Rhododendron macrophyllum

General poisoning notes:

California rose-bay (Rhododendron macrophyllum) is a native shrub found in southwestern British Columbia. This plant has poisoned goats and sheep. Azaleas are now considered part of the genus Rhododendron. Animals and humans have been poisoned after ingesting the foliage, nectar, or honey made from these plants. Klein-Schwartz and Litovitz (1985) found that humans who ingested plant parts of Rhododendron plants exhibited few symptoms of poisoning. Of 152 cases, only nine developed any symptoms and only one resulted in vomiting and transient hypertension. The authors concluded that ingesting moderate amounts of azalea material posed little danger to humans. Azaleas are often used as houseplants. Children and family pets should be prevented from ingesting these plants. Livestock have been poisoned by ingesting foliage of azaleas and rhododendrons. Sheep are most commonly affected in North America. Death has occurred in some cases (Casteel and Wagstaff 1989). Poisoning usually occurs when animals gain access to clippings or when little other forage is available, as in the winter. Rhododendrons retain their leaves over the winter. Goats and cattle have been poisoned as well. Andromedotoxins (grayanotoxins) are the toxins involved.

References:

  • Casteel, S., Wagstaff, J. 1989. Rhododendron macrophyllum poisoning in a group of goats and sheep. Vet. Hum. Toxicol., 31: 176-177.
  • Klein-Schwartz, W., Litovitz, T. 1985. Azalea toxicity: an overrated problem?.Clin. Toxicol., 23: 91-101.

Nomenclature:

Scientific Name
Rhododendron macrophyllum D. Don ex G. Don
Vernacular name(s)
California rose-bay
Scientific family name
Ericaceae
Vernacular family name
heath

Go to ITIS*ca for more taxonomic information on: Rhododendron macrophyllum

References:

  • Agriculture Quebec. 1975. Noms des maladies des plantes du Canada/ Names of plant diseases in Canada. ,Quebec City, Que., Canada. 288 pp.
  • Alex, J. F., Cayouette, R., Mulligan, G. A. 1980. Common and botanical names of weeds in Canada/Noms populaire et scientifiques des plantes nuisibles du Canada. Revised. Agric. Can. Publ., Ottawa, Ont., Canada. 132 pp.
  • Bailey, L. H., Bailey, E. Z. 1976. Hortus third. Revised. MacMillan, New York, N.Y., USA. 1290 pp.
  • Scoggan, H. J. 1978, 1979. The flora of Canada. Nat. Mus. Nat. Sci. (Ottawa) Publ. Bot. 7(1)-7(4). 1711 pp.
  • Van Wijk, H. L. 1911. A dictionary of plant names. Martinus Nijhoff, The Hague, The Netherlands. 1444 pp.
  • Victorin, M. 1964. Flore Laurentienne. 2nd ed. Univ. Montreal, Montreal, Que., Canada. 952 pp.

Geographic Information

  • British Columbia

References:

  • Bailey, L. H., Bailey, E. Z. 1976. Hortus third. Revised. MacMillan, New York, N.Y., USA. 1290 pp.
  • Boivin, B. 1966, 1967. Énumération des plantes du Canada. Provencheria 6. Nat. Can. (Que.) 93: 253-274; 371-437; 583-646; 989-1063. 94: 131-157; 471-528; 625-655.

Image or illustration

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Notes on Poisonous plant parts:

The leaves and stems of this plant have caused poisoning (Casteel and Wagstaff 1989).

Toxic parts:

  • leaves
  • stems

References:

  • Casteel, S., Wagstaff, J. 1989. Rhododendron macrophyllum poisoning in a group of goats and sheep. Vet. Hum. Toxicol., 31: 176-177.

Notes on Toxic plant chemicals:

Andromedotoxins (including grayanotoxin I) are toxic diterpenoids that are present in all the poisonous members of Ericaceae, the heath family (Cooper and Johnson 1984).

Toxic plant chemicals:

  • andromedotoxins

References:

Cooper, M. R., Johnson, A. W. 1984. Poisonous plants in Britain and their effects on animals and man. Her Majesty's Stationery Office, London, England. 305 pp.

Animals/Human Poisoning:

Note: When an animal is listed without additional information, the literature (as of 1993) contained no detailed explanation.

Goats

General symptoms of poisoning:

Notes on poisoning

In one case, several young and adult goats gained access to clippings of California rose-bay; most were poisoned, and some young goats died. Symptoms included initial lateral recumbency and a tonic-clonic convulsive episode starting 6 h after ingestion. Vomiting, ataxia, and weakness occurred. Vomiting continued over 2 days. Intense colic was observed. Lactating goats dried up. Some animals remained recumbent for a couple of days (Casteel and Wagstaff 1989).

References:

  • Casteel, S., Wagstaff, J. 1989. Rhododendron macrophyllum poisoning in a group of goats and sheep. Vet. Hum. Toxicol., 31: 176-177.

Humans

General symptoms of poisoning

Notes on poisoning

Klein-Schwartz and Litovitz (1985) found that only minimal symptoms were exhibited, such as vomiting, after ingesting species of the genus Rhododendron. Lampe and McCann (1985) note that ingesting significant quantities of leaves can cause more severe symptoms such as burning of the mouth, salivation, vomiting, diarrhea, headache, and dimness of vision. Such occurrences are unlikely because of the bitterness of the leaves. Reports occur regarding the toxicity of honey made from azaleas and rhododendrons. This honey is bitter and is unlikely to be ingested in large quantities.

References:

  • Klein-Schwartz, W., Litovitz, T. 1985. Azalea toxicity: an overrated problem?.Clin. Toxicol., 23: 91-101.

Sheep

General symptoms of poisoning:

Notes on poisoning

Ingesting clippings of California rose-bay caused illness in sheep. Symptoms included severe vomiting, ataxia, and weakness. Vomiting continued over a few days. The animals walked a short distance and then fell down. Some animals remained recumbent for many hours. Colic was observed (Casteel and Wagstaff 1989).

References:

  • Casteel, S., Wagstaff, J. 1989. Rhododendron macrophyllum poisoning in a group of goats and sheep. Vet. Hum. Toxicol., 31: 176-177.

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