Myriophyllum

Scientific name

Myriophyllum L.

Common names

water milfoil, parrot feather

Family

Haloragaceae

Native distribution

almost cosmopolitan, very diverse in southern hemisphere, especially in Australia

Species commonly cultivated

Myriophyllum aquaticum (Vell.) Verdc. (South America)

M. matogrossense Hoehne (Ecuador, Brazil)

M. pinnatum (Walter) Britton, Sterns & Poggenb. (eastern North America)

M. simulans Orchard (eastern Australia)

M. spicatum L. (Europe, Asia, Africa)

M. tuberculatum Roxb. (southeast Asia)

M. ussuriense (Regel) Maxim. (Japan, Manchuria)

Adventive distribution

Myriophyllum spicatum is introduced in numerous regions of the world, including North and South America and Southeast Asia. Myriophyllum aquaticum is introduced into New Zealand, Republic of South Africa, Australia, Japan, United States, and various countries in Europe.

Weed status

Myriophyllum spicatum is a serious environmental weed in more than 50 countries around the world. Myriophyllum aquaticum is being quickly recognized as a serious environmental weed also. Both species are regulated or prohibited in numerous countries.

Habit

submersed and emergent, attached stem plant

Brief description

Annual or perennial. Dioecious or monoecious. Adventitious roots often produced from basal nodes. Stem elongate, ascending, floating, or erect. Leaves in whorls or sometimes alternate or opposite, spaced along stem at regular intervals, sessile; strong heterophylly between submersed and emergent forms; leaf blade linear, lanceolate to pinnate, degree of dissection variable; margin entire to serrate. Inflorescence on emergent stems as a terminal spike or axillary on apical nodes. Flowers sessile; sepals 4, reduced, or absent; petals 2-4, white to pink, sometimes absent. Dispersal by seed or stem fragments.

Natural habitat

still or slow flowing water; shallow to deeper waters of lakes, rivers, and streams, especially artificial impoundments

Additional comments

Myriophyllum contains at least 40 species found mainly in the Southern Hemisphere. Various species are cultivated for aquaria or ponds. The taxonomy of the genus has been problematic, resulting in numerous synonyms being used in the trade. Many species are only suitable for pond culture. All species show distinctive heterophylly between submersed and emergent leaf shape. One species, the chiddarcooping myriophyllum (M. lapidicola Orchard), is found in ephemeral pools on rocky outcrops in western Australia and is considered critically endangered due to habitat destruction and overgrazing. Myriophyllum callitrichoides Orchard, a species from ephemeral rock pools in northern Australia, exhibits atypical growth. This submersed plant has a short, thickened stem basally bearing several short leaves. A short distance above the root mass the stem is divided into numerous, narrow stems mostly without leaves, but each stem terminating in a floating apical rosette of small ovate leaves.