Hypericum perforatum L., Clusiaceae

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Present on Pacific Islands?  yes

Threat only at high elevations?  no

Risk assessment results:  High risk, score: 12 (Go to the risk assessment)

Common name(s): [more details]

English: goatweed, Klamath weed, St. John's-wort

French: herbe à mille trous, millepertuis commun

Spanish: corazoncillo, hierba de San Juan

Habit:  herb

Description:  "Rhizomatous perennial herbs; stems 1 to several, erect, becoming somewhat woody toward base, 5-10 dm long, black-dotted.  Leaves linear to elliptic or oblanceolate, primary ones 10-30 mm long, 3-16 mm wide, usually black-dotted.  Flowers in paniculate cymes; sepals connate at base, the lobes lanceolate, 3-5 mm long, glandular punctate; petals obovate, 5-8 mm long, black-dotted along margins; stamens numerous, in 3 clusters; styles 3 (4).  Capsules ovoid, 7-8 mm long.  Seeds dark brown, cylindrical, ca. 1 mm long, the surface pitted"  (Wagner et al., 1999; p. 546).

Habitat/ecology:  "Grass- and woodland, riverbanks, disturbed areas.  This plant forms extensive and dense colonies where invasive, eliminating native vegetation.  Seedlings are sensitive to competition but established plants compete successfully with native forbs and grasses.  The weed cannot survive in densely shaded areas"  (Weber, 2003; p. 210).

Propagation:  Seed, dispersed by water, soil and agricultural activities  (Weber, 2003; p. 210).

Native range:  "Native to Eurasia, widely naturalized" (Wagner et al., 1999; p. 546).

Presence:

Pacific
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
State of Hawaii Hawaiian Islands	Hawai‘i (Big) Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (p. 546) Voucher cited: Fosberg 42087 (BISH)

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)	introduced	U.S. Dept. Agr., Agr. Res. Serv. (2007)
Chile (continental) Chile	Chile (Republic of)		Hafliger, Toni J./Wolf, Matthias (1988) (p. 252)
China China	China (People's Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2007)
Japan Japan	Japan (country)	introduced	U.S. Dept. Agr., Agr. Res. Serv. (2007)
New Zealand New Zealand	New Zealand (country)	introduced invasive	Owen, S. J. (1997)
New Zealand New Zealand	New Zealand (country)	introduced invasive	Webb, C. J./Sykes, W. R./Garnock-Jones, P. J. (1988) (p. 544) "A particularly troublesome weed in tussock grasslands, also very common in pastures, roadsides, riverbeds, waste places and in many modified open communities".

Indian Ocean
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Mascarene Islands Mascarene Islands (Mauritius, La Reunion, Rodrigues)	Mascarene Islands	introduced	U.S. Dept. Agr., Agr. Res. Serv. (2007)

Comments:  "A serious weed, and its potential for photosensitization poses a threat to livestock in many parts of the world" (Wagner et al., 1999; p. 546).

Control: 

Physical:  "Seedlings and smaller plants can be hand pulled or dug out, crowns and rhizomes must be removed.  Repeated defoliation can reduce the plant's density".

Chemical:  "Effective herbicides are 2,4-D, glyphosate, or picloram.  Bare ground resulting from control measures is likely to be colonized by emerging seedlings"  (Weber, 2003; p. 210).

Additional information:  Additional online information about Hypericum perforatum is available from the Hawaiian Ecosystems at Risk project (HEAR).

Taxonomic information about Hypericum perforatum may be available from the Germplasm Resources Information Network (GRIN).

References:

Hafliger, Toni J./Wolf, Matthias. 1988. Dicot weeds, vol. 1. CIBA-GEIGY Ltd., Basle, Switzerland. 335 pp.

Owen, S. J. 1997. Ecological weeds on conservation land in New Zealand: A database. Working draft. Wellington, New Zealand. Department of Conservation.

U.S. Dept. Agr., Agr. Res. Serv. 2007. National Genetic Resources Program. Germplasm Resources Information Network (GRIN). Online searchable database.

Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. 1999. Manual of the flowering plants of Hawaii. Revised edition. Bernice P. Bishop Museum special publication. University of Hawai‘i Press/Bishop Museum Press, Honolulu. 1919 pp. (two volumes).

Webb, C. J./Sykes, W. R./Garnock-Jones, P. J. 1988. Flora of New Zealand, Volume IV: Naturalised pteridophytes, gymnosperms, dicotyledons. Botany Division, DSIR, Christchurch. 1365 pp.

Weber, Ewald. 2003. Invasive plants of the World. CABI Publishing, CAB International, Wallingford, UK. 548 pp.