ï~~2001
THE MICHIGAN BOTANIST
73
MULBERRY WEED (FATOUA VILLOSA) SPREAD
AS FAR NORTH AS MICHIGAN
A.A. Reznicek
University of Michigan Herbarium
3600 Varsity Drive, Suite 112
Ann Arbor, Michigan 48108-2287
reznicek@umich.edu
Mulberry weed, Fatoua villosa (Thunb.) Nakai, also known as hairy crabweed, is a warm temperate annual widespread in Asia and introduced and
rapidly spreading in North America. It first appeared in North America in
Louisiana, where Thieret (1964) noted "Dr. Joseph Ewan of Tulane University
informs me that the plant has been found as a weed in New Orleans for at least
15 years." This implies that it entered North America at least as early as the late
1940s. Thieret comments that "seedlings were frequent on the campus [of the
University of Southwestern Louisiana] this past spring, even following the severe winter of 1962-63, when the temperature in LaFayette dropped to 15 degrees F." This suggested, somewhat ominously, that the plant could become
weedy over a much larger area than the extreme south. Indeed, it was reported
from Florida in 1974 (DuQuesnay 1974) and, by 1975, it had been also found in
Alabama, Georgia, Mississippi, and North Carolina (Massey 1975). In 1977, perhaps belatedly, it was listed as an economically important foreign weed that potentially could be a problem in the United States (Reed 1977). The distribution
of Fatoua as mapped and reported in Flora North America now encompasses all
of the southeast, including Texas, and north to Oklahoma, Arkansas, Indiana,
Kentucky, Maryland, and West Virginia (Wunderlin 1997). It has also been reported from California (Sanders 1996), Washington (Washington State Noxious
Weed Control Board 2001), and is now known from southern Missouri
(Yatskievych & Raveill 2001). Fatoua has recently also been reported from even
closer to Michigan, as Vincent (1993) noted its occurrence in south central Ohio.
Still, it was a surprise to see Fatoua in southern Michigan. Stopping at a rest
area along 1-94 west of Jackson (Jackson County), I noticed Fatoua locally
abundant in some ornamental plantings surrounding the buildings. In some small
areas, the plants were so dense as to be a solid ground cover, and hundreds of
plants were present.
Fatoua is becoming a problem weed in containerized nursery stock (Neal,
1998), and it likely is spread widely and rapidly by planting of containerized
stock. The Michigan station was not likely a new introduction that year, as it was
most frequent in an area of perennial ground cover that had obviously been
planted at least several years before and the plant presumably had been building
up its population for several years at least to reach such numbers.
Morphologically, Fatuoa villosa somewhat resembles a seedling white mulberry (Morus alba L). The alternate leaves are roughly similar in arrangement
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