About Kalmia angustifolia subsp. carolina (Small) A.Haines
This subspecies is Kalmia angustifolia subsp. carolina (Small) A.Haines. It produces attractive small deep crimson-pink flowers in early summer, with a primary flowering period from April to May, and less frequent secondary blooms in fall. Each flower has five sepals, a corolla made of five fused petals, and ten stamens fused to the corolla. Pollination is carried out by bumblebees and solitary bees. Each mature fruit capsule holds approximately 180 seeds, and fruiting occurs in early autumn. This plant is a shrub that varies in height from 15 to 90 cm (6 to 35 inches) when growing in the wild. It produces new shoots from dormant buds on buried rhizomes, and this sprouting process is stimulated by fire. Its narrow evergreen leaves are pale on the underside, and tend to grow in groups of three from the stem. The Latin specific epithet angustifolia translates to "narrow-leaved". A distinct feature of this plant is that leaf clusters usually grow at the end of woody stems, while the flowers are arranged in whorls or clusters below the tip of the stem. Its phenology can depend on whether fire occurred earlier in the year. The parent species Kalmia angustifolia is distributed across eastern North America, ranging from Ontario and Quebec south to Virginia. The southern subspecies K. angustifolia subsp. carolina ranges further south, as far as Georgia. It commonly grows in dry habitats of the boreal forest, and is also found in drier sections of peat bogs and pocosins. It can become the dominant plant over large areas after fire or logging. Kalmia angustifolia is a common understory shrub in boreal forests of eastern North America, and frequently grows in black spruce forests. One study found that under closed forest canopies, this plant mostly reproduces vegetatively and produces very few flowers, while it flowers significantly more in sites where black spruce was harvested and burned. Clearcut harvesting of these ecosystems leads to Kalmia angustifolia dominating cleared sites. It is described as opportunistic, re-sprouting after logging and fire, and often inhibits efforts to restore conifer forests. All Kalmia plants contain a glycoside called andromedotoxin, which is poisonous to mammals, making the species unwelcome in pastures. Several of its common names reflect this toxicity, including lamb-kill, sheep kill, calf-kill, pig laurel, sheep-laurel, and sheep-poison. It is also commonly called narrow-leaved laurel and dwarf laurel. Kalmia angustifolia is cultivated as an ornamental shrub for gardens. It prefers moist, acidic soil and partial shade. The species has earned the Royal Horticultural Society's Award of Garden Merit. Numerous cultivars have been selected for garden use; among these, K. angustifolia f. rubra, which has rich red flowers, has also won the award. Indigenous peoples used Kalmia angustifolia to treat swelling and other inflammatory conditions. Recent research has identified potential cosmetic uses for this plant based on its chemical composition.
