The Biology of Canadian Weeds. 143. Apocynum cannabinum L. Antonio DiTommaso1, David R. Clements2, Stephen J. Darbyshire3, and Joseph T. Dauer4 1Department of Crop and Soil Sciences, Cornell University, Ithaca, NY, USA 14853 (e-mail: [email protected]); 2Department of Biology, Trinity Western University, Langley, British Columbia, Canada V2Y 1Y1; 3Eastern Cereal and Oilseed Research Centre, Agriculture and Agri-Food Canada, Wm. Saunders Building #49, Ottawa, Ontario, Canada K1A 0C6; and 4Department of Crop and Soil Sciences, Oregon State University, Corvallis, OR, USA 97331. Received 28 May 2008, accepted 28 April 2009. DiTommaso, A., Clements, D. R., Darbyshire, S. J. and Dauer, J. T. 2009. The Biology of Canadian Weeds. 143. Apocynum cannabinum L. Can. J. Plant Sci. 89: 977Á992. Hemp dogbane, Apocynum cannabinum (Apocynaceae), is a perennial herb with white to greenish flowers in terminal clusters that produces pencil-like pods 12Á20 cm long. A highly variable plant, A. cannabinum may be distinguished from spreading dogbane (Apocynum androsaemifolium) by its shorter corolla (2Á6mm compared with 5Á10 mm), erect greenish-white petals (compared with recurved or spreading pinkish petals), seeds more than 3 mm long (compared with seeds less than 3 mm), and more erect leaves (compared with spreading or drooping leaves), although frequent hybridization between the two species obscures the identity of some individuals. Hemp dogbane is native to the United States and southern Canada, but most abundant in the upper Mississippi River Valley and east to the Atlantic coast. It has been increasing in other areas, and becoming more of a problem where conservation tillage is adopted. It infests crops such as corn (Zea mays), soybeans (Glycine max), wheat (Triticum aestivum), sorghum (Sorghum bicolor) and forages, and may cause livestock poisoning due to cardiac glycosides within its milky sap (but livestock generally avoid it). Potential medicinal uses of these compounds have been investigated, and the roots are a source of fibre. Control of A. cannabinum with various herbicides is difficult due to a thick cuticle, and one solution may be to target susceptible stages, such as seedlings or early spring growth. Cultivation may also control A. cannabinum, but care must be taken not to promote the proliferation of the plant through regrowth from fragmented roots and rhizomes. Rotation with alfalfa also reduces populations of A. cannabinum. Key words: Hemp dogbane, APCCA, Apocynum cannabinum, Apocynaceae, weed biology DiTommaso, A., Clements, D. R., Darbyshire, S. J. et Dauer, J. T. 2009. La biologie des mauvaises herbes au Canada. 143. Apocynum cannabinum L. Can. J. Plant Sci. 89: 977Á992. L’apocyn chanvrin, Apocynum cannabinum (Apocynace´ es), est une herbace´ e vivace aux grappes terminales de fleurs blanches a` verdaˆ tres qui donnent des gousses en forme de crayon de 12 a` 20 cm de longueur. L’espe` ce connaıˆ t d’importantes variations. A. cannabinum se distingue du gobe-mouches (Apocynum androsaemifolium) par une corolle plus petite (2 a` 6 mm contre 5 a` 10 mm), des pe´ tales blanc verdaˆ tre dresse´ s (plutoˆ t que rosaˆ tres, recourbe´ soue´ tale´ s), des graines de plus de 3 mm de longueur (comparativement a` moins de 3 mm) et des feuilles plus droites (et non e´ tale´ es ou tombantes), bien que la fre´ quente hybridation entre les deux espe` ces rende l’identite´ de certains plants plus obscure. L’apocyn chanvrin est une plante indige` ne des E´ tats-Unis et du sud du Canada qui abonde surtout dans le haut de la valle´ e du Mississipi et a` l’est, jusqu’a` la coˆ te de l’Atlantique. L’espe` ce prolife` re ne´ anmoins dans d’autres re´ gions et s’ave` re plus proble´ matique aux endroits ou` l’on pratique la conservation du sol. Elle infeste les cultures tels le maı¨ s(Zea mays), le soja (Glycine max), le ble´ (Triticum aestivum), le sorgho (Sorghum bicolor)et les plantes fourrage` res, au risque d’intoxiquer le be´ tail en raison des glycosides cardiaques que renferme sa se` ve laiteuse (les animaux l’e´ vitent ge´ ne´ ralement). On s’est penche´ sur les vertus me´ dicinales potentielles de ces compose´ s ainsi que sur les racines de la plante en tant que source e´ ventuelle de fibres. Les herbicides viennent difficilement a` bout d’A. cannabinum a` cause de l’e´ paisse cuticule qui la prote` ge. Une solution serait de s’attaquer aux stades plus fragiles, comme les plantules ou la germination, au printemps. Le travail du sol pourrait aussi faciliter la lutte, mais il faut prendre soin de ne pas favoriser la prolife´ ration de la plante a` partir des fragments de racines et de rhizomes. L’assolement avec la luzerne diminue aussi la population d’A. cannabinum. Mots cle´s: Apocyn chanvrin, APCCA, Apocynum cannabinum, Apocynace´ es, biologie des mauvaises herbes 1. Names Apocynum cannabinum L. Common names: Hemp dog- lechuguilla, Indian hemp dogbane, rheumatism weed, bane, apocyn chanvrin, bitter root, black hemp, blind and westernwall; chanvre