Sagittaria platyphylla (Engelmann) J.G.Smith, Alismataceae

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Present on Pacific Islands?  yes

Primarily a threat at high elevations?  no

Risk assessment results:  High risk; score: 28 (Hawaii-Pacific Weed Risk Assessment for Sagittaria platyphylla)

Other Latin names:  Sagittaria graminea var. platyphylla Michx.; Sagittaria mohrii J. G. Sm.; Sagittaria recurva Engelm. ex Patt.; Sagittaria weatherbiana Fernald

Common name(s): [more details]

English: arrow-head, arrowhead, delta arrowhead, grassy arrowhead, sagittaria, slender arrowhead

Habit:  aquatic herb

Description:  "[Sagittaria platyphylla] has white flowers with three petals on a distinctive stem that is triangular in cross section." (Western Weeds, p. 6)

"[Sagittaria platyphyhlla] is an emergent aquatic plant that grows up to 80 cm in height, and is found in flowing or still fresh water and in marshes and swamps. It has long rhizomes which produce small tubers similar to S. sagittifolia. Large, lance-shaped leaves are held above the water on stems. It also produces strap-shaped submerged leaves. White flowers (6 cm across) are produced on spikes about the same height as leaves, each producing hundreds of seeds." (NZ National Pest Plant Accord 2012, p. 126)

"Herbs, perennial, to 150 cm; rhizomes absent; stolons present; corms present. Leaves submersed and emersed; submersed sessile, phyllodial, flattened, to 26 ´ 0.5 cm; emersed with petiole ± triangular, 21--70.5 cm, blade linear-ovate to ovate, 4.6--16.4 ´ 0.7--6.1 cm. Inflorescences racemes, of 3--9 whorls, emersed, 2.5--10 ´ 2--4.5 cm; peduncles 22--60 cm; bracts connate more than ¼ total length, lanceolate, 3--5.5 mm, delicate, not papillose; fruiting pedicels spreading to recurved, cylindric, 0.5--3 cm. Flowers to 1.8 cm diam.; sepals spreading to recurved, not enclosing flower or fruiting head; filaments dilated, longer than anthers, pubescent; pistillate pedicellate, without ring of sterile stamens. Fruiting heads 0.7--1.2 cm diam.; achenes oblanceoloid, not abaxially keeled, 1.2--2 ´ 0.8--1.2 mm, beaked; faces tuberculate, wings absent, glands absent; beak lateral, horizontal to erect, 0.3--0.6 mm." (eMonocot, accessed 31 October 2017)

"Perennial, glabrous, with subterranean stolons. Emerged leaves erect, narrow-ellipticto lanceolate,acute, gradually narrowed towards the base, 5'/2-10 by 1-3 cm; in extra-Mal. specim. also phyllodes; nerves 5-7, arising at the leaf-base prominent on the undersurface, connected by parallel cross-veins spaced c. 1 mm under an angle of c. 45°; petiole sharply triangular, narrowly winged, ribbed, with air-channels, 25-40 cm in sicco with distinct septations c. 5-7 mm spaced; sheath broad. Peduncles erect, very bluntly triangular, with air-channels, incl. the raceme 30-40 cm. Raceme about 1/4 as long as the peduncle, with 4-6 whorls of 3 flowers, the lower 2 whorls Q, the others d. Bracts connate, broad-ovate to suborbicular, obtuse, margin scarious, c. 3-4 mm. Pedicels 8-20 mm, obliquely erect, fruiting pedicels recurved and strongly thickened. Flowers c. 2 cm diam. Sepals blunt elliptic, broadly scarious margined, recurved after anthesis, 4-4 1/2 mm long. Petals white, transverse elliptic, short-unguiculate, slightly sinuate at the apex, 10 by 13 mm. Stamens 12-18; filaments c. 1 mm, strongly dilated, flattened, slightly hairy; anthers oblong, 4/5-1 mm. Carpels Ϩ, obliquely elliptic, 1 mm; style apical though ventrally inserted, sometimes curved; stigma punctiform. Fruiting heads globular, 8-10 mm. Achenes obovate, 2 by 1 mm, dorsally and ventrally winged, with 2 additional dorso-lateral ribs, slightly compressed; beak 1/3 mm, apical, obliquely erected inward. Seed pale brown." (Hartog 1957)

See also Weeds of Australia (online).

