THE MICHIGAN BOTANIST
Hydrocharis morsus-ranae L. (Hydrocharitaceae). Common Frog-bit.
Previous knowledge. A native of Eurasia, H. morsus-ranae was introduced
into North America in Ontario, Canada, as early as 1932 for horticultural purposes (Catling and Dore 1982). First United States locality was discovered in
New York in 1974 (Roberts et al. 1981). Its current range is throughout much of
central and southwestern parts of southern Ontario into northern New York, Vermont, and eastern Michigan as well as Washington state (Catling et al. 2003). In
the Great Lakes, this species occurs along Lake Erie and Lake Ontario as well as
St. Lawrence and Ottawa Rivers.
Diagnostic characters. Hydrocharis morsus-ranae is a herbaceous, stoloniferous perennial aquatic with white flowers and cordate-orbicular leaves. It is
similar to the native Limnobium spongia but has 2 stipules compared to 1, which
are lateral and free from the petiole as well as the petals being more than 1.5
times as long as the sepals compared to less than 1.5 times. Blooming period is
from June to September. Hydrocharis morsus-ranae is dioecious and some
colonies can be only one sex (Catling and Dore 1982). It reproduces both sexually and asexually. Stolons and overwintering turions are its primary means of
Significance of the report. This is the first documented report of this invasive
species in Ohio (Cooperrider et al. 2001; Haynes 2000). The Ohio locality is also
the first for the southern coastline of Lake Erie. It was collected in the summer
of 2004, on wet muck at the edge of a large, diked marsh in Cedar Point National
Wildlife Refuge, a 2245-acre refuge in Lucas County (410 41' 42" N 83019' 57"
W). The marsh is a mosaic of mixed emergent and submergent marsh communities with a number of state rare plants (Gardner 2004). The marsh contains a
number of invasive species including Butomus umbellatus, Lythrum salicaria,
Myriophyllum spicatum, Phragmites australis ssp. australis, Potamogeton crispus, and Typha angustifolia. Hydrocharis morsus-ranae was local and uncommon with a few colonies along the marsh shore and additional small colonies
floating in the marsh. The population was likely introduced by migrating waterfowl.
Hydrocharis morsus-ranae is considered a highly invasive non-native
species. This is a very significant find as it adds another invasive, non-native
species, to a long list of invasive species for Ohio's southern coastline of Lake
Erie. The discovery is not surprising based on its rate of spread from its initial
introduction to North America (Catling and Porebski 1995). In Ontario, it has
been rapidly spreading in the lower Great Lakes of Ontario and at some sites it
is now the dominant vegetation cover (Jones 2005). Hydrocharis morsus-ranae