Small Tumbleweed Mustard
- Name also: Small Tumble Mustard, Tall Hedge Mustard, False London Rocket
- Family: Mustard Family – Brassicaceae (Cruciferae)
- Growing form: Annual or biennial herb.
- Height: 30–80 cm (12–30 in.). Stem sparsely branched, clearly coarsely haired especially at base.
- Flower: Corolla regular (actinomorphic), yellow, approx. 0.5 cm (0.2 in.) wide; petals 4, approx. 5 mm (0.2 in.) long. Sepals 4. Stamens usually 6, of which 4 long and 2 short. Gynoeciem fused, a single carpel. Inflorescence an elongating raceme during fruiting stage.
- Leaves: Alternate. Blade deeply pinnately lobed, lobes with toothed margin, terminal lobe large, triangular.
- Fruit: Many-seeded, opening lengthwise, 2–3 cm (0.8–1.2 in.) long, slim, cylindrical, rigid, spreading, siliqua arching slightly upwards, tip approx. 0.5 mm (0.02 in.) long. Stalk 5–10 mm (0.2–0.4 in.) long.
- Habitat: Mills, railways, harbours, industrial areas, wasteland, rubbish tips, sometimes fields.
- Flowering time: July–September.
Small tumbleweed mustard is part of quite a large genre, but it seems that only one member is native to the Nordic countries – Sisymbrium supinum, which grows in Sweden and the large islands of the Baltic Sea. Many species have however spread with human help far beyond their original habitats. Hedge mustard (S. officinale) has long been part of Finland’s flora, but its relatives are newer arrivals and mainly casual.
Small tumbleweed mustard is mainly found in Finland in loading areas, harbours, beside railways and other areas where people move around and affect the environment. Small tumbleweed mustard’s native habitat covers south-eastern Europe, south-western Asia and southern Siberia, and it has reached Finland in Russian grain and animal feed. Small tumbleweed mustard has been in Finland for 200 years already and traveled as far north as Rovaniemi and Sodankylä. Stands are usually short-lived, but the species has managed to make itself at home in some southern parts of the country. Although it has clearly originally adapted to a continental climate, it can also be found along the Finnish coastline.
Small tumbleweed mustard has both a hairy and a glabrous form (var. glaberrinum). This form can also be found here, having traveled from its native south-western Asia with traffic and other human activity. In Finland its close relatives grow casually, including tumble mustard (name also tall mustard, tumbleweed mustard, tall sisymbrium, tall hedge mustard, tall rocket, S. altissimum), perennial rocket (S. strictissimum) and Indian hedgemustard (name also eastern rocket, S. orientale).