About Arnica discoidea Benth.
Arnica discoidea Benth. is a North American species of arnica in the sunflower family. It gets the common name rayless arnica because its flower heads only contain disc florets, with none of the larger, more visible ray florets. This plant is native to woodlands, forests, and chaparral habitat in the western United States, occurring in Washington, Oregon, California, and western Nevada’s Washoe County. It is a rhizomatous perennial herb that grows a hairy, glandular stem between 20 and 60 centimeters tall. The lower half of the stem holds several pairs of toothed oval to spade-shaped leaves borne on long petioles. The inflorescence holds anywhere from a few to many flower heads, all covered in glandular hairs. While each flower head only contains disc florets, some of the florets around the edge of the head may be expanded and look like ray florets, which makes identifying this plant by its flower traits quite difficult. The plant produces a fruit that is an achene, approximately 7 millimeters long, not including its light-colored pappus.
