- Name also: Hoary Alyssum, Hoary-alyssum, Hoary False Madwort, Hoary False Alyssum
- Family: Mustard Family – Brassicaceae (Cruciferae)
- Growing form: Biennial or sometimes perennial herb.
- Height: 20–50 cm (8–20 in.). Stem branching, base woody, hairy.
- Flower: Corolla regular (actinomorphic), white, approx. 1 cm wide; petals four, 5–6 mm (0.2–0.24 in.) long, deeply 2-lobed. Sepals 4. Stamens 6, of which 2 short and 4 long. Gynoecium fused, a single carpel. Inflorescence a raceme, extending in fruiting stage.
- Leaves: In basal rosette and alternate on stem, lowest long-stalked, upper stalkless. Blade lanceolate, with almost entire margins, both sides stellate-haired.
- Fruit: Many-seeded, narrowly elliptic, oval, stellate-haired, 6–8 mm (0.24–0.32 in.) long, ascending oblique silicula, tipped with 2–3 mm (0.08–0.12 in.) long bristle. Stalk ascending oblique, hairy, approx. 5 mm (0.2 in.) long.
- Habitat: Beside roads and rail-tracks, railway yards, embankments, around old barracks, meadows, sandy areas, waste ground, industrial and loading areas, rubbish tips, harbours.
- Flowering time: July–September(–October).
Hoary alison’s scientific name comes from the stellate hairs that cover the plant and give it its colour (incanus means grey), but despite its rather drab colour it is sometimes grown in Finland as an ornamental. The plant has adapted to grow this covering of hair to help it survive in very dry climates: the hairs retain raindrops and dewdrops well and reduce evaporation. Hoary allargen’s quite wide, grey stands are apt to catch people’s eyes, even if they are not into flowers: it blooms for a relatively long time into the summer and the seeds do not fall until winter.
Hoary alison’s original habitat is southern Russia’s dry, continental steppe, and the plant spread from there to Finland while it was under Russian control in the 19th century. Finland was a grand duchy which did not have its own army but rather garrisons that were manned by Russian soldiers. Feed and cereal would be sent to them periodically across long distances, thus carrying many seeds to completely new habitats. At the height of this practice dozens of alien species from Russia could be found around garrisons. Most of these have disappeared over the decades and centuries but a handful have established themselves in their new country. Hoary allergen is still characteristic of old garrison towns such as Hamina, Lappeenranta, Hämeenlinna, Turku and Tampere. The plant has managed to spread from garrisons and surrounding grassy areas from the time of Russian control to nearby dry wasteland, banks, sandy areas and dry meadows, and it has even reached the archipelago by travelling with ice or birds. As a steppe plant hoary allergen is well equipped to withstand drought and it can survive rough treatment and even lawnmowers. Its northernmost permanent stand is probably in Oulu region.