Erysimum cheiranthoides / wormseed wallflower

Adjectives: annual, disturbed, non-native, ruderal, weed, widespread

Also known as: treacle mustard, wormseed mustard

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I don’t think you could ask for a better set of common names. Treacle supposedly comes from the Greek word for antidote, in this case for things with poisonous bites. The name “wormseed mustard”, on the other hand, refers to its being part of a potion fed to children to rid them of intestinal worms. I’m not sure about “wallflower”.

This cruciferous annual looks pretty much like many others in the family. As a vegetative plant, it starts with a rosette of leaves at the base. Those, and the stem leaves that develop later, are lance shaped or elliptical, sessile, up to 4 inches long and half an inch across. They vary relatively little in size or shape and this is a diagnostic feature. The margins are either entire or coarsely (but insignificantly) toothed. From the specimens I found in the Valley, it looks like the leaves are thicker, more succulent than others in the family, but this may not be always true. The leaves may look grey-ish because of a covering of star-shaped (stellate) hairs. They are not divided or lobed. The stems themselves are distinctly (and diagnostically) ribbed.

Wormseed wallflower blooms throughout the summer with bright yellow flowers 1/3 inch across or less. The flowers are in rounded clusters at the tips of stems and branches. The four petals are rounded, and each flower has 6 yellow-tipped stamens, 2 of which are shorter than the others.The stem continues to elongate and produce more flowers throughout the season with the new ones opening above the developing fruits.

The fruit is a cylindrical capsule (silique) up to an inch and a half long on a short pedicel. The siliques are ascending to erect, not straight out or pointing downward. Again, this is a diagnostic feature.

Wormseed wallflower grows in open disturbed areas, dry stream beds, roadsides, waste areas etc. This is not different from the other brassicas on this site, for sure.

Like quite a few other brassicas, E. cheiranthoides has a small genome, only 8 chromosomes and is diploid. It grows and reproduces fast, seed to seed in 10 weeks, even in a lab. These are exactly the characteristics that plant molecular biologists like when they propose new “model plants” to probe particular characteristics. The fact that it is a brassica, related to the most commonly studied plant, Arabidopsis thaliana, makes it a likely target as well. In this case, the problem researchers would like to address is that of the pathways for synthesizing defensive chemicals. As a first step, the genome has been sequenced and assembled and open for anyone who wants to see or use it.