Plant of the Month

December 2013

The Secrets of Grape Ferns, Botrychium

Irina Kadis

B. dissectum (20131111ricoh8319sa.jpg)
1. B. dissectum Nov 11, Blue Hills Res., Randolph, MA
B. dissectum (20131111ricoh8320csa.jpg)
2. A closer view of the same
B. dissectum (20090425canon0602csa.jpg)
3. B. dissectum Apr 25,
Great Meadows NWR, Wayland, MA
B. virginianum (20100521canon0533ca.jpg)
4. B. virginianum May 21 Blue Hills Res.,
Quincy, MA
B. virginianum (20100521canon0533sa.jpg)
5 B. virginianum May 21 Blue Hills Res.,
Quincy, MA
B. virginianum (20050729canon0339ca.jpg)
6. B. virginianum Jul 29 Blue Hills Res.,
Randolph, MA

The forest in eastern Massachusetts is not particularly impressive in terms of floor vegetation. This conspicuous emptiness of ground under the tree canopy has a ready explanation: at some point most of eastern Massachusetts was farmland, hence all forests here are young, only recently developed in place of former arable land and pastures. With the onset of cold weather, the forest floor becomes even more deserted, so that every green spot, every little plant overwintering green now is an eye stopper. Things we used to pass without noticing in summer have become prominent: partridgeberry (Mitchella repens), colorful mosses, clones of princess-pine (Lycopodium obscurum and L. hickeyi), and evergreen ferns: rock-cap (Polypodium virginianum), Christmas (Polystichum acrostychoides), and a few woodferns (Dryopteris spp.). Finally, right on the trailside, amidst dry beech and oak leaves, we notice a tiny bright green spot [1], a solitary tender frond (that's how we call a fern leaf), looking quite fresh and unabashed in the freezing temperature. It seems to be divided in three parts—not unlike a tiny bracken fern. This impression is due to the enlarged bottom segments of the frond [2].

This find alone can be a hiker's reward for the overall scarcity of the ground vegetation! What we are looking at is a grape fern. Grape ferns are an extremely ancient group, which split from the rest of the ferns early on. They differ from other ferns in a few important respects: their fronds don't even form fiddleheads when emerging in the spring; their roots don't have root hairs, so that plants depend on the mycorrhiza for their nutrition, the symbyotic fungus residing inside the root bark cells. We don't see grape ferns as often as other ferns, because they are cryptic plants.

Each grape fern frond (or leaf) spends a few years underground before it finally comes out during the spring or summer. The annual crop of a grape fern usually consists of just a single frond! Even though it looks tender and feeble, the plant it represents may actually be as old as the surrounding large trees. The frond may develop a deviating branched fertile blade, its sporangia (spore-bearing structures) resembling a miniature cluster of grapes [4]. In fact, the name 'grape fern' is only a translation of the Latin name. 'Botryo' can be translated as 'a bunch of grapes', thus 'Botrychium' meaning 'a little bunch of grapes.'

Upon developing and releasing spores, the 'bunch of grapes', that is, the fertile segment of the frond dies off [6], while the sterile blade may live on until the next spring in case the species is winter-green. In B. dissectum, it acquires reddish or bronze tint by the end of the winter [3]. In our area, three species (B. dissectum, B. multifidum, and the watch-listed B. oneidense) are overwintering green, while B. virginianum and a few more are green only during the summer [5]. The leathery, fleshy frond of B. dissectum must be somewhat easier to find than those of others, as this is our most common grape fern. Watch for grape ferns in moist shady forest with acid soil, on a forested stream bank, or at a swamp margin.

10 December 2013
© I. Kadis. Photography A. Zinovjev. CC BY-NC-ND 3.0 license