Invasive invaders

It seems pretty innocuous. A tiny plant with equally tiny purple flowers. Five symmetrical petals bursting from red-tinted buds, poking up above dainty cut leaves. This is Herb Robert and he’s not supposed to be here. This little flower is species of cranesbill, a member of the geranium family. Its namesake is thought to be the abbot and herbalist Robert of Molesme, a saint and one of the founders of the Cistercian Order during the eleventh century. Herb Robert was traditionally used as a remedy for toothaches and healing wounds in the British Isles. Other cranesbill species also are native to Eurasia and North Africa.


The British invader Herb Robert

Somehow, over the centuries, Herb Robert and many other plants have made it to the Northwest. Exotic, foreign, alien, non-native, non-indigenous. It is surprising just how many plants we now take to be common wildflowers were actually intentionally or unintentionally introduced from other areas of the world. Some of them came as hitchhikers through international trade. Others came with immigrants who wanted to retain a piece of their homeland, utilizing plants they were familiar with in their gardens or for practical purposes, such as soil stabilization.

Many of the Northwest’s non-indigenous plants arrived during the late 1800s as settlers arrived and towns were established. Periwinkle, yellow salsify, ox-eye daisy and foxglove are all native to Europe. Eurasian-native plants include poison hemlock, Queen Anne’s lace, several thistle varieties, cornflower, the common dandelion, chicory, English daisy, tansy, groundsel, black mustard, wild radish, field bindweed, teasel, red and white clover, yellow flag iris, purple dead nettle and common plantain.

Unfortunately, while many of these plants have a neutral impact on their environment, others do not. The problem comes when these introduced species begin to crowd out native species and adversely affect their surroundings.

The Oregon Department of Agriculture maintains a noxious weed list. Some of the above mentioned also have made it to this list to varying degrees of concern. The ODA defines a noxious weed as “a terrestrial, aquatic or marine plant designated by the State Weed Board under ORS 569.615 as among those representing the greatest public menace”. The ODA has developed two ranking lists, list A and list B, based on the plant’s negative impacts to agricultural, economic and natural resources; its potential to endanger native species; its potential to hinder access to recreational areas; and its poisonous or otherwise harmful effects on plants or animals. From these two lists, the ODA also has designated some of the plants with a T status, which prioritizes control management for that species.

List A contains plants in small infestations, which have an easier possibility of containment, or plant species that are known to grow in nearby states, but have not spread to Oregon. This list contains:

  • African rue (T)
  • Cape ivy (T)
  • Camelthorn
  • Coltsfoot
  • Cordgrass (T) (various)
  • Common frogbit
  • European water chestnut
  • Flowering rush (T)
  • Garden yellow loosestrige (T)
  • Giant hogweed (T)
  • Goatgrass (T) (various)
  • Hawkweed (various)
  • Hoary alyssum (T)
  • Hydrilla
  • Japanese dodder
  • Kudzu (T)
  • Malgrass (T)
  • Oblong spurge (T)
  • Paterson’s curse (T)
  • Purple nutsedge
  • Ravenna grass (T)
  • Silverleaf nightshade
  • West Indian spongeplant
  • Squarrose knapweed (T)
  • Starthistle (T) (various)
  • Syrian bean-caper
  • Thistle (T) (various)
  • Water soldiers
  • White bryonia
  • Yellow floating heart (T)
  • Yellow tuft (T)

List B plants are more regionally abundant and their containment has a higher economic importance. This list contains:

