Trifolium fragiferum (strawberry clover) is a recent
addition to the Wisconsin flora and all information provided here
is from very brief preliminary observations. It has been documented
at 14 locations in Brown County, and one location each in Kewaunee
County (Dykesville), Outagamie County (Shiocton), Oconto County
(Little Suamico), Shawano County and one in Winnebago County (Oshkosh).
The first population was discovered in 2002, for which the size
of the population suggested that it had been present for several
years before discovery. Based on that information and the rapid
spread of the species since 2002, it appears that Trifolium
fragiferum probably arrived in Brown County in the late 1990's
and is spreading outward from the City of Green Bay.
Trifolium fragiferum is similar to T. repens when
sterile or early in flower, but is easily distinguished when the
conspicuously inflated calyx
is present as fruit develops. Fortunately, the fruit develops
quickly once flowering starts. Flowers tend to be more conspicuously
reddish than in many T. repens populations, but there is
some overlap in that regard. The flowering stalks lack cauline
leaves as in Trifolium repens (i.e. the flower
heads are attached to the end of a leafless stalk that arises
from the creeping stolon). The two species can grow
next to one another or even intermingled and I have seen T.
repens, T. fragiferum and T. hybridum growing within one square
meter. Keeping in mind that there is considerable variability
and that there are intermediate stages of development, here is
a comparison of the flowering
and fruiting heads of T. fragiferum and T. repens.
The habitats for the 19 known sites (many smaller sites near
vouchered populations in the City of Green Bay have not been counted)
are all on grassy sites that get mowed more or less regularly.
In general, it seems to occur in the same kinds of sites as T.
repens. The first populations discovered were all along roadsides,
but it appears to be capable of spreading through adjacent lawns
quickly. As is the case with T. repens, mowing is tolerated
well because the stolon runs directly along the surface of the
ground, below the mower height. They also flower later than T.
repens, beginning about the first of July, during a period
when the cool season lawn grasses are growing more slowly and
lawn mowing is not so frequent as it is in June. Soils are variable
from relatively heavy soils with considerable clay content, to
very sandy soils. It appears to do best in moist or even wet soils,
but also appears to tolerate fairly dry conditions in some cases.
It does not appear to present a threat of becoming an invasive
in natural communities, as it has not shown any tendency to grow
outside of mowed areas. However it appears that it may become
very widespread in lawns. The rate of spread is extremely fast
and it appears that it is spread locally by lawn mowers, probably
by seeds rather than vegetative propagules.