Donna Wear and Judy Gordon crouch among the thick, leafy plant clusters that erupt from the rocky bottom of Stevens Creek, counting and cataloging fat green seeds that are the size of olives.

It’s late in the blooming season, but a few plants still exhibit their rare flowers — ghostly and delicate, like inverted parasols of fine white paper, surrounded by a starburst of six finger-like petals.

“I’m reminded of antiquity when I look at these things,” says Wear, a biology professor at nearby Augusta State University in Georgia. “They look ancient, they look old. They’re very fragile as well.”

The shoals spider lily, also commonly known as the Cahaba lily, blooms only from mid-May into early July. Its flowers open and then wither in less than two days.

In the U.S., it’s only found in a swath of streams in Alabama, Georgia and South Carolina. Known populations form a chain of 31 counties across the three states, with a wide gap across central Georgia.

Scientists believe the shoals spider lily once thrived in this Georgia gap. Wear and Gordon fear its habit may be shrinking further along the Savannah River, which forms the Georgia-South Carolina border.

“On the river last year, when we began this project, we could not find a single germinating seed,” Wear says. “One of the biggest reasons for their rarity has to do with the damming of rivers and destroying that shoal habitat.”

Wear has been studying the species for the past year, comparing plants growing in Stevens Creek to those found nearby in the Savannah River.

She wants to know how many seeds they produce, how high the plants can grow to keep their pollen from being washed away, and how changes in flow along streams and rivers affect their ability to reproduce.

The shoals spider lily was first documented in America in 1773 by naturalist and explorer William Bartram.

More than 230 years later, the lilies have attracted a fan base. About 300 people attended the annual Cahaba Lily Festival held in late May in West Blocton, Ala., at the peak of blooming season. South Carolina has its own lily festival at Landsford Canal State Park on the Catawba River.

Much about the plants remains unknown, said Larry Davenport, a biologist at Samford University in Birmingham, Ala., who has studied the lilies since 1989.

“The plant over here is cloaked in mystery,” Davenport said. “It’s probably our most well-known and most beautiful wildflower. It’s mysterious in that it lives in some very inaccessible places.”

The lily grows only in streambeds along southern portions of the Fall Line, the geologic junction where the rocky Piedmont Plateau meets the Atlantic coastal plains from Alabama to New Jersey.

The subtropical plant needs the warm, Southern climate to thrive. It also requires rocky stream beds where its large seeds lodge in crevices, stabilizing the new plants as they take root in rushing water.

What makes these lilies, whose scientific name is Hymenocallis coronaria, so unique is their seeds sink rather than float. Fertilized seeds grow at the end of 3-foot stalks until the stalks bend under their weight, dipping the seeds into the water.

Scientists say the lilies long ago adapted their reproductive cycles to the natural flooding and dry spells of rivers and streams. Those highs and lows have been interrupted by dams built over the last century.

Wear’s work in the Savannah River basin is sponsored by the Nature Conservancy. The nonprofit group hopes the results will help it advise policy makers on ways to manage water releases from the river’s three major dams that help protect the rare lilies.

“Part of the problem is, because of the hydropower dams, the river flows higher than it would normally during blooming season,” drowning the lilies and washing away their pollen, said Amanda Wrona of the Nature Conservancy in Savannah. “But if you keep the flow too low, deer get in and start grazing on the flowers.”

The Nature Conservancy has been working with the U.S. Army Corps of Engineers, which controls the dams, since 2004 on ways to manage water flow on the Savannah River with minimal impact on its native species.

Davenport conducted a census of the shoals spider lily in 1989 and again in 1996 for the U.S. Fish and Wildlife Service to determine if the plant was a candidate for endangered species protection.

Though rare, the lilies didn’t qualify. Thousands of the plants spread for more than a quarter-mile along the Cahaba River in central Alabama and the Catawba River in northern South Carolina. More than 60 smaller populations have also been documented.

However, Davenport says he noticed several smaller lily populations declined in the 17 years between his two studies, and a few disappeared altogether.

In Georgia, the lilies are found in only eight counties — four in the Columbus area along the Alabama border and the other four in the Augusta area on the South Carolina border. Georgia law protects the plants as endangered species, meaning they can’t be removed from public land or sold.

South Carolina lists the shoals spider lily as a species “of concern” but with no legal protection. Alabama has no state endangered species list, but at least two cities with large lily populations — West Blocton and Helena, both south of Birmingham — protect them by local ordinance.

“We had a problem for a while with people poaching the bulbs, digging them up and carrying them off to be sold as house plants,” Davenport said. “They make lousy house plants.

Most people don’t have a flowing stream available to them.”

That’s why Wear and Gordon have kept the exact location of the lilies they’re studying along Stevens Creek a secret — the property owners have found trespassers trying to dig up the flowers with crowbars.

Wear plans to dig up a few of the lilies herself — but for scientific purposes. She plans to create an artificial stream at her laboratory to help measure ideal flow rates for the species.

“It’s a little bit of our history and should be considered part of the heritage of this area,” Wear said. “And because we still have it, we should hang onto it.”

On The Net:

Augusta State University: http://www.aug.edu

The Nature Conservancy: http://www.nature.org