SPECIES BIOLOGY AND POPULATION TRENDS

TAXONOMIC UNIQUENESS: One of 17 species in the genus Machaeranthera. DESCRIPTION: Margins of the basal leaves usually exhibit a few spinulose teeth. Ligule color ranges from white to purple. Plants have more than 15 ray flowers in each head. Has a somewhat subsquarrose to gradate involucre. AIDS TO IDENTIFICATION: Machaeranthera riparia is similar to M. gypsitherma (found in New Mexico), except it lacks basal rosettes of leaves and it has more than 15 ray flowers in each head; M. gypsitherma has 8-12 ray flowers per head (Sivinski, 1999). ILLUSTRATIONS