Plant Assessment Form

More Marrubium vulgare resources

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 committee 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. Unknown

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? Consider the impact on the natural range and variation of abiotic ecosystem processes and system-wide parameters in ways that significantly diminish the ability of native species to survive and reproduce. Alterations that determine the types of communities that can exist in a given area are of greatest concern. Examples of abiotic processes include: - fire occurrence, frequency, and intensity; - geomorphological changes such as erosion and sedimentation rates; - hydrological regimes, including soil water table; - nutrient and mineral dynamics, including salinity, alkalinity, and pH; - light availability (e.g. when an aquatic invader covers an entire water body that would otherwise be open). Select the one letter below that best describes this species' most severe impact on an abiotic ecosystem process: A. Severe, possibly irreversible, alteration or disruption of an ecosystem process. B. Moderate alteration of an ecosystem process. C. Minor alteration of an ecosystem process. D. Negligible perceived impact on an ecosystem process. U. Unknown.	U Reviewed Scientific Publication
Identify ecosystem processes impacted: Sources of information:
Question 1.2 Impact on plant community composition, structure, and interactions? Consider the cumulative ecological impact of this species to the plant communities it invades. Give more weight to changes in plant composition, structure, and interactions that involve rare or keystone species or rare community types. Examples of severe impacts include: - formation of stands dominated (>75% cover) by the species; - occlusion (>75% cover) of a native canopy, including a water surface, that eliminates or degrades layers below; - significant reduction or extirpation of populations of one or more native species. Examples of impacts usually less than severe include: - reduction in propagule dispersal, seedling recruitment, or survivorship of native species; - creation of a new structural layer, including substantial thatch or litter, without elimination or replacement of a pre-existing layer; - change in density or depth of a structural layer; - change in horizontal distribution patterns or fragmentation of a native community; - creation of a vector or intermediate host of pests or pathogens that infect native plant species. Select the one letter below that best describes this species' impact on community composition, structure and interactions: A. Severe alteration of plant community composition, structure, or interactions. B. Moderate alteration of plant community composition. C. Minor alteration of community composition. D. Negligible impact known; causes no perceivable change in community composition, structure, or interactions. U. Unknown.	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? Consider the cumulative impact of this species on the animals, fungi, microbes, and other organisms in the communities that it invades. Although a non-native species may provide resources for one or a few native species (e.g. by providing food, nesting sites, etc.), the ranking should be based on the species' net impact on all native species. Give more weight to changes in composition and interactions involving rare or keystone species or rare community types. Examples of severe impacts include: - extirpation or endangerment of an existing native species or population; - elimination or significant reduction in native species' nesting or foraging sites, cover, or other critical resources (i.e., native species habitat), including migratory corridors. Examples of impacts that are usually less than severe include: - minor reduction in nesting or foraging sites, cover, etc. for native animals; - minor reduction in habitat connectivity or migratory corridors; - interference with native pollinators; - injurious components, such as awns or spines that damage the mouth and gut of native wildlife species, or production of anti-digestive or acutely toxic chemical that can poison native wildlife species. Select the one letter below that best describes this species' impact on community composition and interactions: A. Severe alteration of higher trophic populations, communities, or interactions. B. Moderate alteration of higher trophic level populations, communities, or interactions. C. Minor alteration of higher trophic level populations, communities or interactions. D. Negligible impact; causes no perceivable change in higher trophic level populations, communities, or interactions. E. Unknown.	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? Consider whether the species can hybridize with and influence the proportion of individuals with non-native genes within populations of native species. Mechanisms and possible outcomes include: - production of fertile or sterile hybrids that can outcompete the native species; - production of sterile hybrids that lower the reproductive output of the native species. Select the one letter below that best describes this species' impact on genetic integrity: A. Severe (high proportion of individuals). B. Moderate (medium proportion of individuals). C. Minor (low proportion of individuals). D. No known hybridization. U. Unknown.	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? Assess this species' dependence on disturbance: both human and natural: for establishment in wildlands. Examples of anthropogenic disturbances include: - grazing, browsing, and rooting by domestic livestock and feral animals; - altered fire regimes, including fire suppression; - cultivation; - silvicultural practices; - altered hydrology due to dams, diversions, irrigation, etc.; - roads and trails; - construction; - nutrient loading from fertilizers, runoff, etc. Examples of natural disturbance include: - wildfire; - floods; - landslides; - windthrow; - native animal activities such as burrowing, grazing, or browsing. Select the first letter in the sequence below that describes the ability of this species to invade wildlands: A. Severe invasive potential: this species can establish independent of any known natural or anthropogenic disturbance. B. Moderate invasive potential: this species may occasionally establish in undisturbed areas but can readily establish in areas with natural disturbances. C. Low invasive potential: this species requires anthropogenic disturbance to establish. D. No perceptible invasive potential: this species does not establish in wildlands (though it may persist from former cultivation). U. Unknown.	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? Assess this species' rate of spread in existing localized infestations where the proportion of available habitat invaded is still small when no management measures are implemented. Select the one letter below that best describes the rate of spread: A. Increases rapidly (doubling in <10 years) B. Increases, but less rapidly C. Stable D. Declining U. Unknown	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? Assess the overall trend in the total area infested by this species statewide. Include current management efforts in this assessment and note them. Select the one letter below that best describes the current trend: A. Increasing rapidly (doubling in total range statewide in <10 years) B. Increasing, but less rapidly C. Stable D. Declining U. Unknown	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? Assess the innate reproductive potential of this species. Worksheet A is provided for computing the score.	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? Assess whether this species is currently spread: or has high potential to be spread: by direct or indirect human activity. Such activity may enable the species to overcome natural barriers to dispersal that would not be crossed otherwise, or it may simply increase the natural dispersal of the species. Possible mechanisms for dispersal include: - commercial sales for use in agriculture, ornamental horticulture, or aquariums; - use as forage, erosion control, or revegetation; - presence as a contaminant (seeds or propagules) in bulk seed, hay, feed, soil, packing materials, etc.; - spread along transportation corridors such as highways, railroads, trails, or canals; - transport on boats or boat trailers. Select the one letter below that best describes human-caused dispersal and spread: A. High: there are numerous opportunities for dispersal to new areas. B. Moderate: human dispersal occurs, but not at a high level. C. Low: human dispersal is infrequent or inefficient. D. Does not occur. U. Unknown.	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? We have chosen 1 km as the threshold of "long-distance." Assess whether this species is frequently spread, or has high potential to be spread, by animals or abiotic mechanisms that can move seed, roots, stems, or other propagules this far. The following are examples of such natural long-distance dispersal mechanisms: - the species' fruit or seed is commonly consumed by birds or other animals that travel long distances; - the species' fruits or seeds are sticky or burred and cling to feathers or hair of animals; - the species has buoyant fruits, seeds, or other propagules that are dispersed by flowing water; - the species has light propagules that promote long-distance wind dispersal; - The species, or parts of it, can detach and disperse seeds as they are blown long distances (e.g., tumbleweed). Select the one letter below that best describes natural long-distance dispersal and spread: A. Frequent long-distance dispersal by animals or abiotic mechanisms. B. Occasional long-distance dispersal by animals or abiotic mechanisms. C. Rare dispersal more than 1 km by animals or abiotic mechanisms. D. No dispersal of more than 1 km by animals or abiotic mechanisms. U. Unknown.	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? Assess whether this species has invaded ecological types in other states or countries outside its native range that are analogous to ecological types not yet invaded in your state (see Worksheets B, C, and D for California, Arizona, and Nevada, respectively, in Part IV for lists of ecological types). This information is useful in predicting the likelihood of further spread within your state. Select the one letter below that best describes the species' invasiveness in other states or countries, outside its native range. A. This species has invaded 3 or more ecological types elsewhere that exist in your state and are as yet not invaded by this species (e.g. it has invaded Mediterranean grasslands, savanna, and maquis in southern Europe, which are analogous to California grasslands, savanna, and chaparral, respectively). B. Invades 1 or 2 ecological types that exist but are not yet invaded in your state. C. Invades elsewhere but only in ecological types that it has already invaded in the state. D. Not known as an escape anywhere else. U. Unknown.	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? Refer to Worksheet C and select the one letter below that indicates the number of different ecological types that this species invades. A. Widespread: the species invades at least three major types or at least six minor types. B. Moderate: the species invades two major types or five minor types. C. Limited: the species invades only one major type and two to four minor types. D. Narrow: the species invades only one minor type. U. Unknown.	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? To assess distribution, record the letter that corresponds to the highest percent infested score entered in Worksheet C for any ecological type.	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? Scoring Criteria for Worksheet A A. High reproductive potential (6 or more points). B. Moderate reproductive potential (4-5 points). C. Low reproductive potential (3 points or less and less than 3 Unknowns). U. Unknown (3 or fewer points and 3 or more Unknowns).

