Kalmia latifolia

by Brendan Keegan, Landscape Crew Gardener
June 14, 2019

Kalmia latifolia flowers

Kalmia latifolia

Kalmia latifolia flowers

Kalmia latifolia flowers, photo by Bob Mayer

The small, fast Telico River is a jewel of east Tennessee’s Cherokee National Forest. Its clear waters tumble past moss-covered riverbanks while mountain laurels (Kalmia latifolia) abound on the steep, rocky hillsides. My father often fly-fishes there, casting for the brook trout that sway beneath the rapids. When the Arboretum’s mountain laurels explode with flowers each June, my thoughts drift to the Telico, and to being home.

Kalmia latifolia grows up and down the Appalachian Mountain range. From Quebec to Florida and west to Indiana and Louisiana, the shrub thrives in the cool, acidic, and nutrient-poor soils common on rocky slopes and in coniferous forests. The Arboretum mimics this natural habitat by planting most of its mountain laurels in the acidic soil beneath the hemlocks at the base of Hemlock Hill.

A member of the heath family (Ericaceae), mountain laurel has waxy, evergreen leaves, a multi-stemmed growth habit, and a twisting branch structure. Its trunks grow thick and gnarled with age, albeit slowly. For example, accession 2458*A (K. latifolia ‘Polypetala’) has graced our collection for 133 years, but is less than 8 inches in diameter at breast height. Although K. latifolia rarely exceeds 15 feet tall in New England, it can reportedly top 30 feet in its southern range.

Throughout its extensive distribution, K. latifolia has long been admired. The Cherokee tribe of the Southeast United States carved spoons and trowels from its distinctive, curved branches, inspiring early European settlers to follow suit and to coin the common name “spoonwood.” These days, the shrub’s most celebrated feature is its unique and copious flowers, with their delicate five-sided petals and beautiful pink and white hues. If you look closely, you will see that the flowers bear ten anthers. The tips of each anther are bent backwards, nested in pockets near the edge of the petal. When a pollinator lands on a flower these tension-loaded anthers release and swing forwards, dusting the insect with pollen.

The shrub’s unique characteristics have also enticed researchers at the Arboretum’s Weld Hill Research Building. The Hopkins Lab tapped into the collection to study the mechanics of its pollen dispersal mechanism, while Director William (Ned) Friedman and his research team studied the unique reproductive biology of the ‘Polypetala’ cultivar (see Arnoldia article, “Mutants in our midst” [pdf]). Mary Bryant, of South Deerfield, Massachusetts, discovered this mutant form with narrow, unfused petals, and in 1870 pioneering Harvard botanist Asa Gray became the first to describe it.

Although the mountains may be far away, a walk through the Arboretum’s mountain laurels brings them a few steps closer. In the shade of the hemlocks, you can feel the wind moving through the mountain laurels’ twisting branches and admire the multitude of their brilliant pink and white flowers, popping against a clear June sky. For me, the only thing missing is the whir of a fly reel and, of course, the brook trout, riding the eddies of a cold, Appalachian stream.
 
Originally published in Silva, Spring/Summer 2018

One thought on “Kalmia latifolia

  1. Mountain laurel is the lovely state flower of both Connecticut and Pennsylvania. Now you have opened my eyes to the fact that they are fascinating, as well as beautiful, with their tension- loaded anthers! I’m going outside to check that out in the Kalmia blooming over my mailbox! Thank you.

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