Rare and Invasive Plants

Legal definitions of being rare

Endangered Species Act (1973)

Gave US government jurisdiction over threatened and endangered species.

Directs government agencies to use whatever means necessary to preserve the species in question.

Requires that “critical habitat” be protected, whether on public or private land

Petitions for being “listed” are submitted to US Fish and Wildlife Service (except for marine fishes, which go to the National Marine Fisheries Service)



Endangered: a species which is faced with extinction in all or much of its range

Threatened: a species which is likely to become endangered

Concern: a species whose conservation standing is of concern to the U.S. Fish and Wildlife Service, but for which status information is still needed.

Candidate: the U.S. Fish and Wildlife Service has sufficient information on file to consider for listing as threatened or endangered.


What are primary threats to rare species?

David S Wilcove,  David Rothstein,  Jason Dubow,  Ali Phillips,  Elizabeth Losos.  1998. Quantifying threats to imperiled species in the United States.  Bioscience 48: 307-615

What if a species is rare in Washington State, but not elsewhere in its range within the US?

Washington Natural Heritage Program, managed by Washington Department of Natural Resources, keeps its own lists




Endangered:  In danger of becoming extinct or extirpated in Washington within the near future if factors contributing to its decline continue.  Populations of these taxa are at critically low levels or their habitats have been degraded or depleted to a significant degree.

Threatened:  Likely to become endangered in Washington.

Sensitive:  Vulnerable or declining, and could become endangered or threatened in the state.

Possibly Extinct or Extirpated in Washington. Based on recent field searches a number of plant taxa are considered to be possibly extinct or extirpated from Washington.

Review:  More information is needed to accurately assess their status.

Watch. This status is assigned to each vascular plant taxon that is more abundant and/or less threatened in Washington than previously assumed.

State listing offers no legal protection.

43 plant species are listed as endangered by the Washington Natural Heritage Program.  Four of those are listed as endangered at the Federal Level.

Lomatium bradshawii (Bradshaw's desert parsley, family Apiaceae) was formerly abundant in the Willamette Valley of Oregon and adjacent areas of Washington.  It is currently found in a few small populations of 10s to 1000 plants near Eugene. 


Primary threats: formerly agriculture, currently development

Hackelia venusta (showy stickseed) is a perennial, herbaceous plant in the Borage family (Boraginaceae).
The plant is a short, moderately stout species, 8 to 16 inches in height, and forms 5-lobed, white flowers.

Showy stickseed grows on sparsely vegetated, granitic scree on unstable, steep slopes on the east slope of the central Cascade Mountains of Washington.

The species has always been restricted in its distribution, the one population is found entirely on USDA Forest Service land.

This is the rarest plant in Washington State.



Reasons for listing:

One location that occurs on less than one hectare (2.5 acres).

Surveys conducted in 2001 observed approximately 500 plants.


The major threats to the species are:


physical disturbance to the habitat

intense wildfire

changes to the composition of the plant community brought on by fire suppression

In addition, highway maintenance activities, low seed production, poor germination, competition from native trees and shrubs, and nonnative noxious weeds that encroach upon the habitat of showy stickseed threaten the species.


Biological reasons for being rare:

small population

low seed production

limited vegetative reproduction

dioecious with scattered populations

pollinators not available

limited seed dispersal

limited environmental tolerance

slow growing


Cultural reasons for being rare:

habitat threat - development, agriculture, logging, ...

introduced disease, predator, invasive plant...



Rare Plant Care and Conservation in Washington

University of Washington's Center for Urban Horticulture

visit: http://courses.washington.edu/rarecare/index.htm

Seed collection

Reintroduction to native habitats.

Monitoring of rare plant populations

Conservation research

Training of students and volunteers

Education of general public

2008 Monitoring Results

125 population surveys

70 species

At 64% of the sites, the monitor(s) found and documented the rare plant occurrence.

36% could not be found

37 of the 80 rare plant populations found consisted of fewer than 50 individuals

Invasive species at 39% of the sites

Land use and management concerns at 39% of the sites

Three new locations for rare plants

Cypripedium fasciculatum, 24 individuals in the Okanogan-Wenatchee National Forest.

100 individuals of Polemonium viscosum in the Pasayten Wilderness of the Okanogan-Wenatchee National Forest.

22 clumps of Silene seelyi were observed on a cliff in the Wenatchee River Ranger District of the Okanogan-Wenatchee National Forest.


On the other hand...

Invasive non-native plants

A “weed” is a plant growing where you don’t want it to be.

