Hypericum japonicum Thunb., Hypericaceae

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Present on Pacific Islands?  no

Primarily a threat at high elevations?  no

Common name(s): [more details]

Chinese: di er cao

English: Japanese St. John's wort, matted St. John's-wort, swamp hypericum

Habit:  herb

Description:  "Prostrate to erect perennial herb, often forming mats and rooting at nodes, lacking black glands. Stems very slender, generally < 15 cm long, 4-angled, often brownish or reddish purple, ascending towards apex when flowering; internodes often short. Leaves sessile, (1)-3-7-(10) x (0.5)-1-3-(5) mm, usually ovate, oblong-ovate, elliptic, or obovate, occasionally linear, with pellucid glands; margin flat or undulate and crisped; base cuneate to rounded. Flowers terminal, solitary or few in cymes. Sepals 2-4 mm long, linear-oblong. Corolla (4)-5-8-(c. 10) mm in diameter., orange-yellow, = or a little > sepals. Stamens ± forming 3 bundles. Styles 3. Capsule 2-4.5 mm in diameter., broadly ellipsoid-ovoid to suborbicular, dry. Seeds 0.4-0.6 mm long, broad-cylindric to ellipsoid, reticulate" (Webb et al., 1988; p. 546).

Habitat/ecology:  In New Zealand, "lowland to montane open places, especially wet ground, sometimes in modified communities" (Webb et al., 1988; p. 546).

Propagation:  Seed

Native range:  Southern and eastern Asia, Australia, New Zealand (GRIN).

Presence:

Pacific
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Papua New Guinea Papua New Guinea (eastern New Guinea Island)	Papua New Guinea (eastern New Guinea Island)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Philippines Philippine Islands	Philippine Islands	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Philippines Philippine Islands	Philippine Islands		Merrill, Elmer D. (1923) (p. 75) In open waste places, paddy banks, along streams, and in cultivated ground, altitude 700 to 2,400 m; common in the Mountain Province.

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)	New South Wales	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Australia Australia (continental)	Queensland	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
China China	China (People's Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Indonesia Indonesia	Indonesia (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Japan Japan	Japan	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Malaysia Malaysia	Malaysia (country of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
New Zealand New Zealand	New Zealand (country)	native	Webb, C. J./Sykes, W. R./Garnock-Jones, P. J. (1988) (p. 546)
Singapore Singapore	Singapore (Republic of)	uncertain if introduced invasive	Chong, Kwek Yan/Tan, Hugh T. W./Corlett, Richard T. (2009) (p. 50) Weed of uncertain origin
Taiwan Taiwan Island	Taiwan Island	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
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 Hypericum japonicum, please let us know.