Plant Assessment Form

Conium maculatum

Common Names: poison-hemlock

Evaluated on: 5/22/03

List committee review date: 06/06/2003

Re-evaluation date:

Evaluator(s)

Joe DiTomaso
UC Davis
Weed Science Program, Robbins Hall, Univ. California, Davis CA 95616
530-754-8715
DiTomaso@vegmail.ucdavis.edu

List commitee members

Joe DiTomaso
Peter Warner
Alison Stanton
Carla Bossard
Cynthia Roye
Jake Sigg
Doug Johnson
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 U
Impact?
Four-part score UBAD Total Score
B
1.2 ?Impact on plant community B. Moderate Other Published Material
1.3 ?Impact on higher trophic levels A. Severe 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 C. Stable Observational
2.4 ?Innate reproductive potential
(see Worksheet A)
A. High Reviewed Scientific Publication
2.5 ?Potential for human-caused dispersal C. Low Other Published Material
2.6 ? Potential for natural long-distance dispersal B. Occasional 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 B
3.2 ?Distribution/Peak frequency
(see Worksheet C)
C. Low Other Published Material

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? U
Identify ecosystem processes impacted:

None reported, unknown.


Sources of information:

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

Can form very dense stands and crowd out other vegetation. Pioneer species colonizing disturbed sties and displacing natives during early successional stages. Suppresses light.


Sources of information:

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

Toxic to all organisms including humans, livestock, and wildlife. 10% of elk population on Grizzly Island, CA, died from ingestion of poison hemlock in 1985.


Sources of information:

Mitich, L.W. 1998. Weed Technology 12:194-197; Pitcher, D. 1989. Poison hemlock. Element Stewardship Abstract. TNC; Parsons, W.T. and E.G. Cuthbertson. 1992. Noxious Weeds of Australia. Inkata Press, Sydney; DiTomaso, J.M. and E.A. Healy. 2005. Weeds of California. DANR (pre-print)


Question 1.4 Impact on genetic integrity? D Other Published Material

None No native Conium species in North America


Sources of information:

DiTomaso, J.M. 1999. Poison hemlock. In, Biology and Management of Noxious Rangeland Weeds. Oregon St. Univ. Press, Corvallis.


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

Usually found in disturbed sites, but can invade native plant communities in riparian woodlands and open flood plains of rivers and streams. Common in shady areas


Sources of information:

DiTomaso, J.M. and E.A. Healy. 2005. Weeds of California. DANR (pre-print); Pitcher, D. 1989. Poison hemlock. Element Stewardship Abstract. TNC


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

Spreads rapidly in newly disturbed sites. Probably > 10 years.


Sources of information:

DiTomaso, J.M. 1999. Poison hemlock. In, Biology and Management of Noxious Rangeland Weeds. Oregon St. Univ. Press, Corvallis.


Question 2.3 Recent trend in total area infested within state? C Observational
Describe trend:

Appears to be stable statewide. Has been around for many years.


Sources of information:

DiTomaso-Observational


Question 2.4 Innate reproductive potential? A Reviewed Scientific Publication
Describe key reproductive characteristics:

Seed dispersal from late summer through winter. Dormancy about 3 years. Biennial, flowers in second year.


Sources of information:

Baskin, J.M. and C.C. Baskin. 1990. Seed germination ecology of poison-hemlock. Canadian J. Bot. 68:2018-2024; DiTomaso, J.M. and E.A. Healy. 2005. Weeds of California. DANR (pre-print); DiTomaso, J.M. 1999. Poison hemlock. In, Biology and Management of Noxious Rangeland Weeds. Oregon St. Univ. Press, Corvallis.


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

Can be moved by farm machinery, vehicles, ag practices, clothing, etc., but this is usually from agricultural area to agricultural area.


Sources of information:

Pitcher, D. 1989. Poison hemlock. Element Stewardship Abstract. TNC


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

Most seed fall to base of parent plant. Some long distance movement in water when plants are growing near streams.


Sources of information:

DiTomaso, J.M. and E.A. Healy. 2005. Weeds of California. DANR (pre-print); DiTomaso, J.M. 1999. Poison hemlock. In, Biology and Management of Noxious Rangeland Weeds. Oregon St. Univ. Press, Corvallis.


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

Reported as a weed in South America, Europe, temperate Asia, North Africa, Australia, New Zealand and Canada. Also throughout the US. A weed in 9 crops in 34 contries. Widespread worldwide but in the same type of habitats.


Sources of information:

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

Considered a facultative wetland indicator plant in the western US and an obligate wetland species in AZ and NM. Riparian areas, ditches, pastures, waste places. Introduced to the US as a garden plant in 1800s. First reported in California in 1893 in Berkeley.


Sources of information:

DiTomaso, J.M. and E.A. Healy. 2005. Weeds of California. DANR (pre-print); Drewitz, J. 2000. Conium maculatum. In, Invasive Plants of Californias Wildlands. CalEPPC. UC Press, Berkeley.


Question 3.2 Distribution/Peak frequency? C Other Published Material
Describe distribution:

Common in shady areas, particularly riparian woodlands and open flood plains of rivers and streams.


Sources of information:

Pitcher, D. 1989. Poison hemlock. Element Stewardship Abstract. TNC


Worksheet A - Innate reproductive potential

Reaches reproductive maturity in 2 years or less Yes
Dense infestations produce >1,000 viable seed per square meter Yes
Populations of this species produce seeds every year. Yes
Seed production sustained over 3 or more months within a population annually Yes
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: 8
Total unknowns: 0
Total score: A?

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
Dunescoastal
desert
interior
Scrub and Chaparralcoastal bluff scrub
coastal scrub
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 grassland
Great Basin grassland
vernal poolD, < 5%
meadow and seep
alkali playa
pebble plain
Bog and Marshbog and fen
marsh and swampD, < 5%
Riparian and Bottomland habitatriparian forestC, 5% - 20%
riparian woodlandD, < 5%
riparian scrub (incl.desert washes)
Woodlandcismontane woodland
piñon and juniper woodland
Sonoran thorn woodland
Forestbroadleaved upland forest
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): C

Infested Jepson Regions

Click here for a map of Jepson regions

  • CA Floristic Province
  • Cascade Range
  • Central West
  • Desert Province
  • Mojave Desert
  • Sonoran Desert
  • Great Valley
  • Modoc Plateau
  • Northwest
  • Sierra Nevada
  • Sierra Nevada East
  • Southwest