Linnaea borealis, twinflower
Howard, Janet L. 1993. Linnaea borealis, twinflower. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://research.fs.usda.gov/feis/species-reviews/linbor
| Abbreviation | Common Name | Scientific Name | Classification | Status |
|---|---|---|---|---|
| Plants | ||||
| LINBOR | twinflower | Linnaea borealis | Life Form: Plants/Forb, Plants/Subshrub Kingdom: Plantae Class: Dicot Order: Dipsacales Family: Caprifoliaceae Genus: Linnaea | Fed. Protected: No Nativity: Native Invasiveness: Noninvasive |
Taxonomy
The currently accepted scientific name of twinflower is Linnaea borealis L. [28,33,55,62,62]. It is a monotypic genus [28]. Recognized subspecies are as follows:
- Linnaea borealis ssp. borealis [35]
- Linnaea borealis ssp. americana (Forbes) Hult. [35,45], American twinflower
- Linnaea borealis ssp. longiflora (Torr.) Hult. [35,55,62], Pacific twinflower
Some authorities [33,62] recognize L. b. ssp. borealis and L. b. ssp. longiflora as the only distinct subspecies of twinflower.
Twinflower growing in Alberta, Canada (CC BY-NC 4.0).
Synonyms
- No entry
Other Common Names
northern twinflower, western twinflower
General Distribution
The typical subspecies of twinflower is distributed from eastern Alaska across Siberia and northern Europe [35]. Pacific twinflower occurs along the West Coast from southern Alaska to northern California [35,55]. American twinflower is distributed from interior Alaska across Canada to Newfoundland and south to northern Arizona and New Mexico, South Dakota, Indiana, West Virginia, and New Jersey [28,35,41].
States and Provinces
- United States: AK, AZ, CA, CO, CT, ID, IL, IN, ME, MD, MA, MI, MN, MT, NH, NJ, NM, NY, ND, OH, OR, PA, RI, SD, UT, VT, WA, WV, WI, WY
- Canada: SK, YT
Site Characteristics
Twinflower grows in soils derived from a variety of parent materials. Soil texture and nutrient levels also vary, and soil moisture levels range from xeric to hydric [13,16,30,59]. The pH range of twinflower-supporting soils in peatland bogs of Minnesota and Saskatchewan is 4.0 to 7.0 [31,39]. Twinflower occurs on all aspects [18]. It is found at the following elevations:
| Location | Elevation | Reference |
|---|---|---|
| Northern Idaho; western Montana | 2,200 - 5,900 ft (670 - 1,800 m) | [13,25] |
| Southern Colorado; northern New Mexico | 7,900 - 9,800 ft (2,400 - 2,900 m) | [19] |
| Utah | 6,000 - 9,600 ft (1,830 - 2,900 m) | [67] |
| California | 4,000 - 8,000 ft (1,200 - 2,400 m) | [55] |
Plant Communities
Twinflower occurs in several grassland and many hardwood and coniferous forest types. It is named as a dominant understory or indicator species in numerous published classifications. A partial listing is as follows:
- Preliminary plant associations of the southern Oregon Cascade Mountain Province [4]
- Preliminary plant associations of the Siskiyou Mountain Province [5]
- Ecology of wetlands in Big Meadows, Rocky Mountain National Park, Colorado [12]
- Forest habitat types of northern Idaho: A second approximation [13]
- Classification of montane forest community types in the Cedar River drainage of western Washington, U.S.A. [18]
- A classification of forest habitat types of northern New Mexico and southern Colorado [19]
- Classification, description, and dynamics of plant communities after fire in the taiga of interior Alaska [24]
- Forest vegetation of the Black Hills National Forest of South Dakota and ;Wyoming: a habitat type classification [34]
- Plant communities of Voyageurs National Park, Minnesota, U.S.A. [46]
- Forest habitat types of Montana [57]
Blooming twinflower.
Botanical Description
Twinflower is a native, evergreen, dwarf shrub [20]. It is creeping or trailing in growth form, with numerous short aerial stems rising from the stolon. With time, stolons may become shallowly buried beneath litter and duff layers [17]; maximum depth of twinflower stolons in a mixed conifer old-growth forest of central Oregon was 0.11 inch (0.27 cm) below the soil surface [2]. Aerial stems become woody with age but rarely exceed 0.12 inch (0.30 cm) in diameter. The root crown of these stems is positioned at or just beneath the duff or soil surface [17]. Twinflower has a shallow, fibrous network of roots with their growing points within and slightly below the duff layer [56]. In the central Oregon study mentioned above, average root depth was 0.11 inch (0.28 cm) [2]. Twinflower fruit is a small, dry, one-seeded capsule [30,62].
