Invasive Weeds Wanted by NPR

A note from the National Park Service for Point Reyes visitors:

Please keep an open eye for two highly invasive plant species that are currently in very low abundance in our park:

Oblong spurge (Euphorbia oblongata), yellow flower in the pictures, is an upright perennial with alternate leaves, growing up to 3 feet tall. Its tiny flowers are surrounded by yellow petal-like bracts in spring and summer. This deep-rooted species can form dense colonies that outcompete native and rangeland plants.

I know of 4 populations in the park (SFD on Olema Hill across from the Bolinas Ridge trailhead; adjacent to the Palomarin trailhead parking lot; on McFadden Ranch; and in the Olema pasture across the creek from the campground, between Bear Valley Rd and the creek corridor. A large patch grows at the SFD edge of private property in Inverness.

Purple star-thistle (Centaurea calcitrapa), purple flower in the pictures, is an annual to perennial thistle with long sharp spines below its purple (or white to pink) flower heads. Not currently flowering (though it could begin to flower very soon), it is distinguished from yellow star-thistle by the larger, wider lobed leaves. Young leaves can be grey with cobwebby hairs while older leaves are hairless and 4-8″ long.

There’s a patch on Genazzi Ranch and last week I removed 5 plants on SFD on the east side of the road between Inverness Park and Inverness.

If you or visitors find any other populations, please report to me: the location (as exactly as possible, including distance from trail or road), approximate number of plants and/or patch size, and whether they are flowering. Feel free to remove them as well. Purple star-thistle can be knocked down to ground level and if not flowering, disposal isn’t an issue. Once it starts to flower, please dispose of the flowering heads. If you want to remove oblong spurge, please wear gloves and long sleeves (like all Euphorbias, they contain a toxic milky sap that’s especially damaging to eyes) and bag and throw out all flowering plants.

To familiarize yourself with other early detection species for PORE and GOGA, check out I&M’s excellent online resource:

Ellen Hamingson
Restoration Biologist
Point Reyes National Seashore
1 Bear Valley Road
Point Reyes, CA 94956
phone 415-464-5196 fax 415-464-5183