Burke: Ambrosia chamissonis vs. Ambrosia psilostachya

	Ambrosia chamissonis	Ambrosia psilostachya
	silver beachweed, beach bur, cutleaf beach bur, silver bur-ragweed	perennial ragweed, western ragweed
Habit	Monoecious, succulent perennial 2-10 dm. tall, forming large, lax clumps, the stems much branched below the surface, the herbage silvery with appressed hairs.	Monoecious perennial from creeping rhizomes, 1-10 dm. tall.
Leaves	Leaves mostly alternate, petiolate, the toothed to pinnately dissected blade 2-7 cm. long and 8-40 mm. wide.	Leaves opposite below and alternate above, usually pinnatifid, lance-ovate or elliptic in outline, 3-10 cm. long, sub-sessile.
Flowers	Staminate heads sub-sessile, forming congested, leafless, terminal spikes; pistillate heads borne below, in the axils of bracts; fruiting involucre a bur, 6-11 mm. long, with 2-4 series of flattened prickles.	Staminate heads small, numerous, short-pedunculate, in an open inflorescence of several spike-like flowering shoots arising from the upper leaf axils; pistillate heads borne below, in the leaf axils; fruiting involucre a short-beaked bur, 3-5 mm. long, with a few rounded projections.
Fruits	Achene	Achene

	Ambrosia chamissonis	Ambrosia psilostachya
Flowering time	June-September	July-October
Habitat	Common on sandy beaches above high tide level.	Roadsides, fields, wastelots, and other disturbed open areas.
Distribution	Occurring west of the Cascades crest along the marine coastline beaches in Washington; British Columbia, south along the coast, to California. [WildflowerSearch map] [BONAP county map]	Occurring east of the Cascades crest in Washington; British Columbia to California, east across North America to the Atlantic Coast. [WildflowerSearch map] [BONAP county map]
Origin	Native	Native
Conservation status	Not of concern	Not of concern
Sibling taxa	A. acanthicarpa, A. artemisiifolia, A. psilostachya, A. trifida	A. acanthicarpa, A. artemisiifolia, A. chamissonis, A. trifida
Web links	Local floras: BC, CA, OR, WA Local Web sites: CalFlora, CalPhotos, Flora NW, PNW Herbaria, Turner Photog. WildflowerSearch iNaturalist (observations) USDA Plants Database LBJ Wildflower Center SEINet Plants of the World Online Encyclopedia of Life Wikipedia Google Image Search	Local floras: BC, CA, OR, WA Local Web sites: CalFlora, CalPhotos, Flora NW, PNW Herbaria WildflowerSearch iNaturalist (observations) USDA Plants Database LBJ Wildflower Center SEINet Plants of the World Online Encyclopedia of Life Wikipedia Google Image Search

Ambrosia psilostachya

silver beachweed, beach bur, cutleaf beach bur, silver bur-ragweed

perennial ragweed, western ragweed

Habit

Monoecious, succulent perennial 2-10 dm. tall, forming large, lax clumps, the stems much branched below the surface, the herbage silvery with appressed hairs.

Monoecious perennial from creeping rhizomes, 1-10 dm. tall.

Leaves

Leaves mostly alternate, petiolate, the toothed to pinnately dissected blade 2-7 cm. long and 8-40 mm. wide.

Leaves opposite below and alternate above, usually pinnatifid, lance-ovate or elliptic in outline, 3-10 cm. long, sub-sessile.

Flowers

Staminate heads sub-sessile, forming congested, leafless, terminal spikes; pistillate heads borne below, in the axils of bracts; fruiting involucre a bur, 6-11 mm. long, with 2-4 series of flattened prickles.

Staminate heads small, numerous, short-pedunculate, in an open inflorescence of several spike-like flowering shoots arising from the upper leaf axils; pistillate heads borne below, in the leaf axils; fruiting involucre a short-beaked bur, 3-5 mm. long, with a few rounded projections.

Fruits

Achene