Leprechauns couldn’t have had a better opportunity to sit on a mushroom this summer on the Vineyard. Mushrooms have appeared all over the Island, from Chappaquiddick to Aquinnah.

The phenomenon is tied to the weather, specifically rainfall. Tristan Israel, a Tisbury selectman and a landscaper, said he has not seen a summer with so many mushrooms in 30 years outdoors managing and mowing properties.

“We’ve had a humid, relatively wet summer,” Mr. Israel said. Last year the Island suffered from drought-like conditions. This summer it rained often, with many passing thunderstorms and brief showers.

“There has been a profusion of mushrooms in my own garden,” said Tim Boland, executive director of Polly Hill Arboretum in West Tisbury. “I ride my bike to work. All along the state forest on the bike path I’ve seen them. There are just all kinds. We got just the right amount of moisture.”

Mr. Boland said mushrooms are one of the most under-studied group of plants.

Rainfall totals kept by the National Weather Service in Edgartown tell part of the story. August was not a wet month; rainfall total was 1.73 inches, far short of the monthly average of 4.43 inches. But what is interesting is the number of times it rained. There were at least eight individual days when there was measurable rainfall of at least .01 inches. Most rainfall events offered less than a quarter inch of rain. On two additional days there was at least a trace of precipitation.

Compared with August, July was wet. Total rainfall was 4.15 inches, well above the monthly July average of 2.63 inches.

Mr. Israel said he cannot recall a summer when so many thunderstorms passed over. “The weather is so different from when I first started landscaping,” he said.

And that is perhaps what helped kick off a prolific mushroom season. “You see mushrooms every summer. But this year they were in abundance. I found a fairy ring. That is something else,” Mr. Israel said.

A fairy ring is a circle of mushrooms that grow outward. Mr. Israel said he saw a ring at least 10 feet in diameter. Also sometimes called an elf circle, pixie ring or fairy circle, a fairy ring is perfectly symmetrical, as though someone had deliberately planted the mushrooms that way.

Mr. Boland said: “Mushrooms are decomposers. Primarily they break down all the woody plant tissues and help to restore the organic material in the soil.” He said mushroom spores are the equivalent of plant seeds, and can sit around for years before they will produce a plant. “They await the opportune time,” Mr. Boland said. “Spores in a dry year will remain dormant. They wait for the conditions to get right. They are really quite unique. They’re an ancient group of organisms.”

Mr. Boland issued the usual warning to people to not eat or touch mushrooms; it is very difficult to tell the difference between mushrooms that are poisonous and those that are edible. “It is really critical to know, especially for those who are interested in foraging that you need a strong background in knowing what is edible and what is not. Some that are here are remarkably similar, nearly identical. The ones that are poisonous may be extremely toxic,” Mr. Boland said. He added:

“When you see an animal eating a mushroom, don’t think you are safe. It may be inedible for humans. Humans can’t take that kind of chance.”

Suzan Bellincampi, director of Massachusetts Audubon Society’s Felix Neck Wildlife Sanctuary, agreed. “This summer the mushrooms have been fantastic and that includes the shapes, sizes and colors,” she said, adding:

“It is not about naming them, it is about enjoying the sight of them. Identifying mushrooms is very challenging. You can try and put them in natural categories, but getting them down to genus and species is tricky. Too many variables.”

Ms. Bellincampi said her favorite book is Mushrooms of Northeast North America: Midwest to New England by George Barron. A second choice is the National Audubon Society Field Guide to North American Mushrooms by Gary H. Lincoff. But if you want to buy one of these books at Felix Neck, you will have to wait a bit.

“We sold out of all the mushroom books at our gift shop. We’ve got more on order,” she said.