Myriophyllum spicatum

Eurasian water-milfoil

Nonnative to FloridaFlorida Prohibited Aquatic Plants ListFISC Category 2
Introduction

Non-Native to Florida

Origin: Temperate and tropical Eurasia and Northern Africa1
Introduction to Florida: 1940s (ornamental)2

Eurasian water-milfoil is submersed. It tolerates a wide range of water conditions, and often forms large infestations.

Eurasian water-milfoil stems are reddish-brown to whitish-pink. They are branched and commonly grow to lengths of six to nine feet. The leaves are deeply divided, soft and feather-like. Leaves are about two inches long. The leaves are arranged in whorls of three to six leaves about the stem. The flowers of Eurasian water-milfoil are reddish and very small. They are held above the water on an emersed flower spike that is several inches long.

Description
  • an aquatic weed worldwide
  • seems to prefer lakes, ponds and slow-moving rivers and streams but can also grow in fast-moving water (Newroth 1985)
  • tolerates a wide range of water conditions, including spring water and even brackish water of tidal creeks and bays with salinity of up to 10 parts per thousand (Beaven 1960)
  • temperature tolerance: Eurasian water-milfoil is winter-hardy, able to overwinter in frozen lakes and ponds in northern states and Canada; but is also able to grow in shallow, over-heated bays such as Chassahowitzka Bay in Florida

Myriophyllum spicatum L.
Original description: Linnaeus 1753

  • dicot, perennial
  • there are a number of water-milfoils, native and non-native, that are confusable; this water-milfoil has decidedly feathery-looking leaves
  • plants submersed rooted, attached to the substrate
  • stems slender, smooth, 6 to 20 ft. long; stems reddish-brown to whitish-pink; branching several times near the water surface
  • leaves are olive-green, less than 2 in. long, soft, deeply divided, feather-like; each leaf with a central axis (midrib) and 14 to 24 or so very slender (filiform) segments on each side of the axis
  • leaf whorls are arranged along the stems in whorls of 3 to 6 (usually 4) leaves; whorl nodes are about 3/8 in. apart
  • flowers on an emersed spike, held erect above the water, the spike to 8 inches long; flowers reddish; arranged in 4-flowered whorls along spike; petals 4; petals 1/8 in. long; sepals 4; stamens 8; flowering in Canada from late July to early August
  • fruit 4-lobed; splitting into 4 nutlets
  • roots fibrous; often developing on plant fragments

Myriophyllum spicatum might be confused with a number of other submersed plants, including other water-milfoils and other submersed plants.

  • native northern water-milfoil (Myriophyllum sibiricum = M. exalbescens):
  • — has fewer than 12 leaf segments on each side of the leaf axis, whereas Eurasian water-milfoil leaves have 14 or more leaf segments on each side of the leaf axis; and has somewhat stouter stems than does Eurasian water-milfoil

coontail
coontail

native coontail (Ceratophyllum demersum):

  • — leaves are toothed and the plant feels rough when pulled through the hand, whereas Eurasian water-milfoil leaves are not toothed and the plant does not feel rough
Impacts
  • Myriophyllum spicatum grows quickly to form dense infestations which shade out and replace native plants (Smith & Barko 1990; Madsen 1994; Madsen et al. 1991)
  • Eurasian water-milfoil infestations negatively affect birds and fish (Aiken et al. 1979; Madsen et al. 1995)
  • decaying mats of Eurasian water-milfoil reduce oxygen levels in the water (Honnell 1992)