Colobinae (also called Leaf Monkey) is a subfamily of the Old World monkey family that includes 59 species in 10 genera, including the skunk-like black-and-white colobus, the large-nosed proboscis monkey, and the gray langurs. Some classifications split the colobine monkeys into two tribes, while others split them into three groups. Both classifications put the three African genera Colobus, Piliocolobus, and Procolobus in one group; these genera are distinct in that they have a stub thumb. The various Asian genera are placed into another one or two groups. Analysis of mtDNA confirms that the Asian species form two distinct groups, one of langurs and the other of the "odd-nosed" species, but suggests that the gray langurs are not closely related to either.
Francois' langur or Francois' leaf monkey (Trachypithecus francoisi) is a species of lutung and the type species of its species group. Francois' langur belongs to the Colobinae subfamily, Cercopithecidae family, in the Primates order. Of all of the colobine species, Francois' langur is the least studied of all of the species.
The species is distributed from Southwestern China to northeastern Vietnam. Before 1990, Francois' Langur could be found in 23 different countries with a total population size of 2,000-2,500 individuals. There has been a dramatic decline in the population size by approximately 85% since then, making this species that of very high priority to potential extinction. The total number of wild individuals is unknown, but there are believed to be less than 500 left in Vietnam and 1,400-1,650 in China. There are only about 60 langurs in captivity in North American zoos.
The Mesker Park Zoo in Evansville, Indiana, has made headlines for its success in breeding the rare monkey. The zoo received two females, Liang and Sai, in November 2003 from the San Diego Zoo. Each gave birth to a son in August 2006. The father came from the Cincinnati Zoo in December 2005. In February 2008 Liang gave birth to a female.