Practical
Plants

Rhus diversiloba

Western Poison Oak

a perennial woody deciduous member of the Rhus genus in the family Anacardiaceae.

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Taxonomy and growth

Genus
Rhus
Life cycle
perennial
Foliage
deciduous
Woodiness
woody
Height
2.5 m
Fertility
Self sterile, Bees
Flower type
dioecious
Pollinators
Bees

Uses

Toxicity

Toxicity warning. The historical record reports a hazard for this plant. Do not use it to decide which parts are safe to eat or use medicinally.

This section contains historical Plants For A Future notes marked noncommercial.

All parts of the plant contain resinous phenolic compounds known as urushiols. Direct contacr with the plant, exposure to smoke or fumes from a burning plant or even contact with pets or animals that have touched the plant can cause severe allergic dermatitis in some individuals. There is usually a latent period of about 12 - 24 hours from the moment of contact, this is followed by a reddening and severe blistering of the skin. Even plant specimens 100 or more years old can cause problems[6].

Medicinal uses

Historical medicinal uses. These records describe reported uses. They do not establish safety or effectiveness. Ask a qualified health professional before using any plant medicinally.

This section contains historical Plants For A Future notes marked noncommercial.

Western poison oak was employed medicinally by some native North American Indian tribes who used it to treat various complaints[5]. In view of the potential toxicity of the plant, extreme caution is advised in any use of it. See the notes above on toxicity. A leaf has been swallowed in the spring as a contraceptive[5]. A tincture of the fresh leaves has been used in the treatment of eczema and skin diseases[7]. It is also used in the treatment of warts, ringworm etc[10]. A poultice of the fresh leaves has been applied to rattlesnake bites[5]. The leaf buds have been eaten in the spring in order to obtain immunity from the plant poisons[5] A moxa of the plant has been used in the treatment of warts and ringworm[5]. The juice of the plant has been used as a treatment for warts[5]. An infusion of the dried roots has been taken in order to give immunity against any further poisoning[5]. A decoction of the roots has been used as drops in the eyes to heal tiny sores inside the eyelids and to improve vision[5].

Product or use
Antidote
Product or use
Contraceptive
Product or use
Ophthalmic
Product or use
Warts

Material uses

This section contains historical Plants For A Future notes marked noncommercial.

The leaves are rich in tannin. They can be collected as they fall in the autumn and used as a brown dye or as a mordant[3]. An oil is extracted from the seeds[7]. It attains a tallow-like consistency on standing and is used to make candles. These burn brilliantly, though they emit a pungent smoke[7]. The supple stems are used as the warp in basket making[10]. Slender stems are used as circular withes in basket making[5]. An excellent black dye is obtained by exposing the sap to air[10].

Product or use
Basketry
Product or use
Dye
Product or use
Ink
Product or use
Mordant
Product or use
Oil

Environment

Range
Western N. America - Vancouver to California.
Habitat
Thickets and wooded slopes in foothills, along streams, in washes and hedgerows below 1500 metres[8][10].
Light
full sun
Shade tolerance
no shade
Water
moderate
Hardiness
Zone 5+
Soil textures
sandy, loamy, clay
Soil pH
acid, neutral, alkaline
Drainage
well drained
Tolerates Nutritionally Poor Soil
No
Drought
intolerant

Propagation

This section contains historical Plants For A Future notes marked noncommercial.

Seed - best sown in a cold frame as soon as it is ripe. Pre-soak the seed for 24 hours in hot water (starting at a temperature of 80 - 90c and allowing it to cool) prior to sowing in order to leach out any germination inhibitors[4]. The stored seed also needs hot water treatment and can be sown in early spring in a cold frame[4]. When they are large enough to handle, prick the seedlings out into individual pots and grow them on in the greenhouse for their first winter. Plant them out into their permanent positions in late spring or early summer, after the last expected frosts. Cuttings of half-ripe wood, 10cm with a heel, July/August in a frame[4]. Root cuttings 4cm long taken in December and potted up vertically in a greenhouse. Good percentage[9][4]. Suckers in late autumn to winter[4].

Cultivation

This section contains historical Plants For A Future notes marked noncommercial.

Succeeds in a well-drained fertile soil in full sun[4]. Plants do not require a rich soil[2]. The young growth in spring can be damaged by late frosts. Plants have brittle branches and these can be broken off in strong winds[4]. Plants are also susceptible to coral spot fungus[2]. This species is closely related to R. toxicodendron[1]. Many of the species in this genus, including this one, are highly toxic and can also cause severe irritation to the skin of some people, whilst other species are not poisonous. It is relatively simple to distinguish which is which, the poisonous species have axillary panicles and smooth fruits whilst non-poisonous species have compound terminal panicles and fruits covered with acid crimson hairs[1][7]. The toxic species are sometimes separated into their own genus, Toxicodendron, by some botanists[4]. Plants in this genus are notably resistant to honey fungus[4]. Dioecious. Male and female plants must be grown if seed is required.

References

  1. F. Chittendon. RHS Dictionary of Plants plus Supplement. 1956 Oxford University Press 1951-00-00

    ↩1↩2

  2. Bean. W. Trees and Shrubs Hardy in Great Britain. Vol 1 - 4 and Supplement. Murray 1981-00-00

    ↩1↩2

  3. Buchanan. R. A Weavers Garden.

    ↩

  4. Huxley. A. The New RHS Dictionary of Gardening. 1992. MacMillan Press 1992-00-00 ISBN 0-333-47494-5

    ↩1↩2↩3↩4↩5↩6↩7↩8↩9

  5. Moerman. D. Native American Ethnobotany Timber Press. Oregon. 1998-00-00 ISBN 0-88192-453-9

    ↩1↩2↩3↩4↩5↩6↩7↩8↩9

  6. Diggs, Jnr. G.M.; Lipscomb. B. L. & O'Kennon. R. J Illustrated Flora of North Central Texas Botanical Research Institute, Texas. 1999-00-00 http://artemis.austincollege.edu/acad/bio/gdiggs/NCTXpdf.htm

    ↩

  7. Grieve. A Modern Herbal. Penguin 1984-00-00 ISBN 0-14-046-440-9

    ↩1↩2↩3↩4

  8. Munz. A California Flora. University of California Press 1959-00-00

    ↩

  9. Sheat. W. G. Propagation of Trees, Shrubs and Conifers. MacMillan and Co 1948-00-00

    ↩

  10. Balls. E. K. Early Uses of Californian Plants. University of California Press 1975-00-00 ISBN 0-520-00072-2

    ↩1↩2↩3↩4

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