Overview
A member of the sunflower family (Asteraceae or Compositae), whorled sunflower is a perennial plant arising from horizontal, tuberous-thickened roots with slender rhizomes. The stems are slender, erect, and can be over 2 m (6 ft.) tall. The leaves are opposite on the lower stem; verticillate (whorled) in groups of 3 or 4(6) at the mid-stem; and alternate or opposite along the inflorescence at the end. Individual leaves have a firm texture and prominent mid-vein, but lack the prominent lateral veins found in many members of this genus. The leaves are linear-lanceolate in shape, narrowing at the tip to a point, and 7.5-18.5 cm (3-7.2 in.) long and 0.7-2 cm (0.3-0.8 in.) wide. Flowers are arranged in a branched inflorescence typically consisting of 3-7 heads. Flower heads are about 1 cm high (0.4 in.), 1.5 cm (0.6 in.) wide, and have deep yellow ray flowers and lighter yellow disk flowers. Seeds are 0.4-0.5 cm (0.16-0.2 in.) long.