- Name also: Whitetop
- Latin synonyme: Cardaria draba
- Family: Mustard Family – Brassicaceae (Cruciferae)
- Growing form: Perennial herb. Rhizomatous. Forms stands.
- Height: 30–50 cm (12–20 in.). Stem branched at top, slightly bristly, short-haired at base, upper part often glabrous.
- Flower: Corolla regular (actinomorphic), white, approx. 0.5 cm (0.2 in.) across; petals 4, approx. 3–4 mm (0.12–0.16 in.) long. Sepals 4. Stamens 6. Gynoecium fused, a single carpel. Inflorescence branched, dense, an elongating raceme in fruiting stage. Flowers fragrant.
- Leaves: Alternate, stem leaves stalked, obovate, falling early, upper leaves stalkless, ovate–oblong, sharp-toothed, greyish green.
- Fruit: Broadly cordate, oval, wingless, sharp-pointed, 3–5 mm (0.12–0.2 in.) long silicula. Stalk spreading, longer than silicula.
- Habitat: Roadsides, railways, harbours, river banks, wasteland, rubbish tips, mills.
- Flowering time: May–July.
It is possible for the careful naturalist to find exotic plants in everyday surroundings. Hoary cress is indigenous to Mediterranean countries and the Middle East, but has spread over the years to cultivated land as a weed. It has taken over large swathes of land in Eurasia and successfully established itself as a special plant in southernmost Finland. A long time ago it could be seen growing on ballast soil deposits around harbours. The species has perhaps survived in some places since the era of sailing ships, but mostly it has probably arrived later and by other means, e.g. in grain sacks. Mill areas are traditional treasure troves for plants which have arrived from abroad. Hoary cress has established itself only casually beside railways. In this case it has probably arrived during the Second World War and spread through the transport of grain and food for military battalions.
Hoary cress’s genus’s older scientific name comes from the Greek word kardia, meaning ’heart’, which refers to an excellent identity marker for the plant: its heart-shaped fruit. The species’ Finnish and official names also refers to genus Draba, which belongs to the Mustard family. The plants are not particularly close relatives and they don’t even look so similar, but the old name has simply been adjusted later on to refer to the entire genus. These flowers are often incomplete: the petals are rudimentary or completely lacking. Hoary cress on the other hand has large flowers with a distinct fragrance of honey, which attracts insects well. The plant reproduces efficiently from root buds and forms beautiful stands that cover several square metres.