Ageratum houstonianum Mill., Asteraceae

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Present on Pacific Islands?  yes

Primarily a threat at high elevations?  no

Common name(s): [more details]

English: ageratum, blue billygoat weed, bluemink, flossflower, goatweed

Fijian: botebotekoro, mbotembotekoro, sogovanua, songovanua

French: ageratum du Mexique

Hawaiian: maile hohono, maile honohono, maile kula

Spanish: agérato

Habit:  herb

Description:  "Annual, usually erect and often much branched, the stems leafy throughout, pilose or villous with spreading hairs; leaves opposite, on rather long, slender petioles, very thin, broadly deltoid-ovate, mostly 4-8 cm long, obtuse or acute, generally shallowing cordate at the base, coarsely crenate, thinly villous-hirsute, not punctate beneath; corymbs terminal on the branches, often compound, glandular-hirtellous and villous with several-celled hairs; heads numerous lavender or pale blue, 8 mm broad, about 75-flowered; phyllaries narrowly lanceolate or linear, entire, herbaceous, long-attenuate, ciliolate, usually purplish toward the apex, 2-costate, glandular-puberulent; achenes black, lustrous, commonly hispidulous, at least on the angles, 1.2 mm long; pappus scales 5, lanceolate, fimbriate-margined, long-setiferous, about equaling the corolla" (Nash & Williams, 1976; p. 39).

"Coarse herb, semiprostrate toward base and with ascending branches 0.3-1 m high...  The corolla lobes and styles are pale blue to purple."  (Smith, 1991; pp. 296-297).

Habitat/ecology:  In Hawai‘i, "naturalized in a wide variety of disturbed habitats, especially along trails and roadsides, 40-1,300 m" (Wagner et al., 1999; p. 256). In Fiji, "sometimes cultivated and also naturalized at elevations from near sea level to 1,127 m in open places, along roadsides, on river banks, and on cleared upland slopes and crests"  (Smith, 1991; pp. 296-297). In New Guinea, "established in a few localities above 1000 m" (Henty & Pritchard, 1975; p 63).

Propagation:  Seed

Native range:  Mexico, central America and the West Indies (Wagner et al., 1999; p. 256).

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	Viti Levu Island	introduced invasive cultivated	Smith, Albert C. (1991) (pp. 296-297) Vouchers cited: Parks 20625, Parks 20626, Smith 5019, DA 2729, DA 8530, DA 11114, DA 10371, Vaughan 3246, DA 11327, DA 11123, DA 12117
French Polynesia Society Islands	Huahine Island	introduced invasive cultivated	Welsh, S. L. (1998) (p. 69) Voucher cited: Fosberg 63009
French Polynesia Society Islands	Tahiti Island	introduced invasive cultivated	Welsh, S. L. (1998) (p. 69) Voucher cited: Fosberg 64999
State of Hawaii Hawaiian Islands	Hawai‘i (Big) Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (p. 256)
State of Hawaii Hawaiian Islands	Kaua‘i Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (p. 256)
State of Hawaii Hawaiian Islands	Maui Island	introduced invasive	Oppenheimer, Hank L./Bartlett, R. T. (2000) (p. 2) East Maui. Voucher cited: Oppenheimr H69910 (BISH)
State of Hawaii Hawaiian Islands	O‘ahu Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (p. 256) Voucher cited: Garber 95 (BISH)
Japan (offshore islands) Bonin (Ogasawara) Islands	Bonin (Ogasawara) Islands	introduced	Kato, Hidetoshi (2007)
New Caledonia New Caledonia Archipelago	Île Grande Terre	introduced	MacKee, H. S. (1994) (p. 31) Vouchers cited: MacKee 31210, Fallen 176 (NOU), Fukuoka et al. C-90, H. Brinon 267 (NOU), Toutain 3570 (NOU)
New Zealand (offshore islands) Kermadec Islands	Raoul Island	introduced invasive	Sykes, W. R. (1977) (p. 85)
New Zealand (offshore islands) Kermadec Islands	Raoul Island	introduced invasive	Webb, C. J./Sykes, W. R./Garnock-Jones, P. J. (1988) (p. 206) "Common on Raoul and nearby islets. Waste places and disturbed areas".

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)		Holm, Leroy/Pancho, Juan V./Herberger, James P./Plucknett, Donald L. (1979) (p. 10)
China China	China (People's Republic of)		Holm, Leroy/Pancho, Juan V./Herberger, James P./Plucknett, Donald L. (1979) (p. 10)
Indonesia Indonesia	Indonesia (Republic of)		Holm, Leroy/Pancho, Juan V./Herberger, James P./Plucknett, Donald L. (1979) (p. 10)
New Zealand New Zealand	New Zealand (country)	introduced cultivated	Webb, C. J./Sykes, W. R./Garnock-Jones, P. J. (1988) (p. 206)
Taiwan Taiwan	Taiwan Island		Holm, Leroy/Pancho, Juan V./Herberger, James P./Plucknett, Donald L. (1979) (p. 10)

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

Information about Ageratum houstonianum as a weed (worldwide references) may be available from the Global Compendium of Weeds (GCW).

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

References:

Dassanayake, M. D., gen. ed. 1994. A revised handbook to the flora of Ceylon. Vol VIII. Amerind Pub. Co., New Delhi. 458 pp.

Henty, E. E./Pritchard, G. H. 1975. Weeds of New Guinea and their control. 2nd edition. Department of Forests, Division of Botany, Botany Bull. No. 7. Lae, Papua New Guinea. 180 pp.

Holm, Leroy/Pancho, Juan V./Herberger, James P./Plucknett, Donald L. 1979. A geographical atlas of world weeds. John Wiley & Sons, New York. 391 pp.

Kato, Hidetoshi. 2007. Herbarium records of Makino Herbarium, Tokyo Metropolitan University. Personal communication.

MacKee, H. S. 1994. Catalogue des plantes introduites et cultivées en Nouvelle-Calédonie. Muséum National d'Histoire Naturelle, Paris, 164 p.

Nash, Dorothy L./Williams, Louis O. 1976. Flora of Guatemala. Fieldiana: Botany. Vol. 24, Part XII. Chicago Natural History Museum. 603 pp.

Oppenheimer, Hank L./Bartlett, R. T. 2000. New plant records from Maui, O‘ahu, and the Hawai‘i Islands. In: Evenhuis, Neal L. and Eldredge, Lucius G., eds. Records of the Hawaii Biological Survey for 1999. Part 2: Notes. Bishop Museum Occasional Papers. 64:1-10.

Parham, J. W. 1958. The weeds of Fiji. Department of Agriculture, Fiji. Bulletin No. 35. 196 pp.

Smith, Albert C. 1991. Flora Vitiensis nova: a new flora of Fiji. National Tropical Botanical Garden, Lawai, Kauai, Hawaii. Volume 5. 626 pp.

Sykes, W. R. 1977. Kermadec Islands flora: an annotated checklist. New Zealand Department of Scientific and Industrial Research Bulletin 219, Wellington. 216 pp.

Thaman, R. R./Tuiwawa, M. 1999. Invasive, potentially invasive and adventive alien plant species of Fiji: a preliminary analysis of their status and measures required for their control. Preliminary draft discussion paper prepared for the SPREP Regional Invasive Species Strategy for the South Pacific Islands Region: Regional Workshop, Nadi, Fiji, 26 September-1 October 1999.

U.S. Dept. Agr., Agr. Res. Serv. 2009. 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.

Welsh, S. L. 1998. Flora Societensis: A summary revision of the flowering plants of the Society Islands. E.P.S. Inc., Orem, Utah. 420 pp.