ALLIGATORWEED (Alternanthera philoxeroides)
 
The first confirmed infestation in Los Angeles County was in 1956. A major impetus was given to alligatorweed eradication in California when, in 1965, the weed was found to be infesting irrigation canals adjacent to crop land in Tulare and Kings Counties. This same year, it was estimated that alligatorweed in Los Angeles County had increased to 60 acres scattered over 2,000 acres. An ongoing program has been in place since that time. Although not eradicated, infestations have been confined to small areas along the San Gabriel River. In 2006 a number of large alligatorweed mats were discovered in the Army Corps jurisdiction of the San Gabriel River and Puddingstone Lake, and more recently it was found on a privately owned parcel adjacent to a flood control channel in Alhambra.

Description, Photos, and References

Ratings -
CDFA: Cal-IPC: Photo: © CDFA, 2001
Text: Sherlan Neblett
 
 
 
 
SPOTTED KNAPWEED (Centaurea maculosa)
 
Spotted knapweed are typically found in fields, roadsides, disturbed open sites, grasslands, overgrazed rangelands, and logged areas. In the past, populations of knapweed here in the County were identified in the Tanbark Flats area of the San Dimas Experimental Forest, a small area near a hiking/equestrian trail in Charmlee Park in Malibu, and in Lancaster near the Kern County border.

Description, Photos, and References

Ratings -
CDFA: Cal-IPC: Photo: © Steven Thorsted
Text: Jim Hartman
 
 
 
 
HALOGETON (Halogeton glomeratus)
 
Introduced from the cold desert regions of Eurasia, halogeton is found on alkaline desert soils in disturbed areas such as roadsides, mining areas, and heavily overgrazed ranges. Populations of halogeton have been found and are under treatment near Highway 14 in the Antelope Valley.

Description, Photos, and References

Ratings -
CDFA: Cal-IPC: Photo: © BLM - Bishop Field Office
Text: CDFA, Jim Hartman
 
 
 
 
DALMATION TOADFLAX (Linaria genistifolia spp. dalmatica)
 
Dalmation toadflax is an invasive perennial from Southern Europe. It was brought to California as an ornamental in the late 1800's due to its showy yellow flowers. It quickly escaped cultivation, and is now found throughout the state. Toadflax can be found in disturbed open sites, fields, pastures, degraded rangelands, roadsides, agronomic and perennial crops. Although it was thought to be eradicated in LA County, a population was recently discovered in the Hungry Valley area (near Gorman).

Description, Photos, and References

Ratings -
CDFA: Cal-IPC: Photo: © CDFA, 2001
Text: CDFA, Sherlan Neblett
 
 
 
 
PERENNIAL PEPPERWEED (Lepidium latifolium)
 
Perennial pepperweed has spread rapidly throughout the western U.S. since its introduction from Eurasia around 1936. While its preferred habitat is a wetland, pepperweed can survive in a wide variety of habitats, from open areas in coniferous forests at elevations over 9000 feet to coastal marshes at sea level. Infestations are often found along roadsides, in hay fields, and in disturbed soils. Here in LA County, it currently exists within the Malibu watershed of the Santa Monica Mountains.

Description, Photos, and References

Ratings -
CDFA: Cal-IPC: Photo: © CDFA, 2001
Text: CDFA, Sherlan Neblett
 
 
 
 
GERALDTON CARNATION SPURGE (Euphorbia terracina)
 
Carnation spurge is a fairly new introduction to California and although it is currently only found in Los Angeles and Ventura Counties, it has the potential to spread rapidly. Carnation spurge forms dense patches in disturbed grasslands, coastal bluffs, dunes, salt marshes, riparian areas and oak woodlands, but so far it is typically limited to coastal zones. Within our WMA, this species can be found in the coastal regions of the Santa Monica Mountains, and then further south through the Ballona wetlands and all the way down to the Palos Verdes Peninsula.

Description, Photos, and References


Ratings -
CDFA: Cal-IPC: Photo: © Drew Ready
Text: Cal-IPC, SMMNRA
 
 
 
 
GIANT REED (Arundo donax)
 
Giant reed was brought to North America quite early, as it was abundant by 1820 in the Los Angeles River, where it was harvested for roofing material and fodder. It typically forms dense stands in riparian areas, wetlands, disturbed sites, and sand dunes. In can be found geographically both along the coast and inland (usually below 1000 ft). While populations are spread throughout many of the rivers and streams in our WMA, predominent stands can be seen at a) Whittier Narrows and Santa Fe Dams in the San Gabriel River mainstem, b) Puddingstone Reservoir, c) Glendale Narrows, d) above Hansen Dam, e) and along the upper Santa Clara River mainstem near Santa Clarita.

