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| NAS - Nonindigenous Aquatic Species |
Four Leaf Unlucky?
NonindigenousWATER-CLOVERS
are increasingly being found in ponds,
streams and roadside ditches. Resembling four-leaf
clovers on long leaf stalks, these amphibious plants are ferns (Pteridophyta)
classified under the genus Marsilea (Marsileaceae). A popular addition
to water-gardens and horticultural plantings, Marsilea has been found
in weedy, competitive stands in both aquatic and terrestrial habitats of the
southern United States.
Recent occurrences
in the southern U.S. have been of the Australian Marsilea
mutica and the Asian Marsilea
minuta (map). Both
tropical species, they appear suitably adapted to permanent aquatic environments,
have overwintered as far north as Oklahoma, and may become very weedy.
Recognize Marsilea through the galleries linked below and please contact us if you find escaped populations. Our ongoing studies include determination of their identification and distribution.
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The new water-clovers previewed here are commonly confused with Marsilea quadrifolia a very similar European species that has been well established in the northeastern United States for over 100 years. The introduced range of the cold temperate M. quadrifolia extends south through Pennsylvania and west to Missouri. It may not be as common in today's market as the more tropical species.
Native North American water-clovers, notably Marsilea vestita, occur west of the Mississippi River at ponds, wet depressions, and floodplains (Johnson 1993). Western Marsilea is typified by regions with extended dry periods and intermittent flooding, quite different from the humid climate of the southeast where new tropical plants have been mapped. Contrarily, the native Marsilea vestita and Marsilea macropoda have occasionally been introduced to become locally weedy at lawns and vacant lots in the southeastern United States.
18 March 2002, C.C. Jacono
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