Symphyotrichum spathulatum (formerly Aster spathulatus) is a species of flowering plant in the family Asteraceae native to western North America including northwestern Mexico. Commonly known as western mountain aster, it is a perennial, herbaceous plant that may reach 20to tall. Its flowers, which open in July and August, have violet ray florets and yellow disk florets.
Symphyotrichum spathulatum blooms in July and August and is a colony-forming perennial that grows typically 1–5 hairless or mostly hairless stems from a long rhizome. It ranges from 20to in height and has thin, entire leaves with little to no hair that are 5to long. The leaves are linear or elliptical, narrow, and sometimes obovate at the base of the plant. The upper leaves are shorter at 3to.
The flower heads grow in corymbiform to paniculiform arrays with little branching. The involucres are 5– and bell-shaped, and their phyllaries are in 3–5 series. There are 15–40 violet ray florets that are 9– long and 1– wide. These surround the flower centers composed of 30–80 (sometimes up to 100) yellow disk florets.
The seeds are brown, hairy cypselae NaNabbr=onNaNabbr=on long with about 4 nerves and white pappi that are 5– long.
Symphyotrichum spathulatum has a base number of x = 8. Diploid, tetraploid, hexaploid, and octaploid cytotypes with respective chromosome counts of 16, 32, 48, and 64 have been reported, depending upon the infraspecies, as follows:
Symphyotrichum spathulatum is one of the species within Symphyotrichum sect. Occidentales. S. spathulatum was first formally described by John Lindley in 1834 as Aster spathulatus.
Three varieties of Symphyotrichum spathulatum are recognized, including the autonym:
S. spathulatum is one of the parents of the two allopolyploidal Symphyotrichum species S. ascendens and S. defoliatum.
Symphyotrichum spathulatum is found in the western United States, western Canada, and northwestern Mexico. It is native to British Columbia and Alberta in Canada, and in the United States from Washington state east to Montana, south to New Mexico, west to California, and north again to Oregon. There is no recorded presence in Arizona. In Mexico, it is native to the states bordering the Gulf of California. It grows at NaNm (-2,147,483,648feet) (or lower) in meadows on mountain slopes and open aspen and coniferous forests.
S. spathulatum var. intermedium is native to British Columbia, California, Idaho, Nevada, Oregon, and Washington state, only occasionally being found in California and Nevada. It grows at NaN-2NaN-2 in grasslands and meadows on mountain slopes and in open coniferous forests.
S. spathulatum var. yosemitanum is restricted from southern Oregon to the Sierra Nevada of California. It can be found at NaN-2NaN-2 in oak woodlands and coniferous forests.
, NatureServe listed Symphyotrichum spathulatum as Secure (G5) worldwide and Possibly Extirpated (SX) in Alberta. S. spathulatum var. intermedium and S. spathulatum var. spathulatum were reported as Secure Varieties (T5), and no status rank was given for S. spathulatum var. yosemitanum.