Plant Assessment Form

Marrubium vulgare

Common Names: horehound; white horehound

Evaluated on: 6/10/04

List committee review date: 08/07/2005

Re-evaluation date:

Evaluator(s)

John J. Knapp/ Invasive Plant Program Manager
Catalalina 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

Joe DiTomaso
Alison Stanton
Joanna Clines
Cynthia Roye
Doug Johnson

General Comments

A larger problem on California islands.

Table 2. Criteria, Section, and Overall Scores

Overall Score? Limited
Alert Status? No Alert
Documentation? 3 out of 5
Score Documentation
1.1 ?Impact on abiotic ecosystem processes U Reviewed Scientific Publication
Impact?
Four-part score UBCD Total Score
C
1.2 ?Impact on plant community B. Moderate Other Published Material
1.3 ?Impact on higher trophic levels C. Minor Other Published Material
1.4 ?Impact on genetic integrity D. None Other Published Material
2.1 ?Role of anthropogenic and natural disturbance in establishment C. Minor Other Published Material
Invasiveness?
Total Points
10 Total Score C
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 Other Published Material
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 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 B
3.2 ?Distribution/Peak frequency
(see Worksheet C)
C. Low 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? U Reviewed Scientific Publication
Identify ecosystem processes impacted:

Sources of information:

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

M. vulgare is only browsed by livestock when no other forage matterial is present (2), which gives it a competitive advantage over surrounding species that are more edible (1). Expands range during drought conditions and outcompetes native vegetation most likely for water due to deep tap root in annual grasslands (3). High priority species of significance on the Channel Islands (4). In 1980 in Victoria, Australia, 6 million ha. of which 100,000 ha were dense, 1.5 million ha. were medium, and 4.4 million ha were scattered (5). Forms small to large dense patches greater than 75% cover on Catalina Island, excluding native vegetation and altering grassland structure (6). Not nearly as invasive on mainland California where it rarely forms dense patches. White horehound is sometimes an especially common weed in overgrazed areas. Plants thrive in areas where there is little competition with other vegetation.


Sources of information:

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

No forage value for browsers and grazers (1,2). Livestock generally avoid consuming the bitter-tasting foliage.


Sources of information:

Question 1.4 Impact on genetic integrity? D Other Published Material

No hybridization is known to occur. No native California taxa are in the genus Marrubium (1).


Sources of information:

(1) Hickman, J.C. (ed.). 1993. The Jepson manual of higher plants of California. P. 715. 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:

Roadsides (1,3), dry waste areas, gardens (1), natural pastrures (2,3), conservation areas (3), and open areas (5,4). Dispersed and established in clean country (2), but mostly disturbed sites (5). Dirt piles, ground squirel mounds, and soil around fallen island scrub oak (6).


Sources of information:

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

In Australia, rapid expansion occurs during drought years when it outcompetes native vegetation (1). On Catalina Island, one population was known in 1896 (3), and by 1923 it was considered common every where on the Island, and then in 2003, 2,921 populations were recorded (2). In other areas of California, it has not expanded and has remained static.


Sources of information:

(1) Anonymous. 1988. Horehound (Marrubium vulgare). Tamar Valley Weed Strategy-www.weeds.asn.au. http://www.weeds.asn.au/weeds/txts/horehound.html.
(2) Knapp, J.J. 2004. Catalina Invasive Plant Ranking Plan for the Catalina Island Conservancy. Unpublished.
(3) Millspaugh, C.F. and Nuttall, L.W. 1923. Flora of Santa Catalina Island. P. 239. Field Museum of Natural History, Botany v.5. Chicago.


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

Occurs on all Channel Islands (1,6,7) small to large populations dominated by M. vulgare (2). Hand-pulled in Solstice Canyon, Santa Monica Mountains (3). Tons of M. vulgare was removed in Big Sycamore Canyon (4). Occurs in the mouths of canyons on the side of coastal side of mountain ranges from Santa Barbara to San Diego (5). On Catalina Island, 18,272,200 ft2 (419 ac) are invaded (8).
Appears relatively stable statewide.


Sources of information:

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

Perennial that grows best on alkaline soils (1). Prolific seeder, but is dependent on rainfall and water availability (2). Large seed bank with high germination rates (2). In California, flowers from April to October (3).


Sources of information:

(1) Anonymous. 1988. Horehound (Marrubium vulgare). Tamar Valley Weed Strategy-www.weeds.asn.au. http://www.weeds.asn.au/weeds/txts/horehound.html.
(2) Lippai, A., P. Smith, T. Price, J. Weiss, and C. Lloyd. 1996. Effects of temperature and water potential on germination of horehound (Marrubium vulgare) seeds from two Australian localities. Weed Science 44: 91-99.
(3) Wilken, D. and Hannah, L. 1998. Marrubium vulgare: Channel Islands National Park Service litterature review. Unpublished.


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

Planted for medicinal purposes in gardens (1), but this is uncommon. M. vulgare was one of the two most common seeds found in the hair shed by bison on Catalina Island, and seed had a rate of 85% viability (2). Dispersed on clothing (3). Movement of soil (4). Fruits disperse by clinging to the shoes and clothing of people, and vehicle tires, and with water, soil movement, mud, and human activities. Vast majority of seed fall directly to ground below parent plant.