Description, Photos, and References


Ratings -
CDFA: Cal-IPC: Photo: © Bill Neill
Text: Cal-IPC, SMMNRA
 
 
 
 
TAMARISK (Tamarix ramosissima)
 
Tamarisk was introduced to North America in the 1800s from the Mediterranean region as an ornamental shrub or shade tree. It escaped cultivation quickly and dispersed itself widely along river course throughout the southwestern US. It can be found along streams and lake shores throughout California, but it's largest establishments are within the desert region along the Colorado and Mojave Rivers, as well as along the Salton Sea. In our WMA, larger populations can be found in the Upper San Gabriel River below San Gabriel Reservoir, above Hansen Dam in the Tujunga Wash, and most abundantly, in the upper Santa Clara River in and around Santa Clarita.

Description, Photos, and References


Ratings -
CDFA: Cal-IPC: Photo: © Joe DiTimaso
Text: Bill Neill
 
 
 
 
YELLOW STARTHISTLE (Centaurea solstitialis)
 
Yellow starthistle is native to southern Europe and western Eurasia and was first collected in Oakland, California, in 1869. It was most likely introduced after 1848 as a contaminant of alfalfa seed. It inhabits open hills, grasslands, open woodlands, fields, roadsides, and rangelands, and it is considered one of the most serious rangeland weeds in the State. Not to be confused with it's cousin, tocolote (Centaurea melitensis) (which also is abundant in the foothills of the San Gabriels and Santa Susanas), the largest populations have taken foot in the Santa Monica Mountains from Malibu and north toward Ventura County.

Description, Photos, and References


Ratings -
CDFA: Cal-IPC: Photo: © Carol W. Witham, 2004
Text: J.Gerlach Jr., J. DiTomaso
 
 
 
 
MEXICAN FAN PALM (Washingtonia robusta)
 
Yes, it's true, palm trees are not native to the coastal watersheds of Southern Calfornia (there is one desert palm, Washingtonia filifera, that is native). Commonly cultivated as a landscape ornamental, the Mexican fan palm has become invasive in riparian areas, orchards, disturbed areas, and landscaped areas (sidewalks, transportation right-of-ways, etc.). While they are spread throughout the WMA, the most predominent populations can be seen along the Los Angeles River at Sepulveda Basin and south along the Glendale Narrows stretch, at Whittier Narrows and all along the lower San Gabriel River, Ballona Creek and Kenneth Hahn State Park, and most of the wetlands up the Malibu coast.

Description, Photos, and References


Ratings -
CDFA: Cal-IPC: Photo: © Bill Neill
Text: LASGRWC, Cal-IPC
 
 
 
 
PAMPASGRASS (Cortaderia selloana)
 
Native to Argentina, Brazil, and Uruguay, pampasgrass was planted in 1946 by the Soil Conservation Service throughout Ventura and LA counties to provide supplementary dryland forage and prevent erosion. It's commonly used as an ornamental grass throughout California and has since escaped cultivation and spread along dunes, bluffs, coastal shrublands and marshes, inland riparian areas, and disturbed areas below 1,000 feet. Not to be confused with its cousin, jabatagrass (Cortaderia jubata) (which can be seen spread across the Big Sur coastline), most pampas populations in our WMA occur near the coastal areas of the Santa Monica Mountains south to the Palos Verdes Peninsula. The largest population identified sits in the Ballona Wetlands.

Description, Photos, and References


Ratings -
CDFA: Cal-IPC: Photo: © CDFA, 2001
Text: Joe DiTomaso
 
 
 
 
Cape Ivy (Delairea odorata)
 
Cape ivy is a native to South Africa and was introduced as an ornamental to California in the 1950s. While it typically exists in coastal forests, in recent years populations have appeared in grasslands, open oak forests, coastal scrublands, Monterey pine forest, coastal bluff communities, seasonal wetlands, and even a few serpentine soils. Locally, populations are spread throughout the San Gabriel and Santa Monica Mountains. Larger infestation examples within the San Gabriels can be seen in Santa Anita Canyon, Arcadia Wilderness Park, and along the Arroyo Seco behind JPL.

