Laennecia coulteri
Coulter's horseweed
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Family: Asteraceae · Type: Herb · Native
Laennecia coulteri (Coulter's horseweed) is a native California herb in the Asteraceae family, recognized by Recently segregated genus - split from Conyza based on molecular and morphological differences.
Coulter's horseweed is a California native annual found in southern Sierra Nevada foothills, San Joaquin Valley, coastal western California, southwestern California, and southeastern desert regions in disturbed sites, clayey or sandy soils, often seasonally wet areas at elevations below 3,025 meters. Flowering from May to November, this plant produces small white to pale tan flowers in raceme- or panicle-like clusters with heads 2.5 to 3 millimeters long. Growing 10 to 50 centimeters tall with 1 to several stems branching from the base, becoming much-branched toward the upper portion. Its lower leaves are widely spoon-shaped to oblong, 2 to 7 centimeters long with obscure lobes or coarse teeth, while upper leaves become narrower and more finely toothed. The fruit is small, pale tan, with a delicate white pappus approximately 3.5 to 4 millimeters long.
Identification and appearance
Key characters: Recently segregated genus - split from Conyza based on molecular and morphological differences
Habitat and range
Habitat: Disturbed sites, clayey or sandy soils, often seasonally wet, alkaline
Elevation: < 3025 m
Outside California: to Colorado, Texas, Mexico
Bloom period
Laennecia coulteri blooms May-Nov.
How to tell it apart
vs Erigeron: Laennecia has narrow cylindrical heads and clasping leaves; Erigeron has flat button heads and non-clasping leaves.; vs Heterotheca: Laennecia has narrow cylindrical heads; Heterotheca has flat open daisy heads.; vs Isocoma: Laennecia has stem-clasping toothed leaves; Isocoma has non-clasping entire leaves.; vs Baccharis: Laennecia has cylindrical heads with visible rays; Baccharis has whitish rayless heads on separate-sex plants.; vs Pseudognaphalium: Laennecia has open cylindrical heads with rays; Pseudognaphalium has woolly clustered heads without rays.
Frequently asked questions
Is Laennecia coulteri native to California?
Yes. Laennecia coulteri is native to California (recorded as native).
When does Laennecia coulteri bloom?
Laennecia coulteri blooms May-Nov.
What plant family does Laennecia coulteri belong to?
Laennecia coulteri is in the Asteraceae family, genus Laennecia.
What habitat does Laennecia coulteri grow in?
Laennecia coulteri grows in Disturbed sites, clayey or sandy soils, often seasonally wet, alkaline.
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.