2018-08-11 / Columnists

Nature Notes

Variety of Prehistoric Ferns Carpet Mackinac Island’s Forests
By Patricia Martin

Recently a number of people have asked me about the ferns on Mackinac Island. Ferns, I think, have always held a fascination for people, as these plants date back millions of years and have been abundant in the fossil record from the Carboniferous period to the present day. Closely related groups have occurred as far back as the Devonian period. Most of the modern day species (about two-thirds of the approximately 12,000 species) live in tropical regions, with the other third inhabiting temperate regions of the world, including some found in the desert areas.

Ferns are by far the largest group of non-seed bearing vascular plants. To explain what I mean by that, these plants have xylem and phloem, which are vessels that conduct water, minerals, and food from one part of the plant to another. The water does not just move by osmosis from cell to cell as it does in the mosses and liverworts. Having vessels allows the plants to grow much larger, as they can conduct substances longer distances and they provide structural support. This development of vascular tissue was a pivotal step in the evolution of land plants. Ferns are seedless in that they do not produce seed. Instead, they have a more primitive reproductive cycle which includes two phases. The gametophyte phase produces male and female parts for fertilization and sporophyte then grows out of the fertilized gametophyte generation and eventually produces spores. You may be familiar with other vascular, non-seed producing plants, such as the scouring rush, horsetails, and club mosses.

Fern Way in the spring. Fern Way in the spring. On Mackinac (and I had to go back to my thesis to count) we have 13 species of fern that grow naturally here. These include one of the most common fern, the bracken or brake fern (Pteridium aquilinum) that grows along roadsides and in open fields. It tends to like more open areas and tolerates dryer areas. It is quite an adaptable plant with very light spores, which has allowed it to be disbursed in both hemispheres from temperate to subtropical zones. It likes to colonize disturbed places. This is a herbaceous plant that is deciduous in winter and may stand from three to 10 feet tall. It has large, triangular-shaped fronds produced singly and arising upward from an underground rhizome.

Northern Maidenhair Fern Northern Maidenhair Fern On Fern Way, which was the former North Bicycle Trail, where the old thousand-yard rifle range used to be, there are about six species of ferns. A fern that I am particularly fond of is the northern maidenhair fern (Adiantum pedatum), which is fairly common on rich, damp soils. It is a fern native to eastern North America and is found on rich, wooded slopes, ravine bottoms, and shady, damp woods. Its stem, which arises from the ground, is a distinctive red-brown to black color. When it reaches its maximum height of 1.5 to 2.5 feet, the fronds appear and are palmately divided into finger-like projections. The specific epithet, pedatum, which means “bird foot,” refers to the way the stalk of the frond arises and divides into the leafy parts. It looks like a bird’s foot turned upside down. The fronds are divided again to give it a frilly appearance.

These are deciduous ferns, which like to grow in clumps.

Another fern found along Fern Way is the diminutive oak fern, sometimes called the lime-loving oak fern or limestone oak fern (Gymnocarpium dryopteris). I understand the lime-loving part, but in this area of the Island no oaks grow. These ferns appear in abundance in the spring, popping up with their verdant bright green. The plant grows only about eight inches or so in height and the fronds are about five to 10 inches or so long and have a broadly triangular leaf divided several times. Both the petiole and the underside of the leaf blade have short, glandular hairs. The appearance sort of reminds me of a much smaller bracken fern. It’s no wonder that this plant grows on Mackinac, which has an abundance of limestone.

Another fern found along this same trail is the one which, I believe, gave rise to many of the inquiries about ferns I’ve had recently. It is the ostrich fern (Matteuccia struthiopteris), also known as shuttlecock fern or fiddlehead fern. These are crown-forming, colonial ferns that grow in temperate regions of the northern hemisphere, in central and northern Europe, Northern Asia, and northern North America. It is found in moist to wet deciduous or mixed conifer-hardwood forest, especially abundant on river bottoms and along streams, sometimes persisting in the open after clearing. These are quite tall ferns with vegetative leaves between 39 and 67 inches tall and eight to 14 inches across and appear in a symmetrical, vase-like form. The deciduous, vegetative fronds have a long taper to the base and a short taper to the tip resembling their namesake, the ostrich plume. These ferns are dimorphic (two forms) with the green vegetative frond and the brown shorter fertile frond. The fertile fronds appear in the fall and are only 16 to 24 inches tall. When ripe, they are brown with highly modified and constricted leaf tissue, which covers the sporangia (the structures which produce the spores). These dry out and release the spores late in the growing season and are persistent throughout the winter.

The last one of the questions I got about these ferns is whether they are native or invasive. They are sort of both. I think the question arose from the plantings that are going in along Arch Rock Bicycle Trail (South Bicycle Trail). They are native to North America and Mackinac

County, but ostrich ferns are the most commonly transplanted fern from the wild, as they are easy to grow. Being a colonial plant, they can take over areas crowding out other plants, and, in areas where they are not naturally found, they may crowd out native wildflowers. They are somewhat determined plants, as I’ve seen them coming up through pavement. We’ll have to see how well they grow along the bike path.

Trish Martin is a year-around resident of Mackinac Island, has earned a master’s degree in botany from Central Michigan University, and owns Bogan Lane Inn.

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