Cosmocalyx is a monotypic genus of flowering plants in the family Rubiaceae.

[1] Cosmocalyx spectabilis is a slender tree, up to 15 m (49 ft) in height and 20 cm (7.9 in) in diameter (dbh).

After anthesis, one of the four calyx lobes expands into a reddish, leaf-like structure called a calycophyll.

[3] The generic name is derived from the Ancient Greek words, kosmos, meaning "order", and kalyx, "a calyx".

[4] Cosmocalyx is placed with Deppea, Hoffmannia, Hamelia and several other genera in the tribe Hamelieae.