  • Armenian (Himalayan) blackberry (T)
  • Biddy biddy
  • Broom (various)
  • Buffalo bur
  • Butterfly bush
  • Common bugloss (T)
  • Common crupina
  • Common reed
  • Creeping yellow cress
  • Cutleaf teasel
  • Dodder
  • Dyer’s woad
  • Ivy (various)
  • Eurasian watermilfoil
  • False brome
  • Field bindweed (T)
  • Garlic mustard (T)
  • Geranium (various)
  • Gorse (T)
  • Halogeton
  • Houndstongue
  • Indigo brush
  • Johnsongrass
  • Jointed goatgrass
  • Jubata grass
  • Knapweed (various)
  • Knotweed (various)
  • Kochia
  • Lesser celandine
  • Meadow hawkweed (T)
  • Mediterranean sage
  • Medusahead rye
  • Old man’s beard
  • Parrot feather
  • Perennial peavine
  • Perennial pepperweed (T)
  • Pheasant’s eye
  • Policeman’s helmet
  • Puncture vine
  • Purple loosestrife
  • Ragweed
  • Rush skeletonweed (T)
  • Saltcedar (T)
  • Small broomrape
  • South American waterweed
  • Spanish heath
  • Spikeweed
  • Spiny cocklebur
  • Spurge laurel
  • Spurge (various)
  • St. Johnswort
  • Sulfur cinquefoil
  • Swainson pea
  • Tansy ragwort (T)
  • Thistle (various)
  • Toadflax (T) (various)
  • Tree of heaven
  • Velvetleaf
  • Primrose willow (T) (various)
  • Whitetop
  • Yellow archangel
  • Yellow flag iris
  • Yellow nutsedge
  • Yellow starthistle

There are a few plants on the lists that are more familiar in the Northwest because of their size and visibility: gorse, Scotch broom, European beachgrass, English ivy, Himalayan blackberry and, while actually native, Western juniper.

It’s hard to imagine why gorse made its way to the United States. Made to withstand harsh, rocky climates, this prickly green shrub of the pea family looks like a cross between sagebrush and a cactus. Aesthetically its one saving grace is the plethora of yellow blooms it produces when flowering.

Gorse was introduced to the Bandon-area when the town’s founder wanted a memento of his homeland, Ireland. Over the next several decades, gorse quickly spread through the city until 1936, when sparks from an out-of-control burn lit a patch of gorse on fire. An incident which demonstrated one of gorse’s features: it burns. Really well. In fact, fueled by the thick gorse hedges, the fire destroyed almost the entire town. Ironically, gorse actually needs fire to propagate. Gorse seeds can remain viable in the ground for up to 50 years and the intense heat of a fire allows gorse seed to crack open. In addition, while other plants may be destroyed by fire, even reduced to its roots, gorse quickly resprouts. Despite numerous attempts at control, including the introduction of gorse-eating moths, the plant continues to spread in southern Oregon and California.

One of gorse’s relatives, Scotch broom, arrived in Oregon in a similar fashion. Scotch broom is a shrub that produces sprays of vivid yellow flowers on long, slender, arching branches. In spring, if you see a hillside alive in bright gold shades, Scotch broom has probably moved in. It was originally introduced in the late 1890s as an ornamental plant, but was later used extensively for erosion control. Scotch broom reproduces with peapod-like seed pods. As they mature, they dry and crack open, forcibly emitting the seeds. This allows the plant to spread easily. Scotch broom is known to quickly take over open areas, such as clearcuts, which prevents the regrowth of sapling trees and native plants.


Mature Scotch broom seed pods

You would think not much could live in beach sand. But, another non-native plant has proven that wrong. European beachgrass, or marram grass, has slowly been taking over many beaches and dunes along Oregon’s coast. Native to the North Atlantic Ocean-area, European beachgrass was introduced in the late 1800s in massive intentional plantings. Up until the 1960s, people were encouraged by state and federal governments to use the grass to stabilize sandy areas for real estate development. The grass’s tough fibrous rhizomes spread over the top of sand and create a dense mat of fibers. Beachgrass was a little too good at its job, holding the beach sand in place and creating large foredunes. However, where the sand stopped moving “terrestrialization” began. Behind the foredunes, trees, shrubs and other species took hold, changing the dunes’ ecology into wetlands.

Another plant introduced to the area around the same time and for similar purposes, was English ivy. In Europe, English ivy was traditionally used as a means of erosion control, landscape filler and to beautify walls and facades. Ivy’s propensity for invasion is in part because it is one plant that grows easily in low light. Ivy produces “holdfasts”  that make it an excellent climber, allowing it to grow up and smother trees. It also produces rhizomes and above ground runners, eventually creating thick mats of waxy green leaves that shade out native species. While many bird species eat them, English ivy berries are poisonous to people and livestock. To note, the sale and propagation of English ivy (and butterfly bush) is banned in Oregon.