Habitat/ecology:  "Streams and lakes; 0--900 m." (a tropical garden flora, accessed 31 October 2017)

"A weed of waterways, marshes, swamps, drainage ditches, irrigation channels and rice crops in warmer temperate, sub-tropical and tropical environments. . . . A long-lived (i.e. perennial) aquatic herbaceous plant usually rooted to the ground with stems and leaves emerging up to 80 cm above the water surface. However, plants may sometimes become detached from the substrate form floating mats of vegetation on or near the water surface." (Weeds of Australia (online))

Propagation:  "The Auckland Regional Council (2002) states that, 'S. platyphylla spreads locally by its creeping root system, and to other areas via seed carried in water, by machinery, wildlife and humans. New infestations can also form via rhizome fragments transported by ditch cleaning machinery and spoil.' Parsons and Cuthbertson (1992) state that S. platyphylla can spread from seed, and displaced rhizomes and tubers. Entire plants can break free and float to new locations." (GISD)

Native range:  The native range of Sagittaria platyphylla (Alismataceae) includes Panama, Mexico, and eastern-to-central United States. (GRIN)

Impacts and invaded habitats:  "Sagittaria (Sagittaria paltyphylla [sic]) is regarded as an environmental weed in Queensland, New South Wales and Western Australia, and as an emerging or potential environmental weed in other parts of southern Australia. It was recently listed as a priority environmental weed in at least one Natural Resource Management region." (Weeds of Australia (online))

"A weed of waterways, marshes, swamps, drainage ditches, irrigation channels and rice crops in warmer temperate, sub-tropical and tropical environments. . . . A long-lived (i.e. perennial) aquatic herbaceous plant usually rooted to the ground with stems and leaves emerging up to 80 cm above the water surface. However, plants may sometimes become detached from the substrate form floating mats of vegetation on or near the water surface." (Weeds of Australia (online))

"[Sagittaria platyphylla] is an invasive weed with the potential to block waterways." (NZ National Pest Plant Accord 2012, p. 126); "[Sagittaria platyphylla] is a serious aquatic weed" (Western Weeds, p. 6)

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	Hawaiian Islands	introduced	U.S. National Plant Germplasm System (year unknown) ref accessed 20190123, "Naturalized"
State of Hawaii Hawaiian Islands	O‘ahu Island	introduced invasive	Frohlich, Danielle/Lau, Alex (2014) (p. 7) "Material examined. O'AHU: Windward O'ahu, Waihe'e, lowland cultivated taro patch, hundreds of individuals seen in patch, said to have been introduced from taro starters brought from Kaua'i, 20 Sep 2013, D. Frohlich, A. Lau & J. Beachy 2013092002."; "it was first collected in Hawai'i in 1991, but has likely been in the aquarium trade here for some time before then. it was collected from a lo'i kalo in Waihe'e, O'ahu, where it was occasionally occurring in high density 'thickets' over multiple kalo (Colocasia esculenta) patches, and appeared to be competing for resources and significantly reducing fitness of the planted kalo. it is unclear how it came to occur in this site, though local farmers believe it may have been transferred accidentally as seed in soil when sharing huli from infested lo'i elsewhere."
State of Hawaii Hawaiian Islands	O‘ahu Island		Consortium of Pacific Herbaria (2018)

