Description

This plant is a biennial or short-lived perennial. During the 1st year, a rosette of basal leaves is produced. The basal leaves are up to 4' long and 3' across; they are deeply pinnatifid or bipinnatifid with narrow linear lobes (up to 2' long and less than 1/8' across). They have long petioles. During the 2nd and later years (if any), this plant bolts to become 1½-3½' tall, while the rosette of basal leaves withers away. The central stem and ascending lateral stems are light green to dark red, terete, and longitudinally veined. Usually the young tips of stems are tomentose (with short white cobwebby pubescence), otherwise they are mostly glabrous. The cauline leaves alternate along these stems; they are more common along the lower central and lower lateral stems. The lower cauline leaves resemble the basal leaves, except they have short petioles. Middle cauline leaves are smaller in size and less divided into linear lobes, while the upper cauline leaves are short (less than 1' long) and linear in shape. The upper surfaces of the narrow leaf lobes are whitish green, flat, and tomentose, becoming more glabrous with age. The lower surfaces of the leaf lobes are light to medium green, rounded (convex), and glabrous. The foliage is not strongly aromatic. The upper stems terminate in narrow panicles of flowerheads about 4-16' long. Upper cauline leaves occur along these flowering stalks. Individual flowerheads are whitish green or yellowish green and about 1/8' (3 mm.) long and similarly across. Each flowerhead has 8-30 inner florets that are perfect and 5-20 outer florets that are pistillate. Each inner floret consists of a narrow tubular corolla with 5 teeth along its upper rim, some fertile stamens, and an abortive ovary that is sterile. Each outer floret consists of a narrow tubular corolla with 2-3 teeth along its upper rim and a fertile ovary with a divided style. At maturity, the flowerheads droop downward from short pedicels. The base of each flowerhead is surrounded by appressed bracts (phyllaries); individual bracts are lanceolate to ovate and up to 2 mm. long. The blooming period occurs from mid-summer to early autumn for about 2-3 weeks. The florets are cross-pollinated primarily by the wind. The outer florets of the flowerheads are replaced by bullet-shaped achenes about 0.8-1.0 mm. in length; the achenes are without tufts of hair or a crown of scales. They are usually distributed only a short distance from the mother plant by the wind. The root system consists of a woody taproot or caudex with lateral roots. This plant reproduces by reseeding itself.