Erigeron decumbens is a species of flowering plant in the aster family

Asteraceae

The Asteraceae or Compositae , is an exceedingly large and widespread family of vascular plants. The group has more than 22,750 currently accepted species, spread across 1620 genera and 12 subfamilies...

 known by the common name Willamette fleabane. It is native to Oregon

Oregon

Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...

 and California

California

California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

 in the United States.

The taxonomy

Taxonomy

Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...

 of the plant varies by author. It may be treated as a species with two varieties, the Californian variety var. robustior and the rare and endangered

Endangered species

An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...

 Oregon variety, var. decumbens. Alternately, the rare var. decumbens may be the only variety included within the species description and so named Erigeron decumbens, with var. robusta separated and named Erigeron robusta.

The Oregon plant, var. decumbens or alternately Erigeron decumbens, is a federally listed endangered species of the United States. There are 28 occurrences growing in increasingly rare prairie

Prairie

Prairies are considered part of the temperate grasslands, savannas, and shrublands biome by ecologists, based on similar temperate climates, moderate rainfall, and grasses, herbs, and shrubs, rather than trees, as the dominant vegetation type...

 habitat in the Willamette Valley

Willamette Valley

The Willamette Valley is the most populated region in the state of Oregon of the United States. Located in the state's northwest, the region is surrounded by tall mountain ranges to the east, west and south and the valley's floor is broad, flat and fertile because of Ice Age conditions...

.

The plant is a perennial herb growing up to about half a meter long, and erect or decumbent in form. The Oregon plant is colonial

Colony (biology)

In biology, a colony reference to several individual organisms of the same species living closely together, usually for mutual benefit, such as stronger defense or the ability to attack bigger prey. Some insects live only in colonies...

 with a branching caudex

Caudex

A caudex is a form of stem morphology appearing as a thickened, short, perennial stem that is either underground or near ground level . It may be swollen for the purpose of water storage, especially in xerophytes...

 sending up several stems. The inflorescence

Inflorescence

An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Strictly, it is the part of the shoot of seed plants where flowers are formed and which is accordingly modified...

 may contain many flower heads

Head (botany)

The capitulum is considered the most derived form of inflorescence. Flower heads found outside Asteraceae show lesser degrees of specialization....

with white or blue-tinged ray florets that may dry pinkish. The California plant is not colonial and the caudex branches little or not at all. The inflorescence contains no more than 3 heads. The florets are white or pink-tinged.