Pacific Rim
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Asia Asia	Asia (southeast)	introduced	Randall, R. P. (2017) (p. 2986)
Asia Asia	Asia (southern)	introduced	Randall, R. P. (2017) (p. 2986)
Asia Asia	Israel	introduced	Randall, R. P. (2017) (p. 2986)
Asia Asia	Ukraine	introduced	U.S. National Plant Germplasm System (year unknown) ref accessed 20190123, "Naturalized"
Asia Asia	Ukraine	introduced	Randall, R. P. (2017) (p. 2986)
Asia Asia	USSR	introduced	Kwong, Raelene/Sagliocco, Jean-Louis/Harms, Nathan/Shearer, Judy/Keener, Brian R./Green, Peter (2014) accessed 20190123 "naturalized"
Australia Australia	Australia	introduced	U.S. National Plant Germplasm System (year unknown) ref accessed 20190123, "Naturalized"
Australia Australia	Australia	introduced invasive	Randall, R. P. (2017) (p. 2986)
Australia Australia	Australia	introduced	Martin, Grant D./Coetzee, Julie Angela/Lloyd, Melissa/Nombewu, Sinoxolo E./Ndlovu, Mpilonhle S./Kwong, Raelene (2018) abstract accessed 20190123, "A biological control programme [PIER ed.: for Sagittaria platyphylla (Engelmann) J.G. Smith (Alismataceae)] was initiated in Australia and surveys conducted between 2010 and 2012 yielded potential agents...."
Australia Australia	Australia	introduced invasive cultivated	Kwong, Raelene/Sagliocco, Jean-Louis/Harms, Nathan/Shearer, Judy/Keener, Brian R./Green, Peter (2014) accessed 20190123 "The perennial North American native delta arrowhead, Sagittaria platyphylla (Alismataceae), was introduced to Australia as an aquarium and pond ornamental plant in the 1930s. Today, it is a serious invader of irrigation channels and natural waterways in south eastern Australia and was declared a Weed of National Significance in 2012."
Australia Australia	Australia	introduced invasive cultivated	Global Invasive Species Database (2015) (p. 2) Parsons and Cuthbertson (1992) state that S. platyphylla can spread from seed, and displaced rhizomes and tubers. Entire plants can break free and float to new locations.
Australia Australia	Western Australia (Australia) (state)	introduced	Kwong, Raelene/Sagliocco, Jean-Louis/Harms, Nathan/Shearer, Judy/Keener, Brian R./Green, Peter (2014) accessed 20190123
Australia Australia (continental)	New South Wales	introduced	Kwong, Raelene/Sagliocco, Jean-Louis/Harms, Nathan/Shearer, Judy/Keener, Brian R./Green, Peter (2014) accessed 20190123
Australia Australia (continental)	Australia (continental)	introduced invasive	Weber, Ewald (2017) (p. 412) "Invasive (species has established populations and exerts negative impacts on other species or habitats)" in some areas & "Naturalized (species has established populations" in some areas
Australia Australia (continental)	Queensland	introduced	Kwong, Raelene/Sagliocco, Jean-Louis/Harms, Nathan/Shearer, Judy/Keener, Brian R./Green, Peter (2014) accessed 20190123
Australia Australia (continental)	Victoria (Australia)	introduced	Kwong, Raelene/Sagliocco, Jean-Louis/Harms, Nathan/Shearer, Judy/Keener, Brian R./Green, Peter (2014) accessed 20190123
Central America Central America (Pacific rim)	Panama (Republic of)	introduced	Kwong, Raelene/Sagliocco, Jean-Louis/Harms, Nathan/Shearer, Judy/Keener, Brian R./Green, Peter (2014) accessed 20190123 "naturalized"
China China	China (People's Republic of)	introduced	Randall, R. P. (2017) (p. 2986)
Indonesia Indonesia	Indonesia (Republic of)	introduced	Randall, R. P. (2017) (p. 2986)
Indonesia Indonesia	Indonesia (Republic of)	introduced	Kwong, Raelene/Sagliocco, Jean-Louis/Harms, Nathan/Shearer, Judy/Keener, Brian R./Green, Peter (2014) accessed 20190123 "naturalized"
Malaysia Malaysia	West Java	introduced cultivated	Hartog, Den (1957) accessed 20190124 "introduced in Malaysia: West Java (Dfepok; Bogor). ... In wet rice-fields, between Djakarta and Bogor, up to 250 m, found for the first time by J. H. KERN I.e. in 1950; almost certainly escaped from plants formerly cultivated in the Botanic Gardens, Bogor."
Mexico Mexico	Mexico (United Mexican States)	native	U.S. National Plant Germplasm System (year unknown) ref accessed 20190123
New Zealand New Zealand	New Zealand (country)	introduced invasive	Randall, R. P. (2017) (p. 2986)
New Zealand New Zealand	New Zealand (country)	introduced invasive	Global Invasive Species Database (2015) (p. 2) The Auckland Regional Council (2002) states that, \"S. platyphylla spreads locally by its creeping root system, and to other areas via seed carried in water, by machinery, wildlife and humans. New infestations can also form via rhizome fragments transported by ditch cleaning machinery and spoil.\"
New Zealand New Zealand	North Island (NZ)		Consortium of Pacific Herbaria (2018)
New Zealand New Zealand	North Island (NZ)	introduced	Kwong, Raelene/Sagliocco, Jean-Louis/Harms, Nathan/Shearer, Judy/Keener, Brian R./Green, Peter (2014) accessed 20190123

