Erysimum cheiranthoides aka Treacle Hedge Mustard

Erysimum cheiranthoides belongs to the mustard family, Brassicaceae. Common names include treacle mustard and wormseed mustard. Its native range runs from Europe to northern Japan. Kew places it in the temperate climate zone. The RHS also lists it as native to Britain and Ireland. It grows as an annual, though some plants live two years. It grows fast and has an upright to spreading form.

The green stems are straight, ribbed, angular, and hairy. They grow longer as the plant matures. Few branches form on the upper half of the plant. Narrow, simple green leaves grow in turn along the stems. Each leaf has little or no stalk. Tiny hairs shaped like stars cover the leaf surface. Leaves get smaller toward the top of the stem. The lowest leaves wither when the plant starts to flower. Leaf edges may be smooth or toothed.

Yellow flowers form racemes at the tops of the stems. Bloom runs from late spring into late summer. A group of plants may flower for about two months. Each flower has four petals and four pale green sepals. Of its six stamens, two are shorter than the others. Slender seed pods can hide the small flowers. These pods, called siliquas, form below the flowers. Each holds one row of seeds and splits when ripe. Fruit develops through summer and fall.

Full sun gives the best growth, though partial shade is tolerated. The plant prefers fertile loam but also grows in sand or clay. It can cope with poor soil. Give it moist soil that drains well. Neutral or alkaline soil suits it; it dislikes acid soil. NC State lists USDA hardiness zones 4 through 8. Seeds provide a way to raise new plants. Meadow settings and mass plantings suit its wildflower form.

Bees, flies, and beetles visit the flowers. Most wildlife finds the leaves and seeds bitter. Animals may still eat them when other food is scarce. Self-seeding can make this plant weedy on disturbed ground. It occurs in pastures, beside roads, and along rail lines. Plants For A Future lists no known food use. Past uses include seed remedies for worms and root washes for skin complaints. These records do not establish safe home use. The ASPCA identifies it as toxic to horses. Its isothiocyanates can cause gut irritation and colic.