As it has traits of both swordtails and platies, its discovery confirmed that these two groups should be consolidated into a single genus, Xiphophorus.

Its discovery enabled scientists to definitely conclude that platies and swordtails should be classified in the same genus, for it combines traits that were thought to separate platies from swordtails into different genera.

[2] Namely, X. milleri resembles the swordtails in body shape, pigmentation, and ecology, but shares the platies' secondary sexual characteristics, pigmentary polymorphism, and the absence of a sword.

[4] Xiphophorus milleri was discovered in a steep-banked stream flowing into Lake Catemaco in Mexico.

It prefers clear or white water habitats with sparse green algae growth on a substrate of mostly sand and silt with occasional rocks.