Eupatorium dubium Willd. ex Poir.
-
Authority
Lamont, E. E. 1995. Taxonomy of
section (Asteraceae). Mem. New York Bot. Gard. 72: 1-68. -
Family
Asteraceae
-
Scientific Name
-
Description
Species Description - Erect herb, 0.4-1.2(-l .7) m tall. Stems solid, usually purple-spotted or sometimes uniformly purple throughout, glandular-puberulent near summit glabrous below, scarcely or not at all glaucous. Leaves mostly in 3’s or 4’s; blades thick and firm, often rugose, deltate-ovate or ovate to lance-ovate, usually abruptly contracted to the short petiole, 5-16 cm long, 2-8 cm wide, coarsely serrate, usually with a large gland at apex of each marginal tooth, strongly triplinerved (especially prominent on abaxial surface), rarely pinnately veined, adaxial surface scabrous and sparingly glabrescent, abaxial surface densely atomiferous and sparingly hirsute on the midrib and main veins; petioles usually 0.7-2.5 cm long, glabrous. Inflorescence slightly to strongly convex, sometimes flat-topped in life, less than 20 cm wide in life, heads short pedunculate, peduncles conspicuously glandular pubescent. Involucre 6.5-9 mm high, 2.5-5 mm wide, often purplish, bracts 10-22, lanceolate, obtuse at apex, strongly imbricate, few-striate or at least with prominent midvein; receptacle naked, flat or weakly convex. Flowers (4-)5-9(-10) in a head; corollas usually dark purple, rarely pinkish or white, 4.5-7.5 mm long, 5-toothed, outer surface usually minutely atomiferous-glandular, lobes ovate to deltate; style base puberulous, enlarged. Achenes prismatic, 3.0-4.5 mm long, 5-ribbed, atomiferous-glandular, sometimes with a few setulae along the nerves; pappus a single series of 25-40 slender, capillary, scabrous, persistent bristles. 2n = 20.
-
Discussion
Type (of Eupatorium punctatum Willd.). Protologue: “North America.” Without specific locality, date, and collector’s name [holotype, B fide Cronq.! (microfiche, NY!; photo, GH!)]. Eupatorium purpureum L. var. ß, Sp. pl. 838. 1753. Type. Not cited in protologue [holotype, not seen; by description = E. dubium (there is no specimen of E. purpureum var. ß in the herbarium of Linnaeus according to Savage, 1945, page 143)]. Eupatorium americanum Hill, Brit. Herb. 453. 1756. Type. Not cited in protologue (holotype, not seen; by description = E. dubium. Inquiry to BM and K failed to locate the type). [Hill (1756) did not consistently employ the Linnaean system of binary nomenclature for species; according to Article 23.6(c) (see Ex. 9) of the International Code of Botanical Nomenclature (Greuter, 1988), Eupatorium americanum is a descriptive phrase reduced to two words, not a binary name in accordance with the Linnaean system, and is to be rejected as not validly published.] Eupatorium ternifolium Elliott, Sketch bot. S. Carolina 2: 306. 1823. Eupatorium purpureum var. ternifolium (Elliott) Wood, Class-book, Ed. 1861, 416. 1861. Eupatorium purpureum var. maculatum f. ternifolium (Elliott) Voss, Vilm. Blumengartn. Ed. 3, 1: 447. 1894. Type. Protologue: “The low country of Carolina, in damp soils.” Without specific locality, date, and collector’s name [holotype, not seen; by description = E. dubium (inquiry to CHARL and other major herbaria failed to locate the type; Weatherby (1942) did not include E. ternifolium Elliott in the list of type specimens in Elliott’s herbarium)]. Eupatorium ternifolium var. ß vesiculosum Barratt, Eupatoria verticillata no. 3. 1841. Type. Protologue: “Connecticut. Straddle Hill, west part of Middletown” [holotype, not seen; by description = E. dubium (search at NY and inquiry to other major herbaria failed to locate the type; Grimes & Keller (1982) did not include E. ternifolium var. vesiculosum Barratt in the list of type specimens in Barratt’s herbarium)]. Eupatorium dubium f. elutum Fernald, Rhodora 47: 195. 