The plants below are NOT yet reported from Orange County. However, we believe these are likely to appear in the county soon. We also believe these non-native plants pose significant threats to our local flora, wildlands and ecology. Please learn a few of these and look for them. If you believe you see any of these, report them to invasives@occnps. Instructions for reporting are here.
 
Aquatic plants are not included in the OC CNPS Watch List or Emergant List, due to their difficulty of early detection and often challenging identification. See additional information on the last page of this list.
 Horticultural plant
 

 

Ammophila arenaria                   European beachgrassEuropean beachgrass, photo courtesy Alfred Brousseau, Saint Mary's College

A perennial grass that has invaded sandy beaches, dunes and the immediate coastal areas of Central and Northern California and now as far South as Ventura County, perhaps to the Los Angeles area.

Calflora information                 
Cal-IPC Information                 
 
 

Carduus tenuiflorus                    Slender flowered thistleSlender flowered thistle, photo courtesy  Zoya Akulova

A modest sized annual thistle that is very similar to the more well known Italian thistle (Carduus pycnocephalus) and may be a subspecies or variety. This species generally contains flowerheads of 5-20 flowers each, while Italian thistle generally has heads of 5 or less flowers. A plant of woodland understories and disturbed grassland sites.

Calflora information                 
 

Carrichtera annua                       Ward's WeedWard's weed, photo courtesy of M. Fagg, AUS Nat. Botanic Gardens

An annual member of the mustard family that has recently invaded the north-coastal area of San Diego County, as for north as USMC Camp Joseph Pendleton.

 
 

Centaurea calcitrapa                   Purple star thistlePurple star thistle, photo courtesy Barry Rice.

An annual to perennial spiny-flowered weed of fields, roadsides, waste areas and other disturbed sites. Has become rather common in Northern CA and down the coast. Also now in San Diego County.

Calflora information                 
Cal-IPC Information                 
 
 

Centaurea iberica                        Iberian knapweedIberian knapweed, photo courtesy Fred Hrusa, CDFA

An annual that grows 1-4 feet and closely resembles purple star thistle (above). The leaves are divided into narrow linear segments. Flowering in late spring through early summer. Present at scattered sites throughout much of California. 

Calflora information                 
 
 
 

Centaurea stoebe                        Spotted KnapweedSpotted knapweed, photo courtesy Neal Kramer

Also sometimes referred to as C. maculosa. A species that is well established through much of California, including Los Angeles, Riverside and San Diego Counties (and incorrectly in East Orange, OC). This modest-sized perennial knapweed is very similar to Centaurea diluta - North African knapweed and reminiscent of the more well-distributed, but smaller, Acroptilon repens - Russian knapweed.

Calflora information                 
Cal-IPC Information                 
 

Chloris truncata                          Truncate finger grassTruncate finger grass, photo courtesy Dean Kelch, CDFA

An distinctive invasive annual to short-term perennial clumping grass that has become well established just over the border in western Riverside County. Distinguished by its very large whirled flower heads, arranged like the ribs of an umbrella. The leaves are also quite long.

Calflora information                 
 
 

Skeleton weed, photo courtesy of Luigi RignaneseChondrilla juncea                        Skeleton weed

An annual to short-lived perennial of up to three feet that is well established in Northern California and is now moving along the southern California coast. The plant seeds readily and invades rangelands, fields, grasslands and disturbed sites.

Calflora information                 
Cal-IPC Information                 
 
 

Cirsium arvense                          Canada thistleCanada thistle, photo courtesy Keir Morse

Now found through most of California, but not yet in Orange County. A perennial, it forms dense colonies, which can spread vegetatively as well as from seed. Can be difficult to control, since very small root fragments can generate new plants. Be cautious not to confuse this with our native California thistle (Cirsium occidentale).

