Silver Bur Ragweed

Perennials, 50–150(–350+) cm. Stems prostrate or decumbent. Leaves mostly alternate; petioles 15–30(–45+) mm; blades rounded-deltate to ovate or obovate, 20–45(–70+) × 10–25(–50+) mm overall, not lobed or 1–2(–3)-pinnately lobed, bases cuneate, ultimate margins entire or toothed, abaxial and adaxial faces strigillose to sericeous. Pistillate heads clustered, proximal to staminates; florets 1. Staminate heads: peduncles 0.5–2 mm; involucres shallowly cup-shaped, 4–6+ mm diam., strigillose; florets 8–25(–50). Burs: bodies fusiform to ± pyriform, 4–7+ mm, ± strigillose to pilosulous, spines 8–16+, scattered, stoutly conic or flattened- to triquetrous-subulate, 0.5–1.5+ mm, tips straight. 2n = 36.

Franseria chamissonis Lessing, Linnaea 6: 507. 1831; F. chamissonis subsp. bipinnatisecta (Lessing) Wiggins & Stockwell; A. chamissonis var. bipinnatisecta (Lessing) J. T. Howell

Franseria chamissonis Less. Linnaea 6: 507. 1831
Franseria Chamissonis malvaefolia Less. Linnaea 6: 507. 1831. Franseria cuneifolia Nutt. Trans. Am. Phil. Soc. II. 7: 345. 1840. Franseria Chamissonis cuneifolia T. & G. Fl. N. Am. 2: 293. 1842. Gaertneria Chamissonis Kuntze, Rev. Gen. 339. 1891. Ambrosia Chamissonis Greene, Man. Bay Region 188. 1894.
A perennial herb, with a creeping rootstock; stem decumbent at the base, hirsute, striate, 2-4 dm. high; leaves simple, petioled, densely silky-strigose; blades oblanceolate, elliptic, spatulate, or cuneate, acute or rounded at the apex, cuneate at the entire base, coarsely crenate or dentate to incisely-lobed, 2-5 cm. Ion?; staminate h^ads in a dense terminal spike, subsessile: involucre saucer-shaped, 7-8 mm. wide, somewhat hirsute; lobes 8-10, semi-orbicular or rounded-ovate; paleae of the receptacle filiform, with slightly spatulate tips; corolla with brown angles and margins; pistillate heads in small axillary clusters and at the base of the staminate spike, 1-flowered; fruit about 1 cm. long, hirsute; beak solitary, conic, short; spines 2530, in about 4 series, dilated, not hooked, narrowly lanceolate and boat-shaped, ciliate, their bases connected by low ridges.
Type locality: California.
Distribution: Vancouver Island to California.

Ambrosia chamissonis is a species of ragweed known by the common names silver burr ragweed, silver beachweed and (silver) beach bur(r).

It is known from most of the coastline of western North America from Alaska to Baja California, where it is a resident of beaches and other sandy coastal habitats.