Late summer is a time of shortening days, thunderstorms, and cooling temperatures, especially at night. Frequently in the mornings, new snow can be seen on the higher peaks. It is also a time for late season flowers to show their colors across the park. While spring wildflowers can be induced to bloom by lengthening days or by warming temperatures, most late summer and early fall wildflowers are induced by shortening day length.
Many, though not all, of the flowers blooming in the montane and subalpine parts of the park (7,624 to about 11,500 feet) are composites or members of the aster family (Asteraceae) . These include tasselflower (Brickellia grandiflora), golden or rubber rabbitbrush (Chrysothamnnus nauseosus), Parry rabbitbrush (Chrysothamnnus parryi), Yellow rabbitbrush (Chrysothamnnus viscidiflorus), bush sunflower(Helianthus pumilis), Porter aster (Aster porteri), ragleaf bahia (Bahia dissecta), rough white aster (Aster falcatus), gayfeather (Liatris ligulistylis), and Patterson tansy aster (Machaenthera pattersonii). A few composites, such as rabbitbrush, induce hay fever symptoms for some. One of the rabbitbrushes common in the park, rubber rabbitbrush (Chrysothamnus nauseosus), was investigated during World War II as a source of rubber, and the latex was thought to be used by Native Americans for chewing gum. The species name, nauseosus, suggests it may not be up to our current standards for tasty chewing gum. Rabbitbrush is also valuable as a winter forage food for mule deer, elk, and bighorn sheep.
Other late season bloomers include kings crown (Rhodiola integrifolia), horsemint (Monarda fistulosa var. menthifolia), star pyrola (Moneses uniflora), giant angelica (Angelica ampla), and pine drops (Pterospora andromedea). Among the gentians, the fringed gentian (Gentianopsis thermalis) and the star gentian (Swertia perennis)are blooming in the montane and subalpine, while the arctic gentian (Gentianodes algida) is blooming on the tundra.