Hymenophyllum wrightii gametophytes growing in a tangled clump on rotting wood. (Photo by Aaron Duffy)
A species of fern common in Asia has been found in Southeast Alaska — and it’s far more abundant than first thought.
But unlike invasive species, Wright’s filmy fern is an early colonizer. And figuring out how and when it got here is the next piece of the puzzle.
Mary Stensvold is a botanist with the Alaska Region of the US Forest Service. She does cool stuff like identify plants — even ferns — that are totally new to science.
But figuring out that Wright’s filmy fern has been around Southeast Alaska possibly since the Ice Age and beyond is its own brand of excitement.
“Oh, I am excited. And it’s kind of fun, too. We spent money and time to do these surveys and the genetic work, and now we’ve tied it up in a nice little bundle.”
That bundle is a paper written by Stensvold and her collaborators Aaron Duffy and Donald Farrar in the American Fern Journal. For over five decades, botanists have believed that Wright’s filmy fern was present in North America. Some was identified in 1958 on Haida Gwaii, which used to be known as the Queen Charlotte Islands. And it was also found on Biorka Island near Sitka in 1965, and later on northern Vancouver Island in Canada.
That’s a really small distribution for a plant in this really large ecosystem. So maybe those first botanists just got it wrong. Wright’s filmy fern lives in the wettest, darkest places in Southeast — in rotted logs, under root wads — and it takes a magnifying glass to spot its thin strands, about the size of dental floss.
Stensvold, at first, couldn’t corroborate that early work. She couldn’t find the ferns.
“And I was looking really carefully, but I wasn’t using the right equipment. And the right equipment is a flashlight, magnifying glass, and you’ve got to have a rubber suit. And literally lay on the ground and have your magnifying glass up against the moss. It looks like a moss, almost.”
Stensvold says her collaborator Donald Farrar, at Iowa State University, honed their fern-hunting technique. Stensvold’s team then trooped out to collect new samples, and used the latest technology to confirm the fern’s identity.
“In comparing genetic material from British Columbia, Alaska, and Biorka Island, with genetic material from Asia — these are definitely Wright’s filmy fern.”
Hunting for tiny fern gametophytes under a rotted tree in the rainforest near Sitka, Alaska. Critical equipment includes a magnifying glass and a flashlight.
So you might be thinking, They found some Asian ferns, big deal! But now that that botanists know how to find Wright’s filmy fern, they’re finding it everywhere: In Wrangell and Petersburg; in Sitka on the benchlands road. Just about everywhere in Southeast except the upper Lynn Canal.
And something even more compelling: Botanists are finding only one form of the fern. But before I explain more, let’s get a brief lesson in fern sex.
Let’s say you have a ladyfern in a pot at home. You’ll see little green hearts on the surface of the soil. These are gametophytes. And this is where ferns do something unexpected in the plant world.
“They have sex organs on the bottom of the gametophyte — the little heart-shaped thing — and if you splash water on them the little sperm are released and go to the little female reproductive structures that fertilize the egg.”
That egg grows into a little fiddlehead fern that we all recognize, which then produces spores that are carried on the wind and — if they land in the right soil and water conditions — grow into new gametophytes.
So again, ferns exist in two forms: gametophytes, where all the fern sex is happening, and sporophytes, which look like ferns, produce spores, and spread themselves around.
Now what’s the point of all this? Despite the fact that botanists have found Wright’s filmy fern practically everywhere in Southeast, no one has found the sporophyte generation. No actual leafy ferns. No spores. How does it reproduce all over Southeast?
KCAW – It doesn’t seem like it would really be very prevalent in our island archipelago. How does it get from place to place? How does it spread?
Stensvold – It spreads by producing these little nodules called gemmae. And they’re little bits of filmy fern. And they can get carried around by animals. Or you know how things move between islands — a rotten log can fall in the water and float to the next island. But we also think that they have been here for a very long time, and had the opportunity to spread.
A very long time. Up until 10,000 years ago, most of the Southeast Alaska coastline was covered by ice — the Wisconsin glaciation. Stensvold says that is nothing in botanical time. Maybe Wright’s filmy fern migrated with other organisms — including humans — over the Bering Land Bridge. Maybe its sporophyte went extinct in Southeast Alaska during a dry spell, leaving gametophytes to figure out reproduction on their own.
We don’t know a lot about habitat or climate in Beringia — all we know now, thanks to this research — is that Wright’s filmy fern is thriving here, against expectations. Stensvold says the same genetic studies that have allowed her and her co-authors to understand the full extent of this strange little plant’s range may also one day allow us to understand its history, and our own.
