Near the northern shore of Squibnocket Pond on a recent winter day, Tim Boland and Kristen Fauteux stood up to their necks in water, holding cameras, pruning shears and bulky bags high above their heads.

Mr. Boland, executive director of the Polly Hill Arboretum, and Ms. Fauteux, director of stewardship for the Sheriff’s Meadow Foundation, were in search of plant specimens that have not been documented in more than 60 years, and the only way to collect the specimens was by wading through the pond.

The bulky bags? They contained herbarium presses.

After identifying Mikania scandens, a climbing hempvine that had never been recorded in Chilmark, they carefully placed the plant in the portable press and headed back to Polly Hill where the vine would join 800 other specimens in the arboretum’s herbarium.

An herbarium is essentially a library of dried, pressed plant specimens that is used to document the flora of a region, Mr. Boland explained. The herbarium at the arboretum began in 2001 with the donation of 150 marine algae specimens from the late Rose Treat; since then the Martha’s Vineyard Land Bank, Sheriff’s Meadow, The Nature Conservancy and others have been collecting specimens for the herbarium, expanding on the collections of Island botanists Carol Knapp and Stephen Spongberg.

“We are trying to record new flora for the county and the Island, and get an idea of the distribution of rare plants on the Island, ones that might be endangered,” Mr. Boland said. Of 600 specimens, he said there are 200 distinct species in the herbarium (some are duplicates). The goal is to collect every species of vascular plant occurring in Vineyard flora. There are currently 1,300 taxa recorded on the Island, which means there are hundreds of species to still be collected.

In the early 1900s through the 1950s, Mr. Boland said field collecting was a popular source of documentation.

“In the last 50 years we have not had significant collections using this methodology of voucher specimens,” he said. But a resurgence of field collecting has sprung on the Vineyard in the past 10 years, sending botanists and ecologists into woods and water in search of hybrid oaks and bristly sarsaparilla.

“With the conservation societies today, we have a dedicated collaborative that is really starting to see some success,” he said.

Stewartia pseudocamelia (ballet), a Polly Hill introduction. — Ray Ewing

Volunteers head out in search of specimens in the spring, summer and fall when plants are in bloom. In winter, botanists painstakingly mount and label the dried plants on acid-free paper, later slotting the specimens alphabetically by genus in airtight cabinets.

And now when a specimen is filed, it is also pinpointed on an interactive digital map of Martha’s Vineyard.

Mr. Boland said he and other botanists consult the Harvard University Herbaria to reexamine rare or historic Vineyard plants. But often the descriptions are outdated and vague, said Julie Russell, ecologist for the land bank.

“Up until now there has been little notation,” she said. While an old deed might mark the corner of a property with a description of a long-gone apple tree, a plant might be identified simply in fire line 25 of the state forest near pitch pines.

“First, that’s kind of a long fire lane,” she said. “And maybe the stand of pitch pines doesn’t exist anymore.”

As a result, today when recording, the botanists try to be as descriptive and accurate as possible.

“Rather than saying it was in a swamp, we’ll have a specific description: red maple swamp in Chilmark, dominated by red maple, found in close association with skunk cabbage and jack-in-the-pulpit,” Ms. Russell said.

Then the plant goes onto the map. The map allows botanists to see protected areas and open space areas, as well as the soil associations, topography trends and habitats of a rare plant’s location.

Ms. Russell said she can then find the unique micro-habitat of the plant, allowing her to compare it to other parts of the Island and to predict where else the plant may be found or restored.

The map shows areas of the Island that have concentrations of rare plants, and also areas that are losing plants, and why.

“We can look at water levels where certain plants on the coast might go extinct by being anaerobic,” Mr. Boland said. “If there was a swamp that has become inundated with water, we will look at that climate change.”

The botanists also have found plants that were thought to be extinct, such as the mountain laurel, which has now been propagated from seed and grows inside the Polly Hill greenhouse.

The herbarium acts as a teaching and reference collection for plant-lovers who come bearing unknown flowers from their yard, and homeowners who question which weed is taking over their garden.

And while the climbing hempvine may succumb to disease or the mountain laurel may go extinct, a piece of the plant will remain. The dried specimens will last 200 years.

“It creates a real biological record,” Mr. Boland said.

To view more photos of the specimens, click here.