Kalmia latifolia
Kalmia
mountain American-laurel, mountain laurel
azalea, laurel
erect, (branched and mat-forming in K. procumbens);
twigs glabrous, puberulent, or stipitate-glandular, sometimes glabrescent.
alternate (seemingly whorled on slow-growing twigs);
petiole 10–30 mm, glabrous or puberulent, sometimes stipitate-glandular;
blade elliptic to elliptic-lanceolate, 4–12 × 1.5–5 cm, margins plane, apex acute, surfaces stipitate-glandular, glabrescent abaxially, glabrous, midrib puberulent adaxially.
persistent (deciduous in K. cuneata), alternate, opposite, or in whorls of 3;
petiole present;
blade usually coriaceous, (base cuneate or obtuse), margins entire, (midvein abaxially glabrescent, puberulent, or glandular; buds flattened with 2 exposed, valvate to overlapping scales).
terminal, panicles, (12–)20–40-flowered.
axillary or terminal, racemes, umbels, panicles, or fascicles, 2–40-flowered, sometimes flowers solitary;
perulae present.
20–40 mm.
sepals green to reddish, usually oblong, 3–3.5 mm, apex acute, surfaces glabrous or stipitate-glandular;
petals connate nearly their entire lengths, usually pink (ranging from deep red to white) with purple spots around each anther pocket, 20–25 × 15–30 mm, abaxial surface usually lightly stipitate-glandular, adaxial puberulent;
filaments 4–5 mm;
style 10–18 mm.
bisexual, radially symmetric; (calyx synsepalous, lobes deeply cleft), sepals (persistent, deciduous in K. hirsuta), (4–)5, (green or greenish), connate;
petals 5, connate for nearly their entire lengths or distinct, corolla deciduous, sympetalous and saucer-shaped to polypetalous and campanulate, (tube extending into rotate, shallowly 5-cleft (deeply cleft in K. buxifolia, K. procumbens), commonly 10-keeled limb, limb with 10 saccate pockets in which anthers are held under tension, absent in K. buxifolia, K. procumbens);
stamens 10 (5 in K. procumbens), included; (filaments usually hairy near base);
anthers (usually purple), without awns, (ovoid), dehiscent by apical (or longitudinal) slits;
ovary (2–)5-locular, (glabrous, stipitate-glandular in K. buxifolia);
styles included, (straight or bent);
stigma (5-lobed), capitate.
capsular, (5-valved), subglobose to globose, dehiscence basipetally septicidal.
5-locular, 3–5 × 4–7 mm, stipitate-glandular.
winged, obovoid and curved, 0.5–1 mm.
ca. 100–150, obovoid, oblong, or ovoid, often winged, tailed;
testa reticulate.
= 12.
= 24.
Kalmia latifolia
Kalmia
Kalmia latifolia is a showy and beautiful American indigenous plant. E. S. Rand (1871) wrote that “no words can describe the beauty of this plant on the mountains of the Middle States, where it covers acres, and sheets whole hillsides with pink and white.”
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Dendrium Desvaux; Kalmiella Small; Ledum Linnaeus sect. Leiophyllum Persoon; Leiophyllum (Persoon) R. Hedwig; Loiseleuria Desvaux
Species 10 (8 in the flora).
The inclusion here of Kalmia procumbens and K. buxifolia, traditionally treated as the monotypic genera Loiseleuria and Leiophyllum, is in keeping with the results of recent morphological and molecular phylogenetic studies. P. F. Stevens et al. (2004) also included Leiophyllum and Loiseleuria within an expanded Kalmia. These two species have evolved deeply cleft corollas with nearly separate petals, and thus lost the characteristic pockets of Kalmia; otherwise they are typical for the genus.
Kalmia has beautiful flowers that have long attracted the interests of horticulturists. It is economically important as an ornamental, with the most important species being K. angustifolia and K. latifolia (M. A. Dirr 1998; R. A. Jaynes 1988).
The mechanism of pollen discharge is a distinctive feature of most species of the genus, recognized since at least 1772 (A. Kress 1988). In anthesis, the anthers are snapped out of the pockets when insects disturb the bending filaments, dusting the insect body with pollen grains. Bumblebees (Bombus spp.) were found to be effective pollinators of Kalmia (J. E. Ebinger 1974).
In medicine, it is reported that Kalmia latifolia can be used as a cure for diarrhea and itching, the leaf powder as snuff, and K. hirsuta as a cure for itching and mange in dogs (R. A. Jaynes 1988). Kalmia latifolia has an antimicrobial effect (R. M. Heisey and B. K. Gorham 1992).
It is possible that all Kalmia species are poisonous to humans and livestock, and it is known that K. angustifolia, K. latifolia, K. microphylla, and K. polifolia are poisonous to livestock (B. S. Barton 1802; A. B. Clawson 1933; W. A. Dayton 1931; J. E. Ebinger 1974; R. A. Jaynes 1988; J. M. Kingsbury 1964; C. D. Marsh and A. B. Clawson 1930; W. C. Muenscher 1951). Sheep become sick when given leaves of K. angustifolia totalling as little as 0.15% of the animal body weight (Jaynes). The poisonous compound was identified as grayanotoxin I (andromedotoxin or acetyl-andromedol), a diterpene (J. W. Burke and R. W. Doskotch 1990; S. D. Mancini and J. M. Edwards 1979).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Petals distinct nearly their entire lengths. | K. buxifolia |
1. Petals connate ca. 1/2 to nearly their entire lengths | → 2 |
2. Leaves opposite; inflorescences terminal, corymbiform racemes or umbels | → 3 |
2. Leaves alternate (rarely opposite) or in whorls; inflorescences solitary flowers or fascicles, racemes, or panicles | → 5 |
3. Midribs of leaf blades with purple, clavate trichomes; seeds 1.5-2.2 mm. | K. polifolia |
3. Midribs of leaf blades without trichomes; seeds 0.5-1.4 mm | → 4 |
4. Capsules 5-locular; petals 7-9 mm, shallowly cleft; stamens 10. | K. microphylla |
4. Capsules 2-3-locular; petals 3-5 mm, cleft ca. 1/2 their lengths; stamens 5. | K. procumbens |
5. Leaves usually in whorls of 3 (rarely alternate or opposite) | K. angustifolia |
5. Leaves alternate or seemingly whorled | → 6 |
6. Leaves deciduous; petals white with red band adaxially. | K. cuneata |
6. Leaves persistent; petals white to pink or red | → 7 |
7. Plants 8(-12) m; leaf blade surfaces glabrous adaxially (only midrib puberulent), 4-12 cm; inflorescences terminal panicles | K. latifolia |
7. Plants 0.6(-1.2) m; leaf blade surfaces usually hairy, 0.5-1.4 cm; inflorescences solitary flowers or, sometimes, fascicles or racemes, scattered along stem in leaf axils. | K. hirsuta |
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