This section is from the book "A Guide To The Poisonous Plants And Weed Seeds Of Canada And The Northern United States", by Robert Boyd Thomson, H. B. Sifton. Also available from Amazon: A guide to the poisonous plants and weed seeds of Canada and the northern United States.
Several poisonous species of Kalmia are found in Canada and the United States, growing in dry places and in bogs. Their leathery leaves, and, in fact, all parts of the plants, contain andromedodextrin, a substance stated by Chesnut to be more poisonous than strychnin, though it is almost the reverse in its action. Grouse and deer appear to be immune to its effects. When they have fed on it, however, their flesh is said to be poisonous to human beings and to other animals. It is reported that people have been poisoned by eating honey extracted from the flowers.
Fig. 14. - Mountain Laurel - Kalmia latifolia; b Pale Laurel-
Cattle, sheep, horses and goats have died from eating the leaves, Kalmia latifolia probably causing most deaths. Care should be taken to avoid laurel thickets when herding animals in spring, as the evergreen leaves are tempting.
Cases of human poisoning arise from the use of contaminated meat or honey, from overdoses in "home made" medicine, and from mistaking the young shoots for those of wintergreen. The leaves have been used to increase the intoxicating effect of liquors, sometimes with disastrous results.
Irregular breathing is a very characteristic symptom.
In addition we have persistent nausea, salivation and grating of the teeth, together with dizziness and loss of sight and feeling. Stupor and death follow. In man there is intense headache, perspiration, tingling in the skin, and much vomiting.
As antidotes for the poison, Chesnut suggests atropin or strychnin. He recommends also the use of oil, fat or melted lard when symptoms are first noted.
The Mountain Laurel, Kalmia latifolia L., is found on rocky hills and dry slopes from the eastern coast to Ontario and southward. Miss Fyles quotes Barton, who wrote in 1798 that this species was poisonous to animals and was used by Indians as a means of suicide. In Canada it is a shrub, usually not more than six feet high, but grows much larger in some parts farther south. The evergreen, short-petioled, usually alternate leaves are ovate-lanceolate or oblong, thick, and bright green on both sides. The beautiful pink flowers are flat with a raised edge and depressions for the anthers of the ten stamens. They are one-half to one inch broad, in terminal corymbs, with clammy-pubescent stalks. The seed-pods also are glandular.
The Sheep Laurel or Lambkill, Kalmia angustifolia L.. is found from Labrador to Ontario and southward on hillsides, and in pastures and bogs. It is usually not more than three feet high, and the leaves, smaller than those of the mountain Laurel, are usually opposite or in threes and are pale beneath. The lateral corymbs of crimson flowers are slightly glandular. The flowers are less than one-half inch in diameter.
The Pale Laurel, Kalmia polifolia, Wang., extends across the northern part of the continent and stretches south through all but the Prairie Provinces, being found on mountains and in cold bogs. It is a straggling shrub, not more than two feet high, with opposite, oblong leaves, white-glaucous beneath and with revolute margins. The terminal corymbs have each a few rose purple flowers two-fifths to one inch broad.