What do purple heart, ziricote ebony, cocobolo, bocote and bathbarra have in common?

They're all rare and extraordinarily beautiful tropical hardwoods, and they're all endangered species, their existence threatened by the demise of the South American rain forests.

The exotic woods also are the current medium of Nantucket sculptor, David Hostetler, who wants to save the beauty of as many as possible through his art.

"These woods are very beautiful, too beautiful to be lost forever. I'd like to try to capture, in my sculptures, some of their beauty before it is forever gone," he says.

The logs Hostetler sculpts are saved from commercial use by a network of art patrons, corporate friends and art dealers who divert the exotic woods from commerical markets to Hostetler.

John Sussek, a summer resident, obtained the purple heart log for "Semaphore Woman," one of several sculptures completed this year and on display at the Hostetler Gallery on South Wharf.

"Purple heart is not only one of the most beautiful woods, but it also is a magnificent wood to sculpt, hard and close grained. It's sad to think of it being lost," Hostetler says.

In his wood sculptures, Hostetler makes careful and considered use of the wood's natural grains to highlight the sculptures' flowing curves and details. The wood and the form it portrays become one.

Hostetler also used the wood's natural coloring. For example, in the only log of macassar ebony he, has carved - found by Bill Severens of Nantucket - Hostetler created "Cape lady" by sculpting the lady's dress from the log's beautifulpink sapwood and the lady herself from its ebony-black heart.

Other sculptures Hostetler recently carved include "Fur Cape Lady," from spalted West Indies mahogany that ws shipped from Puerto Rico with help from summer residents John and Marilyn Whitney, and "Feather Cape Lady," from ziricote ebony obtained through the assistance of Rufus Barkley, an art collector from South Carolina.

It was in New York City in 1959 that Hostetler discovered working with exotic woods, a discovery that had immediate ramifications.

"At the time, I was able to get free tropical woods from the Brooklyn Navy Yard, which used them in ship building. I began to carve the woods, using leftover pieces to make tables which I sold to pay my studio rent," he recalls.

During the next two decades, his primary mediums were native American wood, much of it grown on his farm in Ohio, and bronze. In the 1980's, his interest returned to the tropical woods, and today he is the world's only figurative sculptor working in these woods.

"I feel an urgentcy in this work - the tropical rain forests, with trees up to 300 years old, are being destroyed at a rate of 50 acres per minute. By the year 2000, many, if not all, of these tropical woods, could be extinct," he said.'

"I often have this uneasy feeling that each rare log that I recieve could be the last of that variety. I hope not, but that's the reality."

Fueled by his love of the tropical hardwoods and his personal artistic commitment to preserving their beauty, Hostetler intends to sculpt as many of the rare logs as possible.

"I'd like to do at least one piece in each of the different endangered woods."

Hostetler gained national prominence in the 1960's, with graceful and flowing sculptures in native wood in his American Woman Series. He began working in bronze in 1958 in Mexico, creating one-of-a-kind castings from the original wood pieces. Considered among the world's leading sculptors of the human figure, Hostetler has worked for 30 years in such native American woods as persimmon, black walnut, red cedar, catalpa, white oak and elm.