The genus Erysimum (wallflowers) includes more than 220 species, both popular garden plants and many wild forms. They are small, annual, short-lived perennial herbs or sub-shrubs, reaching 10-130 cm tall, with bright yellow to red or pink flowers produced throughout the spring and summer. One species, Erysimum semperflorens, native to Morocco and Algeria, has white flowers. Wallflowers have t-shaped trichomes.

The genus Cheiranthus is sometimes included herein whole or in part.

Distribution

Wallflowers are native to southwest Asia, the Mediterranean region, Europe, Macaronesia (Including Cabo Verde), and North America through Costa Rica. Many wallflowers are endemic to small areas, such as the Teide wallflower E. scoparium, endemic to the Teide volcano on Tenerife, E. aetnense endemic to the Etna volcano in Sicily, the Franciscan wallflower E. franciscanum, endemic to the northern California coast, the Sierra Nevada wallflower E. nevadense, endemic to the Sierra Nevada of Spain, E. moranii from Guadalupe Island (Mexico), and the endangered Santa Cruz wallflower E. teretifolium, endemic to the inland sandhills of Santa Cruz County, California. Erysimum kykkoticum, found only on Cyprus, is nearly extinct.

Ecology

Erysimum species are used as food plants by the larvae of some Lepidoptera (butterfly and moth) species including the Garden Carpet (Xanthorhoe fluctuata). In addition, some species of weevils, like Ceutorhynchus chlorophanus, live inside the fruits feeding on the developing seeds. Many species of beetles, bugs and grasshoppers eat on the leaves and stalks. Some mammalian herbivores, for example Mule Deer (Odocoileus hemionus) in North America, Red Deer (Cervus elaphus) in Central Europe, or Spanish Ibex (Capra pyrenaica) in the Iberian Peninsula, feed on wallflower flowering and fruiting stalks.

Most wallflowers are pollinator-generalists, their flowers being visited by many different species of bees, bee flies, hoverflies, butterflies, beetles, and ants. However, there some specialist species. For example, Teide wallflower is pollinated almost exclusively by Anthophora alluadii.

Selected species

Cultivation

Most wallflower garden cultivars (e.g. Erysimum 'Chelsea Jacket') are derived from E. cheiri (often placed in Cheiranthus), from southern Europe. Growth is best in dry soils with very good drainage, and they are often grown successfully in loose wall mortar, hence the vernacular name. Their flowers are often purple or brown.

External links

• Evoflor, a web page on Erysimum floral evolution
• Erysimums.org, webpage of a UK collector of erysimums