The bane of city parks, English ivy

Himalayan blackberry is another vine that has become problematic due to its tenacity in taking over open space. The same reason this plant is still liked today, is the same reason why it was introduced to the area: fruit production. Himalayan blackberry produces large, plump berries, and many people take to out of the way areas when the fruit is ripe, filling bucketfuls of berries for pies and jams. Himalayan blackberry vines grow up to 15 feet tall and 40 feet long. Their canes can be as big around as an adult man’s thumb. The problem is that they out compete native species, forming impenetrable thickets of sharp spikes that shade out understory plants and prevent larger mammals from accessing food and water supplies. Himalayan blackberry not only reproduces by seed, but it also forms root buds where the vines touch the ground. A Washington state survey determined that in some areas there was more acreage covered by Himalayan blackberry than all other invasive plant species combined.

It isn’t only foreign invaders that create problems. Changes in land use also can affect where and how native plants grow. In today’s world, wild fires are suppressed to ensure the safety of people and their property. But, that suppression has allowed Western juniper to thrive in Eastern Oregon. Between 1936 and 1988, it is estimated the amount of acreage that juniper covers has increased by 5.3 times. Juniper is a long-lived hardy tree, which provides food and habitat for migratory birds and native animal species. However, it also shades out native species of grass and sagebrush, while puting an immense pressure on the ground water supply. Land use officials have long debated effective means of juniper control and whether the wood itself can be made marketable.

While most non-native plants came to Oregon and the Northwest through traditional means (agriculture, shipping, nurseries, settlers), there’s a new threat in the mix. Genetically modified plants also have been introduced in recent decades.  Just like their predecessors, the qualities that made them appealing for certain purposes, have made them detrimental to the areas they move into. While genetic modification has been going on through selective breeding for thousands of years, in recent decades it has moved into laboratories. The genetic engineering usually focuses creating higher yield strains or making plants resistant to diseases, pests, or, in one instance, to herbicides.

If you’ve ever played golf, you’re probably familiar with bentgrass. It grows from horizontal stems, creating low maintenance grass, that stands up to heavy foot traffic. The problem came when Scott’s and Monsanto attempted to develop an herbicide-resistant turf from creeping bentgrass. The plan was abandoned in the early 2000’s, when trouble brewed over passing United States Department of Agriculture and Animal and Plant Health Inspection Service standards. Unfortunately, nobody told that to the bentgrass. Proximity and major windstorms have spread seeds from their original test fields in Oregon and Idaho throughout Eastern Oregon. Now farmers are finding themselves stuck with the clean-up as the bentgrass moves into drainage ditches and irrigation canals.

Today, we can order things from across the globe on the internet. We spend trillions of dollars annually on tourism and outdoor activities. Our world is coming to our doorstep. Be aware, invasive species are not limited to plants. They include bacteria, viruses, fungi, insects, fish, birds and mammals. Here are a few things we can do to help stop the spread of non-native and invasive species:

  • Consider volunteering at your local park for clean-up outings. It’s difficult to visit any city park without encountering English ivy and Himalayan blackberry. Check with your local parks department to find out when volunteer crews are meeting to clear these invaders from city and state parks.
  • Check your shoes. Visitors can often find boot cleaning stations at the entrance to parks and hiking trails. Take a moment to swipe your shoes through them. Remove any burs or seeds that may have hitched a ride on your pant legs and clothing when leaving an area. If you are enjoying time on the water, ensure you properly clean your kayak, jet ski or boat after your trips.
  • Be mindful of what you plant in your own garden. Make sure you aren’t planting a species considered invasive in your area. Look into planting native species. Native species often are more tolerant of local weather, require less water and are less prone to disease and pests. They also will attract native birds and insects, providing them with food and shelter.

Full story: For more information on Oregon invasive species, contact the ODA at Noxious Weed Control, 635 Capitol St. NE, Salem, OR 97301, or call (503) 986-4621.

For more on the creeping bentgrass problem, check out

More about the Bandon gorse fire can be found at


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