European waterclover, water shamrock
FULL SCIENTIFIC NAME
Marsilea quadrifolia L.
FAMILY NAME COMMON
FAMILY SCIENTIFIC NAME
Marsilea quadrifolia is an aquatic fern which anchors itself to the muddy bottoms of quiet, shallow lakes and streams. The plant roots both at the nodes and internodes of the rhizome. The slender petioles are usually glabrous (sometimes pubescent) and 5.5-17 cm (2-6 in.) long. They can occasionally reach 30 cm (1 ft.) if the plant is rooted deeply. The leaves resemble a four-leaf clover, giving it the common name water shamrock. The four leaflets are triangular-obovate in shape. The ones on emergent leaves are 7-30 mm (0.25-1 in.) long and about the same in width, while the leaflets of floating leaves are a bit larger. They are usually glabrous, but can be sparsely pubescent when young. The peduncles bearing the dark brown sporocarps (fruit case containing sporangia) are attached 1-12 mm (0.04-0.5 in.) above the base of the petiole. The peduncles are 3-20 mm (0.1-0.8 in.) long and can be simple or branched. They bear 2 or 3 sporocarps that are 4-5.5 mm (0.2 in.) long and 3-4 mm (0.1 in.) wide and 2.5 mm (0.1 in.) thick. They are oval to elliptical in shape, pubescent when young, but soon glabrate. Page References Crow & Hellquist 14, Fernald 51, Flora of North America 332, Gleason & Cronquist 30, Holmgren 30, Magee & Ahles 96. See reference section below for full citations.
Local reproduction of this plant is mainly through clonal means. However, Marsilea quadrifolia disperses itself over longer distances by means of sporocarps. These reproductive structures can move the plant downstream to new areas. Ducks and other waterfowl also help to move this species between different bodies of water.
Marsilea quadrifolia is native to Europe, from Spain to France, to northern Italy and east to Turkey. In the United States it has been reported from Iowa, Missouri, Illinois, Indiana, Ohio, Michigan, Kentucky, Georgia, North Carolina, Maryland, Delaware, New Jersey, New York and Pennsylvania. In New England it has been found in Maine, New Hampshire, Massachusetts and Connecticut.
HISTORY OF INTRODUCTION IN NEW ENGLAND
The first introduction of this plant in North America was detected in Connecticut in 1860 at Bantam Lake in Litchfield County. This introduction was likely intentional, though there is some speculation at this time about it being introduced by Siberian aquatic birds. From here, the plant was introduced into the Harvard Botanical Garden in Cambridge, Massachusetts sometime before 1868. The gardener then introduced in into Fresh Pond, also in Cambridge, Massachusetts in 1872. It became intentionally established in the Concord River in 1879. By 1900, this plant was intentionally introduced into many other places in Connecticut, Massachusetts, Maine and New Hampshire.
HABITATS IN NEW ENGLAND
Aquatic, Lake or Pond, River or Stream, Yard or Garden. Marsilea quadrifolia prefers aquatic habitats with still or very slow moving water. It can be totally submerged except for the leaves, or in shallow situations can be more emergent in its habit.
This plant has the ability to form monotypic stands within quiet ponds and streams. These stands can exclude native aquatic plants from these habitats. Marsilea quadrifolia is also being sold for water gardening, and can escape through careless disposal into local waterbodies. Though this plant has not yet become a major problem, it has the potential to do so, and should be monitored carefully.
Documentation required: A photograph of the leaves. Best time for documentation: Summer, fall.
Integrated Taxonomic Information System - Taxonomic information
The PLANTS Database - General information including map
Britton, N.L. and A. Brown. 1970. An Illustrated Flora of the Northeastern United States vol. 1. Dover Publications Inc., New York.
Crow G.E. and C.B. Hellquist. 2000. Aquatic and Wetland Plants of Northeastern North America. Vol #1. University of Wisconsin Press, Madison.
Fernald, M.L. 1950. Gray's Manual of Botany 8th ed. American Book Co., Boston.
Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. Volume #. Oxford University Press.
Flora of North America Association ed. 2000. Flora of North America vol. 2. Oxford University Press, Oxford, New York.
Gleason H.A. and A.C. Cronquist. 1991. Manual of Vascular Plants of the Northeastern United States and Adjacent Canada. 2nd ed. New York Botanical Garden, Bronx, New York.
Holmgren N.H. 1998. Illustrated Companion to Gleason and Cronquist's Manual. New York Botanical Garden, Bronx, New York.
Les, D.H. and L.J. Mehrhoff. 1999. Introduction of nonindigenous aquatic vascular plants in southern New England: a historical perspective. Biological Invasions 1:281-300.
Lin, BL. and W.J. Yang. 1999. Blue light and abscisic acid independently induce heterophyllous switch in Marsilea quadrifolia. Plant Physiology 119 (2): 429-434.
Magee D.W and H.E. Ahles. 1999. Flora of the Northeast. University of Massachusetts Press, Amherst.
USDA, NRCS. 2001. The PLANTS Database, Version 3.1. (//plants.usda.gov). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.