Plant Assessment Form

Carduus pycnocephalus

Common Names: Italian thistle

Evaluated on: 5/22/04

List committee review date: 08/07/2005

Re-evaluation date:

Evaluator(s)

John J. Knapp/ Invasive Plant Program Manager
Catalina Island Conservancy
P.O. Box 2739 Avalon, CA 90704
(310) 510-1299
jknapp@catalinaconservancy.org
Joseph DiTomaso
University of California-Davis
Dept. Plant Sci., Mail Stop 4, Davis, CA 95616
530-754-8715
jmditomaso@ucdavis.edu

List commitee members

Carla Bossard
John Randall
Carri Pirosko
Dan Gluesenkamp
Gina Skurka
Brianna Richardson

General Comments

No general comments for this species

Table 2. Criteria, Section, and Overall Scores

Overall Score? Moderate
Alert Status? No Alert
Documentation? 3 out of 5
Score Documentation
1.1 ?Impact on abiotic ecosystem processes C Other Published Material
Impact?
Four-part score CABD Total Score
B
1.2 ?Impact on plant community A. Severe Other Published Material
1.3 ?Impact on higher trophic levels B. Moderate Other Published Material
1.4 ?Impact on genetic integrity D. None Other Published Material
2.1 ?Role of anthropogenic and natural disturbance in establishment B. Moderate Other Published Material
Invasiveness?
Total Points
12 Total Score B
2.2 ?Local rate of spread with no management B. Increases less rapidly Other Published Material
2.3 ?Recent trend in total area infested within state B. Increasing less rapidly Other Published Material
2.4 ?Innate reproductive potential
(see Worksheet A)
B. Moderate Other Published Material
2.5 ?Potential for human-caused dispersal B. Moderate Other Published Material
2.6 ? Potential for natural long-distance dispersal C. Rare Other Published Material
2.7 ?Other regions invaded C. Already invaded Other Published Material
3.1 ?Ecological amplitude/Range
(see Worksheet C)
A. Widespread Other Published Material
Distribution?
Total Score A
3.2 ?Distribution/Peak frequency
(see Worksheet C)
B. Moderate Observational

Table 3. Documentation

Scores are explained in the "Criteria for Categorizing Invasive Non-Native Plants that Threaten Wildlands".

Section 1: Impact
Question 1.1 Impact on abiotic ecosystem processes? C Other Published Material
Identify ecosystem processes impacted:

C. pycnocephalus increases fire frequency and movement into overstory of island scrub oak chaparral, and dense populations of rosettes inhibit light penetration to the soil surface. Fire is carried into the oak overstory by C. pycnocephalus midstory. This may or may not increase the threat compared to native vegetation or annual grasses in the same area, but the Italian thistle plants tend to grow taller and be a better fire ladder than other species.


Sources of information:

Wilken, D. and Hannah, L. 1998. Carduus pycnocephalus. Channel Islands National Park Service Species Literature Review. Unpublished.
Anonymous. 2003. Written findings of the State Noxious Weed Control Board-Class A Weed. http://www.nwcb.wa.gov/weed_info/Written_findings/Carduus_pycnocephalus.html


Question 1.2 Impact on plant community composition,
structure, and interactions?
A Other Published Material
Identify type of impact or alteration:

Both rosettes and mature adults populations can reach nearly 100% cover over large areas inhibiting seedling recruitment and survivorship. Within island scrub oak chaparral habitat, C. pycnocephalus can form an midstory layer. 85% of seeds produce germination inhibitors, but they are readily leached. Both the depth and density of grasslands are altered. Harbors insect pests.
Host plant for introduced weevil Rhynocilus conicus, which attacks native thistles, thereby reducing populations of the native plants (Gluesenkamp and Randall).


Sources of information:

Wilken, D. and Hannah, L. 1998. Carduus pycnocephalus. Channel Islands National Park Service Species Literature Review. Unpublished.
Knapp, J.J. 2004. Catalina Invasive Plant Ranking Plan for the Catalina Island Conservancy. Unpublished.
Pitcher, D. and Russo, M.J. 1997. The Nature Conservancy Element Stewardship Abstract: Carduus pycnocephalus. California Field Office, San Francisco
Dan Gluesenkamp, Audubon Canyon Ranch, and John Randall, The Nature Conservancy, pers. obs.