Sources of information:

(1) Baker, H.G. 1986. Patterns of plant invasion in North America. Pp. 44-57 in: Mooney, H.A. and J.A. Drake, eds. Ecology of biological invasions of North America and Hawaii. Ecological Studies Volume 58. New York: Springer-Verlag.
(2) Constible, J.M., Sweitzer, R.A., Van Vuren, D.H., Schuyler, P.T. and Knapp, D.A. 2004. Differential dispersal of non-native plants by introduced bison in and island ecosystem. In press.
(3) Anonymous. 1988. Horehound (Marrubium vulgare). Tamar Valley Weed Strategy-www.weeds.asn.au. http://www.weeds.asn.au/weeds/txts/horehound.html.
(4) Knapp, J.J. 2004. Personal observation from 2002-2004, construction areas containing piles of soil on Catalina Island, CA. jknapp@catalinaconservancy.org.


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

Fruits are transported on the fur of animals (1). Animal fur (3,4) and water along drainage lines and creeks (3). Fruits disperse by clinging to the fur, feathers, and feet of animals, and with water. Seeds survive ingestion by horses. (5) Again, these are probably minor means of spread as most seed fall direct to soil surface.


Sources of information:

(1) Baker, H.G. 1986. Patterns of plant invasion in North America. Pp. 44-57 in: Mooney, H.A. and J.A. Drake, eds. Ecology of biological invasions of North America and Hawaii. Ecological Studies Volume 58. New York: Springer-Verlag.
(2) Whitson, T.D., ed. 2001. Weeds of the West. 9th edition. Western Society of Weed Science in cooperation with the Western United States Land Grant Universities Cooperative Extension Services.
(3) Anonymous. 1988. Horehound (Marrubium vulgare). Tamar Valley Weed Strategy-www.weeds.asn.au. http://www.weeds.asn.au/weeds/txts/horehound.html.
(4) Constible, J.M., Sweitzer, R.A., Van Vuren, D.H., Schuyler, P.T. and Knapp, D.A. 2004. Differential dispersal of non-native plants by introduced bison in and island ecosystem. In press.
(5) DiTomaso and Healy. 2006. Weeds of California. UC DANR Publ. #3488.


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

Southern Canada and continental United States (1,3). Declared a noxious weed in Australia and Tasmania (2,3), New Zealand, South Africa, and Hawaii (3).


Sources of information:

(1) Baker, H.G. 1986. Patterns of plant invasion in North America. Pp. 44-57 in: Mooney, H.A. and J.A. Drake, eds. Ecology of biological invasions of North America and Hawaii. Ecological Studies Volume 58. New York: Springer-Verlag.
(2) Anonymous. 1988. Horehound (Marrubium vulgare). Tamar Valley Weed Strategy-www.weeds.asn.au. http://www.weeds.asn.au/weeds/txts/horehound.html.
(3) Wilken, D. and Hannah, L. 1998. Lactuca serriola: Channel Islands National Park Service litterature review. Unpublished.


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

First reported near San Francisco in 1870, and was considered naturalized in southern California by the late 19 century (4). First collected on Catalina Island in 1896 (5). In California, open, wet or dry often rocky places, from lowlands to middle and even upper elevation in the mountains up to 3300 meters (2). On Catalina Island, 18,272,200 ft2 are infested by 2,921 populations, and the following is the percentage of habitats invaded: bare-<0.00%, beach-0.00%, coastal scrub-0.02%, coastal scrub/grassland-7.9%, grassland-1.3%, chaparral-0.02%, riparian-3.2%, and 591 populations in non-native communities (3). Pastures, especially those that are overgrazed, fields, roadsides, rangeland, disturbed natural areas, waste places, ditches, other disturbed places. Most often grows in dry places, but is considered a facultative wetland species (6).


Sources of information:

(2) Cronquist, A. 1984. Intermountain flora: vascular plants of the intermountain west, USA. Volume 4. The New York Botanical Garden, Bronx. 573 pp.
(3) Knapp, J.J. 2004. Catalina Invasive Plant Ranking Plan for the Catalina Island Conservancy. Unpublished.
(4) Wilken, D. and Hannah, L. 1998. Marrubium vulgare: Channel Islands National Park Service litterature review. Unpublished.
(5) Millspaugh, C.F. and Nuttall, L.W. 1923. Flora of Santa Catalina Island. P. 239. Field Museum of Natural History, Botany v.5. Chicago.
(6) DiTomaso and Healy. 2006. Weeds of California. UC DANR Publ. #3488.


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

See 3.1.


Sources of information:

Knapp, observational.
DiTomaso, 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 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 Unknown
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: 7
Total unknowns: 1
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
DunescoastalD, < 5%
desert
interior
Scrub and Chaparralcoastal bluff scrub
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 prairieC, 5% - 20%
valley and foothill grasslandD, < 5%
Great Basin grassland
vernal pool
meadow and seepD, < 5%
alkali playa
pebble plain
Bog and Marshbog and fen
marsh and swamp
Riparian and Bottomland habitatriparian forest
riparian woodland
riparian scrub (incl.desert washes)D, < 5%
Woodlandcismontane woodlandD, < 5%
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
  • Great Valley
  • Northwest
  • Sierra Nevada
  • Southwest
  • Modoc Plateau
  • Sierra Nevada East
  • Mojave Desert