Raunkiaer Life Form (Raunkiaer 1934)
- Chamaephyte
Seasonal Development
Twinflower blooms from June through September throughout most of its range [30,36]. Flowers last about 7 days, and fruits mature approximately 36 days after flowering [32]. The leaves persist for 2 years [21]; season of leaf abscission was not reported in the literature.
Regeneration Processes
Vegetative reproduction by stolons is the primary method of twinflower regeneration [2,21]. Twinflower first produces stolons at 5 to 10 years of age [21].
Sexual reproduction is uncommon, but seedlings are occasionally found in burned or other disturbed areas [21,65]. Pollination is effected by native bees and syrphid wasps [6,30]; rarely, plants are self-fertile [30]. Twinflower produces abundant seed [29], which apparently does not persist in seed banks. A study in a paper birch-balsam fir (Betula papyrifera-Abies balsamea) forest on Mont Jacques-Cartier in Quebec showed a twinflower seed density of six seeds per square meter, with none of the seeds proving viable [54]. In British Columbia, Kellman [42] found only one viable twinflower seed in 34 samples collected from the litter, A, and B soil horizons. Twinflower seed attaches to the fur, hides, or feathers of animals, which serve as dispersal agents.
Successional Status
Twinflower tolerates a wide spectrum of light intensity. It grows in full daylight in alpine meadows and peat bogs [12,39], but subcanopy light has been measured at 2 percent of full daylight in a closed-canopy mountain hemlock-western redcedar (Tsuga heterophylla-Thuja plicata)/twinflower type near Vancouver, British Columbia [51].
Twinflower is found in recently disturbed, seral, and climax plant communities. Irwin [37] reported it as "abundant" after shelterwood cutting in a western hemlock-western redcedar forest of northern Idaho. Several authors have noted its presence in various climax forest types [13,17,18,24,25,38].
In a study of understories of young (30-80 yrs), mature (80-195 yrs), and old-growth (195-900 yrs) Douglas-fir forests of the Cascade Range of Washington and Oregon, percent occurrence of twinflower by forest age was as follows [63]:
| Forest age | Occurrence (%) |
|---|---|
| Young | 89 |
| Mature | 80 |
| Old-growth | 98 |
Immediate Fire Effects
Twinflower is killed even by low-intensity fire [9,17,23,50,65].
Postfire Regeneration Strategy (Stickney 1989)
- Surface rhizome/chamaephytic root crown
- Secondary colonizer - off-site seed
Fire Adaptations
Twinflower is a fire avoider [56]. During fire, small patches of twinflower in draws, moist duff, or other protected places usually escape burning [15,17]. Twinflower most commonly establishes in burn areas from stolons produced by these unburned plants. It also establishes from animal-dispersed seed [3,56].
Plant Response to Fire
Twinflower sometimes colonizes new areas after fire. In northwestern Montana, broadcast burning was conducted to remove slash following logging of subalpine fir (Abies lasiocarpa). Twinflower had previously been absent from the site. Twinflower seedlings first appeared at postfire year 6, showing 1 percent ground cover. At postfire year 9, twinflower cover was still at 1 percent [65]. Broadcast burning was also conducted at a nearby site where prefire twinflower cover was 8 percent. The fire removed 11 percent of the duff, and all existing twinflower was killed. As with the previously mentioned fire, twinflower seedlings first established at postfire year 6, showing 1 percent cover. By postfire year 8, twinflower cover at this site had increased to 8 percent [65].
In Pacific silver fir (Abies amabilis)-subalpine fir forests of central British Columbia, twinflower frequency on 4- to 22-year-old burns was 60 percent. Frequency on 37- to 75-year-old burns was 70 percent [26].
Two consecutive annual, low-intensity prescribed fires were conducted on the Petawawa Experimental Station in Ontario. Prefire relative twinflower density was 9.65 percent. After the first fire, twinflower relative density lowered to 0.14 percent. It dropped to 0.11 percent after the second fire [52].
Fire Regimes
For fire regime information, search FEIS for this species by entering the species name on the Advanced Search page and selecting “Fire Regime” as the publication type.
Fire Management Considerations
Brown and Marsden [11] have developed an equation for estimating fuel weight of twinflower and other small woody plants, grasses, and forbs in coniferous forests of western Montana and northern Idaho. Brown [10] developed a method of determining bulk densities of nonuniform surface fuels in subalpine fir/twinflower and other forest types of that region.
Federal Status
None
Other Status
No entry.
Importance to Wildlife and Livestock
Bighorn sheep of Alaska and caribou of northern Canada use twinflower as incidental forage [7,61]. It provides 9.7 percent of winter diets of Roosevelt elk of British Columbia, Washington, and Oregon, but only 0.5 percent of their summer diets [40]. It is listed as a food item of ruffed grouse of Idaho [36].