Calflora information                 
Cal-IPC Information                 
 

Cytisus scoparius                       Scotch Broom             Scotch broom, photo courtesy Zoya Akulova

One of many brooms in the Cytisus and related genera that are problematic in wildlands. It is a medium to large shrubby perennial that can invade many different habitats, change fire regimes and overwhelm native vegetation. It is present at several sites in Los Angeles County and was recently discovered in San Diego County.

Calflora information                 
Cal-IPC Information                 

Dipsacus fullonum                      TeaselTeasel, photo courtesy Eric Wrubel

Like Dipsacus sativus (below), this large upright biennial has the ability to invade natural areas, form dense stands and crowd out native plants, especially in moist fields and riparian areas. Long thin bracts below the flower are flexible.The distinctive flower heads are used ornamentally and occasionally in floral arrangements. Present in all our surrounding counties.

Calflora information                 
Cal-IPC Information                 
 

Dipsacus sativus                         Indian teaselIndian teasel, photo courtesy Eric Wrubel

Like Dipsacus fullonum (above), this large upright biennial has the ability to invade natural areas, form dense stands and crowd out native plants, especially in fields and riparian areas. The distinctive flower heads are used ornamentally and occasionally in floral arrangements. The long thin bracts below the flower are stiff. Present in surrounding counties.

Cal-IPC Information                 
 

Elymus caput-medusae              MedusaheadMedusahead, photo courtesy Steve Matson

An annual invasive grass that can overwhelm montane grasslands, similar to cheatgrass (Bromus tectorum). The long awns are obvious on bending, wispy flower heads and are reminiscent of several other invasive grasses. As the awns dry, they twist and spread in all directions, similar to a multi-headed Medusa.

Calflora information                 
 
 

Enchylaena tomentosa               Ruby SaltbushRuby Saltbush, photo courtesy Eugene Sturla

A modest-sized spreading irregular plant that has invaded portions of souther-coastal San Diego County and has the potential to do the same in Orange County. Prefers poorly drained alkaline or saline areas. The distinctive yellow, green, pink or red, fleshy fruits are present through much of the year. Leaves and stems are covered in wooly hairs.

Calflora information                 
 

Euphorbia terracina                    Carnation SpurgeCarnation spurge, photo courtesy Luigi Rignanese

Destined to appear in Orange County, this weedy annual/perennial Euphorbia is already well established as an invasive in the Santa Monica Mountains and on the Palos Verdes Peninsula. In can be confused with other native and invasive Euphorbias, especially Euphorbia peplus (non-native) and Euphorbia spathulata (native).

Calflora information                 
Cal-IPC Information                 
 

Euphorbia virgata                        Leafy SpurgeLeafy spurge, photo courtesy Dean Kelch, CDFA

May be the same species as Euphorbia esulaA rhizomatous perennial species that can invade and colonize several plant communities. Present in both Los Angeles and San Diego Counties. The leaf margins are smooth on this species and toothed in Euphorbia terracina.

Calflora information                 
Cal-IPC Information                 
 

Genista monosperma                 Bridal broomBridal broom

Has established infestations as near as Fallbrook and the southern edges of USMC Camp Pendleton. Also sometimes referred to as Retama monosperma. A large brushy member of the pea family, closely related to many of the problematic brooms in the genera Cytisus and Retama, but with white flowers.

Calflora information                 
 

Genista monspessulana             French broom            French broom, photo courtesy Barry Breckling

Another of the large, rank growing shrubby and invasive brooms; others are in the genera Cytisus or Retama. This species is already present in each of the counties surrounding Orange County. Very similar to Cytisus scoparius and only distinguished by small subtilties of the fruit and flower.

Calflora information                 
Cal-IPC Information                 

Helichrysum petiolare                 Licorice plant             Licorice plant, photo courtesy Nicholas Stevenson

A horticultural plant that has shown up in a few places in San Diego County and central and northern California. We are uncertain of its invasiveness, but believe it may appear in our area, due to the plant's popularity in gardens. This is similar, but not to be confused with the also invasive, Plecostachys serpyllifolia - petite licorice plant. 