1945. Type. United States. Connecticut. [Middlesex Co.]: Saybrook Junction, low ground near Long Island Sound, 14 Sep 1914, Woodward s.n. (holotype, GH!). The taxonomic status of Eupatorium dubium has been less understood than any other species in sect. Verticillata. In the 120 years following Willdenow’s (1809) original description of E. dubium, only de Candolle (1836) recognized the species as it is presently understood. Identification of E. dubium still remains difficult for many field botanists, as evidenced by many misidentified herbarium specimens. The most prominent character distinguishing E. dubium from its relatives is the triplinerved leaf venation: The lowest pair of lateral veins are more prominent and more prolonged than the others (Figs. 23 & 24). This character is best observed on abaxial leaf surfaces. However, all leaves on an individual plant are not always conspicuously triplinerved, and sometimes several leaves must be inspected before the venation character is seen. Rarely the triplinerved leaf character is not present on a specimen; when absent, identification in the field can be accomplished by locating the character on other individuals in the same population. Identification of herbarium specimens can be difficult when the triplinerved leaf character is absent. Eupatorium dubium differs from E. fistulosum, E. purpureum, and E. steelei in stem and leaf characteristics. Eupatorium dubium has solid stems that are usually purple-speckled and non-glaucous; leaves are often deltate-ovate and usually in whorls of 3 or 4. Eupatorium fistulosum has hollow stems that are usually purple throughout and strongly glaucous; leaves are often lance-ovate and usually in whorls of 5 or 6. In addition, E. dubium rarely exceeds 1.5 m in height; E. fistulosum commonly exceeds 1.5 m in height. Eupatorium purpureum usually has stems with anthocyanic pigment concentrated in 1-2-cm bands at leaf nodes; internodes are usually green. Eupatorium dubium usually occurs in moist habitats, while E. purpureum usually occurs in drier upland habitats. Eupatorium steelei has green, glandular-hairy stems, glandular-hairy abaxial leaf surfaces, and occurs in dry upland habitats. Eupatorium dubium has glabrous stems below the inflorescence and atomiferous abaxial leaf surfaces. Eupatorium dubium is not sympatric with E. steelei. Eupatorium dubium and E. maculatum are morphologically rather similar. Both species have solid, purple-speckled stems that are glabrous below the inflorescence, pubescent above. The inflorescence of E. maculatum is usually flat-topped; E. dubium has a convex inflorescence but sometimes it is somewhat flat-topped (especially in some pressed herbarium specimens). Both species commonly have four leaves at a node, coarsely toothed leaf-blade margins, atomiferous abaxial leaf-blade surfaces, and similar leaf length/width ratios. The two species are strongly allopatric (Figs. 8 and 9); however, ranges overlap along the upper Connecticut River and throughout southern Nova Scotia. Eupatorium dubium is local and rare in southern Nova Scotia, where it grows in isolated clumps on rocky lake shores in the Tusket Valley, Yarmouth Co., scattered east to Halifax and Lunenburg Counties. Eupatorium maculatum is common and conspicuous in wet habitats throughout northern Nova Scotia from Digby Neck to northern Cape Breton, but is rare southward. Triplinerved leaf venation readily distinguishes E. dubium from E. maculatum. When this character is obscure or absent, the two species sort out by correlation of multiple characters. Eupatorium dubium has (4-)5-9(-10) flowers in a head, rugose, deltate-ovate leaf blades often less than 15 cm long and abruptly contracted to the petiole, and usually grows in acid soils. Eupatorium maculatum has (8-)9-18(-22) flowers in a head, relatively thin, lance-ovate leaf blades often over 15 cm long and gradually narrowed to the short petiole, and usually grows in calcareous soils.
-
Distribution
Habitat and distribution. Predominantly in moist habitats, especially in sandy or gravelly, acid soil, commonly in open sun or partial shade. Occurring naturally in wet lowlands, especially in margins of tidal marshes, swamps, ponds, and occasionally in shaded thickets along streams. Common as a weed along wet roadside ditches and depressions and in moist abandoned fields. Restricted to the coastal plain (and inland along major river systems) of eastern North America from South Carolina to Massa
United States of America North America| Canada North America|