Invasive non-native (or exotic or alien) plants are those that can or have spread into native wilderness or managed ecosystems, develop self-sustaining populations, and become dominant or disruptive to those systems. 

How long must a plant be here to be considered native? 

Pre-European contact, about 400 years.

Noxious weeds

A noxious weed is ”a plant that when established is highly destructive, competitive or difficult to control by cultural or chemical practices"      

The original purpose behind Washington’s primary noxious weed law,Chapter 17.10 RCW, was to limit economic loss due to the presence and spread of noxious weeds on or near agricultural land. In 1987, RCW 17.10 was revised, with an expanded focus to control the negative impacts of noxious weeds in all natural areas.


Washington State Noxious Weed List

Class A Noxious Weeds:
Non-native species that are limited in distribution in Washington. State law requires that these weeds be eradicated.

Class B Noxious Weeds:
Non-native species that are either absent from or limited in distribution in some portions of the state but very abundant in other areas. The goals are to contain the plants where they are already widespread and prevent their spread into new areas.

Class C Noxious Weeds:
Non-native plants that are already widespread in Washington State. Counties can choose to enforce control, or they can educate residents about controlling these noxious weeds.

How do invasive organisms get here?

Escaped ornamentals

Scotch broom

purple loosestrife



Accidentally imported with international trade

Eurasian water milfoil

zebra mussels

plant pathogens such as Chestnut blight and Dutch elm disease


Beware of wildflower mixes

University of Washington grad student

Grew 19 packets of “wildflower mixes”

Each contained from three to 13 invasive species

Eight had seeds of noxious weeds


Features of invasive plants

high seed production

extensive vegetative reproduction

pollinated by wind or other abundant agent

small seeds with effective seed dispersal

broad environmental tolerance

fast growing


Problems caused by invasive plants

displace native species

change ecosystem  processes

nutrient cycles

water cycles

fire regimes

increase storm damage

Bromus tectorum

Native to Mediterranean region

first introduced to North America by 1860

arrived as a seed lot contaminant

spread around the country in straw that was used in trains as packing material

Annually, cheatgrass costs wheat farmers an estimated $350-370 million dollars in lost yields and control costs in the western U.S.

Also affects natural areas

Birds of Prey National Conservation Area, Idaho

native vegetation

Bromus tectorum

cheatgrass is flammable, promotes fire

fire eliminates sagebrush

prey for raptors disappears


Senecio jacobaea
tansy ragwort

Tansy ragwort is toxic

lethal to cattle and horses

to a lesser extent goats

seldom sheep

contains several alkaloids toxic when broken down by liver

Irreversible liver damage, including liver cancer

Human potentially affected through contaminated herbal remedies, flour, milk, or honey

Senecio jacobaea
tansy ragwort

Chemical control is effective against tansy ragwort

(2,4-D and others)

Hand pulling is effective on small infestation sites

Mowing is not recommended

Biocontrol Potentials:  In its native range (Europe), tansy ragwort is controlled by over 60 species of natural enemies

Three natural enemies of tansy ragwort were introduced in California between 1959 and 1966 and are effectively used to control tansy ragwort in Oregon, California, and Washington.

ragwort flea beetle (Longitarsus jacobaeae) 

ragwort seed fly (Pegohylemyia seneciella)

cinnabar moth (Tyria jacobaeae)

Pueraria lobata

Introduced in 1876 at the Centennial Exposition in Philadelphia

The Japanese government constructed a garden with Japanese plants.

The large leaves and sweet-smelling blooms of kudzu were attractive, and US gardeners started growing the plant

Pueraria lobata

Grows 60 ft/ summer


Cytisus scoparius
Scotch broom

Introduced as a highway beautification project

Member of the pea family

Nitrogen-fixing bacteria associated with root nodules

Allows plant to successfully invade nutrient-poor sites

High N remains in soil following plant removal – alters nutrient cycling long-term

Common in disturbed areas




Cytisus scoparius
Scotch broom

Hedera helix
English ivy

Climbing vine

Native to England

Adventitious roots cling to brick buildings

Introduced to give “old world” feel to America

Successful invader by vegetatively spreading into any environment

Seed dispersal in berries by birds

Chokes out most understory vegetation, climbs bark of trees, increases storm damage

Hedera helix
English ivy

Which tree is more likely to fall in a windstorm?

Invasive species survey recently completed at Seminary Hill Natural Area

Lythrum salicaria
Purple loosestrife

Introduced in the early 1800's as a garden ornamental

escaped into wetlands

displaces the native vegetation like cattails that acts as food for native wildlife

native pollinators prefer loosestrife to native plants, reducing seed production in native species