Desert Madwort

Mediterranean region.

Southeast Europe, east Mediterranean region, southwest and central Asia.

Sandy and rocky ground.

Annual.

A variable species and the status of the var. prostratum Dudley, is not definite. It appears that not only here, but in some other species of Alyssum also, plants become prostrate, reduced with somewhat condensed inflorescence, probably due to dry conditions. I suppose, this variation is not constant, and more of ecological nature than taxonomic.

Dudley (Notes Roy. Bot. Gard. Edinburgh 24: 157-165. 1962) divided Alyssum desertorum into three varieties distinguished largely on the basis of minor differences in fruit trichomes. In the present authors' opinion, these varieties do not seem to merit recognition. The occurrence in Xizang of this species, which was not recorded in Fl. Xizang. (vol. 2. 1985), is based on the holotype of var. himalayense, Hügel 1191 (W).

Annual, 5-20 (-25) cm long, erect, spreading or ascending, branched mostly from the base, densely covered with stallate rough hairs. Leaves oblanceolate or linear-lanceolate, 10-30 mm long, 1-5 mm broad, sessile. Racemes 30-40-flowered, ebracteate, up to 10 cm long in fruit. Flowers c. 2 mm across, pale yellow or dull-whitish; pedicel up to 3 mm long in fruit, ascending or horizontal. Sepals c. 1.5 mm long. Petals c. 2.5 mm long, broadest in the middle, apex obscurely emarginate, sparsely hairy at the back, specially on the veins. Stamens c. 1.5:2 mm long; filaments of the outer two smaller stamens with scale-like, notched appendages. Siliculae 2.5-4 mm in diameter, ± orbicular; apex slightly emarginate; style usually c. 0.5 mm long; valves uniformly tumid with a flat narrow margin, glabrous; septum not veined; seeds 2 in each locule, c. 1.5 mm long, ovate-orbicular, very narrowly winged (margined), brown.

Herbs annual, (2-)5-18(-28) cm tall, canescent throughout (except fruit) with appressed, sessile, 8-20-rayed stellate trichomes. Stems erect, ascending, or decumbent, often several from the base. Cauline leaves subsessile or lowermost attenuate to petiolelike base to 5 mm; leaf blade linear to oblanceolate-linear, (0.3-)0.5-2.5(-3) cm × (0.5-)1-3(-4) mm, gradually smaller upward, base attenuate, apex acute. Fruiting pedicels ascending or subdivaricate, (1-)1.5-3.5(-4.5) mm, stout, straight, covered with stellate trichomes only. Sepals oblong, 1.4-1.8(-2) × 0.4-0.5 mm, deciduous, stellate. Petals pale yellow, oblanceolate, 2-2.5 × 0.5-0.6 mm, sparsely stellate outside, caducous, base attenuate, apex obtuse or retuse. Filaments 1-1.8(-2) mm; median pairs gradually expanded from apex to narrowly winged base, not toothed; lateral pair with a broadly winged appendage apically notched into 2 teeth; anthers ovate, 0.1-0.2 mm. Ovules 2 per locule. Fruit orbicular, 2.5-4(-4.5) mm in diam., apex shallowly emarginate; valves not veined, uniformly inflated at middle, broadly flattened at margin, glabrous and often glaucous; style 0.3-0.7 mm, slender, glabrous. Seeds often 2 per locule, ovate, 1.2-1.5 × 0.9-1.1 mm, slightly compressed, margined or not. Fl. and fr. Apr-Jun. 2n = 32.

Distribution: S.E. Europe, N. Africa, C. and S.W. Asia to Pakistan and N.W. Himalaya.

Xinjiang, Xizang [Afghanistan, India, Kashmir, Kazakhstan, Mongolia, Pakistan, Russia, Tajikistan, Turkmenistan, Uzbekistan; Europe; naturalized in North America].

Fl. Per.: March-June.

Deserts, rocky areas; near sea level to 2600 m.

Alyssum minimum Willdenow, Sp. Pl. 3: 464. 1800, p.p., not Linnaeus (1753); A. desertorum var. himalayense T. R. Dudley; A. desertorum var. prostratum T. R. Dudley; A. turkestanicum Regel & Schmalhausen var. desertorum (Stapf) Botschantzev; Psilonema minimum Schur.

Alyssum desertorum is a species of flowering plant in the family Brassicaceae known by the common name desert madwort. It is native to Europe, North Africa and Asia, and it is found in parts of western North America as an introduced species and sometimes a weed. This is a hairy annual herb producing upright stems up to about 20 centimeters tall. The leaves are linear to oblanceolate-linear in shape, 0.5-4 millimeters long and 0.3-3 millimeters wide. The entire plant is covered by 8-20 rayed stellate trichomes, giving the plant a grayish appearance. It produces small yellowish flowers with petals that are 2-2.5 millimeters long and round, notched fruits 2.5-4.5 millimeters long. The brown seeds are winged, arranged two to a locule, and are about 1.5 millimeters long.

Pronghorn antelope eat this plant in the winter. Western harvester ants have been recorded harvesting the seeds in Wyoming.