Ageratina riparia (Regel) R.M.King & H.Rob., Asteraceae

Click on an image for links to BIGGER PICTURES

Present on Pacific Islands?  yes

Threat only at high elevations?  no

Risk assessment results:  Reject, score: 26 (Go to the risk assessment)

Other Latin names:  Eupatorium riparium Regel

Common name(s): [more details]

English: creeping croftonweed, mist flower, river eupatorium, spreading mistflower, William Taylor

French: abessouris, faux orthosiphon, Iapana malgache, jouvence, orthochifon, yapana malbare

Hawaiian: hāmākua pāmakani

Habit:  herb

Description:  "Spreading subshrubs from a creeping rootstock; stems sprawling, 5-10 dm long, sparsely puberulent. Leaves lanceolate to elliptic, 4-8 (-12) cm long, 1-1.5 cm wide, margins sharply serrate, petioles 0.5-1.3 cm long. Inflorescences lax; involucral bracts 4-5 mm long, puberulent; corollas white, 3-3.5 mm long. Achenes black, 1.5-2 mm long, puberulent on the angles" (Wagner et al., 1999; p. 255).

Habitat/ecology:  In Hawai‘i, dry disturbed habitats to mesic and wet forest, 3-1,200 m (Wagner et al., 1999; p. 254). “Mistflower rapidly invades disturbed areas and tends to spread along gullies and river banks. It is shade tolerant and can become a dominant understory plant. Chemicals from the leaf-litter suppress the growth of other plants e.g. native species, giving mistflower a further competitive advantage.” (Northern Territory of Australia Agnote No. 628).

Propagation:  Seed. “Spread of seeds can occur by wind, running water, contamination of agricultural produce, and seeds sticking to clothing, animals, vehicles and machinery. Existing colonies increase in size and density by layering, thus forming a mat of interwoven stems” (Northern Territory of Australia Agnote No. 628).

Native range:  Mexico and the West Indies.

Presence:

Pacific
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Australia (Pacific offshore islands) Norfolk Islands	Norfolk Island	introduced invasive	Ziesing, P. (1997) (pp. 30-31)
Australia (Pacific offshore islands) Norfolk Islands	Norfolk Island	introduced invasive	Orchard, Anthony E., ed. (1994) (p. 7) "A serious weed in areas of degraded forest, and an invader of the margins of undisturbed forest, smothering ferns and seedlings". Vouchers cited: G. Uhe 1100 (K), R.M. Laing (CHR), the Administrator of Norfolk Is. (NSW), J.D. McComish 96 (NSW), P. Ralston 312 (A, K)
State of Hawaii Hawaiian Islands	Hawai‘i (Big) Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (p. 255)
State of Hawaii Hawaiian Islands	Kaua‘i Island	introduced invasive	Herbst, Derral R./Wagner, Warren L. (1996) (p. 9) Voucher cited: Flynn et al. 5279 (BISH, PTBG, US)
State of Hawaii Hawaiian Islands	Lāna‘i Island	introduced invasive	Oppenheimer, Hank L./Bartlett, Randal T. (2002) (p. 3) Voucher cited: Oppenheimer H109924 (BISH)
State of Hawaii Hawaiian Islands	Maui Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (p. 255)
State of Hawaii Hawaiian Islands	Moloka‘i Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (p. 255)
State of Hawaii Hawaiian Islands	O‘ahu Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (p. 255)

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 invasive	U.S. Dept. Agr., Agr. Res. Serv. (2007)
Indonesia Indonesia	Indonesia (Republic of)		Holm, Leroy/Pancho, Juan V./Herberger, James P./Plucknett, Donald L. (1979) (p. 153)
Mexico Mexico	Mexico (United Mexican States)	native	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. 205) "Forest margins and clearings, waste places, damp banks and streamsides".

Indian Ocean
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
La Réunion (France) La Réunion Island	La Réunion Island	introduced invasive	Lavergne, Christophe (2006) "Très envahissant"
Mauritius Mautitius Islands (Mauritius and Rodrigues)	Mauritius Island		Mauramootoo, J. (year unknown)

Comments:  A problem species in Mauritius (John Mauramootoo, pers. com.). A declared noxious weed in Hawai‘i and the Northern Territory, Australia.

Control: 

Physical:  Hand pull or dig out seedlings and small plants.

Chemical:  Treat freshly cut stumps with 2,4-D or dicamba.

Biological: "Biological control attempts on mistflower have included the introduction of a gall-fly (Procecidochares alani) to Queensland, which has had little impact due to the attack by native parasites. However the recent introduction of a white rust fungus (Entyloma ageratinae) to New Zealand has proven to be highly specific to Ageratina riparia, with early indications it will provide useful control" (Northern Territory of Australia Agnote No. 628).

"Mist flower, a low-growing perennial with tiny white daisy-like flowers, was accidentally introduced to Hawai‘i in 1925. By 1972 it had occupied 52,000 ha of rangeland.  A plume moth (Oidematophorus beneficus), a gall wasp (Procecidochares alani), and a smut fungus (Entyloma ageratinae), were introduced to attack this aggressive weed in the mid-1970s.  Biological control of mist flower in Hawai‘i has been an outstanding success. Of the three agents the fungus was the most effective and it achieved total control of the plant in wet areas within eight months, and in dry areas within 3-8 years. The plant has remained under control ever since. Dense stands of mist flower have been reduced to isolated patches of sickly, stunted plants on dry rocky outcrops, where there is little competing vegetation, and the rangeland has been returned to productive use.

Mist flower has increasingly become a problem in northern New Zealand. A feasibility study showed that infested areas of New Zealand were likely to be suitable for the mist flower agents, so the smut fungus and the gall fly were released in New Zealand in 1998 and 2001 respectively.  Both are establishing and spreading rapidly and it looks promising that successful control of the plant will be achieved here too" (Landcare Research, New Zealand).

Additional information:  Northern Territory of Australia Agnote No. 628 (PDF format).
Photos and additional information at the Environment Bay of Plenty, New Zealand, web site of the Bay of Plenty Regional Council.

Additional online information about Ageratina riparia is available from the Hawaiian Ecosystems at Risk project (HEAR).

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

References:

Herbst, Derral R./Wagner, Warren L. 1996. Contributions to the Flora of Hawai‘i. V. In: Evenhuis, Neal L. and Miller, Scott, E., eds. Records of the Hawaii Biological Survey for 1995. Part 2: Notes. Bishop Museum Occasional Papers. 46:8-12.

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.

Lavergne, Christophe. 2006. List des especes exotiques envahissantes a La Reunion. Unpublished manuscript (Excel file). .

Mauramootoo, J. 0. John Mauramootoo, pers. com.

Oppenheimer, Hank L./Bartlett, Randal T. 2002. New plant records from the main Hawaiian Islands. In: Evenhuis, Neal L. and Eldredge, Lucius G., eds. Records of the Hawaii Biological Survey for 2000. Part 2: Notes. Bishop Museum Occasional Papers. 69:1-14.

Orchard, Anthony E., ed. 1994. Flora of Australia. Vol. 49, Oceanic islands 1. Australian Government Publishing Service, Canberra.

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.

Ziesing, P. 1997. Norfolk Island weed control manual for selected weeds occurring in Norfolk Island National Park. Environment Australia, Norfolk Island.