common comfrey Symphytum officinale L. - Alaska Natural Heritage ...

common comfrey 

Symphytum officinale L. 

Synonyms: Symphytum officinale ssp. uliginosum (Kern.) Nyman, Symphytum uliginosum Kern. 

Other common names: asses-ears, backwort, boneset, bruisewort, consolida, consound, gum plant, knitback, knit-bone, 

slippery-root 

Family: Boraginaceae 

Invasiveness Rank: 48 The invasiveness rank is calculated based on a species’ ecological impacts, biological 

attributes, distribution, and response to control measures. The ranks are scaled from 0 to 100, with 0 representing a 

plant that poses no threat to native ecosystems and 100 representing a plant that poses a major threat to native 

ecosystems. 

Description 

Common comfrey is a perennial herb that grows 

between 50 and 150 cm tall from a thick, branched 

taproot. The plant is covered in spreading, downwardcurved, 

conical, bristly hairs. Stems are ascending to 

erect and hollow. Stem ridges, which run down the 

stems from the leaf bases, are present on the internodes. 

Basal leaves are obovate to oblong, 15 to 30 cm long, 

and 7 to 12 cm wide with long petioles. Stem leaves are 

5 to 15 cm long, oblong-lanceolate, long-tapering, 

entire, and alternate. They usually have shorter petioles 

but are sometimes sessile. Leaves decrease in size up the 

stem. The inflorescences consist of several to many pairs 

of drooping, coiled flowers. Flowers are radially 

symmetrical and 12 to 18 mm long. They can be deep 

purple, pale purple, blue, pink, or cream colored. 

Flowers are comprised of five petals, fused into a bell 

shape. Each flower produces four ovoid nutlets. Nutlets 

attach to the base of the flower, and contain 1 seed each. 

Seeds are are glossy black, 4 or 5 mm long, and 3 mm 

wide (DiTomaso and Healy 2007, Klinkenberg 2010, 

NatureGate 2010). 

Similar species: Common comfrey looks similar to two 

other non-native plants that are tracked in Alaska: 

prickly comfrey (Symphytum asperum) and common 

borage (Borago officinalis). Prickly comfrey can be 

differentiated from common comfrey by the absence of 

stem ridges on its internodes. Common borage can be 

differentiated from common comfrey as it is an annual 

and has bowl- opposed to bell-shaped flowers. Also, 

common borage flowers have petals that are fused at the 

base and have widely spread lobes. Common comfrey 

looks superficially similar to the native tall bluebells 

(Mertensia paniculata), however tall bluebells can be 

differentiated by its heart-shaped basal leaves, lack of 

ridges along the stem, and flowers that with five bulges 

at their throats. In contrast to the bristly hairs of 

common comfrey, tall bluebells is glabrous or has short, 

appressed hairs (AKEPIC 2010, Hultén 1968, DiTomaso 

and Healy 2007, Klinkenberg 2010). 

Symphytum officinale L. Photo by T. Heutte. 

Symphytum officinale L. Photo by R. Old 

Ecological Impact 

Impact on community composition, structure, and 

interactions: Thick clumps of common comfrey may 

change the density of forb layers. Common comfrey 

appears to increase the plant density of mixed forbgraminoid 

roadside and lot habitats in Southeast Alaska 

(AKEPIC 2010). It has the potential to reduce the 

number of individuals in surrounding native species 

populations through a combination of increased 

Last Updated: 2010-10-28 by Timm Nawrocki 

http://aknhp.uaa.alaska.edu

competition for space, nutrients, water, bees and other 

pollinating insects, and seed dispersal agents such as 

ants (DiTomaso and Healy 2007, Goulson et al. 1998, 

Peters et al. 2003). It contains pyrrolizidine alkaloids 

that can cause liver damage in herbivores, resulting in 

death if enough alkaloids are consumed (DiTomaso and 

Healy 2007, Medicinal Plants for Livestock 2008). The 

seeds of common comfrey are very attractive to ants in 

Germany (Peters et al. 2003), and they may alter antplant 

interactions in Alaska. The flowers are pollinated 

by insects, especially long-tongued bees (DiTomaso and 

Healy 2007, Goulson et al. 1998). Native plantpollinator 

relationships could be impacted by the 

presence of common comfrey. 

