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Erysimum (wallflowers) is a genus that includes about 180 species, both popular garden plants and many wild forms. The genus Cheiranthus is sometimes included herein whole or in part. Erysimum has recently adscribed to a monogeneric cruciferous tribe, Erysimeae. This tribe is characterized by sessile, stellate and/or malpighiaceous trichomes, yellow to orange flowers and multi seeded siliques
Wallflowers are small, annual, short-lived perennial herbs or sub-shrubs, reaching 10-130 cm tall. Most species have stems erect, somewhat winged, canescent with an indumentum of 2-fid hairs, usually 25 ± 53 cm x 2-3 mm in size, and t-shaped trichomes. Leaves narrow and sessile. Lower leaves linear to oblanceolate pinnatifid with backwardly directed lobes, acute, 50-80 mm x 0.5-3 mm. Stem leaves linear, entire; all canescent with 2-fid hairs; 21-43 mm x 1.5-2 mm. Inflorescence in raceme, with bright yellow to red or pink bilateral and hermaphodite, hypogynous and ebracteate flowers. Flowering occurs during spring and summer. One species, Erysimum semperflorens, native to Morocco and Algeria, has white flowers. Floral pedicel ranges between 4 and 7 mm. Four free sepals somewhat saccate, light green, 5-7 mm x 1.5-2 mm.
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.
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.
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