Calflora information                 
Cal-IPC Information                 
 

Heliotropium supinum                Drawf HeliotropeDwarf heliotrope

A small, prostrate invasive annual of low, exposed alkaline or saline soils. The stems and leaves are both hairy, unlike our native Heliotropium curassavicum. This plant recently appeared at the far southern end of coastal San Diego county. 

Calflora information                 
 
 

Lathyrus tingitanus                     Tangier pea                                               Tangier pea

An annual "sweet pea" relative that grows at a couple of roadside loactions along Hwy 74, just East of the OC line. There are old records for Orange County that appear to now be extirpated. Somewhat similar to our native San Diego Pea - Lathyrus vestitus as well as the occasionally invasive everlasting pea - Lathyrus latifolius and the common garden sweet pea - Lathyrus odoratus.

Calflora information                 
 

Lythrum salicaria                         Purple loosestrife

Purple loosetrife, photo courtesy Barry Rice

A flowery perennial that has been well established in Northern California for some time, but recently has established just inland of The San Elijo Lagoon, near Encinitas in San Diego County. It is a concern in areas of moist wetlands, streamsides, flood control areas, etc.

Calflora information                 
Cal-IPC Information                 
 
 
 

Pentameris airoides                     Annual Pentachistis

Annual pentachistis, photo courtesy Kier Morse

An annual to perennial small grass that was discovered recently at the southeast edge of USMC Camp Pendleton in San Diego County.

Calflora information                 
 
 
 
 
 
 

Phragmites australis                   Common reed                                          Common reed

Very similar to the well known giant reed - Arundo donax, but smaller in stature. This riparian invader is confirmed from all of our surrounding counties and may already occur in Orange County. Before any management begins, carefull inspection of a colony will be needed to ensure that the plants do not represent a remnant of the native population.

Calflora information                 
 

Phytolacca americana                American pokeweed                           

American pokeweed

A significant perennial plant pest in Northern CA that now may be moving into the southern part of the state. Recorded just across the OC line near San Clemente as well as in surrounding counties. Look for it especially in moist disturbed sites and waste areas. A prolific seeder. Similar to Phyrtolacca heteropetala, which has been recorded once in Orange County.
 
Calflora information                 
Cal-IPC Information                 
 

Senecio dolicocephalus             Cotton Burnweed

 

Cotton burnweed

Previously identified as Senecio quadridentatus. A colony of this new invasive has become established only about five miles south of San Clemente at USMC Camp Pendleton. Additional plants occur in Santa Barbara County. An bushy-upright annual to perennial herb with long, slender leaves and branched, yellow flowers on top.

 

 
 
 

Sesbania punicea                        Rattlebox                    Rattlebox, photo courtesy Jean Pawek

A pea family relative with conspicuous flowers that grows as a large deciduous shrub. A threat to riparian edges and waterways, where it can create dense monocultures. The seed is very long-lived. First discovered in 1999, it is now well established in parts of northern California and has now colonized an area of San Diego County. A single plant found at Upper Newport Bay appears to have been a waif.

Calflora information                 
Cal-IPC Information                 

Ulex europaeus                            GorseGorse, photo courtesy Simon J. Tonge

A member of the pea family that can colonize nutrient poor soils, especially in disturbed sites, pastures, roadsides, etc. it is superficially similar to many of the brooms in the genera Cytisus, Genista and Retama. Gorse is recorded in Los Angeles, San Bernardino and San Diego Counties.

 Cal-IPC Information                 

 


Aquatic Plant Note

True aquatic plants are not included in the OC CNPS Watch List or Emergent List, due to their difficulty of early detection and often challenging identification. Nonetheless, species of concern in or near Orange County include:
 
Alternanthera philoxeroides          Alligatorweed
Hydrilla verticillata                         Hydrill
Ludwigia hexapetala                      Creeping water primrose 
Myriophyllum aquaticum               Millfoil 
Myriophyllum spicatum                 Millfoil 

 

 

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