Xanthium strumarium L., Asteraceae

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Present on Pacific Islands?  yes

Primarily a threat at high elevations?  no

Risk assessment results:  Reject, score: 7 (Go to the risk assessment)

Other Latin names:  Xanthium occidentale Bertol.; Xanthium pensylvanicum Wallr.; Xanthium pungens Wallr.

Common name(s): [more details]

English: California bur, Noogoora burr, cocklebur, ditchbur, heartleaf cocklebur, sheepbur

Fijian: nggatima ni vavalangi, ovuka, qatima ni vavalagi

Hawaiian: kīkānia

Japanese: ōnamomi

Habit:  herb

Description:  "Plants 2-20 dm tall, appressed pubescent or subglabrous.  Leaf blades broadly ovate to reniform, 2-8 cm long, 1.5-10 cm wide, scabrous and glandular-dotted, margins coarsely and irregularly toothed, base usually cordate, petioles 1.5-10 cm long.  Heads in several to numerous short axillary inflorescences.  Burs broadly cylindrical to ovoid, ellipsoid, or sometimes subglobose, (1-) 1.5-3.5 cm long, covered with stout, hooked prickles, terminated by 2 straight or incurved beaks" (Wagner et al., 1999; pp. 376-377).

Habitat/ecology:  "It is found along streams, rivers, in low-lying areas subject to flooding, and in waste places.  It frequents roadsides, railway banks, small streams, and riverbanks, as well as the edges of ponds and freshwater marshes and poorly managed or overgrazed pastures.  It cannot stand shading.  The weed can grow on a wide range of soils, from sands to heavy clays, and in a wide range of moisture supply.  On rich soils with high moisture and little competition from other plants, it grows tall and luxurious, forming pure stands.  In dry, poor soils, if the seedlings have become established, the plant may grow to only a few cm in height, persisting under drought, but still fruiting and setting seeds.  This ability to grow under a wide range of conditions results in a constant seed supply if the plant is not controlled" (Holm et al., 1977; p. 480).  "An extensive root system and rapid growth make these plants strong competitors with desirable forages and crops"  (Motooka et al., 2003).

"In Hawai‘i a common weed of low elevation, relatively dry, disturbed habitats" (Wagner et al., 1999; pp. 376-377). In Fiji, "occurring near sea level or at low elevations probably not exceeding 100 m as a naturalized weed in open places, cultivated areas, and grasslands, and along roadsides, sometimes locally abundant" (Smith, 1991; pp. 289-290).  In Australia, "riparian zones along river systems where it forms dense thickets.  Also invades grazing and cultivated lands, and seasonally wet areas" (Smith, 2002; pp. 67-68). "A weed of grazing land; the burrs are troublesome to livestock and the plants are harmful and even fatal if eaten" (Henty & Pritchard, 1975; p. 87).

Propagation:  "The spiny fruit...adhere to wool, fur, clothing, hay bales, mud, etc. The fruits float and are readily dispersed by water. Fruits are also spread in contaminated pasture seed" (Smith, 2002; pp. 67-68).  "As is true of X. spinosum, the two seeds in the fruit...germinate at different rates.  The lower seed germinates more readily than the upper seed, which has a seed coat of low permeability to oxygen.  Both seeds show dormancy, but the lower is less dormant than the upper" (Holm et al., 1977; p. 480).

Native range:  "Probably native to the New World, now a cosmopolitan weed"  (Wagner et al., 1999; pp. 376-377).

Presence:

