Photo credit: Katja Schulz from Washington, D.C., USA
Mountain laurel (Kalmia latifolia) is a familiar shrub. While common, it is also extraordinary. A part of Pennsylvania’s folklore as the state flower and also studied by scientists for its biomechanics, this broadleaf evergreen abounds in mystique.
Since the early 18th century, mountain laurel has been cultivated as a flowering ornamental, an exotic addition to English gardens. English breeders later shipped it back across the Atlantic to be sold to Americans as a potted plant. At least 75 cultivars, mostly propagated through tissue culture, are available today. Its native range, however, is the eastern United States, extending from southern Maine to Louisiana and northern Florida. A total of seven species are known throughout North America, including sheep laurel (Kalmia angustfolia) and bog laurel (Kalmia polifolia). Along with rhododendrons, azaleas, huckleberries, and Indian pipe, Kalmias are ranked among the Ericacea (heath) family.
Mountain laurel is the most prolific of the Kalmia species. In the woods, it can grow in dense gnarly thickets known colloquially in southern states as “laurel hells.” Foresters and lumbermen in Pennsylvania have been heard to curse it with off-color expressions and not-so-nice epithets, the least offensive being “ankle breaker” or “ankle twister.” Mature plants average heights from seven to ten feet, but some specimens have been recorded as tall as 40 feet. Ascending and horizontal branches are often contorted and considered picturesque, and although a shrub, the healthiest of mountain laurel can take on the stature of a small tree. Its growth rate, however, is slow, four to eight feet over the course of a decade. Laurel wood and its burls have been used for various tools and utensils, explaining one of its many monikers, “spoonwood.”
The corymb is the marquee attraction. The fused petals of mountain laurel’s florets are shaped like inverted parasols. They range from near white to a blush of pink, while their corollas include subtle markings that can reveal either cinnamon, scarlet, rose, or burgundy. Like the symmetrical shapes of dancers in a 1930s Busby Berkeley musical, each floret is perfectly formed. From late May to late June, scores of these corymbs appear in one of two stages, bud or bloom.
As mountain laurel blooms, something extraordinary happens. A recent study publicized in the Harvard Gazette called Kalmia latifolia “one of the fastest-moving plants on the globe.” How can a shrub, planted with its roots in the ground, be all about motion?
For more than a century botanists have observed that the opening of a bloom literally creates a tension in the filament similar to the cocking of a catapult. Scientists have slowed down their observations using high-speed cameras to study mountain laurel and its pollinators. Sacs of pollen, attached to ten separate anthers, are nestled into the base of the bud that will open into the corolla. As the bloom swells, then opens, the filaments attached to each anther are pulled backward in an arc, creating a hair-like trigger. When a bumblebee begins to explore, the filament hurls the pollen at the underside of the bee. A video in this article "Harvard researchers study flower that catapults pollen" demonstrates that phenomenon.
Governor Gifford Pinchot dubbed mountain laurel the state flower of the Commonwealth of Pennsylvania in 1933. One factor in its designation concerned the shrub being located in nearly all of the state’s sixty-seven counties, but the public’s concern for conservation might have also played a role.
Generations of Pennsylvanians have been admonished by their parents, scout leaders, and camp counselors that it was against the law to pick the state flower. This is not true, according to the Department of Conservation and Natural Resources. There are also no legal restrictions on cultivating Kalmia latifolia, although special permits and inspections from the Pennsylvania Department of Agriculture are required to sell any collected native specimens.
During the 1920s, an estimated twenty million pounds of laurel foliage was picked annually throughout its range and used for decorations, especially holiday wreaths, boughs, and floral arrangements. It is still used by florists to a much lesser extent.
In 1913, the New York Botanical Gardens published a booklet entitled, “Wild plants needing protection.” Among fourteen plants, such as two-leaf lady slipper and wild azalea, the author, Elizabeth Britton, made a case for mountain laurel. She posed a question that goes to the heart of commercial exploitation of any natural resource. “Rhododendrons and laurel are being shipped in carload lots by dealers from the mountains of Pennsylvania and the southern Alleghenies, who supply florists and nurserymen from wild sources. How long can they last?”
It wasn’t until the 1980s in Pennsylvania, following the passage of the federal Endangered Species Act of 1973, that specific plant populations were tracked and assigned special protection. So how did the unwritten prohibition against picking begin? Did public sentiment, intertwined with its status as a state flower, create the taboo that protected mountain laurel? At one time, even the National Council of State Garden Clubs had a rule prohibiting laurel flowers and foliage from being used in floral arrangements that were part of competitive judging. To what degree, if any, did a concern for overpicking of mountain laurel play in its conservation? Likely there is more to the story.