Noccaea caerulescens -group
- Name also: Alpine Pennygrass, Alpine Penny-cress
- Latin synonym: Thlaspi alpestre, Thlaspi caerulescens
- Family: Mustard Family – Brassicaceae (Cruciferae)
- Growing form: Biennial or perennial herb.
- Height: 15–40 cm (6–16 in.). Stem usually unbranched, cylindrical, commonly 2–3-leaved (sometimes many-leaved).
- Flower: Corolla regular (actinomorphic), white–pink (light purple when young), approx. 0.5 cm (0.2 in.) wide; petals four, 1–4 mm (0.04–0.16 in.) long. Sepals 4, commonly reddish. Stamens 6, of which 4 long and 2 short, anthers commonly dark violet (sometimes pale). Gynoecium fused, a single carpel. Inflorescence a dense raceme, extending in fruiting stage.
- Leaves: In basal rosette and alternate on stem, rosette leaves stalked, stem leaves stalkless, amplexicaul. Blade (narrowly) elliptic–obovate, with almost entire margins, glabrous, bluish green.
- Fruit: Many-seeded, narrowly obovate, winged, notched at apex, 6–8 mm long silicula(0.24–0.32 in.). Bristle tip usually extends as far as wing (sometimes clearly shorter). Stalk approx. 4 mm (0.16 in.).
- Habitat: Banks, gardens, yards, lawns, pastures, field margins, quite dry hillside meadows, forest margins.
- Flowering time: (April–)May(–June).
Alpine pennycress is native to the mountains of central and southern Europe. It arrived in Finland at the end of the 19th century, partly with sea traffic which brought it to harbours but mainly with uncleaned German hay and clover seed, which took it to hay fields. Unlike many other species that arrived with hay seed, alpine pennycress spread easily to nearby meadows, hedgerows and banks to establish a firm foothold among wild plants. In the first decade of the 20th century the species became rapidly more common, initially in Uusimaa and parts of southern Häme in particular. Nowadays alpine pennycress is common in many kinds of dry meadows, banks and lawns in the southernmost third of Finland, and it grows rarely as far north as Oulu. At least in abundant stands it is very eye-catching when it is in full bloom in May.
Finland is home to two subspecies of alpine pennycress, of which the type species (ssp. caerulescens) is clearly more common. It is low-growing and has sparsely-leaved stems to the point that it is often leafless, and it has a long inflorescence which extends to more than half the length of the stem in its fruiting stage. Ssp. brachypetalum on the other hand is clearly rarer (it is not yet completely established), flowers slightly later is larger and many-leaved. It has a relatively shorter inflorescence which remains less than half the length of the stem even during the fruiting stage. Alpine pennycress’s more common and more widely spread relative field pennycress (T. arvense) lacks a basal rosette, has a bristly stem and roundish fruits. The plants can only occasionally be compared side-by-side: alpine pennycress has usually already withered when field pennycress is just beginning to flower.