By Susan Milius
From Mobile, Ala., at the Botany 2003 meeting
The signature plant of the Everglades switches gender twice during a week of flowering, according to a Florida study. This synchronized sex change may prevent self-fertilization except in a reproductive emergency.
Great sweeps of sawgrass (Cladium jamaicense) inspired the region’s nickname, “river of grass,” although botanists classify the plant not as a grass but as a sedge, explains Jenise M. Snyder of Florida International University in Miami. Sawgrass does have saws, though. “If you put your hands on the edges of the leaves, you’ll get the worst paper cut you could have,” she says.
“It’s the dominant plant in the Everglades, but there’s very little known about its biology,” Snyder adds. As the $8-billion, 30-year restoration of the Everglades moves forward, she and her colleague Jennifer Richards are starting to work out the biological basics for the crucial species.
Sawgrass expanses look as if they might have arisen from one plant spreading vegetatively, but Richards’ earlier work indicated that the plants often reproduce sexually. Of the dozens of meter-square plots she tested, only 20 percent comprised a single clone of sawgrass. The great sawgrass vista comes from intermingled, small clones.
Richards’ finding prompted interest in sawgrass sexuality. A plant’s flowering stalk may stretch 3 meters high and scatter 5,000 seeds, Snyder says. Tiny individual flowers bristle on this stalk, and their sex organs mature in close synchrony. At first, one set of male parts in each pair of flowers releases its pollen; then, a female organ matures and captures pollen from other plants. Finally, a second set of male parts releases pollen.
To test whether the wind-pollinated plants could fertilize themselves, Snyder kept sawgrass flowers in bags and dusted ripe female parts with pollen from the same clone. To make sure that the brief exposure to air during hand pollination didn’t let windborne pollen confuse the results, the researchers opened other bags for the same amount of time. Quick bag openings proved trivial, and the hand-pollinated flowers set as many seeds as did flowers left to natural pollination.
Botanists haven’t analyzed many wind-pollinated plants, Snyder says, but she speculates that the synchronous gender switching reduces a plant’s chances of pollinating itself. A complete barrier of self-incompatibility, however, might invite occasional disaster if a plant does get surrounded by clones of itself.
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