The forked ferns, family Gleicheniaceae, are some of the more striking looking. Their forked habit of branching sets them aside as something truly unique. On Kyushu, southern Japan, two species are common, Dicranopteris linearis and Gleichenia japonica, where they inhabit lower elevations on slopes either in woodlands or on exposed sites. Let’s have a closer look at these odd ferns.
Gleichenia japonica is an evergreen vining fern with long trailing rhizomes. Crosiers can originate from the rhizome or from the fork of the branched fronds (pseudodichotomous branching). The new fronds are brilliant lime green and mature to a light green or to dark green depending on exposure to the sun. Each branch is 20-70 cm long and forms a distinct forked frond. Total frond length can be 1 m. The stipe is relatively short, 15-30 cm long, and the thicken base is covered in dark brown scales
As new crosiers are formed, the resulting vine-like chain of fronds can extend for several meters and form dense colonies. The frond is twice pinnate, but the pinnules are unlobed. The undersides of the fronds are a white-blue color (hence the Japanese name, urajiro, meaning “below white”). Spore production is rare. The circular and naked sori grow in pairs on either side of the costa.
Forming large, dense colonies on hillsides, this species can often be seen growing alongside its near relative Dicranopteris linearis, but often is found on moister sites in heavier shade. It also is a much larger fern. Colonies can adorn whole hillsides, creating a startling visual impact, albeit a bit rambling and “messy” looking.
In Japan this species is famous for being part of New Year’s decorations. The long connected stipes are also used in weaving traditional baskets. It is a common fern of well drained, yet moist hillsides in both sun and shade, often seen in tree plantations, along roadsides, and bright woods. Generally found at lower elevations but found also in mid elevation forests, 0-700 meters.
Dicranopteris linearis is a smaller relative, in fact its Japanese name is koshida, which translates as “small fern”, possibly referring to it being smaller than G. japonica, yet similar in habit. Like its larger relative, crosiers can originate from the rhizome or from the fork of the branched fronds. The new fronds are brilliant lime green and mature to a nice deep green. Each branch of the forked frond is 5-20 cm long and a group of six or more forms what looks like a palmate frond or even a whorl. These whorls can be 35 cm across.
As new crosiers are formed, the resulting vine-like chain of fronds can extend for 3 or more meters. The stipe can be very short or quite long and is completely smooth, anywhere from 5-40 cm long. The undersides of the fronds are a white-blue color with a few red-brown hairs.
This species forms small to large colonies on low hillsides, sometimes creating dense colonies that can cover large areas. An interesting feature is the paucity of spores produced, at least in my observations. I’ve checked entire hillsides and found few if any sori, making me wonder how this species reproduces. Although it is a colony forming plant, it doesn’t appear terribly invasive. Raw cuts on hillsides, either by landslide or by human disturbance, are quickly colonized by this and other ferns.
Occasionally I’ll see large areas where it has died back, making me further wonder if these areas were in fact just one plant.
This plant could be easily mistaken for Gleichenia if not for the fact that it is both smaller and more importantly is only once pinnate while former is twice pinnate (see the photo for comparison). Hillsides colonies are actually quite attractive since they form a nice lush ground cover.
When I first saw these, they reminded me of pictures of Hawaii. I later found out that this species is actually quite common there! This is a fern of well drained slopes especially in openings in forests where it often receives quite a bit of sunshine. It also is common on road cuts, in plantation forests, and in bright shade of loose tree canopies. It is found mostly at low elevations, 0-300 meters.
Given their rambling habit one would think these ferns would be a poor choice for the garden, yet in my experience they are modest growers. In fact, both appear to be quite sensitive to being moved. For example, some years ago I pulled a loose clump of rhizomes of D. linearis from a roadside hill that was erroding away. It was planted into a mix of kanuma and peatmoss and there it sat doing almost nothing for the next couple years. It was planted out and after two years it finally started filling out, even venturing off into new areas. I’m experimenting with seedlings now to see if they do any better.
While these quickly colonize raw dirt of recent road cuts or landslides, they are much less aggressive in the garden and from what I can see are easily restrained. Of course, G. japonica, being much larger will require more elbow room. In the garden, expect D. linearis to grow no more than 50 cm tall and G. japonica up to a meter high.
Unfortunately, these subtropical evergreen ferns shouldn’t prove too cold hardy however, probably only surviving to the very warmest parts of USDA cold hardiness zone 7 where the soil never freezes significantly. Locally, plants see temperatures routinely in the freezing range, but anything below – 5 C (24 F) will probably cause damage. Still, they would make a dynamite tropical looking ground cover, especially on a hillside, as an underplanting of palms or tree ferns.
Odd and beautiful, and worth a try if you’ve got the space and live in a relatively warm climate.