This section is from the book "Sub-Alpine Plants Or Flowers Of The Swiss Woods And Meadows", by H. Stuart Thompson. Also available from Amazon: Sub-Alpine Plants: Or, Flowers of the Swiss Woods and Meadows.
About 30 species indigenous to Southern Europe and America. (Silicule globular, many-seeded).
Stem 12-18 inches high, rather woody at the base. Leaves entire, oblong, glabrous; lower leaves ciliated, almost spathulate. Inflorescence umbellate at first, elongated later. Flowers yellow, rather large. Petals longer than the calyx. Silicules 8-12 mm. long, oval, glabrous. Seeds broadly winged.
Rocky places and limestone debris in the sub-alpine region and lower valleys. Very local in Switzerland.
Switzerland (Lower Rhone Valley, Trient and Bagnes valleys), Savoy, Dauphiny; Southern Europe as far east as Greece; Bithynia.
Annuals or low-branching perennials, with hoary or short stellate down and white or yellow flowers. Filaments of the stamens usually winged near the base, or thickened, or furnished with small teeth. Pod sessile within the calyx, orbicular or oval, the partition broad, the valves convex and not veined. Seeds 1-4, or very rarely more.
A large genus extending over Europe and Northern Asia. Distinguished from Draba chiefly by the short few-seeded pod, with more convex valves.
Stem diffuse, downy, woody at the base, whole plant greyish green, with adpressed, stellate pubescence. Leaves oboval or oblong-lanceolate. Flowers bright yellow. Petals emarginate; longer filaments winged. Silicule circular, swelling in the middle, slightly emarginate. Style equalling the silicule or shorter. Seeds narrowly winged.
Sandy places and limestone hills, in sunny places, 2000-6000 feet. May to July.
Alps, Pyrenees; Central and Southern Europe, Western Asia, N. Africa.
Stem somewhat shrubby at base, diffuse, hoary, like the whole plant. Raceme simple, corymbose. Flowers yellow. Petals entire, rounded. Silicules small, obovate-oblong, swelling in the middle. Seeds slightly winged. Plant covered with stellate hairs.
Rocky and sandy places in the mountains, especially in river beds. June to August. Very variable.
Savoy, Dauphine, Provence, Cevennes, Eastern Pyrenees; Zermatt Valley in Switzerland; Mont Cenis, Southern Europe; Western Asia; North Africa.
A. serpyllifolium Desf. is a small-leaved, pale yellow-flowered, and very hoary variety, found at Mont Cenis and in Spain, etc.
Plant shrubby, I foot high, with twisting branches. Leaves oblong, obtuse, silvery. Flowers white, large. Petals slightly emarginate, oval. Fruiting-spike a dense corymb. Silicules circular, glabrous, twice as long as the style. Seeds broadly winged.
Limestone rocks in the low mountains of the South. May, June.
Maritime Alps and Department of the Var; Liguria, Col di Tenda, and Piedmont. Very local.
This very distinct species might be more cultivated in warm places in limy soil on the rockery.
All the rock and Alpine Alyssums are easily grown in light, sandy, or other dry soil. A. saxatile, from Southern Russia, is the best-known species in gardens, where it makes great masses of yellow colour in April and May. None of the Alyssums can have too much sun in summer, or too little damp in winter. Several are very liable to attacks by slugs.