sauvage (Crockett 1977; hemp, bowman root, Canadian hemp, choctaw root, Becker 1981; Darbyshire et al. 2000; Darbyshire 2003; clasping-leaved dogbane, dropsy root, honey bloom, USDA-NRCS 2004). European and Mediterranean 977 978 CANADIAN JOURNAL OF PLANT SCIENCE Plant Protection Organization (Bayer) code: APCCA. reddish at the base. Branches usually arise in the upper Apocynaceae, dogbane family, Apocynace´ es. half with the lateral branches surpassing the central stem Apocynum is derived from Greek roots, with apo at flowering. Leaves opposite or rarely whorled or meaning ‘‘off’’ or ‘‘away from’’, and kunon meaning alternate, yellowish-green to dark green or sometimes ‘‘dog’’ (Dalby 2004). glaucous, erect or slightly spreading (leaves tend to be more spreading in prostrate forms), glabrous or sparsely 2. Description and Account of Variation pubescent beneath, oval to lanceolate, rounded to acute (a) Species Description * The following description is at the apex and usually abruptly mucronate (Fig. 2). The based on information taken from the literature (Fernald largest leaves arise near the middle of the stem, the size 1950; Gleason and Cronquist 1991; Voss 1996), supple- diminishes toward the top and bottom, (1) 4Á12 (14) cm mented by observations made by the authors. Measure- long, 0.5Á5.5 cm wide. Leaves acute to rounded or ments are given as the typical range with unusual cordate at the base (Fig. 2) and may be sessile or on extremes in parentheses. short petioles to about 1 cm long. Inflorescences A herbaceous perennial (Fig. 1) producing a milky compact paniculate cymes, usually terminal on branches latex sap. Plants tough and fibrous, usually glabrous but and only rarely axillary. Flowers hermaphroditic, may be variously pubescent on stems, leaves and 5-merous, (2) 2.5Á4.5 (6) mm long, whitish to greenish- inflorescences. Root system extensive with long vertical white and cylindric to urceolate (urn-shaped) (Fig. 1C). and horizontal roots and short rhizomes. Stems usually Calyx lobes lanceolate, about half as long as to nearly erect or sometimes prostrate, (1) 3Á10 (15) dm tall, often equal the corolla. Corolla lobes (petals) more or less lanceolate and acute to oblong-lanceolate and erect or slightly spreading. Pistil with two semi-inferior ovaries. Each flower produces two thin pods (follicles) (4) 8Á20 (22) cm long straight or slightly sickle-shaped (Fig. 1D). Seeds 4Á6 mm long, 0.75 mm wide, with a coma (tuft of white silky hairs) (1) 3Á5.5 cm long (Fig. 1E, F). Cotyledons strap-like (Fig. 3), 4Á11 mm long, about 1.5 mm wide. Some authors have reported a chromosome numbers of n8 (Schu¨ rhoff and Mu¨ ller 1937) and 2n16 (Van der Laan and Arends 1985) for A. cannabinum of unknown provenances; although these counts have been called into question. Counts of 2n22 have been reported by Breslavetz et al. (1934) from an unknown Fig. 2. Variation in the shape of leaves from the middle of the Fig. 1. Apocynum cannabinum var. cannabinum. A. habit, scale stem in Apocynum cannabinum as drawn from herbarium bar10 cm; B. roots, scale bar10 cm; C. flower, scale bar specimens. Upper row with short petioles and rounded or 1 cm; D. follicles, scale bar10 cm; E. seed with coma, scale clasping base of the blade attributed to var. hypericifolium; bar5 cm; F. seeds, scale bar1 cm. Illustration by Regina lower row with longer petioles and tapering base of the blade O. Hughes, United States Department of Agriculture. attributed to var. cannabinum. Scale bar1 cm. DITOMMASO ET AL. * APOCYNUM CANNABINUM L. 979 asclepioid features of pollinaria and anthoecial coronae (hoods and horns) in Asclepias. (c) Intraspecific Variation * Highly variable in both shape (Fig. 2) and pubescence of the leaves (Gleason and Cronquist 1991), A. cannabinum is self-sterile (see Section 8a) with out-crossing promoting variability and hybridization (Ransom et al. 1998b). This variability is evident from the number of papers claiming plants are glabrous (Anonymous 1970; Hartman 1986; Bradley and Hagood 2001), tomentulose (Doll 1994) or both (Balbach 1965; Becker 1981; Gleason and Cronquist 1991). It is not known what proportion of this varia- bility is due to phenotypic plasticity versus genetic diversity. Within the hemp dogbane complex, various species, subspecies or varieties have been distinguished in different ways by different authors (cf., Woodson Fig. 3. Seedling of Apocynum cannabinum var. hypericifolium 1930; Fernald 1950; Boivin 1966; Gleason and with cotyledons and first true leaves. Scale bar5 mm. Cronquist 1991) with taxa recognized and ranked based primarily on growth habit, pubescence, leaf shape and petiole length. The bewildering array of intermedi- provenance, Lo¨ ve and Lo¨ ve (1982) from Manitoba, and ate forms between the described taxa provides little Hill (1989) from Virginia. Studies by Balbach (1965) on confidence in intraspecific classifications (e.g., Hartman a number of populations in the United States and 1986; Gleason and Cronquist 1991; Voss 1996).