American thorow wax
The northern Rocky Mountains, plus small areas of Colorado, Oregon and New Mexico
Rocky places, grassy hillsides, meadows; 4,000 to 12,000 feet
Linear or narrowly lanceolate, undivided, up to 5 inches long and less than half an inch wide
June to September
Bupleurum americanum is the only native US species of this small genus, and has a limited distribution, generally restricted to the northern Rocky Mountains, but also found in the San Juan Mountains of southwestern Colorado, and Lincoln county, New Mexico. Unusually for a plant in the apiaceae family, the leaves are simple, and undivided, growing mostly around the base. Stems and leaves are grey-green in color (glaucous), and hairless. Stems grow vertically upwards, or at an angle.
Flowers form at the tip of the stems, and also from the upper leaf nodes; a compound umbel of between 4 and 14 umbellets, with rays up to 2 inches long. Individual clusters are compact, and hemispherical, typically containing 10 to 20 tiny yellow flowers. A whorl of 2 to 6 light green, ovate, differently-sized bracts subtends each cluster, and also the base of the umbel. Flowers become reddish as they wither.