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The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

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Common name: Australian water-clover

Synonyms and Other Names: Marsilea brownii A.Braun

Taxonomy: available through www.itis.gov

Identification: As described in Jacono and Johnson (2006) and Nagalingum et al. (2007):

Habit: perennial fern; aquatic and occasionally terrestrial

Rhizomes: rooting at nodes and sometimes internodes; adventitious and creeping; glabrous [hairless], sometimes with scattered pubescence

Leaves: quadrifoliate compound leaves, with two pairs of leaflets; obdeltoid [flipped triangle] shaped; margins entire [smooth]; glabrous, with pubescence occasionally at the base; variegated leaflets appear two-toned with the lighter color at the base; petioles [leaf stems] are slightly inflated at the apex in aquatic forms (Senn 1909)

Sporocarps: arising near the base of the petioles on single or branched peduncles [sporocarp stems]; peduncles glabrous; sporocarps glabrous to slightly pubescent; lacking distal and proximal teeth and a raphe [peduncle joined along the sporocarp]

Size: 9-18 cm tall petioles (to 100 cm in aquatic form) and 2-3 cm wide leaves (to 8 cm in aquatic form) (Jacono and Johnson 2006)

Native Range: Australia and New Caledonia (Jacono and Johnson 2006)

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Ecology:

Habitat: lakes and ponds; sandy to heavy clay soils; littoral shoreline to 1 m deep (Yen and Myerscough 1989a, Knepper et al. 2002, Jacono and Johnson 2006)

Life History: In the United States populations, Marsilea mutica spreads vegetatively via rhizomes more than sexually via sporocarps (Jacono and Johnson 2006).

Environmental Tolerances: Marsilea mutica prefers warm climates of eastern Australia and southeastern United States (Jacono and Johnson 2006), but may be able to endure colder winters in higher latitudes of the northern hemisphere due to the depth of rhizomes in sediment (Redman 2008). Sediment samples from a Marsilea mutica stand in Bushells Lagoon, near Sydney, Australia had a pH of 4.7 and sand/silt/clay percentages of 5/40/55% (Yen and Myerscough 1989a). Also in Bushells Lagoon, M. mutica had the highest growth rates and dry weights between 10 and 40°C after eight weeks (Yen and Myerscough 1989b).

Means of Introduction: Aquarium releases are likely the initial introduction vector (Jacono and Johnson 2006). Dispersal via waterfowl and recreation vehicles are possible secondary vectors (Peck 2011), but not as likely as the initial vector.

Status: Established in Alabama, Georgia, North Carolina, Texas, and Washington.

Impact of Introduction: The impacts of this species are currently unknown, as no studies have been done to determine how it has affected ecosystems in the invaded range. The absence of data does not equate to lack of effects. It does, however, mean that research is required to evaluate effects before conclusions can be made.

Remarks: The floating leaf habit and structure of Marsilea species, with a circular outline and peltate [central] leaf attachment, allows for optimum stability during heavy wind and wave action (Sculthorpe 1967, Yen and Myerscough 1989b).

References: (click for full references)

Jacono, C.C., and Johnson, D.M. 2006. Water-clover ferns, Marsilea, in the Southeastern United States. Castanea 71(1):1-14.

Knepper, D.A., D.M. Johnson, and L.J. Musselman. 2002. Marsilea mutica (Marsileaceae) in Virginia. American Fern Journal 92(3):243-244. http://www.bioone.org/bioone/?request=get-document&issn=0002-8444&volume=092&issue=03&page=0243.

Nagalingum, N.S., H. Schneider, and K.M. Pryer. 2007. Molecular Phylogenetic Relationships and Morphological Evolution in the Heterosporous Fern Genus Marsilea. Systematic Botany 32(1):16-25. https://doi.org/10.1600/036364407780360256.

Peck, J.H. 2011. New and noteworthy additions to the Arkansas fern flora. Phytoneuron 30:1-33. http://www.phytoneuron.net/PhytoN-Arkansasferns.pdf.

Redman, D.E. 2008. Marsilea mutica in Maryland. American Fern Journal 98(3):176-177.

Sculthorpe, C.D. 1967. The biology of aquatic vascular plants. Edward Arnold, London, UK.

Senn, G. 1909. Schwimmblase und intercostalstreifen einer neukaledonischen wasserform von Marsilea. Berichte der Deutschen Botanischen Gesellschaft 27:111-119.

Yen, S., and P.J. Myerscough. 1989a. Co-existence of three species of amphibious plants in relation to spatial and temporal variation: Field evidence. Austral Ecology 14(3):291-303. http://onlinelibrary.wiley.com/doi/10.1111/j.1442-9993.1989.tb01438.x/full.

Yen, S., and P.J. Myerscough. 1989b. Co-existence of three species of amphibious plants in relation to spatial and temporal variation: Investigation of plant responses. Austral Ecology 14(3):305-318. http://onlinelibrary.wiley.com/doi/10.1111/j.1442-9993.1989.tb01439.x/full.

Author: Pfingsten, I.

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.