Alyssum tenuifolium Stephan

Except for differences in the trichomes, Alyssum canescens and A. tenuifolium overlap in plant height, petal length, and seed size, and they are sometimes separated with difficulty. A critical field study in parts of their ranges where they overlap, especially in Nei Mongol, Mongolia, and Siberia, is needed in order to reach a better understanding of their limits. Hybridization between the two species (Botschantzev, Bot. Zhurn. (Moscow & Leningrad) 44: 1486. 1959) was suggested, but no experimental work supports that hypothesis.

Alyssum tenuifolium was not listed in FRPS but was recorded for China (as Ptilotrichum tenuifolium) in Fl. Intramongol. (ed. 2, 2: 648. 1990). Several collections from Nei Mongol were examined by the present authors, including Roerich Expedition 375 (US) and Petrov s.n. (LE). Another species, P. dahuricum Peschkova (Novosti Sist. Vyssh. Rast. 15: 230. 1979), if indeed distinct from A. tenuifolium, was said to occur in China (Fl. Siberiae 7: 107. 1994), but the present authors have seen no Chinese material.

Herbs perennial, (5-)8-25(-30) cm tall, silvery canescent throughout, with short-stalked, stellate trichomes lanceolate in outline and with 2, branched, principal rays from stalk apex. Stems usually erect or ascending, often several from woody base, sterile shoots often several. Cauline leaves fleshy, sessile; leaf blade linear, very rarely narrowly oblanceolate, (0.5-)1-2(-2.5) cm × 0.5-2(-4) mm, often grooved adaxially, base attenuate, apex obtuse or subacute. Fruiting pedicels ascending or suberect, 3-12 mm, slender, straight. Sepals oblong, 1.5-2.2 × 1-1.5 mm, deciduous, stellate. Petals white, obovate or suborbicular, (3-)3.5-5 × (2-)2.5-3.5 mm, glabrous outside, caducous, apex rounded; claw often pink, minutely papillate at base. Filaments 1-2.5 mm, dilated and papillate at base, neither winged nor appendaged; anthers ovate or oblong, 0.4-0.6 mm. Ovules 1(or 2) per locule. Fruit broadly ovate or lanceolate-ovate, 4-6 × 2-4 mm, apex acute or acuminate; valves not veined, slightly flattened, densely stellate; style 1-2.5 mm, slender, glabrous. Seeds 1 per locule, ovate, (1.8-)2-2.5 × 1-1.5 mm, compressed, not margined. Fl. Jun-Aug, fr. Jul-Oct. 2n = 88, 92.

Nei Mongol [Kazakhstan, Mongolia, Russia (Siberia)].

Steppe, rocky places, sandy ravines, dry sandy slopes; 900-2400 m.

Alyssum canescens de Candolle var. elongatum de Candolle; Ptilotrichum canescens (de Candolle) C. A. Meyer subsp. tenuifolium (Stephan ex Willdenow) Hanelt & Davamzac; P. elongatum (de Candolle) C. A. Meyer; P. tenuifolium (Stephan ex Willdenow) C. A. Meyer.