keys to the vascular plants of east texas - Botanical Research ...

SALVINIA/SALVINIACEAE 381
NM, and NY. Sporulating spring and fall (Nauman 1993d). [S. rotundifolia of authors, not Willd.]
In TX it is considered a “harmful or potentially harmful exotic plant” and it is illegal to release,
import, sell, purchase, propagate, or possess this species in the state (Harvey 1998). In certain
parts of East Texas, populations of this species are so large that recreational access (e.g., boating
and hunting) is being impeded (H. Elder, pers. comm.). This species had been considered to be
native to the se U.S. (Nauman 1993d) but is now considered to be introduced from tropical
America. (Jacono et al. 2001; BONAP 2000); it was probably introduced into FL in the late 1920s
or early 1930s (Jacono et al. 2001). It was introduced into TX in 1992, apparently from w LA “on
a ‘marsh buggy,’ during geologic exploration” (Jacono et al. 2001; see also Hatch 1995). � I
m/297
Salvinia molesta D.S. Mitch., (annoying or burdensome, in reference to the rapid vegetative
growth), GIANT SALVINIA, KARIBA WEED, AQUARIUM WATER-MOSS, AFRICAN PYLE. Floating leaves
ca. 13–30(–38) mm long, usually cordate basally, usually notched apically, often folded and
compressed into dense chains (flat when young). Lakes and other aquatic habitats, reproducing
vegetatively very effectively; Robertson (BAYLU, BRIT, TAMU, TEX), Fort Bend, Harris, Houston,
Liberty, Montgomery, Newton, Orange, Sabine, Shelby, and San Jacinto (H. Elder, pers.
comm.; R. Helton, pers. comm.) cos.; it has also been reported from the Gulf Prairies and
Marshes (Brazoria and Chambers cos.—H. Elder, pers. comm.) and as far nw as Flower Mound
(Denton Co.) in North Central TX (Jacono 2001) and Wichita Co. (H. Elder, pers. comm.) in the
Rolling Plains. It was first observed in TX in 1997 (Jacono 1999c), and as of summer 2000, it was
known in TX from 4 reservoirs and ca. 40 private water bodies (R. Helton, pers. comm.). Since
that time it has been discovered in a number of additional localities (e.g., total of 11 public water
sites—reservoirs and rivers—as of February 2004) and is continuing to spread in the state (H.
Elder, pers. comm.). Now known to be present in the se U.S. from AL, FL, LA, SC, and TX. Considered
“one of the world’s worst weeds” (Jacono 1999c), it is thought to be native to South
America (se Brazil—Forno & Harley 1979; Forno 1983; U.S. Geological Survey 2000) and is possibly
of hybrid origin. The sporangia abort and the somatic chromosome number of 45 suggests
a pentaploid condition (Jacobsen 1983). Jacono (2001b) noted that “Salvinia molesta is not
known to reproduce by spores. It reproduces vegetatively, that is, new plants develop as fragments
break off from mature individuals.” It has been introduced by humans to fresh waters of
Africa, Asia, Australia, s Europe, New Zealand, and the South Pacific and has resulted in severe
economic and environmental problems (Jacono 1999a, 1999b; Garbari et al. 2000). The plants
can grow rapidly and under good conditions doubling can occur in ca. one week, with a range
of four to ten days (Mitchell & Tur 1975); some authorites indicate that populations can double
in a little more than two days (Moran 2004). GIANT SALVINIA covers the surface of lakes and
streams, and the floating mats shade and crowd out native plants. Additionally, the mats
(sometimes to a meter thick!) reduce oxygen content, degrade water quality, and can cause
physical problems including hindering boats, clogging irrigation and drainage canals, and
blocking water intakes. The mats can become so dense that they are able to support the weight
of a cinder block. Plants used in aquaria or water gardens are among the likely sources for the
escaped populations (Thomas & Room 1986; Jacono 1999a, 1999b, 1999c; Wood et al. 2001;
Moran 2004). According to R. Helton (pers. comm.), “all reservoirs in East TX are imminently
threatened” by this species. In TX, it is considered a “harmful or potentially harmful exotic
plant” and it is illegal to release, import, sell, purchase, propagate, or possess this species in the
state (Harvey 1998). GIANT SALVINIA is listed as a federal noxious weed (USDA Natural Resources
Conservation Service 2002), and as such is prohibited in the U.S. by federal law. Jacono
(1999a) indicated that, if seen, the species should be eradicated immediately and that the Texas
Parks and Wildlife, Inland Fisheries Division should be contacted at (409) 384-9965. Biological
control by the salvinia weevil (Cyrtobagous spp.) is being tested in East TX; this weevil, native to
South America, has been successfully used in control programs in various places in the Old