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Photo: Prenanthes racemosa

Prenanthes racemosa Michx.

Glaucous Rattlesnake Root

Habitat: Calcareous riverbanks, shores and damp prairies. [Non-tidal rivershore (non-forested, seasonally wet)]

Range: Quebec to Alberta, south to New Brunswick, northern Maine, and west to Colorado; disjunct populations in southeastern New York and northern New Jersey.

Aids to Identification: Prenanthes racemosa grows along open, cobbly rivershores, and in bloom, the plants stand 30 cm tall, sometimes overtopping nearby vegetation. The stem and oval to oblong leaves (which occur alternately on the stem) are smooth and have a distinctive bluish-grey bloom. The capitula (flowerheads) are borne in an elongated raceme-like inflorescence which is characteristically bent like a hairpin to the lower stem while in bud, straightening up as the flowers open. The flowerheads themselves are upright to slightly drooping, surrounded by an involucre of rather stiffly-hairy bracts (which is unique among Maine Prenanthes), and the flowers within (ray flowers) are a dusty pink color.

Photo: Prenanthes racemosa

Ecological characteristics: In Maine, this species is restricted to a few spots along the St. John and Aroostook Rivers, in the northernmost part of the state. It grows along cobbly, ledgy, or gravelly shores where calcium is available from the bedrock or weathering till and where it is subjected to high water and/or ice scouring at least annually. It is commonly associated with other unusual or rare northern calciphiles, such as Allium schoenoprasum var. sibiricum, Primula mistassinica, Tanacetum bipinnatum ssp. huronense, etc.

Phenology: A perennial; blooms from late July (southward) through August; fruits in fall.

Photo: Prenanthes racemosa

Family: Asteraceae

Synonyms: Formerly known as Nabalus racemosus (Michx.) Hook. and Harpalyce racemosa (Michx.) D. Don ex Beck.

Known Distribution in Maine: This rare plant has been documented from a total of 14 town(s) in the following county(ies): Aroostook.

Dates of documented observations are: 1938, 1939, 1941, 1942, 1980, 1984 (2), 1989 (3), 1991 (2), 1993 (7), 1997 (3), 1999 (12), 2001 (14)

Reason(s) for rarity: At southern limit of range and suitable calcareous habitat naturally scarce.

Conservation considerations: Maintain hydrologic integrity of its rivershore habitat, including the natural disturbance by water and ice. Populations along rivershores could be harmed if all-terrain vehicle use of the habitat increases.

For more information, see the New England Wild Flower Society's Conservation Plan for Prenanthes racemosa-pdf link-133 KB.