Soldier thistle is an erect annual herb growing to 1 m high. Yellow-green in appearance due to numerous yellow spines on the leaves. Stems of soldier thistle are ranched with spiny wings and dense white hairs. They are woolly in appearance. Soldier thistle leaves are covered with fine white hairs and yellow spines, 1-1.5 cm long. White hairs on the leaves give them a woolly appearance. Rosette leaves grow to 30 cm long while stem leaves alternate and are long and narrow, about 1-1.5 cm in length. Soldier thistle has pink or purple flower heads, growing 2-4 cm long and can be solitary or in groups at the end of branches. Flowers are formed in late spring from September to November with the plant flowering in early summer. The seeds of soldier thistle are smooth and shiny with a detachable parachute of bristles on one end about 4-6 mm long. Seed germinates mainly in autumn, but has been seen to germinate after sufficient summer rainfall in disturbed areas.