Matricaria occidentalis
Valley mayweed
(c) Steve Matson, some rights reserved (CC BY), uploaded by Steve Matson · licence
Family: Asteraceae · Type: Herb · Native
Matricaria occidentalis (Valley mayweed) is a native California herb in the Asteraceae family, recognized by habitat preference and non-shattering heads.
Valley mayweed is a California native annual herb found in northern coastal and inner coastal ranges, Central Valley, San Francisco Bay Area, southern coastal California, Channel Islands, and western Mojave Desert in alkali flats, vernal pools, and salt marsh edges at elevations below 2,400 meters. Flowering from March to August, this plant produces white disk flowers in compact, nearly spherical heads up to 1.5 centimeters in diameter. Growing 15 to 45 centimeters tall with often branched stems toward the top, it forms a delicate, open structure. Its leaves are sessile, glabrous, and can reach up to 7 centimeters long, with a fine, feathery appearance. The fruit is distinctive, with angled surfaces and wide brown glands extending halfway down its length, topped with a two-lobed tip.
Identification and appearance
Key characters: 1 sympatric species; distinguished by habitat preference and non-shattering heads
Habitat and range
Habitat: Common. Undisturbed alkali flats, vernal pools, edges of salt marshes
Elevation: < 2400 m
Outside California: Oregon
Bloom period
Matricaria occidentalis blooms Mar-Aug.
How to tell it apart
vs Oncosiphon: Matricaria smells sweet and has egg-shaped heads; Oncosiphon smells intensely foul and has spherical heads.; vs Anthemis: Matricaria has egg-shaped heads that become hollow inside; Anthemis has rounded heads with solid, chaffy receptacles.; vs Chamaemelum: Matricaria has egg-shaped mature heads; Chamaemelum has conical or dome-shaped receptacles at maturity.; vs Cotula: Matricaria has sweet scent and egg-shaped heads; Cotula lacks strong scent and has flattened button-like heads.; vs Glebionis: Matricaria often lacks ray petals and has egg-shaped heads; Glebionis has showy yellow or white rays.
Frequently asked questions
Is Matricaria occidentalis native to California?
Yes. Matricaria occidentalis is native to California (recorded as native).
When does Matricaria occidentalis bloom?
Matricaria occidentalis blooms Mar-Aug.
What plant family does Matricaria occidentalis belong to?
Matricaria occidentalis is in the Asteraceae family, genus Matricaria.
What habitat does Matricaria occidentalis grow in?
Matricaria occidentalis grows in Common. Undisturbed alkali flats, vernal pools, edges of salt marshes.
Related species
Other California species in the same genus, family, or bioregion.
Sources: Jepson eFlora · Index of California Plant Names · CalPhotos
Last updated 2026-10-07
Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, Cal-IPC, and more.