Pacific
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Cook Islands Southern Cook Islands	Ma‘uke Island		McCormack, Gerald (2013)
Cook Islands Southern Cook Islands	Rarotonga Island		McCormack, Gerald (2013)
Cook Islands Southern Cook Islands	Rarotonga Island		National Tropical Botanical Garden (U.S.A. Hawaii. Kalaheo.) (2002) (voucher ID: PTBG 333) Taxon name on voucher: Xanthium strumarium
Fiji Fiji Islands	Viti Levu Island	introduced invasive	Smith, Albert C. (1991) (pp. 289-290) Vouchers cited: Greenwood 715, 715B; DA 10701; DA 10430; DA 9466; DA 10175; DA 10674; DA 9144; O. & I. Degener 31909; Greenwood 715A; DA 2808; DA 10813; DA 6088
French Polynesia Gambier Islands	Mangareva (Gambier) Island	introduced invasive	Florence, J./Chevillotte, H./Ollier, C./Meyer, J.-Y. (2013) Adventice
French Polynesia Marquesas Islands	Hiva Oa Island	introduced invasive	Lorence, David H./Wagner, Warren L. (2013)
French Polynesia Marquesas Islands	Hiva Oa Island	introduced invasive	Florence, J./Chevillotte, H./Ollier, C./Meyer, J.-Y. (2013) Voucher cited: M.-H. Sachet 1208 (PAP) Adventice
French Polynesia Marquesas Islands	Hiva Oa Island		National Tropical Botanical Garden (U.S.A. Hawaii. Kalaheo.) (2003) (voucher ID: PTBG 39536) Taxon name on voucher: Xanthium strumarium
French Polynesia Marquesas Islands	Nuku Hiva (Nukahiva) Island	introduced invasive	Lorence, David H./Wagner, Warren L. (2013)
French Polynesia Marquesas Islands	Nuku Hiva (Nukahiva) Island	introduced invasive	Florence, J./Chevillotte, H./Ollier, C./Meyer, J.-Y. (2013) Adventice
French Polynesia Society Islands	Moorea Island	introduced invasive	Florence, J./Chevillotte, H./Ollier, C./Meyer, J.-Y. (2013) Adventice
French Polynesia Society Islands	Raiatea (Havai) Island	introduced invasive	Welsh, S. L. (1998) (p. 82) Voucher cited: Moore 704
French Polynesia Society Islands	Tahiti Island	introduced invasive	Welsh, S. L. (1998) (p. 82) Voucher cited: Setchell & Parks 187
State of Hawaii Hawaiian Islands	Hawai‘i (Big) Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (pp. 376-377) var. canadense
State of Hawaii Hawaiian Islands	Kaho‘olawe Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (pp. 376-377) var. canadense
State of Hawaii Hawaiian Islands	Kaua‘i Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (pp. 376-377) var. canadense
State of Hawaii Hawaiian Islands	Lāna‘i Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (pp. 376-377) var. canadense
State of Hawaii Hawaiian Islands	Ni‘ihau, Lehua Islet	introduced invasive	Wood, K. R./LeGrande, Maya (2006) (p. 21)
State of Hawaii Hawaiian Islands	Maui Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (pp. 376-377) var. canadense
State of Hawaii Hawaiian Islands	Moloka‘i Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (pp. 376-377) var. canadense
State of Hawaii Hawaiian Islands	Ni‘ihau Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (pp. 376-377) var. canadense
State of Hawaii Hawaiian Islands	O‘ahu Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (pp. 376-377) var. canadense
New Caledonia New Caledonia Archipelago	Île Grande Terre	introduced invasive	Tassin, Jacques (2005)
New Caledonia New Caledonia Archipelago	Île Grande Terre	introduced	MacKee, H. S. (1994) (p. 39) Vouchers cited: MacKee 31251, Sopéna in MacKee 34187
Papua New Guinea Papua New Guinea (eastern New Guinea Island)	Papua New Guinea (eastern New Guinea Island)		Waterhouse, D. F. (1997) (p. 66)
Philippines Philippine Islands	Philippine Islands	introduced invasive	Holm, Leroy G./Plucknett, D. L./Pancho, J. V./Herberger, J. P. (1977) (p. 476)
United States (other Pacific offshore islands) Midway Atoll	Midway Atoll	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (pp. 376-377) var. canadense

Pacific Rim
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Australia Australia (continental)	Northern Territory	introduced invasive	Smith, Nicholas M. (2002) (p. 67)
Australia Australia (continental)	Queensland	introduced invasive	Smith, Nicholas M. (2002) (p. 67)
China China	China (People's Republic of)	introduced invasive	Holm, Leroy G./Plucknett, D. L./Pancho, J. V./Herberger, J. P. (1977) (p. 476)
Japan Japan	Japan	introduced invasive	Holm, Leroy G./Plucknett, D. L./Pancho, J. V./Herberger, J. P. (1977) (p. 476)
South Korea South Korea	South Korea (Republic of)	introduced invasive	Holm, Leroy G./Plucknett, D. L./Pancho, J. V./Herberger, J. P. (1977) (p. 476)
Mexico Mexico	Mexico (United Mexican States)	introduced	Weber, Ewald (2003) (p. 457)
New Zealand New Zealand	New Zealand (country)	introduced invasive	Webb, C. J./Sykes, W. R./Garnock-Jones, P. J. (1988) (p. 227) "Cultivated land".
Taiwan Taiwan Island	Taiwan Island	introduced invasive	Holm, Leroy G./Plucknett, D. L./Pancho, J. V./Herberger, J. P. (1977) (p. 476)
Taiwan Taiwan Island	Taiwan Island	uncertain if native	Ching-I Peng, ed. (2013) "River banks, seacoasts, and waste fields throughout the lowland".
Thailand Thailand	Thailand (Kingdom of)	introduced invasive	Holm, Leroy G./Plucknett, D. L./Pancho, J. V./Herberger, J. P. (1977) (p. 476)

Control: 

Physical:  "Control measures should aim at preventing seed formation.  Small plants can be hand pulled or hoed.  Prescribed burning is also effective if the fire is hot enough"  (Weber, 2003; p. 457).  "Australian officials have imposed strict quarantines to keep uninfested areas clear of this weed.  Small infestations can be effectively cleared by hand pulling or hoeing with care to collect, remove and burn any burs.  Controlled burning my also be effective on larger areas"  (Motooka et al., 2003).

Chemical:  "An effective chemical control method is spraying 2,4-D or MCPA before flowering commences"  (Weber, 2003; p. 457).  "Sensitive to dicamba and metsulfuron.  Clopyralid, 2,4-D, glyphosate, triclopyr also effective"  (Motooka et al., 2003).

Biological:  "Several biocontrol insects and pathogens have been introduced in Australia with variable results"  (Motooka et al., 2003).