Mountain Laurels - What's In A Name?

by Thomas Sullivan, class of 2009
When I first learned of the Texas Mountain Laurel (Sophora secundiflora), I presumed it was related to the Mountain Laurel (Kalamia latifolia), the State Flower of my native Pennsylvania. If these Master Gardner classes have taught me anything, it was not to presume. Research, research, research.

The two mountain laurels share a name and great intrinsic beauty but little else. In some ways, they are direct opposites.

Two examples of the Texas Mountain Laurel

And two examples of the Pennsylvania’s Mountain Laurel:

Family Relatives

The family classifications immediately show how different they are. The Texas Mountain Laurel, while essentially an ornamental, is a member of the legume family, Fabacaeae, which includes important agricultural plants such as soybeans, alfalfa, and peanuts. It is native to the Texas Hill Country and ranges throughout the arid and semi-arid high alkaline soils of Texas, New Mexico, Chihuahua, Coahuila, Hidalgo, and Puebla. Conversely, Pennsylvania’s Mountain Laurel is in the Ericaceae family which is literally “lime-hating”. Its family includes azaleas, rhododendron, blueberries and cranberries. It thrives in the moist acidic suits of the Appalachian Mountains from northern Florida to southern Maine. Unlike the Texas Mountain Laurel which does not tolerate temperatures below 10°, it is extremely cold hardy.

Size, Leaves, and Flowers

Both mountain laurels are spring bloomers, although spring comes significantly later in Pennsylvania. The Texas Mountain Laurel blooms in March and lasts for months. The Pennsylvania variety blooms in late May and peaks in June. By July, it is done.

Each is a shrub or small tree growing 6-15 feet with the Pennsylvanian somewhat larger. There is one on record at 40 feet, but most range less than 20.

Both varieties have gorgeous show-stopping flowers. The Texas Mountain Laurel has purple wisteria-like drop down blossoms with a strong aroma described as grape “Kool-Aid”. Pennsylvania’s Mountain Laurel has large showy clusters of pink/white symmetrical flowers with a deep pink or red center. Both have strong evergreen leaves. They both do best in full sun or light shade although the Pennsylvanian tolerates full shade. Curiously, both are toxic. More on this below.

Propagation and Cultivation

The Texas Mountain Laurel is reportedly tricky to transplant. Container plants may require a year or more to establish themselves and bloom. Seeding appears to be preferred by some authors. Dr. William Welch of Texas A&M suggests planting the seeds while they are still unripe and pink. They should be planted in late June or early July. However, since they do not transplant well, better to plant them where you want them.

Pennsylvania’s Mountain Laurel grows wild through out the Appalachian Mountains and is available commercially in containers. Seeds are small and mature late in the season. At least one author suggested propagation is enhanced by cold-moist stratification.

Toxicity

The leaves of the Texas Mountain Laurel are very poisonous and authors warn parents of small children. This may be connected to the myth generated by the plant’s “other” name, Mescal Bean. The bean is not used in the production of mescal or tequila and does not contain any mescaline. However, it does contain alkaloid cytisne which is chemically related to nicotine.   The seeds are toxic if ingested.

The Pennsylvania Mountain Laurel is another story entirely. The leaves, bark, and all green portions of the plant contain andromedotoxin and arbutin which routinely kill horses, cattle, sheep, and deer. It is related to another variety called “sheep laurel” and “lambkill” which, by it very name, certainly indicates its potency.

The Pennsylvanian by birth and Texan by adoption is hard pressed to pick a favorite. So I will just appreciate the extraordinary beauty of each mountain laurel of my homelands.

Acknowledgments:

Horticulture Update: April 2002. Edited by Douglas F. Welsh, Ph.D.

Landscape Horticulture: William C. Welsh, Ph.D. Texas A & M University

Extension Horticulture: Texas Cooperative Extension, Texas A&M University System.

Fabaceae Family: Master Gardeners of the University of Arizona Pima County Cooperative Extension.

USDA National Resources Conservation Service.

Pennsylvania Botanical Society.

Connecticut Botanical Society.