Kalmia polifolia has many common names: bog laurel, swamp laurel, bog kalmia, mountain laurel and alpine laurel, among others. I always called this native shrub (also often listed as a wildflower) bog laurel and will continue to do so. Additionally, over the years bog laurel, depending on geographic location and other small physical differences, was assigned different species and subspecies names and is often referred to as Kalmia microphylla or K polifolia sp microphylla.
This wide-ranging species can be found throughout much of North America. Its habitat is wet, acidic mountain meadows and bogs.
Bog laurel is not a true laurel or bay, but is probably colloquially called a laurel because the aroma and shape of the leaves are similar to true laurel leaves.
Bog laurel has a low, branching form. Its leathery, evergreen leaves are opposite and narrowly lance-shaped with rolled-under margins. Dark green on the upper side of the blade, the underside has fine hairs and often looks grey or whitish. This trait is noted in the species name, polifolia (grey-leaved), which comes from the Greek “polios” meaning “hoary or whitish-grey”.
The inflorescence is a loose terminal cluster of saucer-shaped, rose-pink to lavender flowers. The flower has five sepals, five petals, a five-celled ovary and ten stamens. The top of each stamen is tucked into a small pouch on the petal and is under tension like a bow. When an insect searching for nectar touches the stamen, the stamen pops out of the pouch and dusts the insect with pollen.
The fruits of bog laurel are five-valved, spherical capsules containing many minute seeds. The seeds are winged distally. K polifolia reproduces by seeds, rhizomes and layering (the branches droop to the ground and root).
Native Americans used infusions of bog laurel to treat skin ailments and open sores. They also drank a bog laurel tea as a remedy for spitting up blood. Care must be taken when using bog laurel internally. This plant contains a toxic glycoside, andromedotoxin, which lowers blood pressure, and causes breathing problems, diarrhea, cramps, vomiting and dizziness. Bog laurel is poisonous to sheep and cattle.
Pehr (Peter) Kalm (1716 – 1797), an explorer, botanist and student of Linnaeus is honored by the genus designation.
An example of how common names can cause confusion arises because another “mountain laurel” is the State Flower of Pennsylvania (also Connecticut). Growing up in Pennsylvania I knew one mountain laurel (Kalmia latifolia). Now as a resident of the West Coast, Kalmia polifolia is the plant often called mountain laurel. Scientific names are usually more reliable to identify plants. If only they were as easy to remember as common names.
In August these bog laurel were growing in the Upper Kings Creek Meadow at Lassen Volcanic National Park CA.