Flower paintings and rare watercolors by Georgia O'Keeffe and six works by iconic American illustrator and painter Norman Rockwell will be among the highlights of Sotheby's sale of American art this month, the auction house said on Thursday.

All of the O'Keeffe paintings, which include "Autumn Leaf II," with a pre-sale estimate price of up to $2.5 million, and the pastel "A White Camellia," which could fetch as much as $1.8 million, are from a private collection.

Sotheby's said the O'Keeffe works in the November 29 sale in New York "represent one of the most significant groups of works by the artist to appear on the market" since a 1987 auction of 10 painting from her sister's estate.

Among the six works by Rockwell that will go under the hammer are: "When the Doctor Treats your Child (The Prescription)," which appeared in the Saturday Evening Post in 1943; "Is It Play for Eyes Too?" from 1929; and "The Muscleman," featuring a young boy and his puppy that the artist completed in 1941.

Sotheby's expects each will sell for more than $600,000, and some for more than $800,000.

The sale will also feature Impressionist works by Theodore Robinson and Mary Cassatt. Robinson's "Correspondence," which could sell for $1.5 million, has not been seen in public since 1946.

"Robinson, best known as a pioneer of American Impressionism, was born in Vermont and trained in both the United States and Giverny, France, blending his experiences into the style for which he is known today," Sotheby's said in a statement announcing the sale.

The Cassatt painting, "Sketch for "Margot Embracing her Mother" (No. 2)" depicts the artist's neighbors in France and has an estimated price of $600,000 to 800,000).

(Reporting by Patricia Reaney; Editing by Jill Serjeant and Dan Grebler)