IT WAS the first decade of the 20th century when a young American teenager daringly proclaimed to her fellow classmates: "I am going to live a different life from the rest of you girls. I am going to give up everything for my art."

That young girl was Georgia O'Keeffe (1887-1986), and she went on to become one of America's most important modernist painters. Her artistic career spans almost the entire 20th century;

her first exhibition was in 1916 and she continued painting until the late 1970s, when her eyesight began to fail.

O'Keeffe has attained an almost mythic status, known as much for her solitary, black-clad figure and craggy face of old age as for her famous largescale flower paintings. And while we Irish may like to claim her as our own - her paternal grandparents hailed from Co Cork, after all - her artistic vision was truly American.

What is particularly striking about her six-decade career is its enduring individuality and originality - but also its unwavering cohesiveness of vision. As a pioneer of a unique form of American modernism, O'Keeffe was a painter who constantly focused on integrating nature and abstraction, as attested by the excellent, wide-ranging exhibition of her work at the Irish Museum of Modern Art. Spanning her entire oeuvre - and featuring flower and leaf studies, abstracts, landscapes, and images of trees and bones - it demonstrates her "consistent determination to transform known or recognisable things into painted, abstracted entities", according to curator Richard D Marshall.

While O'Keeffe's early determination to become an artist is admirable, particularly for a young girl at the turn of the century, it was not a foregone conclusion that she would realise her ambition. O'Keeffe was born in Sun Prairie, Wisconsin in 1887, the second of seven children. While she received artistic training at the Art Institute of Chicago and the Arts Students' League in New York, the need to make a living meant that, from 1908 to 1910, she worked as a poorly-paid freelance illustrator in Chicago. But following a bad bout of measles, she returned to live with her family in Charlottesville, Virginia.

It was there, while attending a summer school at the University of Virginia in 1912, that O'Keeffe discovered the artistic theories of Arthur Wesley Dow, who advocated creating harmonious compositions based on line, colour and tone. Later, in 1914, she enrolled in the Teachers College at Columbia University in New York, primarily to train as an art teacher - a suitable career for a woman - but also to come under the direct instruction of Dow.

In 1915, while working as an art teacher in South Carolina, she decided to take a new direction in her art: "I had been taught to work like others and, after careful thinking, I decided that I wasn't going to spend my life doing what had already been done? I have things in my head that are not like what anyone has taught me, " she recalled.

The result was a series of abstract charcoal drawings, some of which she posted to her friend Anita Pollitzer in New York. Unbeknownst to O'Keeffe, on new year's day 1916, Pollitzer brought the drawings to the avant-garde Gallery 291 - renowned for bringing the work of European modernist masters such as Picasso and Matisse to New York - and showed them to its owner, the photographer and publisher Alfred Stieglitz. The impressed gallerist proclaimed that they were the "purest, finest, sincerest things that have entered 291 in a long while".

Stieglitz held onto the works and later in the year exhibited them in a group show - without O'Keeffe's knowledge. Outraged, O'Keeffe arrived in New York to demand he take them down. He persuaded her to leave them on display and this first meeting was the beginning of a legendary relationship between O'Keeffe and Stieglitz, 23 years her senior.

In 1918, Stieglitz organised for her to come to live in New York, paying for upkeep and allowing her to focus on pursuing a career as an artist. Within a month of her arrival, they began an affair.

Stieglitz divorced his wife of 25 years and, in 1924, O'Keeffe and Stieglitz were married. He took on the role of mentor, tirelessly promoting O'Keeffe's work, while she became his muse, the subject of an evolving series of photographic portraits he took over a 15-year period.

Following her arrival in New York, O'Keeffe graduated from watercolours and charcoals to oil painting, and she was soon being championed as a pioneer of modernism within a circle of artists known as the Seven Americans.

Over the next decade, she became increasingly famous for her sensuous flower paintings, New York views and paintings of the landscape at Lake George, where she holidayed with Stieglitz's family.

"Nobody sees a flower - really it is so small? So I said to myself? I'll paint it big so they will be surprised into taking time to look at it, " she later recalled.

O'Keeffe developed a unique way of using extreme close-ups and cropping techniques so that recognisable sections of flowers, trees or landscapes dissolved into abstract meditations on form, line and colour. Even her most abstract works always had some basis in reality. As she once said: "I often paint fragments of things because it seemed to make my statement as well or better than the whole could."

But as she was achieving professional success, Stieglitz's attention turned elsewhere and he began having an open affair with a new prot�g�. From 1929, O'Keeffe began holidaying alone in Sante Fe, New Mexico each summer. She had first visited the place in 1917, recalling, "I loved it immediately.

From then on I was always on my way back." However, in 1933, O'Keeffe had a nervous breakdown, was hospitalised and did not paint for an entire year.

Following her recovery, these summers in New Mexico led to a new direction in her paintings - dramatic, simplified, vibrant landscapes of dusty red deserts and undulating hills. She created some of her most pared down, abstract massings of shape and colour, almost unidentifiable but for the titles. She also began collecting animal bones, as featured in Pelvis with Distance, in which a detailed pelvic bone stretches across a simple landscape background. She once said: "The bones are as beautiful as anything I know. To me they are strangely more living than the animals walking around."

Three years after Stieglitz died in 1946, O'Keeffe moved to Ghost Ranch in Sante Fe, where she lived for the rest of her life. In later years she began travelling extensively, leading to a series of landscapes seen from the air, such as Winter Road I, or dramatically simplified paintings of clouds viewed from above, in which endless expanses of white cloud and blue sky become simple bands of colour.

During her 40 years in Santa Fe, O'Keeffe's work fell out of and then back into fashion, with a series of major retrospectives in the 1960s and 1970s and her election to the prestigious American Academy of Arts and Letters. She completed her last unassisted oil painting in 1972 and died at the age of 98 in 1986.

O'Keeffe is many things to many people: a pioneer of American modernism, a confident feminist who lived an independent existence, a solitary, childless recluse of the desert. But when asked how she would like to be remembered, O'Keeffe is said to have replied simply: "As a painter, just as a painter."

'Georgia O'Keeffe: Nature and Abstraction' runs in Imma until 13 May 2007