KODIAK, Alaska - A rare plant that had been documented only three times before in the world is suddenly making appearances in two different parts of Kodiak.

It's called sessile-leaved scurvy grass and it does not look like much. It's a short plant between 1 and 2 inches tall with small white flowers and big green seedpods.

What is special about it at first glance is that it lives in an unusual place for a type of plant that usually grows on land. It seems to thrive below the tide line in lagoons, where it is completely submersed in brackish water twice a day.

The plant's name comes from its relation to the common scurvy grass, a vitamin C-rich plant once eaten by sailors to treat and prevent scurvy. It is a member of the cabbage family.

Previously the plant had only been observed two times on the Kodiak Archipelago and once on the Kenai Peninsula. The last time it was identified by scientists was in the 1930s.

But this year Kodiak botanist Stacy Studebaker came across it three times in one summer. First on Sitkalidak Island and then close to Kodiak near the mouth of the Buskin River.

"Nobody knows much about it," she said. "That's what is so exciting about it. How does it disperse its seeds? How does it get pollinated when it is under water half the time? Nobody knows."

Studebaker discovered the sessile-leafed scurvy grass populations on Sitkalidak Island as part of her annual plant survey of a part of the Kodiak National Wildlife Refuge. She first found it in McCord Bay and then found it in similar habitat in Sitkalidak Lagoon.

The discovery on the Buskin River came by accident when she described the plant to refuge biologist Bill Pyle, who said the plant sounded like something he had seen before at the Buskin.

An investigation of the Buskin revealed a large population not far from the mouth of the river.

The search also found two other rare plants, the mist maiden and the popcorn flower, neither as rare as the scurvy grass. Both have white flowers, although the popcorn flower has long skinny leaves while the mist maiden has large, scalloped leaves.

Studebaker said the presence of rare plants made her want to get more involved in a local conservation issue she was already watching closely, the planned expansion of the Kodiak State Airport runway.

The project is part of a required safety expansion to add buffer zones around airport runways. For the north-south runway the Federal Aviation Administration (FAA) is considering an alternative that would extend the land around the end of the runway by 1,200 feet toward the mouth of the Buskin.

Studebaker favors an alternative that would expand the runway toward the Coast Guard Base to the south. An expansion of the runway to the north would be devastating to the newly discovered plants, she said.

"They (the FAA) have this whole team of biologists and scientist who supposedly looked at this area," she said. "They didn't find anything. That makes me wonder what else they might have missed."

Studebaker wrote the FAA to tell the agency about the plant after her new discovery.

She has long been skeptical that an expansion toward the Buskin could be done without harming the river's salmon run.

The FAA has been working on its environmental impact statement for the project since 2007. It recently announced it is going to push back its public release of a draft environmental impact study from fall 2010 to some time in the first half of 2011.

The sessile-leaved scurvy grass is not considered an endangered species because so little is known about it. But it is in the category of rarest plants on the Alaska Natural Heritage Program rare vascular plant tracking list.