Myriophyllum pinnatum
(cutleaf watermilfoil)

Myriophyllum pinnatum is a perennial aquatic herb only reported as invasive in Cuba, where it is included in the management plan of the Ciénaga de Zapata Biosphere Reserve as a species that needs to be managed to prevent invasion of that wetland system. In some areas of its native range in North America, it is considered rare, endangered or extirpated due to habitat fragmentation and loss. In the USA, the species is considered endangered in Connecticut, Massachusetts, Indiana, New Jersey, New York, Rhode Island and Tennessee. M. pinnatum belongs to a genus recognized for the invasive species M. spicatum, M. aquaticum and M. heterophyllum. 

M. pinnatum is native to North America, with evidence of its presence in Iowa since the Holocene (Baker et al., 1996; USDA-NRCS, 2017). Urquiola Cruz and Betancourt Gandul (2000) consider the species native to Cuba, but Maldonado González (2009-2010) and Oviedo Prieto et al. (2012) list it as introduced in the country. M. pinnatum has also been introduced to Mexico (in 1974) and to Jamaica (in 1976) (Proctor, 1982; Red de Herbarios del Noroeste de México, 2017). Although the species is not listed as naturalized elsewhere, it is sold commercially worldwide and on the internet to be used in freshwater aquaria.

M. pinnatum is an aquatic herb with a low to medium risk of introduction. Although it is available commercially at aquarium supply stores, its specific water temperature and pH might limit its distribution (Live Aquaria, 2017). Where used only as a plant for indoor aquaria, the threat to natural environments is low. It can become problematic if its popularity increases or if used in sewage treatment plants (Mohan et al., 2010; Live Aquaria, 2017).

M. pinnatum occurs in shallow water, in ditches and ponds, usually less than 1 m deep (Knepper et al., 2002; SEINet, 2017). It is also reported from forest swales, wetlands, creeks, borders of brackish marshes, swamps and rivers (Fernald, 1936; Abbott and Judd, 2000; Rosen et al., 2003; Hercombe et al., 2007; Maldonado González, 2009-2010). 

Genetics

The chromosome number reported for M. pinnatum is n = 5 (Moody and Les, 2002). DNA barcode information for the species is available at the Barcode of Life Data Systems (BOLD, 2017). Although hybridisation with M. heterophyllum was initially reported by Moody and Les (2002), the same authors later confirmed it to be between M. heterophyllum and M. laxum (Moody and Les, 2010).

Reproductive Biology

M. pinnatum reproduces by cuttings and by flowers, if tips are left to grow outside of water (Live Aquaria, 2017). Propagation procedures in vitro have been developed for the species by Kane and Gilman (1991).

Physiology and Phenology

M. pinnatum is a rapid growing aquatic herb that can grow partially above water (Live Aquaria, 2017). It is reported to flower in July (SEINet, 2017).

Associations

Sorrie (1987) reports the species to occur in small, shallow, muddy, brackish ponds, together with Typha latifolia, Phragmites communis [Phragmites australis], Eleocharis smallii [Eleocharis palustris], Scirpus validus [Schoenoplectus tabernaemontani], Hibiscus palustris [Hibiscus moscheutos], Ludwigia palustris, Proserpinaca palustris and occasionally Diplachne maritima [Leptochloa fusca subsp. fascicularis]. In some cases, P. australis can be a threat to M. pinnatum populations, by severely reducing the open water and exposed mud available.

Environmental Requirements

Most information available concerns cultivation of M. pinnatum as an aquarium plant. The species grows in shallow water in full to partial shade, at water temperatures of 16-24°C. It grows in clay, sand, limestone and gravel substrates, with water pH of 6.5-7.5 and water hardness of 3-8 mg/l CaCO₃ (Maldonado González, 2009-2010; Live Aquaria, 2017).

Although information about environmental requirements from natural habitats is lacking, the species is likely able to tolerate freezing temperatures, given the fact that it is native in Canada (Missouri Botanical Garden, 2017).

The species is foraged by Procambarus clarkii, P. spiculifer, Branta canadensis and Aix sponsa (Drobney and Fredrickson, 1979; Cronin et al., 2002; Parker et al., 2007).

Animal feed, fodder, forage

• Fodder/animal feed

Environmental

• Amenity

General

• Botanical garden/zoo
• Pet/aquarium trade

M. pinnatum has both alternate and whorled leaves, while other Myriophyllum species have only whorled leaves (SEINet, 2017). The species is similar to M. farwellii, but the fruits are smaller in M. pinnatum. Also, the carpels of M. pinnatum are broadly two-winged on the back, strongly scabrate or toothed and deeply grooved between the wings, while in M. farwellii carpels are roughly tuberculate or slightly toothed and with shallow groves between them (Morong, 1891).

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Prevention

M. pinnatum is included in the Ciénaga de Zapata Biosphere Reserve management plan as a species that needs to be managed in order to prevent its spread in this wetland system (Oviedo Prieto et al., 2012).

More detailed information about the species impacts on invaded habitats or on other species is needed. Details about its biology and environmental requirements in natural habitats are also needed.

28/02/17 Original text by:

Jeanine Vélez-Gavilán, Department of Biology, University of Puerto Rico,  Mayaguez, Puerto Rico, USA