Ambrosia chamissonis is a large, sprawling perennial herb exceeding 3 metres (9.8 ft) in maximum width. The stems are roughly or softly hairy and longitudinally ridged. The plentiful leaves are a few centimeters long, woolly and silver-green, and variable in shape.
The plant is monoecious, with male and female flowers on each individual. Staminate (male) flower heads containing many pale colored florets occur at the tip of the inflorescence, with pistillate (female) flower heads clustered below them. Each pistillate head contains a single tiny flower which develops into a fruit. The fruit is a brown bur up to a centimeter wide covered in sharp spines.
- The Plant List Ambrosia chamissonis (Less.) Greene
- Calflora taxon report, University of California, Ambrosia chamissonis (Less.) E. Greene Silver Beachweed, beach bur
- Flora of North America Vol. 21 Page 16 Ambrosia chamissonis (Lessing) Greene, Man. Bot. San Francisco. 188. 1894.
- Biota of North America Program 2014 county distribution map
- Jepson Manual Treatment — Ambrosia chamissonis
- Ambrosia chamissonis in the CalPhotos Photo Database, University of California, Berkeley
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