American Madwort

The records in FRPS and Fl. Intramongol. (ed. 2, 2: 646. 1990) of Alyssum sibiricum Willdenow, as occurring in Nei Mongol and Heilongjiang, are based on misidentified plants of A. obovatum. True Alyssum sibiricum is restricted to the Balkan Peninsula, Turkey, Crimea, and the Caucasus. Although the present authors have seen no material of A. obovatum from Xinjiang, the species is likely to be gathered from Altay Shan, where it has been extensively collected from the Russian and Mongolian parts of this range. The records herein of A. obovatum from Heilongjiang and Nei Mongol are based on Litvinov 147 (LE) and Wang Zhan 507 (PE), respectively.

Herbs perennial, cespitose, 7-15(-20) cm tall, often woody at base, canescent throughout, with sessile, 10-25-rayed stellate trichomes. Stems usually erect or ascending, often several from caudex, sterile shoots often several. Cauline leaves subsessile; leaf blade broadly oblanceolate, obovate-spatulate, or obovate, 0.6-1.4(-1.7) cm × (1-)2-6 mm, gradually smaller upward, base attenuate, apex rounded, obtuse, or subacute. Racemes corymbose, simple or in a panicle terminating each stem. Fruiting pedicels divaricate, (2-)3-7(-9) mm, slender, straight, uniformly stellate. Sepals oblong, 1.5-2 × 0.7-1 mm, deciduous, stellate. Petals yellow, broadly spatulate, 2.5-3.5(-4) × 1-1.5 mm, glabrous outside, caducous, base attenuate, apex often obtuse or rounded. Filaments 1.5-2 mm; median pairs unilaterally broadly winged, apically 1-toothed; lateral pair with a lanceolate or narrowly oblong basal appendage apically obtuse or subacute; anthers oblong, 0.3-0.4 mm. Ovules 1(or 2) per locule. Fruit broadly elliptic or obovate, 3-4.5(-5) × 2.5-3.5 mm, apex obtuse to rounded; valves not veined, inflated at middle or on 1 side, flattened at margin, densely covered with stellate trichomes; style 1.5-2 mm, slender, glabrous. Seeds 1(or 2) per locule, ovate, 1.1-1.4 × 0.8-1.1 mm, compressed, not margined. Fl. May-Jul, fr. Jun-Aug. 2n = 16, 30, 32.

Heilongjiang, Nei Mongol [Kazakhstan, Mongolia, Russia; North America (Alaska, Canada)].

Mountain slopes, cliffs, gravel, rocky places; 500-1500 m.

Odontarrhena obovata C. A. Meyer in Ledebour, Fl. Altaic. 3: 61. 1831; Alyssum americanum Greene; A. biovulatum N. Busch; A. fallax E. J. Nyárády.