mountain laurel

Kalmia latifolia is an evergreen shrub growing 3–9 m (9.8–29.5 ft) tall. The leaves are 3–12 cm (1.2–4.7 in) long and 1–4 cm (0.39–1.57 in) wide. The flowers are pentagonal, ranging from light pink to white, and occur in clusters. There are several named cultivars that have darker shades of pink, red and maroon. It blooms in May and June. All parts of the plant are poisonous. The roots are fibrous and matted.

The plant is naturally found on rocky slopes and mountainous forest areas. It thrives in acid soil, preferring a soil pH in the 4.5 to 5.5 range. The plant often grows in large thickets, covering great areas of forest floor. In the Appalachians, it can become a tree, but is a shrub farther north. The species is a frequent component of oak-heath forests. In low, wet areas it grows densely, but in dry uplands has a more sparse form. In the southern Appalachians, laurel thickets are referred to as "laurel hells” or “laurel slicks” because it is nearly impossible to pass through one.

Kalmia latifolia has been marked as a pollinator plant, supporting and attracting butterflies and hummingbirds. It is also notable for its unusual method of dispensing its pollen. As the flower grows, the filaments of its stamens are bent and brought into tension. When an insect lands on the flower, the tension is released, catapulting the pollen forcefully onto the insect. Experiments have shown the flower capable of flinging its pollen up to 15 cm (5.9 in). Physicist Lyman J. Briggs became fascinated with this phenomenon in the 1950s after his retirement from the National Bureau of Standards and conducted a series of experiments in order to explain it.

The plant was originally brought to Europe as an ornamental plant during the 18th century. It is still widely grown for its attractive flowers and year-round evergreen leaves. Elliptic, alternate, leathery, glossy evergreen leaves (to 5" long) are dark green above and yellow green beneath and reminiscent of the leaves of rhododendrons. All parts of this plant are toxic if ingested. Numerous cultivars have been selected with varying flower color. Many of the cultivars have originated from the Connecticut Experiment Station in Hamden and from the plant breeding of Dr. Richard Jaynes. Jaynes has numerous named varieties that he has created and is considered the world's authority on Kalmia latifolia. In the UK the following cultivars have gained the Royal Horticultural Society's Award of Garden Merit:

'Freckles' – pale pink flowers, heavily spotted 'Little Linda' – dwarf cultivar to 1 m (3.3 ft) 'Olympic Fire' – red buds opening pale pink 'Pink Charm'

Kalmia latifolia is also known as ivybush or spoonwood (because Native Americans used to make their spoons out of it). The plant was first recorded in America in 1624, but it was named after the Finnish explorer and botanist Pehr Kalm (1716–1779), who sent samples to Linnaeus. The Latin specific epithet latifolia means "with broad leaves" – as opposed to its sister species Kalmia angustifolia, "with narrow leaves". Despite the name "mountain laurel", Kalmia latifolia is not closely related to the true laurels of the family Lauraceae.