Rosalie Barbara Pike (born Johannesburg, 1933) is a South African botanical illustrator whose work is closely tied to the scientific documentation of the country's flora. Born in Johannesburg to an industrial chemist, Barend Elzas, and Klara Kindinger, she studied botany and zoology at the University of the Witwatersrand, graduating in 1952.
After a short spell as a biochemist and medical artist at the university's Department of Surgery and Medicine and a year at the CSIR, she returned to Witwatersrand as botanical illustrator for the Botany Department, a post she held from 1957 to 1985. That year she joined the Geological Survey Museum in Pretoria as an artist.
Her illustrations appear in books such as Wild Flowers of the Witwatersrand (1971), Ferns of the Witwatersrand (1973) and A Passion for Plants (2001), and her paintings are held in private collections. She received Kirstenbosch awards in 2000, 2002, 2004 and 2006, and her first prize came in 1945 at the National Eisteddfod.