Kalmia latifolia, the mountain laurel,[3] calico-bush,[3] or spoonwood,[3] is a species of flowering plant in the heath family Ericaceae, that is native to the eastern United States. Its range stretches from southern Maine south to northern Florida, and west to Indiana and Louisiana. Mountain laurel is the state flower of Connecticut and Pennsylvania. It is the namesake of Laurel County in Kentucky, the city of Laurel, Mississippi, and the Laurel Highlands in southwestern Pennsylvania.[4]
Kalmia latifolia is an evergreen shrub growing 3–9 m (9.8–29.5 ft) tall. The leaves are 3–12 cm long and 1–4 cm wide. The flowers are hexagonal, sometimes appearing to be 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.[5]
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.[5] The species is a frequent component of oak-heath forests.[6][7] 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" because it is nearly impossible to pass through one.
Kalmia latifolia has been marked as a pollinator plant, supporting and attracting butterflies and hummingbirds.[8]
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.[9] Experiments have shown the flower capable of flinging its pollen up to 15 cm.[10] 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.[11]
Kalmia latifolia is also known as ivybush or spoonwood (because Native Americans used to make their spoons out of it).[12][13]