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? A means >50% of type occurrences are invaded; B means 20% to 50%; C means 5% to 20%; D means present but <5%; U means unknown (unable to estimate percentage of occurrences invaded)
Marine Systems	marine systems
Freshwater and Estuarine	lakes, ponds, reservoirs
Aquatic Systems	rivers, streams, canals
Aquatic Systems	estuaries
Dunes	coastal	D, < 5%
	desert
	interior
Scrub and Chaparral	coastal bluff scrub
	coastal scrub	C, 5% - 20%
	Sonoran desert scrub
	Mojavean desert scrub (incl. Joshua tree woodland)
	Great Basin scrub
	chenopod scrub
	montane dwarf scrub
	Upper Sonoran subshrub scrub
	chaparral	D, < 5%
Grasslands, Vernal Pools, Meadows, and other Herb Communities	coastal prairie	C, 5% - 20%
	valley and foothill grassland	D, < 5%
	Great Basin grassland
	vernal pool
	meadow and seep	D, < 5%
	alkali playa
	pebble plain
Bog and Marsh	bog and fen
Bog and Marsh	marsh and swamp
Riparian and Bottomland habitat	riparian forest
	riparian woodland
	riparian scrub (incl.desert washes)	D, < 5%
Woodland	cismontane woodland	D, < 5%
	piñon and juniper woodland
	Sonoran thorn woodland
Forest	broadleaved upland forest
	North Coast coniferous forest
	closed cone coniferous forest
	lower montane coniferous forest
	upper montane coniferous forest
	subalpine coniferous forest
Alpine Habitats	alpine boulder and rock field
Alpine Habitats	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

California Invasive Plant Council

Protecting California’s environment and economy from invasive plants

Plant Assessment Form

More Marrubium vulgare resources

Marrubium vulgare

Evaluator(s)

List committee members

General Comments

Table 2. Criteria, Section, and Overall Scores

Table 3. Documentation

Worksheet A - Innate reproductive potential

Related traits:

Worksheet C - California Ecological Types

Infested Jepson Regions