Centaurea calcitrapa aka Purple Star Thistle

Centaurea calcitrapa belongs to the daisy family, Asteraceae. It is a biennial, with a two-year life cycle. Its common names include red star thistle and caltrops. Kew lists Sicily as its native range. The RHS also lists it as native to Britain and Ireland. These sources thus differ on where the plant is native. PFAF lists it across Europe, northern Africa, and western Asia. That list does not say which plants are native or introduced.

The plant grows to about 2 feet (0.6 metres) tall. PFAF records it by roads and on disturbed ground. It grows at these sites in sand, gravel, and chalk soils. The supplied species accounts give no details of leaves or stems. They give no width for the full-grown plant. The RHS uses the name red star thistle. Its broad notes on leaf and flower form cover the genus. They do not refer to this species alone.

PFAF gives the flowering season as July to September. Each flower has both male and female organs. Bees, flies, moths, and butterflies pollinate the plant. It is self-fertile, so it can breed without another plant. Seeds ripen from August to October. The evidence gives no more facts about the fruit. The records of insects that pollinate it show its value to them.

Grow it in full sun, in soil that drains well. PFAF says it cannot grow in shade. It grows in sand, loam, and clay, including poor soil. Rich soil suits it, but it grows in less fertile soil too. It accepts mildly acid, neutral, and alkaline soil, even very alkaline soil. Dry or moist soil suits it, and it can withstand drought. PFAF lists cultivated beds as a place to grow it. Sow seed in a cold frame in April. Move the seedlings to separate pots. Then plant them out in summer. Or sow straight into the ground in August or September.

PFAF lists leaves and young stems as edible, raw or cooked. It gives the plant a low rating for food use. It also notes past uses of powdered seeds and roots as treatments. These reports do not prove that such treatments work. PFAF reports no known hazards, but this does not prove safety. The supplied evidence gives no pest or disease account for this species.