Centaurea solstitialis aka Golden Star Thistle

Centaurea solstitialis is known as yellow star thistle or Barnaby’s thistle. It belongs to the daisy family, Asteraceae. Kew lists its native range from Europe to central Asia and Iran. That range also includes the Arabian Peninsula. NC State includes North Africa in its account of origin. The plant now occurs across the United States and southern Canada. It grows in fields, pastures, waste ground, and along transport routes. NC State calls it a winter annual; Kew allows a biennial habit.

The plant grows fast and forms an upright, branched clump. Its thin, hairy stems reach 3 feet [0.91 metres] tall. A stout taproot grows fast during winter and early spring. It can reach deeper than 3 feet [0.91 metres]. Young plants form a rosette of leaves at ground level. These leaves may have narrow lobes and short stalks. Woolly hairs give the foliage a grey-green look. The rosette dies back as the plant starts to flower. Higher leaves are smaller, narrow, and lack lobes. Their bases run down the stems to form wavy wings.

Yellow flower heads appear in summer and autumn. Each head is less than an inch wide. Pale, sharp spines grow from the bracts around each head. These spines extend outward, giving the head a star-like outline. The flowers provide nectar for bees and butterflies. The fruit is a small, dry achene with fine hairs. Short brown bristles form a tuft at its tip. Seeds may stay in the heads into late autumn or winter. The plant relies on seeds to spread.

Full sun and soil that drains well suit this species. It does not grow in shade. It tolerates drought, poor soil, and a broad pH range. Clay, loam, sand, and rocky soils can support it. NC State lists USDA zones 5a through 9a. Its spread makes it a poor choice for garden beds. It is invasive in parts of the western and upper midwestern United States. Small patches can be pulled before stems begin to lengthen.

PFAF records vegetable use, though the cited account leaves the part unclear. It also lists old medicinal uses of powdered roots and seeds. These reports do not establish safe or effective treatment. Horses can suffer severe poisoning after prolonged feeding on this plant. Affected horses lose the ability to feed or swallow. Dehydration and lack of food can lead to death. ASPCA lists it as non-toxic to dogs and cats.