Palatability and Nutritional Value
Dry matter nutrient content of twinflower in Manitoba is 7.0 percent protein and 39.3 percent acid detergent fiber. Estimated dry matter digestibility for caribou is 59.5 percent [60].
Cover Value
No entry.
Value for Rehabilitation or Restoration of Disturbed Sites
No entry.
Other Uses
No entry.
Other Management Considerations
No entry.
Table A1— Forest and range ecosystems, Bureau of Land Management (BLM) physiographic regions, Kuchler plant associations, Society for American Foresters (SAF) forest cover types, and Society for Rangeland Management (SRM) rangeland cover types in which this species occurs.
Forest and Range Ecosystems (Garrison et al. 1977)
- FRES10 White - red - jack pine
- FRES11 Spruce – fir
- FRES18 Maple - beech – birch
- FRES19 Aspen – birch
- FRES20 Douglas-fir
- FRES21 Ponderosa pine
- FRES22 Western white pine
- FRES23 Fir – spruce
- FRES24 Hemlock - Sitka spruce
- FRES25 Larch
- FRES26 Lodgepole pine
- FRES27 Redwood
- FRES28 Western hardwoods
- FRES38 Plains grasslands
- FRES44 Alpine
BLM Physiographic Regions (Bernard and Brown 1977)
- 1 Northern Pacific Border
- 2 Cascade Mountains
- 3 Southern Pacific Border
- 4 Sierra Mountains
- 5 Columbia Plateau
- 6 Upper Basin and Range
- 8 Northern Rocky Mountains
- 9 Middle Rocky Mountains
- 10 Wyoming Basin
- 11 Southern Rocky Mountains
- 12 Colorado Plateau
- 15 Black Hills Uplift
- 16 Upper Missouri Basin and Broken Lands
Kuchler Plant Associations (Kuchler 1964)
- K001 Spruce - cedar - hemlock forest
- K002 Cedar - hemlock - Douglas-fir forest
- K003 Silver fir - Douglas-fir forest
- K004 Fir - hemlock forest
- K005 Mixed conifer forest
- K006 Redwood forest
- K008 Lodgepole pine - subalpine forest
- K011 Western ponderosa forest
- K012 Douglas-fir forest
- K013 Cedar - hemlock - pine forest
- K014 Grand fir - Douglas-fir forest
- K015 Western spruce - fir forest
- K016 Eastern ponderosa forest
- K017 Black Hills pine forest
- K018 Pine - Douglas-fir forest
- K020 Spruce - fir - Douglas-fir forest
- K021 Southwestern spruce - fir forest
- K028 Mosaic of K002 and K026
- K029 California mixed evergreen forest
- K052 Alpine meadows and barren
- K066 Wheatgrass – needlegrass
- K067 Wheatgrass - bluestem – needlegrass
- K093 Great Lakes spruce - fir forest
- K094 Conifer bog
- K095 Great Lakes pine forest
- K096 Northeastern spruce - fir forest
- K106 Northern hardwoods
- K107 Northern hardwoods - fir forest
- K108 Northern hardwoods - spruce forest
- K109 Transition between K104 and K106
SAF Cover Types (Eyre 1980)
- 1 Jack pine
- 5 Balsam fir
- 12 Black spruce
- 13 Black spruce – tamarack
- 15 Red pine
- 16 Aspen
- 18 Paper birch
- 20 White pine - northern red oak - red maple
- 21 Eastern white pine
- 22 White pine – hemlock
- 23 Eastern hemlock
- 24 Hemlock - yellow birch
- 25 Sugar maple - beech - yellow birch
- 26 Sugar maple – basswood
- 27 Sugar maple
- 30 Red spruce - yellow birch
- 31 Red spruce - sugar maple – beech
- 32 Red spruce
- 33 Red spruce - balsam fir
- 35 Paper birch - red spruce - balsam fir
- 37 Northern white-cedar
- 38 Tamarack
- 51 White pine - chestnut oak
- 60 Beech - sugar maple
- 107 White spruce
- 201 White spruce
- 202 White spruce - paper birch
- 203 Balsam poplar
- 204 Black spruce
- 205 Mountain hemlock
- 206 Engelmann spruce - subalpine fir
- 210 Interior Douglas-fir
- 211 White fir
- 212 Western larch
- 213 Grand fir
- 215 Western white pine
- 216 Blue spruce
- 218 Lodgepole pine
- 251 White spruce – aspen
- 252 Paper birch
- 253 Black spruce - white spruce
- 254 Black spruce - paper birch
SRM Rangeland Cover Types (Shiflet 1994)
- No entry
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