The genus Eudocimus appears to be most closely related to (but more primitive than) Plegadis, the latter distinguished anatomically by the conformation of the tarsometatarsus.

[2] It has two foramina in the intertrochlear groove of its distal tarsometatarsus, as do Plegadis in contrast to the single foramen of Eudocimus and many other bird species.

[3] A 2010 study of mitochondrial DNA of the spoonbills by Chesser and colleagues, which included E. ruber, Nipponia nippon and Threskiornis aethiopicus found that E. ruber was an early offshoot and not closely related to a clade containing the spoonbills and Old World ibises.

[3] Two species, one living and one extinct, have been recovered from the Talara Tar Seeps in northern coastal Peru.

The plumage is all-white (albus) or all-scarlet (ruber), except for the black wing-tips, which are easily visible in flight.