Ernest Biéler was a Swiss artist active in the late 19th and early 20th centuries whose works incorporates elements of Art Nouveau and Symbolism.
Biéler studied in Paris at the académie Julian, returned to Switzerland and later moved back and forth between there and Paris, staying for years at a time.
His painting style varied from naturalistic oils to beautifully graphic watercolors, including a fascinatingly graphic series of watercolor and tempera portraits.
One of the best sources I’ve found for his work is a LiveJournal blog in Russian, with a section on his watercolor portraits. (You can use Google Translate to roughly translate from Russian to English, or another language.)
You can also look for Bieler tagged posts on Tumblr, and I’ve listed what other resources I could find below.