BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Linnaea borealis | Twinflower 



GENERAL BOTANICAL CHARACTERISTICS : 
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 : 
   Chamaephyte


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 seedbanks.  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.


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:

                                  feet            meters
northern ID; western MT      2,200 - 5,900      670 - 1,800 [13,25]
southern CO; northern NM     7,900 - 9,800    2,400 - 2,900 [19]
UT                           6,000 - 9,600    1,830 - 2,900 [67]
CA                           4,000 - 8,000    1,200 - 2,400 [55]


SUCCESSIONAL STATUS : 
Facultative Seral Species

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]:

     young:       89
     mature:      80
     old-growth:  98


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.

Related categories for Species: Linnaea borealis | Twinflower