They are perennial herbaceous plants, ranging in height from dwarf alpine species 5–10 cm tall, to tall thistle-like plants up to 3 m tall. The leaves are produced in a dense basal rosette, and then spirally up the flowering stem. The flowers form in a dense head of small capitula, often surrounded by dense white to purple woolly hairs; the individual florets are also white to purple. The wool is densest in the high altitude species, and aids in the thermoregulation of the flowers, minimising frost damage at night and also preventing ultraviolet light damage from the intense high-altitude sunlight.