Description, Photos, and References


Ratings -
CDFA: Cal-IPC: Photo: © Michael Nickel
Text: Carla Bossard
 
 
 
 
ICEPLANT (Carpobrotus edulis)
 
Native to coastal areas of South Africa, a region with a Mediterranean climate similar to that of coastal California, highway iceplant was brought to California in the early 1900s for stabilizing soil along railroad tracks and later used by Caltrans for similar purposes. Along with Carpobrotus hybrids, it is still abundant along highways, on military bases, and in other public and private landscapes. It spreads beyond landscape plantings and has invaded foredune, dune scrub, coastal bluff scrub, coastal prairie, and most recently maritime chaparral communities up to 500ft. Within our WMA, it typically can be seen from many of our freeway right-of-ways, but it has spread to coastal areas around Malibu down to some of our larger coastal wetlands (Ballona and Los Cerritos).

Description, Photos, and References


Ratings -
CDFA: Cal-IPC: Photo: © PlantRight
Text: Marc Albert
 
 
 
 
FOUNTAINGRASS (Pennisetum setaceum)
 
Originally native to Africa, fountaingrass was introduced as an ornamental. It has since spread into grasslands, deserts, canyons, and disturbed areas along roadsides, especially adjacent to urban centers. With that in mind, fountaingrass can be seen throughout the Los Angeles region: sidewalks, right-of-ways...you name it. Larger populations can be seen spreading along the right-of-ways of the 2 Freeway, up the hillside near the entrance of Arcadia Wilderness Park, and within Big Dalton Canyon inside the San Dimas Experimental Forest.

Description, Photos, and References


Ratings -
CDFA: Cal-IPC: Photo: © Rick Harter
Text: LASGRWC, Jeffrey Lovich
 
 
 


To the right is a shortlist of weeds that have either been problematic in the past or are current concerns here in Los Angeles County. By no means does this represent the extent of all invasive plants that are currently invading our region; this is just a snapshot of some of the nastier ones.

Each weed profile contains a) a short description of the plants distribution here in the County, b) a link to additional information regarding ID, treatment, photos, and so forth, and c) an "impact" rating from both the California Dept. of Food and Agriculture (CDFA) system and the California Invasive Plant Council (Cal-IPC). Click on a photo to enter the CalPhoto library for that particular plant.


RATINGS
CDFA ratings are primarily based on the plant's negative effect on State agriculture, while the Cal-IPC ranking relates to a plant's invasiveness in open space/wilderness throughout the State. Because these are statewide rating systems, rankings may not necessarily reflect conditions locally. Below are definitions for each ranking system.

If you happen to come across any CDFA A-rated weeds, please contact the County Agricultural Commissioner's Office!

CDFA :


Eradication, containment, rejection, or other holding action at the state-county level. Quarantine interceptions to be rejected or treated at any point in the state.
 
Eradication, containment, control or other holding action at the discretion of the commissioner.
 
State endorsed holding action and eradication only when found in a nursery; action to retard spread outside of nurseries at the discretion of the commissioner; reject only when found in a cropseed for planting or at the discretion of the commissioner.
 
Temporary "A" action outside of nurseries at the state-county level pending determination of a permanent rating. Species on List 2, "Federal Noxious Weed Regulation" are given an automatic "Q" rating when evaluated in California.
 
Not rated.
 
Cal-IPC:

Severe ecolgical impacts on physical processes, plant, and
animal communities, and vegetation structure.
Reproductive biology and other attributes conducive to
moderate to high rates of dispersal and establishment.
Most are widely distributed ecologically.

 
Substantial and apparent, but generally not severe, ecological impacts on physical processes, plant and animal communities, and vegetation structure. Reproductive biology and other attributes are conducive to moderate to high rates of dispersal, though establishment is general dependent on ecological disturbance. Ecological amplitude and distribution may range from limited to widespread.

 
Invasive but ecological impacts are minor on a statewide level or there was not enough information to justify a higher score. Reproductive biology and other attributes result in low to moderate rates of invasiveness. Ecological amplitude and distribution are generally limited, but these species may be locally persistent and problematic.

 
Not rated. Not enough information.
 
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