(bog Labrador tea)
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Photo of Rhododendron groenlandicum by Jacob Frank
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Bog labrador tea is a lowland shrub occurring in spruce and mixed forests with aromatic, leathery leaves and clusters of white flowers. Plants are usually erect, growing 30-80 cm tall. Leaf blades are
lanceolate-
ovate, 5-12 mm wide (broader than the leaves of
R. tomentosum ssp.
decumbens). The leaves are thick, with inrolled margins, and obtuse tips. The upper surface is dark green and the lower surface is beset with rusty-brown hairs. The stems are densely rust-haired.
Inflorescences grow at the tips of branches, many flowered, in a rounded cluster. Flowers have five white petals, 5-7 mm long. There are typically 8
stamens, but there can be as few as 5 or as many as 10. The
pedicels curve downward in fruit (not abruptly bent as in
R. tomentosum ssp.
decumbens). The fruit is a
capsule, which splits open from the bottom into five parts, releasing many seeds.
Bog labrador tea flowers in mid-summer, fruiting in autumn. The fruits remain attached to the plant most of the winter. The leaves are evergreen. In the fall, leaves take on a reddish-brown hue and are bent downwards. In early spring, this color and orientations serves to protect leaves from the sun until later in the season, when water is available for photosynthesis. In a study in southern Ontario,
Rhododendron groenlandicum leaves lasted two seasons, dropped in the summer or fall of their second year (
Reader 1978). Older leaves had lower photosynthetic rates than new leaves, but contributed nitrogen and phosphorous to the growing region before they senesced. Leaf lifespan increases with latitude, and leaves in Denali may last closer to three years (
Kudo 1995). Flowers appear mid-summer.
Bog labrador tea has bisexual flowers. In an experiment in New Brunswick, Canada, bog labrador tea was both out-crossing and self-fertile (
Wheelwright et al. 2006). Plants had the highest level of fruit set when out-crossed, but did not suffer significantly from being self-pollinated. Flowers also set fruit when bagged and left alone, meaning they are adapted to auto-depositing pollen. However the numbers of seeds in these self-fertilized fruits was much lower. Hand-selfed and hand out-crossed fruits had similar seed set, meaning the species suffers little from inbreeding depression. The many small seeds are wind-dispersed. Plants also spread vegetatively from their roots.
The Noctuid moth
Eugraphe subrosea uses
R. groenlandicum as a host plant (
Biological Records Centre 2008). Spruce needle rust (
Chrysomyxa ledicola) infects both
R. groenlandicum and spruce trees at different stages of its life cycle (
Hennon 2001).
Like the more common narrow-leaved labrador tea, the leaves of R. groenlandicum are boiled in water to make a tea, used as a beverage and a medicine. The tea has also been used for treating colds/flu, arthritis, constipation, cuts and scrapes, hangovers, indigestion and gas, and other stomach troubles.
Disclaimer for Known Uses.
Rhododendron groenlandicum (=Ledum groenlandicum) is a North American boreal species that occurs across all of Canada to Greenland, ranging southwards into the Pacific Northwest, upper Midwest, and New England states. This species occurs over most of the boreal areas of Alaska, but is most common in the eastern half of the state, and rare along the west coast. In Denali, it is common in the boreal zone north of the Alaska Range crest, with a few localities to the south in the region of Broad Pass.
Details are shown in the Plots & Charts found at right, depicting recent Denali data.
This species has the high amount of cover at 20-28 degrees incline, but it is dwarfed by R. tomentosum subsp. decumbens on all other slopes. It is most frequent at less than 300 m elevation, with a second peak at 700-900. It is slightly more common on south facing slopes. This species has a lower elevational range than R. tomentosum subsp. decumbens, found from 122 to 1361 m (or 1000 m, excluding outliers).
Details are shown in the Plots & Charts found at right. For more on how to interpret these figures, visit Understanding Data Presented.
Wide-ranging; moist to somewhat dry lowland sites.
