Tropical Umbrella Sedge
Yesterday John and George wandered the Danforth Conservation Area in Palm City, a low pine woods with ponds, seasonal pools, and squishy places with mud to your ankles. Beauty was everywhere, including a natural “botanical garden” of the Aster Family with white, violet, and yellow blooms.
In the squishy zone we encountered a worldwide super-weed seldom seen in Florida, Fuirena umbellata. We’ll call the species Tropical Umbrella Sedge for lack of a better English name.
Of course invasive exotics are abundant in Florida. Collectively grass and sedge invaders are remarkably plentiful, and include such conspicuous cases as Guinea Grass, Napier Grass, Natal Grass, and Para Grass. Many additional less conspicuous species have snuck in. The problem has a name, even if it is misleading, “The Africanization of American Grasses.” Not all the invaders are African, but a large number of our invasive grass and sedge species are of Old World origins. It would be depressing to know what percent of Florida grass and sedge biomass is not indigenous. Given that grasses are the fuel for grass fires, and occupy the bottom rung of the ecological pyramid, the quiet species shift is a little worrisome.
Umpteen forces from hurricanes to imported nursery material move grassy weeds to and around Florida. This complex of forces plus deficiency of historical data make it uncertain that Global Warming is crucial in the grass and sedge invasion. But to our limited experience here at the latitude where tropics meets frost it seems like the invasive drift might have a northbound tilt. (The biological literature offers many examples of species shifting northward presumably due to Global Warming.)
Even if Global Warming is not directly responsible for northward weed migration, it no doubt warms the reception for tropical invasives, such as Cyperus hyalinus, Cyperus pumila, Kyllinga squamulata, to list three sedges now in Florida from points South. Our favorite example is the grass Steinchisma laxa, a tropical weed unknown in Florida until 2007, then suddenly abundant. Perhaps Wilma helped.
That brings us back to Fuirena umbellata. In cases of worldwide tropical weeds, it is tough to pinpoint an exact original distribution, perhaps the Tropical Pacific and Tropical Asia? In any event, the weed, often associated with rice, is abundant in warm-climate Asia, Pacific Islands, Africa, and tropical America. Yet we are aware of only one other collection in Florida, in Broward County, although we have not conducted an exhaustive scientific search. The abundance south of Florida coupled with scarcity in Florida and a surprise appearance in arctic Martin County is consistent with interpretation as another seemingly northbound weed.
Fuirena umbellata can be so plentiful in other countries as to serve as green manure in rice cultivation. The species is salt-tolerant, and in places is burned to recover salty ashes; it serves as a (saline?) cleansing bath for babies in Africa. Reminiscent of Scouring Rushes, the plants contain silica, limiting their utility as livestock fodder.
Fuirena has about four other species in Florida. Southern Umbrellasedge (F. scirpoidea) is a common presence along muddy shores, as are a couple smaller species. Although the flower clusters in today’s species look “just like” a Fuirena, the overall appearance of the plant is out of line with the more familiar species; it stands up to about six feet tall, making it a giant among Fuirenas, with a distinctive 5-angled stem. Fuirenas are among the few sedges that have “petals” in the flowers, and those of F. umbellata, as seen with a hand lens, are big, broad to the base, and persistent around the seedlike fruit.
The first species known to us to be documented as migrating (to higher latitudes) due to Global Warming was Edith’s Checkerspot Butterfly in California. This was reported in 1996, just 16 years ago. The list has grown since then, and we’re hoping that we are wrong about Fuirena umbellata being an “Edith’s Checkerspot” of the Florida grass and sedge world.