Impact on ecosystem processes: Specific ecosystem 

impacts caused by common comfrey are largely 

unknown. While this species may reduce the nutrients 

and moisture available for native species, it is unlikely 

to have any major impacts on ecosystem processes. 

Biology and Invasive Potential 

Reproductive potential: Common comfrey reproduces 

by seed and vegetatively from root fragments. Each 

flower produces four seeds, and plants are capable of 

producing large numbers of flowers (DiTomaso and 

Healy 2007). Seeds remain viable in soil for several 

years although the exact amount of time is unknown 

(Crop Compendium 2010). 

Role of disturbance in establishment: Common comfrey 

requires moist, nutrient-rich soil in a disturbed area or 

garden (DiTomaso and Healy 2007). 

Potential for long-distance dispersal: Seeds are 

dispersed by ants (Peters et al. 2003) and water 

(Moggridge et al. 2009). The seeds have elaiosomes, 

fleshy-oily protuberances that attract ants (Pemberton 

and Irving 1990). Common comfrey has spread by seed 

in Southeast Alaska from planted populations (Rapp 

2006). 

Potential to be spread by human activity: Common 

comfrey is planted by people in Alaska as an ornamental 

and a medicinal plant. Planted populations in Glacier 

Bay National Park have caused several infestations in 

surrounding areas (Rapp 2006). 

Germination requirements: Seeds germinate rapidly in 

moist soils of open sites. They germinate especially well 

in gardens, peat and loam. They are also able to 

germinate in water (DiTomaso and Healy 2007). 

Growth requirements: Common comfrey usually grows 

on moist, nutrient-rich soils. In regions with cold 

winters, the foliage dies during the winter and 

regenerates from the roots with the return of warm 

weather. It can tolerate semi-shade (DiTomaso and 

Healy 2007, Plants for a Future 2010). 

Congeneric weeds: Prickly comfrey (Symphytum 

asperum) is a tracked non-native plant in Alaska and it 

is considered noxious in California (AKEPIC 2010, 

USDA 2010). 

Legal Listings 

Has not been declared noxious 

Listed noxious in Alaska 

Listed noxious by other states 

Federal noxious weed 

Listed noxious in Canada or other countries (QC) 

Distribution and Abundance 

Common comfrey grows on moist, fertile soils in 

disturbed areas or gardens (DiTomaso and Healy 2007). 

In England, it grows especially well in riparian 

environments (Goulson et al. 1998, Moggridge et al. 

2009). However, it is not documented as being invasive 

in riparian environments in the U.S., nor has it invaded 

any riparian environments in Alaska (AKEPIC 2010, 

DiTomaso and Healy 2007). 

Native and current distribution: Common comfrey is 

native to Europe and was introduced to North America 

as an ornamental and a medicinal herb. It can now be 

found in Europe, North America, Japan, and Australia. 

Infestations are documented from Southeast Alaska 

(AKEPIC 2010, DiTomaso and Healy 2007, Ibaraki 

Nature Museum 2010, National Herbarium of South 

Wales 2010). It is not known from arctic or subarctic 

regions. 

Pacific Maritime 

Interior- Boreal 

Arctic-Alpine 

Collection Site 

Distribution of common comfrey in Alaska 

Management 

Common comfrey can be difficult to remove due to the 

potential for vegetative regeneration from root 

fragments. Digging is required to remove the plant and 

the large network of roots. Populations in Glacier Bay 

National Park persisted after multiple years of manual 

removal efforts. Mowing plants before they produce 

seeds can prevent populations from spreading 

(DiTomaso and Healy 2007, Rapp 2006). 



