The Nepenthes , often known as Tropical Pitcher Plants or Monkey Cups , are a genus of carnivorous plants in the family of the Nepenthaceae consisting of about 120 species ( this number is fast increasing , with one to two new species being described each year ) . The Nepenthes , popularly known as tropical pitcher plants or monkey cups , are a genus of carnivorous plants in the monotypic family Nepenthaceae .