fleabanes and horseweeds (Erigeron) — identification, habitat & look-alikes

Fleabanes and horseweeds are a group of plants found in meadows, along roadsides, and on rocky mountain slopes, and are especially diverse in North America. Many fleabanes have a yellow center surrounded by numerous narrow, petal-like flowers, while horseweeds have outer flowers so short that their heads look almost petal-free.

In this group

annual fleabaneErigeron annuus

This eastern North American native grows in fields, pastures, roadsides, and other disturbed places. Its many narrow white outer flowers form loose clusters above broad lower leaves.

Philadelphia fleabaneErigeron philadelphicus

This native spring fleabane often has pink-tinged outer flowers and stem leaves that clasp the stem. Its drooping buds help separate it from annual fleabane.

horseweedErigeron canadensis

This tall native pioneer has many tiny heads with outer flowers that barely show.

Mexican fleabaneErigeron karvinskianus

This low, spreading ornamental has small heads that often age from white to pink. It escapes cultivation in mild parts of the United States.

aspen fleabaneErigeron speciosus

This showy western native grows in sunny mountain meadows and open woodland. Purple to blue outer flowers and several heads on leafy stems make it a familiar western fleabane.

Appearance

Growth form: The genus includes , , and perennials. Plants range from low alpine mats to tall, upright herbs.
Leaves: Leaves are usually alternate. Some species keep a , while others carry narrow leaves up the stem; leaf shape is an important clue at species level.
Fruit: Each tiny dry fruit usually carries a of fine bristles. Wind can move these fruits away from the parent plant.
How to recognize it: Many fleabanes have a yellow center surrounded by numerous very narrow white, pink, blue, or purple petal-like flowers. Horseweeds within the genus have tiny outer flowers and many small heads in branched clusters.

Look-alikes

American astersSymphyotrichum

Both groups can have purple or white petal-like flowers around a yellow center. Fleabanes often have many more, much narrower outer flowers, but overlap is broad and a clear photo of leaves and the small leaflike parts under the head may be needed.

Why they get mixed upBoth are members of the aster family and share the same basic daisy-like head.

Where it lives

Typical habitats: meadows and prairies
roadsides and disturbed ground
mountains and rocky slopes
Range: Erigeron occurs nearly worldwide, especially in temperate regions, and is particularly diverse in North America.
Preferred conditions: Species occupy habitats from coastal bluffs and deserts to forests, meadows, and alpine rock. Annual fleabanes and horseweeds are especially noticeable on open, disturbed soil.

Behavior

Activity: Flowering time varies widely. Native western mountain fleabanes often bloom during the short warm season, while annual fleabanes and horseweeds can flower for much longer in disturbed ground.

Life cycle

Reproduction: Annual and biennial species rely mainly on seed. Many perennial fleabanes also resprout from persistent roots or .
Seed dispersal: Annual fleabanes and horseweeds can produce abundant windblown seed, helping them colonize fields, roadsides, and bare ground.

Name and classification

About the name: Horseweed (Erigeron canadensis) was formerly called Conyza canadensis.
Group name: “Fleabane” usually refers to the daisy-like members, while “horseweed” is used for tall members whose outer flowers are barely visible.

Culture and stories

Culture and stories: The old common name ‘fleabane’ came from a belief about repelling fleas; it does not describe a reliable modern use.

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