According to the authors of the article on "Art Nouveau" on the Wikipedia website, "Art Nouveau . . . is an international style of art, architecture and applied art, especially the decorative arts, that was most popular between 1890 and 1910. A reaction to the academic art of the 19th century, it was inspired by natural forms and structures, particularly the curved lines of plants and flowers."
"The distinguishing ornamental characteristic of Art Nouveau is its
undulating, asymmetrical line, often taking the form of flower stalks
and buds, vine tendrils, insect wings, and other delicate and sinuous
natural objects; the line may be elegant and graceful or infused with a
powerfully rhythmic and whiplike force. In the graphic arts the line subordinates all other pictorial elements—form, texture, space, and colour—to its own decorative effect" ("Art Nouveau | artistic style")