The author of Eat Pray Love (EPL) earned her place in posterity as the author of the international best-selling phenomenon that became both a film and an excuse for thousands of women to flock to Italy, India and Bali looking for pasta, peace and passion.

But not so fast. A line may need to be added to that tombstone (hopefully not too soon). Because now Gilbert has pulled off something which will confound those who dismiss her as merely the author of a pop-psychology Oprah favourite incarnated by Julia Roberts on screen. She has written a hefty, erudite, big-hearted and inquiring novel set in the 19th century that makes it impossible to ignore her as a literary talent.

The Signature of All Things, a sweeping title that hints at the book's universality and ambition, overflows with the same infectious vitality and humour that make Gilbert so likeable in the flesh. Her subject matter is unlikely: in a nutshell, The Signature of All Things is about moss and masturbation.

But before we get to botany and desire, confounding her critics is something Gilbert does well. She may now be one of the most popular speakers on the list of TED talk alumni but when she fronted up to deliver her 16 minutes on the nature of creativity in 2009, she faced an audience that had dismissed her as a lightweight before she even started to speak.

After all, TED audiences are filled with Nobel laureates and other heavy lifters. What could they learn from someone so shamelessly popular? A lot, as it turns out: the audience gave her a standing ovation.

The talk has been viewed more than five and a half million times; and Prince quoted from it during a recent interview.

Success of the kind Gilbert experienced with EPL can be a curse. But she proved her mettle with Committed, a confessional disquisition on the pros and cons of marriage, before taking the plunge with the man she met in Bali and with whom she now lives happily in New Jersey.

''After EPL I had nothing to lose. I knew I could only disappoint and I hate to disappoint. So I bought back my liberty with Committed. It was the personal sacrifice I made in being so revealing and it was scary to publish. But it broke the spell and helped silence the haters.

''I was tempted to pull a Harper Lee [author of To Kill a Mockingbird, who never published again] and just garden, except that I love writing too much. The world can live without another book from me, but I can't.''

The spirited heroine of Gilbert's novel, Alma Whittaker, is not troubled by success or expectations. She is a botanist, or to be more specific, a bryologist, specialising in the study of mosses, those small, modest and unobtrusive organisms.

''I chose something she could study without having to leave her home, a universe in miniature that replicated the scale of needlepoint and other women's craft to demonstrate how women's frustrations were reduced to magnificent but tiny things.

''But I had another reason,'' says Gilbert, pausing like an actor delivering a punchline. ''Moss is where ferns have sex.''

Alma is an independent woman with a mind shaped by curiosity much as Gilbert's is, and a body that craves pleasure much as Gilbert's does. So when Alma finds her own moist interior, she explores it thoroughly, as any good scientist would, and makes an astonishing discovery. From then on there is no stopping her.

''Masturbation is the one truly universal sexual act regardless of age, orientation or culture,'' Gilbert says, while sucking lasciviously on Pacific oysters.

''Right now, in my country, the anti-abortion movement is using photographs of foetuses masturbating to prove there's life and that it's sacred. But wait a minute! When you're born, you are not supposed to do it, right?'' She admits she was a latecomer to the practice. ''Maybe 16, but I wish it had been sooner.''

Alma uses the word ''quim'' to name the source of her private satisfaction. ''I had no shortage of porno slang of the time to choose from but I can imagine her having heard that one and I liked the fact it rhymes with prim. It is Shakespearean - old, but not as filthy as some of the alternatives.''

Gilbert spent three years researching the novel, plunging into the 19th-century world from abolitionism to evolution, from religion to colonialism, contrasting big ideas with small details of domestic life.

Although The Signature of All Things took her to Britain, Tahiti and Australia, it began closer to home.

''I have a book that had belonged to my great-grandfather, a keen bibliophile who had bought it from a Philadelphia used bookstore for $35. It was a 1784 edition of James Cook's voyages, written after the third voyage. As a child, I had played with this book and destroyed its value by signing my name on the frontispiece when I was four.

''Finding the subject of your next book is like a scavenger hunt. This book seemed like a message from the past to my future self. Once I started reading about Joseph Banks, that was it.''

Banks employs Alma's father, Henry, an entrepreneurial rogue who becomes rich stealing plants for wealthy collectors, allowing him to build himself a showy property of his own, where he raises Alma to be inquisitive about everything.

''I had Alma first. I knew I wanted her to be born in 1800 so that she had a foot in the Enlightenment and one in the Industrial age and could reach Darwin.''

The diversity of knowledge in The Signature of All Things makes the experience of reading it similar to gazing into a cabinet of curiosities. So what was Gilbert surprised to learn in the process of writing it?

'That in the decades leading up to Darwin's great theory, the entire scientific world was discussing evolution. Everyone knew that species were mutating, they just did not understand the mechanism. Darwin closed off debate by answering the question. I also discovered that he corresponded with a woman, Mrs Mary Treat, in New Jersey about carnivorous plants. He never patronised her and she never hero-worshipped him.''

One big difference between Alma and her creator is that Alma is plain. Why did Gilbert make her so? ''Everything of her is in me,'' she says. ''I bet you even Angelina Jolie knows what it's like to feel ugly, even if it's just a memory from her youth … The fact is that most literary heroines are not plain but most women in real life are not stunning. Literature is a bit disproportionate and I wanted to correct that. So Alma is a tree among flowers.

''Most of us don't get everything we wanted from life but we still have an interesting time despite the disappointment,'' says Gilbert, pointing to an oyster. ''That's the grit that makes the pearl.

''In 19th-century women's literature there were only two possible endings: you were shamed because of sensual error or you were happily married. That is just too cruel and narrow. When in literature have you seen a woman who is full of desire, but not desirable? Lots of sexy people are not evident. And lots of great-looking people would love not to be lusted after.''

For Alma and for Gilbert, work and love are equal firsts, not competing aspirations. ''I feel like the last truly rebellious thing you can do as an artist is love your work. You are not really allowed to say that. Well f--- you, everybody, I love my work, just as Alma does.

''You better love what you do in life because you might not get the other things you desire. Alma refuses to choose between love and work because she knows it's a false choice. I'm the same, I'm grateful for both. And when love fails, you need to find something to do.'' (In this, Alma is a kindred spirit to Middlemarch's Dorothea; it is easy to imagine the two enjoying a warm friendship by correspondence.)

Among the many individuals she thanks in the acknowledgments, Gilbert includes fellow writer Ann Patchett. ''We have been pen pals writing long letters to each other every month for nearly 10 years now about work. Like me, she had huge success with her fourth book [Bel Canto] at around the same age and like me she had an unfortunate first marriage and married a man 17 years older in her second marriage, and like me, she's figuring out how to be a good person.''

It was Patchett who advised Gilbert to let Alma undertake the boldest adventure in the book, leaving the privileged sanctuary of her father's eccentric kingdom on a journey that perhaps echoes Gilbert's original EPL hungering quest. ''She told me I had to let her go, so I did.''

The Signature of All Things is published by Bloomsbury on October 1, $29.99. Purchase the e-book here.