2024 Invasive Watch List Species

The plants below are NOT yet reported from Orange County, but are in adjacent areas. We believe these are likely to appear in the county soon.  Please learn a few of these and look for them. If you believe you see any of these, post your observation to Calflora and/or iNaturalist and report them to invasives@occnps. Instructions for reporting are here.


Aquatic plants are not included in the OC CNPS Emergent List, due to their difficulty of early detection and often challenging identification. However, several are listed here for reference. See additional information at the bottom of this page.



Invasive Watch List 2024


Ammophila arenaria – European Beachgrass

Calflora information                 
Cal-IPC Information                 


Arctotheca calendula – Cape Weed

Calflora information                 
Cal-IPC Information                 


Brassica juncea – India Mustard

Calflora information                 


Carduus tenuiflorus – Slender Flowered Thistle


Carrichtera annua – Ward’s Weed


Centaurea calcitrapa – Purple Star Thistle

Calflora information                 
Cal-IPC Information                 


Centaurea iberica – Iberian Knapweed

Calflora information                 


Centaurea stoebe – Spotted Knapweed

Cal-IPC Information                 


Chloris truncata – Truncate Finger Grass


Chondrilla juncea – Skeleton Weed


Cirsium arvense – Canada Thistle


Cortaderia jubata                         


Cytisus scoparius – Scotch Broom          


Dipsacus fullonum – Teasel


Dipsacus sativus – Indian Teasel


Elaeagnus angustifolius – Russian Olive


Elymus caput-medusae – Medusahead


Enchylaena tomentosa – Ruby Saltbush


Euphorbia virgata – Leafy Spurge


Helichrysum petiolare – Licorice Plant             


Heliotropium supinum – Drawf Heliotrope


Kochia scoparia – Summer Cypress


Lepidium appelianum – Hairy Whitetop


Lythrum salicaria – Purple Loosestrife


Myoporum acuminatum – Strichnine Bush


Pentameris aroides – Annual Pentameris


Perilla frutescens – Shiso

Wikipedia information               


Phragmites australis – Common Reed


Sisymbrium erysimoides


Ulex europaeus – Gorse



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
  • Iris pseudacorus – Yellow flag iris
  • Ludwigia hexapetala – Creeping water primrose
  • Myriophyllum aquaticum – Millfoil
  • Myriophyllum spicatum – Millfoil 
  • Pistia stratioites – Water lettuce
  • Potamogeton crispus – Crispate leaved pondweed
  • Salvinia minima – Water spangles
  • Salvinia molesta – Kariba weed