Sisymbrium austriacum aka Austrian Rocket

Sisymbrium austriacum, commonly called Austrian rocket or jeweled rocket, is a herbaceous flowering plant in the mustard family (Brassicaceae). It was first described by Nikolaus Joseph von Jacquin in 1775 in his Flora Austriaca, and is native to a broad swathe of southern, western, and central Europe — from Spain east to Moravia and Vienna and north into Thuringia, with additional South-European to South-Siberian outliers. Different European floras treat it as variously annual, biennial, or short-lived perennial: the German-language treatment notes it can be "ein-, zweijährige bis ausdauernde", while the Italian Acta Plantarum tradition records it as a perennial scapose hemicryptophyte (H scap), reflecting genuine variability across subspecies and habitats.

The plant typically grows 15–60 cm tall, occasionally reaching 80–90 cm, with branched, mostly hairless stems. Lower leaves are stalked and deeply pinnately lobed almost to the midrib, with broadly triangular segments. Inflorescences are terminal raceme-like clusters of small four-petalled flowers in characteristic Brassicaceae cross form. Petals are golden-yellow and 6–8 mm long, the sepals 3–3.5 mm and the anthers 1.2–1.6 mm. The species blooms from May to June in most of its range, and into early autumn for naturalised lowland populations along rivers such as the Maas. Slender erect siliques (fruits) 2–4(–6) cm long and only about 0.5–1 mm thick develop on short pedicels and tend to curve back toward the stem.

Several subspecies are recognised, most prominently subsp. erysimifolium, subsp. villarsii, and subsp. chrysanthum. Subsp. chrysanthum, known in Dutch as Maasraket, was introduced into Belgium in 1858 via the wool-processing industries along the Vesder and into the Netherlands by 1913, and has subsequently naturalised on calcareous riverbank rubble along the Meuse. The species has also been recorded as introduced in Argentina, Chile, the Russian Far East (Primorye), Ukraine, and parts of North America, though it is not generally regarded as a major invasive.

Ecologically, S. austriacum favours warm, sunny, calcareous and stony habitats: rocky debris slopes, walls, rock crevices, gravel banks, marl and clay pits. It tolerates a substantial elevational range, occurring from the lowlands up to about 2,500 m in the Alps. Soils are typically neutral to basic and only moderately nutrient-rich. In Switzerland the species is uncommon and largely restricted to Valais and Grisons; the national assessment classes it as Near Threatened (NT) on regional Red List criteria B2ab(iii), although it has not been formally evaluated on the global IUCN Red List. Pollination is primarily by insects, with self-pollination also recorded; seed is dispersed by gravity and wind. The shoots contain glucosinolates (mustard oils) characteristic of Brassicaceae, and the German botanical literature additionally notes the presence of cardiac glycosides, which together render the plant toxic to people and animals.