Maine has many ferns, and they come in many varieties and shapes. You can find them in gardens, woodlands and along the side of roads. Sometimes it seems like they are everywhere.

In fact, when you consider the number of fern varieties worldwide, Maine has a comparatively small number. Most ferns live in the tropics, Michael Sundue, a botany professor at the University of Vermont who specializes in ferns and lycophytes (the more primitive predecessor to ferns), told a recent online class. Around the world, some 11,000 species of ferns exist. Only 450 species make their home in the United States, Sundue said, and fewer than that in Maine. The class was sponsored by Coastal Maine Botanical Gardens and the Maine Landscape and Nursery Association.

Ferns are vascular plants, which means that water and nutrients travel inside the plants. The leaves have multiple veins. All fern leaves develop from fiddleheads in the spring, but Sundue was quick to point out that the ostrich fern is the only fern from which humans harvest the fiddleheads.

Ferns lack flowers, fruits and seeds. Instead, they are dispersed by spores, which are held in small capsules on the back of a fern’s leaves that are called sori or sporangia.

One of the oldest types of plants on Earth, ferns can be traced back more than 300 million years, long before there were flowering plants. Many fern species arrived much later, Sundue said, developing alongside flowering plants.

It is possible to plant ferns using collected spores. Doing so can be a fun science project, Sundue said: You create pin pricks in paper so not too many spores fall on the soil. But these plants develop and grow slowly, so such propagation is not practical for the home garden. The timeline works for nature – ferns are among the first plants to show up in disturbed land – but not for the limited time frame of most home gardens. Instead, it is better to plant ferns with rhizomes, which spread horizontally underground from the mother fern.

In some parts of the country, ferns can be aggressive and disturb neighboring plants, but not in New England, Sundue said.

It’s ethical to harvest rhizomes from most ferns you find while walking through woods and fields, Sundue said. With one exception, it won’t harm them. That exception is the small ferns that grow in the crevices of rocks. “Don’t wild harvest cute rock ferns,” he said multiple times while showing pictures of them.

To plant the rhizomes, place them close to the surface of the soil. Most prefer shade or dappled sunlight, but some, like the hay-scented fern, will grow well in full sun. Ferns like high humidity, good drainage and rich soil that is slightly acidic. They don’t like much fertilizer. And you should never use a hoe to remover non-fern weeds around the roots, because you will damage the ferns.

So which ferns should you plant?

The ostrich fern is a good choice because of the edible fiddleheads. It spreads well, likes moist and sandy locations, but – heads up – may suffer if trampled.

Hay-scented fern spreads well, enjoys sunny locations and makes a good groundcover. Though Sundue didn’t mention this, many gardeners recommend it for areas where plows dump a lot of snow.

Bracken fern is aggressive – it can take over huge hillsides in the wild. It also gets much taller than many other ferns. Sensitive fern, which has an unusual leaf shape, also spreads quickly.

There are several varieties of Maidenhair fern. Though it doesn’t spread as quickly as most 0ther ferns, it does have nice fan-shaped leaves.

Japanese painted fern comes in a variety of colors, including red and purple, perhaps one reason it’s a popular choice. Lady fern is also popular, and grows more uprightly than many other varieties. A cultivar called Lady in Red, with red stems, is especially popular.

Wood ferns are big and colonize well.

Sundue is partial to cinnamon fern, named so because after the spores have aged a bit, its spore-bearing leaves look like cinnamon sticks.

Interestingly, horsetail, which has the botanical name equisetum, is now classified as a fern, Sundue told his audience. And some varieties can be planted in a landscape. Irene Brady Barber, who coordinated the lecture, quickly interrupted to say she and most others in Maine would not recommend that. It is highly aggressive, spreads, and is impossible to get rid of.

I agree, skip the horsetail. There are too many wonderful other ferns to try.

Tom Atwell is a freelance writer gardening in Cape Elizabeth. He can be contacted at: tomatwell@me.com.