Trifari was known for some designs using glass poured into molds. You can find such jewelry from the 1950s, with leaves and flower petals made from poured glass. This pin is unsigned but dates to the 1960s.
According to Answers.com, Art Nouveau is a “style of decoration and architecture of the late 19th and early 20th centuries, characterized particularly by the depiction of leaves and flowers in flowing, sinuous lines.” [French : art, art + nouveau, new.]
The jewelry shown in this post is very typical of Art Nouveau styling.