Question 1.3 Impact on higher trophic levels? B Other Published Material
Identify type of impact or alteration:

Stem and leaves have spiny wings and phyllaries that are spine tipped, and may be injurous components to wildlife. Dense populations can alter habitat structure. A diversity of insects pollinate C. pycnocephalus. Competes with native vegetation for multiple pollinator visitation due to numerous seed heads.


Sources of information:

Wilken, D. and Hannah, L. 1998. Carduus pycnocephalus. Channel Islands National Park Service Species Literature Review. Unpublished.
Anonomous. 2003. Written findings of the State Noxious Weed Control Board-Class A Weed. http://www.nwcb.wa.gov/weed_info/Written_findings/Carduus_pycnocephalus.html


Question 1.4 Impact on genetic integrity? D Other Published Material

No hybridization is known to occur with California native taxa. No taxa native to California are within the genus Carduus.


Sources of information:

Hickman, J.C. (ed.). 1993. The Jepson manual of higher plants of California. P. 220. University of California Press, Berkeley.


Section 2: Invasiveness
Question 2.1 Role of anthropogenic and natural disturbance
in establishment?
B Other Published Material
Describe role of disturbance:

Disturbed sites such as: fallow fields, margins of cultivated fields, irrigation canals, roadsides, fire breaks, landsides, feral pig rooting, grazed heavily, and canyon bottoms are areas of establishment.


Sources of information:

Wilken, D. and Hannah, L. 1998. Carduus pycnocephalus. Channel Islands National Park Service Species Literature Review. Unpublished.
Anonomous. 2003. Written findings of the State Noxious Weed Control Board-Class A Weed.
Cowan, B. 2000. Italian thistles: an ominous threat. California Exotic Pest Plant Council News, 8(1):15.
Elkhorn Slough National Estuarine Research Reserve. 2000. Weed control by species. Elkhorn Slough National Estuarine Research Reserve. Pp. 1-57.


Question 2.2 Local rate of spread with no management? B Other Published Material
Describe rate of spread:

Populations are maintained annually by a majority of seed that fall within a few meters of the population each year. Long distance wind dispersal allows for new satellite populations to form. C. pycnocephalus is described as an aggressive species. Ants are suspected of microdistribution of seed. New populations are being detected each year, and are increasing in size along the Big Sur Coast and Catalina Island. Neither the 1923 or 1967 floras for Catalina Island recorded populations of C. pycnocephalus, but in 2003, 200 population were rcorded throughout the Island. Germinates rapidly in large numbers.


Sources of information:

Anonamous. 2004. Tamar Valley Weed Strategy- www.weeds.asn.au. http://www.weeds.asn.au/weeds/txts/slen_thstle.html.
Anonomous. 2003. Written findings of the State Noxious Weed Control Board-Class A Weed.
Moore, P.E. and Gerlach, J.D. 2001. Exotic species threat assessment in Ssequoia, Kings Canyon, and Yosemite national parks. Crossing boundaries in park management: proceedings of the 11th conference on research and resource management in parks and on public lands. The George Wright Society.
Cowan, B. 2000. Italian thistles: an ominous threat. California Exotic Pest Plant Council News, 8(1):15.
Massera, J. 2001. More about Italian thistle. California Exotic Pest Plant Council New, spring.
Knapp, J.J. 2004. Catalina Invasive Plant Ranking Plan for the Catalina Island Conservancy. Unpublished.
Elkhorn Slough National Estuarine Research Reserve. 2000. Weed control by species. Elkhorn Slough National Estuarine Research Reserve. Pp. 1-57.


Question 2.3 Recent trend in total area infested within state? B Other Published Material
Describe trend:

San Miguel, Santa Rosa and Catalina islands are invaded, along with the California coast from Mendocino to San Diego counties, lower Sacramento River Valley, Sierra nevada foothills. It is listed as a noxious weed by California State Department of Food and Agriculture. C. pycnocephalus control has occurred at Ring Mountain and Jepson Prairie preserves, Sequoia, Yosomite, Kings Canyon, and Channel Islands National Parks, Inland Empire- California State Parks, Elkhorn Slough National Estuarian Research Reserve, and the Catalina Island Conservancy. Currently 8,324,425 square feet are invaded on Catalina Island.


