Grass

Grass is a 1989 science fiction novel by Sheri Tepper. This is another re-read for me, my third time through if memory serves.

from the back of the book:

Here is a novel as original as the breathtaking, unspoiled world for which it is named, a place where all appears to be in idyllic balance.

Generations ago, humans fled to the cosmic anomaly known as Grass. Over time, they evolved a new and intricate society. But before humanity arrived another species had already claimed Grass for its own. It, too, had developed a culture....

Now, a deadly plague is spreading across the stars. No world save Grass has been left untouched. Marjorie Westriding Yrarier has been sent from Earth to discover the secret of the planet's immunity. Amid the alien social structure and strange life-forms of Grass, Lady Westriding unravels the planet's mysteries to find a truth so shattering it could mean the end of life itself.

Infinity Plus calls it "one of the most significant works of 1980s SF: a spacious, well-plotted, wise and thought-provoking book with an exceptionally cover scanwell-drawn central character and a beautiful twist on the 'beauty and the beast' mythos at its heart." SF Site says it's "Sheri Tepper's first fully-successful novel and perhaps still her best."

Kirkus Reviews says it's too long but "Imaginative and well worked out". Publishers Weekly says, "Tepper ... delves into the nature of truth and religion, creating some strong characters in her compelling story".