E-Flora BC: Electronic Atlas of the Flora of British Columbia

Prenanthes alata (Hook.) D. Dietr.
western rattlesnake-root (western rattlesnakeroot)
Asteraceae (Aster family)

Introduction to Vascular Plants

© Doug Murphy  Email the photographer   (Photo ID #71381)

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Distribution of Prenanthes alata
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Species Information

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Perennial herb from a slightly thickened taproot; stems erect, solitary, branched above, long-hairy, exuding milky juice when broken, 15-80 cm tall.
Basal leaves arrowhead-shaped, long stalked, blades irregularly toothed, glabrous, 3.5-17 cm long, 0.5-11 cm wide; stem leaves similar below, middle and lower ones with winged stalks, becoming short-stalked or unstalked, reduced upwards.
Heads with strap-shaped flowers, numerous in an open or round-topped inflorescence; involucres 10-13 mm tall; involucral bracts lance-oblong, the principal ones about 8, sparsely long-hairy; ray flowers white or sometimes pinkish.
Achenes finely lined between the nerves, cylindric or tapering to the summit, glabrous, 4-6 mm long; pappus of brownish hairlike bristles.

Source: The Illustrated Flora of British Columbia

Habitat / Range

Moist forests and streambanks in the lowland and montane zones; infrequent in BC S of 56degreeN; N to AK, E to AB and S to OR.

Source: The Illustrated Flora of British Columbia


Ecological Framework for Prenanthes alata

The table below shows the species-specific information calculated from
original data (BEC database) provided by the BC Ministry of Forests and Range.
(Updated August, 2013)

Site Information
Value / Class




Elevation (metres) 0 362 1835
Slope Gradient (%) 0 21 150
Aspect (degrees)
[0 - N; 90 - E; 180 - S; 270 - W]
0 286 360
Soil Moisture Regime (SMR)
[0 - very xeric; 4 - mesic;
8 - hydric]
1 4 7
Modal Nutrient Regime
Number of field plots
 species was recorded in:
Modal BEC Zone Class
All BEC Zones (# of stations/zone) species was recorded in: BWBS(1), CWH(202), ESSF(12), ICH(21), MH(12), SBS(20)

Ecological Indicator Information

A shade-tolerant/intolerant, submontane to montane, Pacific North American forb. Occurs in maritime to submaritime wet cool mesothermal climates on fresh to moist, nitrogen­rich soils (Moder and Mull humus forms); its occurrence decreases with increasing elevation and continentality. Grows on water-receiving and water-collecting sites (usually stream-edge sites) where it inhabits recently deposited mineral materials. Sporadic in open­canopy broad-leaved forests; often associated with Adiantum pedatum, Aruncus dioicus, and Oplopanax homdus on flooded sites. A nitrophytic species characteristic of Moder and Mull humus forms.

SourceIndicator Plants of Coastal British Columbia (Information applies to coastal locations only)


The climate type for this species, as reported in the: "British Columbia plant species codes and selected attributes. Version 6 Database" (Meidinger et al. 2008), is cool mesothermal.

Synonyms and Alternate Names

Prenanthes alata var. sagittata A. Gray
Prenanthes lessingii Hultén

Taxonomic and Nomenclatural Links

Additional Photo Sources

General References