- Name also: Tall Rocket, Tall Tumblemustard, Jim Hill Mustard, Tall Mustard
- Family: Mustard Family – Brassicaceae (Cruciferae)
- Growing form: Annual herb.
- Height: 30–80 cm (12–32 in.). Stem spreading from base, branched, sparsely hairy, lower part coarsely hairy. Rigid and leafless when old.
- Flower: Corolla regular (actinomorphic), pale yellow, approx. 1 cm (0.4 in.), across; petals four, 5–8 mm (0.2–0.32 in.) long. Sepals 4. Stamens usually 6, of which 4 long and 2 short. Gynoecium fused, a single carpel. Inflorescence an elongating raceme in fruiting stage.
- Leaves: Alternate. Blade deeply pinnately lobed, with toothed margin, lower leaves broadly lobed, upper leaves narrowly lobed (lobes linear).
- Fruit: Many-seeded, opens lengthwise, 7–10 cm (2.8–4 in.) long, round, often slightly curved, rigid, spreading siliqua, terminated by a usually approx. 0.5 mm (0.02) bristle. Stalk 5–10 mm (0.2–0.4 in.) long, as thick as siliqua.
- Habitat: Wasteland, heaps of earth, roadsides, railways, harbours, factory- and loading areas, rubbish tips, sea shores.
- Flowering time: July–September.
Spherically branched plants, which roll along on the wind across deserts and prairies are only familiar to Finns from cowboy films. When the seeds are ripe they break off at the root joint and leave on the wind, shaking off seeds as they go. Certain kinds of perennial tumblers are able to set down new roots and carry on growing.
Annual tumble mustard spreads by rolling and dropping its seeds as it goes both in its native south-east European and west Asian steppes and as an established alien around the world, including the American prairies – and southern Finnish wasteland. It has plenty seeds to spread as it forms a huge amount in its long siliquae, up to a couple of million in a good-sized plant. The species have grown casually in Finland since they arrived in ballast soil in the 1850s. It managed to establish a foothold in the wild by travelling to railway yards around Helsinki in the 1910s and ‘20s, and it also arrived from Russia and North America in sacks of grain and animal feed.
Tumble mustard grows casually at least everywhere along the railway network. Its most northerly reach is beside the Kemijärvi track, and it travels even further north by road. The species is probably increasing in Finland, but the soil and the climate keep it mainly as an exotic weed around inhabited areas. The size of tumble mustards shoots and its outward appearance vary tremendously according to its habitat, from ten-centimetre (4 in.) weaklings to 2-metre (80 in.) giants. Abundantly-branched plants set off after breaking free in high winds. In Finland tumbling plants get the clearest runs across winter ice or across open ground during times of hard snow.