Also reported from
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Eurasia Eurasia	Georgia	introduced	Randall, R. P. (2017) (p. 2986)
Eurasia Eurasia	Georgia	introduced	Global Invasive Species Database (2015) (p. 2)
Europe Europe	Europe	introduced	Randall, R. P. (2017) (p. 2986)
Europe Europe	Italy	introduced	U.S. National Plant Germplasm System (year unknown) ref accessed 20190123, "Naturalized"
Europe Europe	Italy	introduced	Randall, R. P. (2017) (p. 2986)
Europe Europe	Switzerland	introduced	Randall, R. P. (2017) (p. 2986)
Europe Europe	United Kingdom	introduced	Randall, R. P. (2017) (p. 2986)
North America North America	North America	native	Hartog, Den (1957) accessed 20190124 "Native in North America (Mississippi & Gulf of Mexico)"
South Africa South Africa	South Africa (Republic of)	introduced invasive	Randall, R. P. (2017) (p. 2986)
South Africa South Africa	South Africa (Republic of)	introduced	Martin, Grant D./Coetzee, Julie Angela/Lloyd, Melissa/Nombewu, Sinoxolo E./Ndlovu, Mpilonhle S./Kwong, Raelene (2018) abstract accessed 20190123, "Sagittaria platyphylla (Engelmann) J.G. Smith (Alismataceae) was first recorded in South Africa in 2008 and is considered to be an emerging weed with naturalised populations occurring throughout the country."
United States of America United States	United States	native	Randall, R. P. (2017) (p. 2986)
United States (continental except west coast) United States (other states)	United States (other states)	native	U.S. National Plant Germplasm System (year unknown) ref accessed 20190123, see ref for details re states in which the species occurs
World World	Worldwide	invasive	Randall, R. P. (2017) (p. 2986)

Comments:  Sagittaria platyphylla (Alismataceae) has become established (outside its native range; "naturalized") in Australia, Ukraine, Italy, and Hawaii (USA). (GRIN)

"Parsons and Cuthbertson (1992) state that http://www.hear.org/pier/references/pierref108946.htm has been cultivated as an ornamental and this has aided spread." (GISD)

Control:  Chemical control options/recommended herbicides: Bentazone; metsulfuron; bensulfuron; glyphosate (for more details, see Government of Western Australia (online))

RE: aquatic weeds in general (including Sagittaria platyphylla): "Mechanical control such as cutting, mowing, dredging, drying and chaining may be necessary and effective in small areas, particularly where chemical control is not appropriate. Mechanical control is generally expensive, and short-lived. It can even help spread of weeds due to propagation from root or stem fragments." (Government of Western Australia (online))

"The Auckland Regional Council (2002) reports that, 'Small infestations can be cleared by hand or machinery but all the roots, rhizomes and tubers must be removed and plant material disposed of carefully.'" (GISD)