Rose Treat, a renowned Island naturalist and artist who was best known for her unique seaweed collages, died on Nov. 17 at her home in Sengekontacket, two weeks shy of her 103rd birthday.

A self-taught expert in the natural world whose specialty was mushrooms and seaweed, Mrs. Treat was a well-known figure on the Vineyard where she led mushroom walks and attracted attention in both academic and art circles for her graceful, unusual collages, made from seaweed she had collected herself and mounted on special paper using a process she developed to ensure lasting color.

Seaweed was Rose Treat’s paint and she gathered it year-round from the clean ocean waters around the Island. And while she had no formal training in phycology, she was highly knowledgeable about the many varieties and habits of plants that grew in saltwater and earned recognition for it. Her seaweed artwork has been shown at Harvard University, the Marine Biological Laboratory in Woods Hole and the Alias Gallery in Paris, among others. In 1995 the Smithsonian called her asking for a seaweed specimen for their Ocean Planet exhibit.

“How would they know about me?” she wondered aloud in an interview with the Martha’s Vineyard Magazine in 2004. “Seaweed is a living thing, unlike paint,” she said in the interview, describing her collection of seaweed roosters. “I hear them crowing.”

In 2001 Rosie, as she was known to her family and friends, donated her extensive collection of more than 350 seaweed pressings to the Polly Hill Arboretum in West Tisbury where they are permanently housed.

Rose Treat was born on Dec. 7, 1908, in Czechoslovakia. Her family immigrated to the United States in 1910. Raised in a German-speaking family, she did not learn English until she went to school. Each day she taught her mother what she had learned in school that day, and in the evening, taught her father. As a result, her parents learned to speak, read, and write English.

As recounted by her in her own written life story, from the age of five to eight her family lived for six months on the Lower East Side and for six months on a farm in New York state. Rose learned the ABCs on a slate in a rural one-room schoolhouse, where each child had a janitorial chore to do before classes started: sweeping the room, gathering wood for the big black stove or raising the flag. Along with another child, Rose’s job was to take the water bucket to the nearest farmhouse, about half a mile away, where the farmer would dip her bucket into the well and pour it into the school bucket. Then Rose and the other student would carry the bucket of water to the schoolhouse, place it with a dipper in a corner of the room, and each child would drink from the dipper. Her teacher had only two years of high school education, but a great love of nature, which she imparted to the students. Although Rose’s early education was lacking in many ways, she was always glad and thankful to have had the unique opportunity to live in this 19th-century setting.

She graduated from Mt. Sinai Hospital School for Nurses in New York and worked as a public health nurse for the Henry St. Visiting Nurse Service for several years. Following that she worked with the Westchester County Department of Health. She later graduated from Teachers College at Columbia University, where in her last year she received a scholarship.

She met Lawrence Treat, a mystery writer, in 1942, and they were married the following year. She volunteered as a Red Cross nurse, teaching home nursing in public schools and at Bedford Women’s Prison. She also worked in the Sing Sing Prison blood bank.

In 1959, the Treats spent August on Lobsterville Beach where they purchased a summer cottage. That is when Rose began to create her seaweed collages. In the following years, more summer months were spent on Martha’s Vineyard, and in 1972, they moved to the Vineyard year-round. Rose’s artwork was exhibited in many Island galleries and is in the permanent collections of the Marine Biological Laboratory of Woods Hole, Harvard University, the Smithsonian Institute, and the Martha’s Vineyard Historical Society.

She taught workshops in the art of seaweed collage in public schools on the Cape and on the Vineyard, at senior citizen centers, Camp Jabberwocky, the Martha’s Vineyard Museum, and with her friends in the Polar Bear Club.

Henry Beetle Hough, late editor of the Gazette, told her that she made the Island aware of mushrooms and seaweed.

In 1985, she published The Seaweed Book.

An avid mycologist, Rose also was an expert on wild mushroom identification and led fall mushroom walks ending in delectable feasts.

Petite, outgoing and outspoken, she could frequently be found on the shoreline in her trademark tall rubber boots and kerchief, collecting seaweed with a long-handled net. In an interview with the Gazette on her 100th birthday, she offered her prescription for a long life: “Nature gave you a good thing. Don’t get into smoking and drugs and other crazy things. Be a good driver. Don’t endanger your life.” And she added: “Be aware of your surroundings. I’ve always been interested in my environment; it keeps me busy.”

She was a member of the Oak Bluffs Polar Bear Club, and loved swimming and collecting seaweed in the early hours on Inkwell Beach. She was a fierce Scrabble player and played up to (and including) the day she died (she won). She was the jam and jelly judge for more than 40 years at the Martha’s Vineyard Agricultural Society Fair.

With her husband, Larry, she traveled extensively to Japan and Europe. Their rich social circle of many artistic and literary friends included William Maxwell, Milton Avery, Wallace Putnam, and Conseulo Kanaga. Larry Treat died in 1998.

She is survived by her sister, Laura Lohman, and her brother, Judge Norbert Ehrenfreund, as well as her nephews and nieces, Steve Lohman of West Tisbury, Deborah Lohman Rubin, Jon Lohman, Cathy Enthof, Zach Ehrenfreund, Laurel Ehrenfreund, Dan Ehrenfruend, and Janet Ehrenfreund and all their families, and also her caregiver, Deborah Giuffre.

A celebration of her life will be held at the Polly Hill Arboretum in the spring.

In lieu of flowers, her friends are asked to please take a walk on a beach and look at the seaweed and think of Rose.