Sources of information:

Wilken, D. and Hannah, L. 1998. Carduus pycnocephalus. Channel Islands National Park Service Species Literature Review. Unpublished.
Pitcher, D. and Russo, M.J. 1997. The Nature Conservancy Element Stewardship Abstract: Carduus pycnocephalus. California Field Office, San Francisco.
Moore, P.E. and Gerlach, J.D. 2001. Exotic species threat assessment in Ssequoia, Kings Canyon, and Yosemite national parks. Crossing boundaries in park management: proceedings of the 11th conference on research and resource management in parks and on public lands. The George Wright Society.
Knapp, J.J. 2004. Catalina Invasive Plant Ranking Plan for the Catalina Island Conservancy. Unpublished.
California State Parks. 2000. Urban edge effects and their relationship with the natural environment. Pp. 1-30. California State Parks Inland Empire District.


Question 2.4 Innate reproductive potential? B Other Published Material
Describe key reproductive characteristics:

C. pyconocephalus is an annual or biennial that is bisexual and self-compatable. It is pollinated by a diversity of insects. Spreads by seeds only, and is mainly wind dispersed, but seeds become mucilaginous when wetted. Seeds can germinate under water-limiting conditions such as drought. C. pyconocephalus has 83-96% germination rate, with greater germination on clay soils. Seeds remain dormant under shaded conditions, and are thought to remain viable for over 7-10 years in the soil. Individual plants produce hundreds of seeds. Seed can set without vernalisation or stem elongation. Seeds can germinate at lower temperatures (zero to five degrees Celcius) than other thistle species. Presence of musk thistle biocontrol agent (Rhinocyllus conicus) has been reported to reduce seed production by about 50%.


Sources of information:

Wilken, D. and Hannah, L. 1998. Carduus pycnocephalus. Channel Islands National Park Service Species Literature Review. Unpublished.
Anonamous. 2004. Tamar Valley Weed Strategy- www.weeds.asn.au. http://www.weeds.asn.au/weeds/txts/slen_thstle.html.
Pitcher, D. and Russo, M.J. 1997. The Nature Conservancy Element Stewardship Abstract: Carduus pycnocephalus.
Moore, P.E. and Gerlach, J.D. 2001. Exotic species threat assessment in Ssequoia, Kings Canyon, and Yosemite national parks. Crossing boundaries in park management: proceedings of the 11th conference on research and resource management in parks and on public lands. The George Wright Society.
Groves, R.H. and Kaye, P.E. 1989. Germination and phenology of seven introduced thistle species in Southern Australia. Australian Journal of Botany, 37:351-359.
Elkhorn Slough National Estuarine Research Reserve. 2000. Weed control by species. Elkhorn Slough National Estuarine Research Reserve. Pp. 1-57.


Question 2.5 Potential for human-caused dispersal? B Other Published Material
Identify dispersal mechanisms:

Seeds are dispersed by humans, vehicles, machinery, soil, and hay, but long distance transport is probably uncommon.


Sources of information:

Anonymous. 2003. Written findings of the State Noxious Weed Control Board
Moore, P.E. and Gerlach, J.D. 2001. Exotic species threat assessment in Ssequoia, Kings Canyon, and Yosemite national parks. Crossing boundaries in park management: proceedings of the 11th conference on research and resource management in parks and on public lands. The George Wright Society.


Question 2.6 Potential for natural long-distance dispersal? C Other Published Material
Identify dispersal mechanisms:

Seed is dispersed mainly by wind; however, mucilagious seeds are dispersed by livestock and short distances by ants. Some movement long distance by animals and by water.


Sources of information:

Anonymous. 2004. Tamar Valley Weed Strategy http://www.weeds.asn.au/weeds/txts/slen_thstle.html.
Moore, P.E. and Gerlach, J.D. 2001. Exotic species threat assessment in Sequoia, Kings Canyon, and Yosemite national parks. Crossing boundaries in park management: proceedings of the 11th conference on research and resource management in parks and on public lands. The George Wright Society.
Brown, K. and Brooks, K. 2002. Bushland Weeds: a practical guide to their management with case studies from the Swan Coastal Plain and beyond. The Environmental Weeds Action Network.


