Also known as silver beachweed and silver bur ragweed, this herbaceous perennial is native to maritime strand beaches and dunes of western North America from Baja California to Alaska. It is a member of the aster family, Asteraceae, that also includes sunflower, yarrow, and lettuce. The plant grows up to 4′ tall from a tap root and has succulent stems that are hairy, longitudinally ridged, and sprawl to form a mat up to 10′ wide. The woolly, silver-green leaves are variable in size and shape; they may be .5-2″ long, oblanceolate to elliptical to triangular, and toothed, or pinnately lobed or divided. In summer, yellow green male and female florets appear on the same plant. The male flower heads are at the tip of the stems with female flower heads clustered beneath them. Each female flowerhead contains a single tiny flower that develops into an ovoid, bur-like fruit almost 1/2″ wide and covered with sharp spines. Beach bur is tolerant of drought, salt spray, and is valued for use in stabilizing beaches and restoring sand dunes. The genus name, Ambrosia, is from the ancient Greek word ἀμβροσία (ambrosía) meaning immortality. The specific epithet, chamissonis, honors German botanist and poet Adelbert von Chamisso (1781-1838).
Type: Herbaceous perennial
Bloom: Green to yellow male and female flowers in flower heads on the same plant in summer
Size: 4′ H x 10′ W
Light: Full sun
Soil: Sandy, dry to medium moist, well-drained
Hardiness: Zones 9-10
Care: Low maintenance
Pests and Diseases: Leafhopper
Propagation: Seed, layering, division
Companion Plants: Sand verbenas (Abronia spp), Beach evening primrose (Camissonia cheiranthifolia), saltgrass (Distichlis spicata)
Outstanding Selections: None available
Photo Credit: Krzysztof Ziarnek, Kenraiz Wikimedia Commons