References: 

AKEPIC database. Alaska Exotic Plant Information 

Clearinghouse Database. 2010. Available: 

http://akweeds.uaa.alaska.edu/ 

Crop Compendium. 2010. Bayer CropScience AG, 

Bayer. Available at 

http://compendium.bayercropscience.com 

DiTomaso, J., and E. Healy. 2007. Weeds of California 

and Other Western States. Vol. 1. University of 

California Agriculture and Natural Resources 

Communication Services, Oakland, CA. 834 p. 

Goulson, D., J. Stout, S. Hawson, J. Allen. 1998. Floral 

display size in comfrey, Symphytum officinale 

L. (Boraginaceae): relationships with visitation 

by three bumblebee species and subsequent 

seed set. Oecologia. 113(4). 502-508 p. 

Hultén, E. 1968. Flora of Alaska and Neighboring 

Territories. Stanford University Press, Stanford, 

CA. 1008 pp. 

Ibaraki Nature Museum, Vascular Plants collection. 

2010. Accessed through GBIF (Global 

Biodiversity Information Facility) data portal 

(http://data.gbif.org/ datasets/resource/8030, 

2010-09-15). National Museum of Nature and 

Science. Ibaraki, Japan. 

Invaders Database System. 2010. University of 

Montana. Missoula, MT. 

http://invader.dbs.umt.edu/ 

ITIS. 2010. Integrated Taxonomic Information System. 

http://www.itis.gov/ 

Klinkenberg, B. (Editor) 2010. Symphytum officinale L. 

In: E-Flora BC: Electronic Atlas of the Plants 

of British Columbia. Lab for Advanced Spatial 

Analysis, Department of Geography, University 

of British Columbia. Vancouver, BC. [10 

September 2010] Available: 

http://www.geog.ubc.ca/ 

biodiversity/eflora/index.shtml 

Medicinal Plants for Livestock. 2008. Symphytum 

officinale – comfrey. Department of Animal 

Science, Cornell University. [15 September 

2010]. Available at http://www.ansci.cornell 

.edu/plants/medicinal/comf.html 

Moggridge, H., A. Gurnell, and J. Mountford. 2009. 

Propagule input, transport, and deposition in 

riparian environments: the importance of 

connectivity for diversity. Journal of Vegetation 

Science. 20(3). 465-474 p. 

National Herbarium of New South Wales. 2010. 

Accessed through New South Wales Flora 

Online (http://plantnet.rbgsyd.nsw.gov.au, 

2010-09-15). Royal Botanic Gardens and 

Domain Trust. Sydney, Australia. 

NatureGate. 2010. Finland Nature and Species. 

Helsinki, Finland. [4 October 2010] Available: 

http://www.luontoportti.com/ suomi/en/ 

Pemberton, R. and D. Irving. 1990. Elaiosomes on 

Weed Seeds and the Potential for 

Myrmecochory in Naturalized Plants. Weed 

Science. 38(6). 615-619 p. 

Peters, M., R. Oberrath, and K. Böhning-Gaese. 2003. 

Seed dispersal by ants: are seed preferences 

influenced by foraging strategies or historical 

constraints Flora – Morphology, Distribution, 

and Functional Ecology of Plants. 198(6). 413- 

420 p. 

Plants for a Future. 2010. [5 October 2004] Available: 

http://www.pfaf.org/user/default.aspx 

Rapp, W. 2006. Exotic Plant Management in Glacier 

Bay National Park and Preserve, Gustavus, 

Alaska: Summer 2006 Field Season Report. 

Exotic Plant Program, Glacier Bay National 

Park and Preserve, National Park Service, U.S. 

Department of the Interior. Gustavus, AK. 124 

p. 

USDA. 2010. The PLANTS Database. National Plant 

Data Center, Natural Resources Conservation 

Service, United States Department of 

Agriculture. Baton Rouge, LA. 

http://plants.usda.gov

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