Images: ©Jouko Lehmuskallio
Tower Mustard
Arabis glabra
- Family: Mustard Family – Brassicaceae (Cruciferae)
- Growing form: Biennial herb.
- Height: 50–120 cm (20–47 in.).
- Flower: Regular (actinomorphic). Petals four. Cream coloured to pale yellow, slender, 4–6 mm (0.2–0.25 in.) long. Sepals four, with rounded tip, slender, ca. 3 mm long, and often tinged with red. Pistil formed from two fused carpels. Stamens six.
- Leaves: Alternate. Basal leaves hairy and shallowly lobed. Stem leaves stalkless, with sagittate base, erect, taper-pointed, bluish-green, hairless, and with entire margins.
- Fruit: A 4–7 cm (1.6–2.8 in.) long pod divided in two by a membranous wall (a siliqua). Erect, parallel to stem. Apical beak ca. 1 mm long. Fruit-stalk erect, ca. 1 cm (0.4 in.) long. Seed oval, flat, with black margins, and narrowly and imperfectly winged.
- Habitat: Dry meadows, rock outcrops, roadsides, and other dryish places near habitation.
- Flowering time: June–July.
The tower mustard is a biennial which usually occurs in association with human influence. It has spread to disturbed sites from its natural habitats, such as sunny, weathered rock outcrops. The bluish-green shoots are usually found in small groups extending above the surrounding lower plants. The tower mustard avoids shady sites with thick vegetation.
The hairy rockcress (Arabis hirsuta) can be distinguished from the tower mustard by its hairiness and saw-like leaf margins.
