Kalmia latifolia

Kalmia latifolia, commonly called Mountain-laurel or Spoonwood, is a flowering plant in the family Ericaceae, native to the eastern United States, from southern Maine south to northern Florida, and west to Indiana and Louisiana.

It is an evergreen shrub growing to 3-9 m tall. The leaves are 3-12 cm long and 1-4 cm wide. Its flowers are star-shaped, ranging from red to pink to white, and occurring in clusters. It blooms between May and June. All parts of the plant are poisonous. Roots are fibrous, matted.^[1]

The plant is naturally found on rocky slopes and mountainous forest areas. The plant often grows in large thickets, covering large areas of forest floor. In North America it becomes a tree on the mountains of the Carolinas but is a shrub further north.^[1]

It is also known as Ivybush, Calico Bush, Spoonwood (because native Americans used to make their spoons out of it), Sheep Laurel, Lambkill and Clamoun.

Mountain-laurel is the state flower of Connecticut and Pennsylvania.

The plant was first recorded in America in 1624, but it was named after Pehr Kalm, who sent samples to Linnaeus in the 18th century.

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Description

• Bark: Dark brown tinged with red, furrowed and scaly. Branchlets at first light reddish green, downy, later smooth, red green and shining, finally all a bright red brown.
• Wood: Brown tinged with red; heavy, hard, rather brittle, close-grained. Sp. gr., 0.7160; weight of cu. ft., 44.62 lbs.
• Winter buds: Leaf-buds naked, forming in midsummer in the axils of leaves just below those from which the clusters of flower-buds are produced by which they are almost covered. The tip of the branch dies when these axillary buds are formed. Inner scales enlarge with the growing shoot, becoming an inch long before falling.
• Leaves: Alternate, or in pairs, or in threes, simple, persistent, oblong, three to four inches long, one to one and a half inches wide, wedge-shaped at base, entire, acute or rounded at apex and tipped with a callous point. They come out of the bud conduplicate; each leaf enclosed by the one directly below it, slightly tinged with pink and covered with glandular white hairs, when full grown are thick and rigid, dark shining green above, pale yellow green beneath; midrib broad, yellow, rounded above and below, veins obscure. They remain green and fall during the second summer. Petioles are short, stout, slightly flattened.
• Flowers: Flowers appear in May or June from buds which are formed in autumn in the axils of the upper leaves in the form of slender cones of downy green scales. These buds usually develop two or more lateral branches, the whole forming a compound many-flowered corymb four or five inches in diameter and overlapped at the flowering time by the leafy branches of the year. Pedicels are red or green, hairy or scurfy and furnished with two bracts at base and developed from the axils of large bracts.
• Calyx: Five-parted; lobes imbricate in bud, narrow, acute, covered with glutinous hairs. Disk prominent, ten-lobed.
• Corolla: Saucer-shaped, rose colored, white, or pink. Tube short with ten tiny sacs just below the five-parted limb; lobes ovate, acute, imbricate in bud. The border is marked on the inner surface with a waving rosy line and is slightly purple above the sac. The buds are ten-ribbed from the sacs to the acute apex of the bud.
• Stamens: Ten, hypogynous, shorter than the corolla, at first held in the sacs of the corolla; filaments thread-like; anthers oblong, adnate, thwo-celled; cells opening by a short longitudinal pore.
• Pistil: Ovary superior, five-celled; style thread-like, exserted; stigma capitate; ovules many in each cell.
• Fruit: Woody capsule, many seeded, depressed-globular, slightly five-lobed, five-celled, five-valved. Crowned with the persistent style, surrounded at base by the persistent calyx, covered with viscid hairs. Seeds oblong.^[1]\

The blossoms of this plant are equipped with a most evident device to secure cross-fertilization. Nature has many such arrangements, but it is not often that they are so openly displayed. Each flower has ten stamens and each corolla is provided with ten little pockets. When the flower opens each stamen is found bent back with its anther thrust into one of these tiny cavities. In the center of the flower lies the nectar, and when the bee comes to get it, she brushes against the filaments, which fly up and scatter their pollen over her body. She leaves on the stigma of the next flower she visits the pollen he has gathered in the first, and so on he goes from flower to flower.^[1] The honey made from this plant is toxic.^[2]

Cultivation and uses

The plant was originally brought to Europe as an ornamental plant during the 18th century. It is still widely grown for its attractive flowers. Numerous cultivars have been selected with varying flower color. Does not flourish in a limestone country.

This is one of the most satisfactory shrubs for lawn or garden. When in full bloom it is of surpassing beauty, and its bright evergreen leaves make it conspicuous at any time.^[1]

A little known American use of the plant was in the making of arbors for early wooden-works clocks. Mountain-laurel is a foodplant of last resort for gypsy moth caterpillars, utilized only during outbreaks when moth densities are extremely high.

Toxicity

Mountain laurel is poisonous to several different animals, including horses, goats, cattle, sheep, and deer, due to andromedotoxin and arbutin. The green parts of the plant, the flowers, twigs, and pollen are all toxic, and symptoms of toxicity begin to appear about 6 hours following ingestion. Poisoning produces anorexia, repeated swallowing, profuse salivation, depression, uncoordination, vomiting, frequent defecation, watering of the eyes, irregular or difficulty breathing, weakness, cardiac distress, convulsions, coma, and eventually death. Autopsy will show GI irritation and hemorrhage.

See also

• List of late spring flowers
• List of early summer flowers

References

• Germplasm Resources Information Network: Kalmia latifolia
• USDA Plant Profile: Kalmia latifolia
• Connecticut Botanical Society Profile: Kalmia latifolia
• Kalmia latifolia images at bioimages.vanderbilt.edu

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