The Double Cone Quarterly
Window to the Wilderness
Summer Solstice 1999 || Volume II, Number 2

Invasive Exotic Plants in the Wilderness
a series

Sticky Eupatorium: Yet Another Biological Threat to the
Ventana Wilderness

by Dave Nelson

Sticky Eupatorium invades coastal canyons from San Diego County north to Marin and has earned a place on the B list of Exotic Pest Plants of Greatest Ecological Concern of CalEPPC, a non-profit organization which deals with problem plants throughout the state. Locally known as sticky eupatorium, it goes by other names - pamakani in Hawaii, Crofton weed or Mexican devil in Australia and sometimes eupatory or dog fennel in the U.S. Taxonomists recently split Eupatorium adenophorum out of that genus, which includes eastern U.S. medicinal natives like joe-pye weed (E. fistulosum, purpureum) and boneset (E. perfoliatum), and made it Ageratina adenophora. By any name it is one of the invasive plants that is spreading throughout California wildlands, including the Ventana Wilderness, impacting ecosystems and diminishing biodiversity .

In an article for the Pacific Weed Science Society's conference of 1981, T. C. Fuller described it as follows:

"The plants are tall herbaceous perennials that become woody at the base. The several stems arise from a taproot that also has short lateral yellowish rootstocks which have a carrot-like odor when broken. The upright stems are somewhat weak and form a tangled mass of the clumps of plants..." The stems have a purplish-reddish cast. The flowers are white and those in sunny areas are now browning out with the summer solstice. They are airborne like many other sunflower family members. Those in deep redwood shade won't mature til late summer.

Fuller continues "the biggest damage this weed has done has been to occupy the few areas of permanent water during the extensive summer dry period found throughout the major portion of California... The native vegetation has suffered from the invasion of this weed by occupying summer wet areas and taking the places of many of the rare distributions of native plants formerly found in such areas."

Fuller was referring mainly to southern California where eupatorium spread in wetlands and irrigated areas. In the Northern Santa Lucias we've seen eupatorium in all plant communities, except grassland, below 1000 feet. This plant is equally successful on roadsides or steep rocky slopes in full sun (look up at the Big Slide at Julia Pfeiffer Burns State Park), amidst dense coastal scrub in the fog zone or under deep shade in a redwood canyons and other wetlands where it can completely overrun streamside natives. It proliferated under redwoods after the 1985 Rat Creek fire when rains in the heavily burned canyons caused flooding and removed the understory. John Smiley of UCSC's Big Creek Reserve noticed eupatorium appear in a seasonal stream near his house, replacing the ferns that were there, after the '87- '90 drought. Eupatorium also spread by seed in flooded coastal canyons during heavy rains of the 1990's and it sprouts readily when its stems are buried by sediment.

I'm noticing it most now in upland coastal scrub. Local observers believe it is spreading in this plant community without the benefit of any disturbance which makes it a particular concern. Only careful analysis of aerial photos could confirm this.

The good news is that you can pull it out pretty easily. It may prove only a successional species in redwoods canyons and gradually be replaced by native redwood streamside plants. Where we removed it by hand in McWay canyon, the thimbleberry, five-finger fern, sorrel and other natives appear to be holding their own. I know it exists from the Big Sur drainage south to at least Nacimiento Road, and is common on the lower stretches of the Kirk Creek/ Vicente Flat trail. Last Fall I saw a few plants in the creek at Vicente Flat and I wonder if it's down in the middle fork of Limekiln too. Has anyone seen it in the Little Sur redwoods? If you see it above the fogbelt (above 1500 feet) please let me know.

Sticky Eupatorium is native to Mexico. Its first recorded appearance in California was near San Francisco in 1878. It's also in a collection from the Pasadena area from 1896. It was recorded in the Santa Lucia mountains of Big Sur in the 1920's. Perhaps it has a medicinal value like its cousins named above and was in the pharmacopoeia of the padres and early Mexican settlers. Its showy white flowers and ease of growth may have made it a garden selection.

Some members of the eupatorium genus are poisonous to horses and this accounts for its listing as a noxious weed with the USDA. The toxic mechanisms in sticky eupatorium have apparently not been studied but it contains pyrrolizidine (the same alkaloid found in Cape Ivy), saponin and three steroids.

There are a few web addresses that will tell you all you want to know about sticky eupatorium and other exotic plant problems all over the world. The statewide California Native Plant Society links page is extensive.

This plant is ubiquitous once you start to recognize it and though we don't see it much yet on trails of the the Ventana proper, it may be off trail and not noticeable yet in wet areas. Keep an eye out and pull a few while you're at it.

Sticky eupatorium casts a white haze over coastal scrub above Highway One in Big Sur

The author, with his hands full of local flora.

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