Question 2.7 Other regions invaded? C Other Published Material
Identify other regions:

C. pycnocephalus is invasive in Australia, New Zealand, South Africa, North America, wetern Asia, Iran, and Pakistan. Naturalized in temperate regions around the world.


Sources of information:

Wilken, D. and Hannah, L. 1998. Carduus pycnocephalus. Channel Islands National Park Service Species Literature Review. Unpublished.
Anonomous. 2003. Written findings of the State Noxious Weed Control Board-Class A Weed.


Section 3: Distribution
Question 3.1 Ecological amplitude/Range? A Other Published Material

C. pycnocephalus was introduced to California during the 1930's. It is not listed in either the 1923 or 1967 Santa Catalina Island Floras. In 2003, 200 populations were detected, and the following is the percentage of habitats invaded: bare-<0.00%, beach-<0.00%, coastal bluff scrub-8%, coastal scrub-0.02%, coastal scrub/grassland-0.01%, grassland-1.5%, mixed chaparral-<0.00%, scrub oak chaparral-<0.00%, riparian-0.12%, oak woodland-<0.00%; and the following is the number of populations by non-native communities: 15-roadside, 1-non-native woodland, and 9-non-native herbaceous.


Sources of information:

Anonymous. 2003. Written findings of the State Noxious Weed Control Board-Class A Weed.
Knapp, J.J. 2004. Catalina Invasive Plant Ranking Plan for the Catalina Island Conservancy. Unpublished.


Question 3.2 Distribution/Peak frequency? B Observational
Describe distribution:

Very common in Oak woodlands throughout the state.


Sources of information:

Joe DiTomaso, UC Davis, observational


Worksheet A - Innate reproductive potential

Reaches reproductive maturity in 2 years or less Yes
Dense infestations produce >1,000 viable seed per square meter No
Populations of this species produce seeds every year. Yes
Seed production sustained over 3 or more months within a population annually No
Seeds remain viable in soil for three or more years Yes
Viable seed produced with both self-pollination and cross-pollination Yes
Has quickly spreading vegetative structures (rhizomes, roots, etc.) that may root at nodes No
Fragments easily and fragments can become established elsewhere No
Resprouts readily when cut, grazed, or burned No
Total points: 5
Total unknowns: 0
Total score: B?

Related traits:

Worksheet B - Arizona Ecological Types is not included here

Worksheet C - California Ecological Types

(sensu Holland 1986)
Major Ecological Types Minor Ecological Types Code?
Marine Systemsmarine systems
Freshwater and Estuarine lakes, ponds, reservoirs
Aquatic Systemsrivers, streams, canals
estuaries
DunescoastalD, < 5%
desert
interior
Scrub and Chaparralcoastal bluff scrubD, < 5%
coastal scrubC, 5% - 20%
Sonoran desert scrub
Mojavean desert scrub (incl. Joshua tree woodland)
Great Basin scrub
chenopod scrub
montane dwarf scrub
Upper Sonoran subshrub scrub
chaparralD, < 5%
Grasslands, Vernal Pools, Meadows, and other Herb Communitiescoastal prairieD, < 5%
valley and foothill grasslandD, < 5%
Great Basin grassland
vernal pool
meadow and seep
alkali playa
pebble plain
Bog and Marshbog and fen
marsh and swamp
Riparian and Bottomland habitatriparian forest
riparian woodlandD, < 5%
riparian scrub (incl.desert washes)D, < 5%
Woodlandcismontane woodlandB, 20% - 50%
piñon and juniper woodland
Sonoran thorn woodland
Forestbroadleaved upland forestD, < 5%
North Coast coniferous forest
closed cone coniferous forest
lower montane coniferous forest
upper montane coniferous forest
subalpine coniferous forest
Alpine Habitatsalpine boulder and rock field
alpine dwarf scrub
Amplitude (breadth): A
Distribution (highest score): B

Infested Jepson Regions

Click here for a map of Jepson regions

  • Central West
  • Desert Province
  • Mojave Desert
  • Sonoran Desert
  • Great Valley
  • Modoc Plateau
  • Northwest
  • Sierra Nevada
  • Southwest