Spartina anglica (common cordgrass) is a rhizomatous perennial grass (family Poaceae) found in salt marshes and mudflats in northern San Francisco Bay. Common cordgrass is a recently evolved species that was first described in the late 1800s. The new species resulted from the hybridization of smooth cordgrass (S. alterniflora) and small cordgrass (S. maritima) in […]

Sisymbrium irio (London rocket) is a winter annual forb/herb (family Brassicaceae) native to northern Africa, southern Europe, and the Middle East that occurs in abandoned fields, waste places, roadsides, and orchards across southern and central California. London rocket rosette leaves are deeply and narrowly lobed to sometimes compound and nearly hairless, with bluntly pointed tips. […]

Sinapis arvensis (wild mustard, charlock) is an annual herb (family Brassicaceae) that is native to the Mediterranean region and naturalized in California and many other parts of the world. It can grow up to more than 1 m tall and has yellow flowers that are typical of mustards. Unlike many other mustards, plants do not […]

Silybum marianum (blessed milk thistle) is a winter annual or biennial with prickly leaves (family Asteraceae). It is widely spread throughout California in overgrazed pastures and along fencelines and other disturbed areas. Blessed milk thistle produces tall, dense stands that outcompete native species.

Sesbania punicea (red Sesbania, scarlet Wisteria) is a deciduous shrub or small tree (family Fabaceae), up to 4 meters tall. Sesbania punicea is mostly found in riparian areas in the Central Valley, forming clusters so thick that access to the river becomes difficult to impossible. It displaces native plants used by wildlife and contributes to […]

Senecio jacobaea (tansy ragwort) is a noxious perennial, biennial, or sometimes annual weed (family Asteraceae) native to northern Africa, Asia, and Europe, that that occurs mostly in northern California. Plants are ruffled rosettes when young and erect when mature, growing up to  4′ . Leaves are twice pinnately compound and dark green. Flower heads have […]

Schismus arabicus (Mediterranean grass) is an annual grass (family Poaceae) found mostly in disturbed areas and deserts. It is difficult to distinguish from its close relative Schismus barbatus. Both species contribute to the conversion of desert shrubland into annual grassland by carrying fire across open areas, where they ignite and kill native shrubs.

Schinus terebinthifolia (Brazilian peppertree) is an evergreen shrub or tree found along portions of the southern coast of California. Brazilian peppertree prefers riparian areas, canyons, fields and roadsides where some water is available throughout the year. Its pink fruits are sold as peppercorns, but they may be toxic to humans and animals if too many are […]

Schinus molle (Peruvian peppertree) is an aromatic, evergreen shrub or tree (family Anacardiaceae) found in central and southern California. It is native to more arid parts of the Andes and elsewhere in south America and has been widely introduced as a street tree elsewhere around the world. Like its close relative, Brazilian peppertree (S. terebinthifolius), […]

Saponaria officinalis (bouncing-bet) is a perennial (family Caryophyllaceae)  that is native to Europe and Siberia. It has escaped gardens where it has been grown as an ornamental and medicinal plant and is now broadly naturalized across the continental United State. In California it is especially problematic near Mono Lake. Bouncing-bet can be distinguished by its […]