Cryptic species complex

In biology, a cryptic species complex is a group of species which satisfy the biological definition of species, that is, they are reproductively isolated from each other, but they are not morphologically distinguishable (or at least are not readily or reliably distinguishable on a morphological basis).

The individual species within the complex can usually only be separated using non-morphological data, such as from DNA sequence analysis, bioacoustics, or thorough life history studies. They can, but need not be, parapatric, quite often are sympatric, and sometimes allopatric.

Examples
 * Gray-cheeked Thrush and Bicknell's Thrush
 * tapaculos
 * Two-barred Flasher (suspected)

A related concept is the superspecies. This is a group of at least two more or less distinctive species with approximately parapatric distributions. Not all cryptic species complexes are superspecies, and vice versa, but many are. A superspecies consisting of two sister species is called a species pair.

Examples:
 * Puffinus puffinus group of shearwaters - not a superspecies, but the P. yelkouan group formerly contained therein is indeed one.
 * Phylloscopus collybita group of leaf warblers
 * tapaculos

Evidence from the identification of cryptic species has led some to conclude that current estimates of global species richness are too low. For example, research published in January 2008 based on the mitochondrial DNA sequences of giraffes suggested that there are at least 11 genetically distinct populations in Africa. . Similar methods also found that the Amazonian frog Eleutherodactylus ockendeni is actually at least 3 different species that diverged over 5 million years ago. The authors concluded

"Our research coupled with other studies suggests that species richness in the upper Amazon is drastically underestimated by current inventories based on morphospecies,"