Polygonum dichotomum Blume, Polygonaceae

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Present on Pacific Islands?  yes

Primarily a threat at high elevations?  no

Common name(s): [more details]

Chinese: er qi liao

Tahitian: pitorea

Habit:  herb

Description: 

Genus:  "Erect, sprawling, or scandent herbs or shrubs; leaves with an amplexicaul ocrea, this often with longitudinal nerves extending into bristles on its upper margin; inflorescences usually spicate, the spikes sometimes aggregated into compound inflorescences; flowers hermaphrodite or sometimes polygamous, usually cymose-fascicled in axils of bracts or sometimes in leaf axils; tepals 5, acyclic, sometimes colored, subequal after anthesis; stamens 4-9; ovary compressed and with 2 styles (in our species [Fiji]) or trigonous and with 3 styles, the stigmas capitate; fruit lenticular (in our species) or trigonous-subglobose"  (Smith, 1981; pp. 306-307).

Species:  "As seen in Fiji, Polygonum dichotomum is a perennial, sprawling herb, with branches ascending to 1.2 m when support is available...  Its leaf blades are ovate-lanceolate and up to 20 x 5 cm but often smaller, usually abruptly obtuse at base, and its tepals are white"  (Smith, 1981; pp. 306-307).

"A glabrous annual herb; stems 4-ridged, branched and retrosely prickly, prostrate and rooting at nodes in the lower part, ascending or erect in the upper part.  Leaves membranous, broadly lanceolate, 5-10 cm long, acute or obtuse at apex, deeply cordate or sagittate at base, glaucous, glabrous on both sides, the margins entire; petioles 7-20 mm long, often with recurved prickles; ochreae scarious, 15-20 mm long, obliquely cut, not ciliate.  Inflorescence leaf-opposite, mostly 1-2 times dichotomously branched; flowers in terminal dense short-spikes, the spike together with the glandular peduncle 2-2.5 cm long; perianth pinkish or reddish-purple, 2-3 mm long, 5-lobed, the lobes broadly elliptical.  Nuts orbicular, biconvex, striate, black, punctulate" (Li et al., 1976; pp. 236, 270).

Description from Flora of China online.

Habitat/ecology:  In Fiji, "occurring from near sea level to an elevation of 825 m in swampy areas, on the shores and in the shallow water of lakes and ponds, and in moist areas in the forest-grassland transition" (Smith, 1981; pp. 306-307).  In Taiwan, "usually along irrigation ditches or in swampy places at lower altitudes throughout the island" (Li et al., 1976; pp. 236, 270).

Propagation:  Seed

Native range:  "Indigenous in India, China, and Formosa and into Malesia and Queensland.  It is probable that the species occurs east of Malesia only as an adventive, perhaps inadvertently carried by aboriginal voyagers" (Smith, 1981; pp. 306-307).

Presence:

Pacific
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Fiji Fiji Islands	Taveuni Island	introduced invasive abo. intro.	Smith, Albert C. (1981) (pp. 306-307) Vouchers cited: DA 12401, DA 14366, Seemann 370 (K)
Fiji Fiji Islands	Viti Levu Island	introduced invasive abo. intro.	Smith, Albert C. (1981) (pp. 306-307) Vouchers cited: Smith 5390, Vaughan 3335, DA 1501, DA 894, DA 2726
French Polynesia Society Islands	Raiatea (Havai) Island	introduced invasive	Welsh, S. L. (1998) (p. 222) Vouchers cited: Moore 770, BRY 26367
French Polynesia Society Islands	Tahiti Island	introduced invasive	Welsh, S. L. (1998) (p. 222) Vouchers cited: Parks & Setchell 128, Grant 4501
Tonga Tonga Islands	Tonga Islands		Swarbrick, John T. (1997) (p. 95)
Wallis and Futuna Wallis and Futuna (Horne) Islands	Wallis and Futuna Islands		Swarbrick, John T. (1997) (p. 95)

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)	Australia (continental)	native	Smith, Albert C. (1981) (pp. 306-307)
Australia Australia (continental)	Queensland	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
China China	China (People's Republic of)	native	Smith, Albert C. (1981) (pp. 306-307)
China China	China (People's Republic of)	native	Zhengyi, Wu/Raven, Peter H./Deyuan, Hong (2013) "Ditches, marshy areas; 100-1000 m".
China China	Hong Kong	native	Wu, Te-lin (2001) (pp. 82-83) In wet places in valleys.
Indonesia Indonesia	Indonesia (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Japan Ryukyu Islands	Ryukyu Islands	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Malaysia Malaysia	Malaysia (country of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Taiwan Taiwan Island	Taiwan Island	native	Smith, Albert C. (1981) (pp. 306-307)
Thailand Thailand	Thailand (Kingdom of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Vietnam Vietnam	Vietnam (Socialist Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)

Control:  If you know of control methods for Polygonum dichotomum, please let us know.