Ambrosia chamissonis - Silver Burweed



General Herb.[E-flora] Sprawling clumps [WildPNW] "whole plant silky or the stems woolly" [HNW] Somewhat succulent. 20-100 cm tall. [PCBC2004]
Lifecycle Perennial[IFBC-E-flora]
Flowers Rayless and greenish.[WildPNW] Male (sterile) heads nearly unstalked or short-stalked. Female (fruiting) heads egg-shaped, 1-flowered.[IFBC-E-flora] involucral bracts that have several rows of prickles. [PCBC 2004]

Fruits "Achenes enclosed within the involucral bracts; pappus lacking."[IFBC-E-flora] "...the whole forming 6-11 mm long burs with 2-4 series of somewhat flattened prickles".[PCBC 2004]
Leaves Finely whitish- or silvery-haired. [IFBC-E-flora] 2-7 cm long. [PCBC 2004] Mostly alternate.[PWOBC] "Coarsely toothed or the lower dissected, or the leaves once or twice dissected in var. bipinnatisecta" [HNW]
Stem "Decumbent stems much branched".[WildPNW] Forming mats.[PWOBC] More or less prostrate. [HNW] "Stems leafy, spreading-hairy, stout, branched just below the surface."[IFBC-E-flora]
Root Long, creeping rhizomes.[IFBC-E-flora]
Habitat "Moist to mesic coastal sandy or gravelly upper beaches and shorelines in the lowland zone". [IFBC-E-flora] Coastal beaches.[HNW] "limited to backshores of sandy beaches, sandy edges of salt marshes, and other maritime situations."[PWOBC]
Range "Common in coastal BC; S to CA." [IFBC-E-flora]
Status Native [E-flora]
Similar Species "Ambrosia chamissonis var. chamissonis is more common in Calif. and Oreg. than farther N. Where it and var. bipinnatisecta occur together, they intergrade freely and some specimens are intermediate." [PWOBC]



Medicinal Uses




Family: Asteraceae (Compositae)
Habit: Annual to small tree; monoecious. Leaf: simple, opposite or alternate, generally petioled, entire to 1--4-pinnately lobed or divided, distal-most often reduced, bract-like. Inflorescence: staminate heads and pistillate heads together in distal leaf axils or in terminal, spike-like clusters, or staminate heads in spike- or raceme-like clusters distal to pistillate heads; staminate involucre +- cup-shaped, phyllaries in 1 series, +- fused, receptacle flat or rounded, paleate; pistillate phyllaries 0 or few, in 1 series, free, +- thin, receptacle paleate, palea bases fused, becoming a hard bur with each pistillate flower in a separate chamber, tips (occasionally not evident in flower heads) becoming hard knobs, spines, or scarious wings. Staminate Flower: 3--many; corolla translucent to yellow or red-purple; filaments fused, anthers free; style unbranched, ovary vestigial, pappus 0. Pistillate Flower: 1--5; corolla 0; style branches elongated. Fruit: inside bur with beak(s) surrounding style(s); pappus 0.
Species In Genus: 45--50 species: native to America, especially southwestern United States, northern Mexico.
Etymology: (Greek: early name for aromatic plants; mythic food of the gods) Note: Wind-blown pollen often allergenic.
Unabridged Note: Spines of bur derived from paleas, not phyllaries. [Jepson]


1. Involucres with 2-4 series of short, sharp spines; leaves mostly alternate................Ambrosia chamissonis
1. Involucres with a single series of short spines or tubercles above the middle; leaves, or at least the lower ones, opposite.

2. Plants annual from fibrous roots; leaves mostly stalked, mostly twice pinnatifid; involucres with short spines..................Ambrosia artemisiifolia
2. Plants perennial from creeping roots; leaves short-stalked or nearly unstalked, only once-pinnatifid; involucres with tubercles...................... A. psilostachys
Dry roadsides and waste areas in the lowland and montane zones; rare in S BC east of the Coast-Cascades Mountains; introduced from SW U.S. -- 2 records near Vancouver, on the mainland.[IFBC-E-flora]

Local Species

  • Synonyms:
    • Ambrosia artemisiifolia var. elatior [E-flora]2
  • Status: Exotic [E-flora]2
  • General: "Annual from fibrous roots; stems slender, stiff-hairy, branched, at least above, 10-100 cm tall." [IFBC-E-flora]2
  • Leaves: "Alternate above, opposite below, triangular to rounded in outline, 3-10 cm long with narrowly margined stalks 1-5 cm long, the blades once to twice pinnately cut with toothed or incised divisions, stiff-hairy, uppermost leaves becoming linear and entire." [IFBC-E-flora]2
  • Flowers: "Male (sterile) heads numerous in terminal, often panicled racemes about 2-3 mm in diameter; female (fruiting) heads clustered in upper leaf axils or at the base of male racemes; fruiting involucre short-beaked, 3-5 mm, long-hairy and glandular, bearing 1-7, abruptly sharp-pointed, short, conic spines at the apex." [IFBC-E-flora]2
  • Fruits: "Achenes egg-shaped, 3-3.8 mm long, hairy, glandular, with short, conic tubercles around apex of body; pappus lacking." [IFBC-E-flora]2
  • Habitat/Range: "Dry roadsides and waste areas in the steppe and montane zones; rare in S BC; introduced from SW U.S." [IFBC-E-flora]2

Generic Uses



Page last modified on Friday, January 11, 2019 8:24 PM