unaided eye, but they give the leaves a slightly roughened texture.

Flowers are produced in cylindrical clusters at the branch ends. The clusters elongate as flowers mature and fruits develop. The youngest flowers are uppermost and on the same level as the developing buds, giving the cluster a flat-topped look. Each flower has four sepals, in two pairs of slightly different size and shape. There are four petals that are usually yellow to orange but may also be red, purple or blue.¹¹⁴  Local plants are bright yellow. Petals have basal claws, concealed by the sepals, and conspicuous, rounded outer limbs. There are six stamens, two shorter than the others; the anthers curl backward after the pollen has been released. There is one pistil with a straight-sided, superior two-chambered ovary, a short style, and a two-lobed, capitate stigma. The main bloom time is March – July;¹ our blooms usually peak in March and April.

The fruit is a long, thin, four-sided seedpod (a silique), that splits open lengthwise from the bottom, exposing two rows of small brown seeds attached to a central membrane.

Classification ^2,11,44,143

Western wallflower is dicot angiosperm in the mustard family (Brassicaceae), a family of major economic importance that has very broad distribution. There are many well-known species and cultivars in the family including common vegetable crops such as cabbage, cauliflower, broccoli, turnips, watercress and radish, and ornamentals such as sweet alyssum and stock; there are also invasive weeds such as black mustard, wild radish, and sea rocket. Interestingly, six of our common vegetables–cabbage, cauliflower, kohlrabi, Brussels sprouts, broccoli, and kale–were all bred from a single species of mustard, Brassica oleracea.¹⁴³

Members of the mustard family are characterized by four petals in a cross shape (from which came the former family name Cruciferae, or cross-bearing); and by six stamens, four long and two short. Mustard seedpods come in different shapes. When mature, they split open from both sides, exposing the seeds on a central membrane. Seedpods occur radially around the flower stalk, “like a spiral staircase for the little people.”¹⁴³

Sixteen species in the mustard family have been reported from the Reserve.⁴⁸ Eight of these are non-native weeds, including black mustard and field mustard (Brassica nigra and B. rapa), wild radish (Raphanus sativus), sea rocket (Cakile maritima) and stock (Matthiola incana). Others include lovely spring natives such as milkmaids (Cardamine californica).

There is uncertainty about the taxonomy of western wallflower. Some researchers would place E. capitatum and the closely related E. asperum into a single species.²⁵³  A number of subspecies and varieties of E. capitatum have been proposed. At present, CalFlora⁷ recognizes four in California, three of which have very restricted distributions. Jepson recognizes only two. According to the location, ours is likely to be variety capitata,⁴⁸ which is the most widespread of the varieties and the only one reported from this area.

Ecology ^41,254

Western wallflower is a pollinator-generalist,²⁵⁵ a plant that is pollinated by a large variety of organisms; such plants have flowers that are not adapted either to attract or to exclude any type of insect. The advantage of being a pollinator-generalist is that it provides reproductive security especially when pollinator populations are low or fluctuate widely. Thus, a pollinator-generalist may be more easily able to disperse into other habitats or to survive in extreme habitats. In contrast, a plant with flowers adapted for one or a few pollinators (yuccas are an extreme example) may more efficiently distribute its pollen, since the pollinators are more likely to visit a plant of the same species.

The relationship between a flower and its pollinator (or pollinators) is thought to be a driving force in flower adaptation, diversification, and evolution. Several such studies have focused on Erysimum species and their pollinators,^{255, 256} but all of the studies are beyond the scope of this discussion.

Human Uses ¹¹⁴

We have found no reports that western wallflower was used by local Native Americans. Elsewhere in North America, a variety of medicinal uses have been recorded, including treatments for nasal congestion, toothache and muscle soreness; also flowers have been used to make a yellow dye.

Interesting Facts ^59,252

“Wall flower” seems an unlikely name for this bold, showy plant. In truth, it was named for a similar European relative that commonly grows on or near old stone fences and walls.