Within Oryzomyini, Drymoreomys appears to be most closely related to Eremoryzomys from the Andes of Peru, a biogeographically unusual relationship, in that the two populations are widely separated and each is adapted to an arid or a moist environment.

With a body mass of 44–64 g (1.6–2.3 oz), Drymoreomys is a medium-sized rodent with long fur that is orange to reddish-buff above and grayish with several white patches below.

[2] The animal was not, however, formally described until 2011, when Alexandre Percequillo and colleagues named it as a new genus and species within the tribe Oryzomyini: Drymoreomys albimaculatus.

[2] Percequillo and colleagues found little geographic variation among samples of Drymoreomys, although a few traits differ in frequency between populations from the states of São Paulo and Santa Catarina.

Sigmodontinae is the largest subfamily of the family Cricetidae, other members of which include voles, lemmings, hamsters, and deermice, all mainly from Eurasia and North America.

[13] On the short, fairly broad hindfeet, the upper side is covered densely with silvery to white hairs near the tips of the feet and toes, and with brown fur otherwise.

The nasal and premaxillary bones extend in front of the incisors, forming a rostral tube, which is shared among oryzomyines only with Handleyomys.

[10] The roof of the mesopterygoid fossa, the opening behind the palate, is completely closed or contains small sphenopalatine vacuities.

[16] There is no noticeable capsular process (a raising at the back of the jaw that houses the root of the lower incisor).

[17] The upper incisors are opisthodont (with the cutting surface oriented backwards) and have orange to yellow enamel.

[10] The valleys between the cusps of the upper molars extending from the inner and outer sides overlap slightly across the midlines of the teeth.

On M1, the anterocone (the front cusp) is divided into two cuspules on the lingual (inner, towards the tongue) and labial (outer, towards the lips) sides of the teeth.

The mesoloph, a crest near the middle of the labial side of the tooth, is long and well developed on each of the three upper molars.

On the lower molars (m1 to m3), the cusps on the labial side are located slightly in front of their lingual counterparts.

Blocks of heterochromatin are present on all autosomes and the long arm of Y. Telomeric sequences are found near the centromeres of the sex chromosomes.

[19] Aspects of this karyotype—with a high number of mostly acrocentric chromosomes and the presence of heterochromatin on the Y chromosome—are consistent with the pattern seen in other oryzomyines.

[20] Other species in clade D have fewer chromosomes, down to 16 in Nectomys palmipes, although the karyotype of Eremoryzomys polius is unknown.

[21] Drymoreomys albimaculatus occurs in the Atlantic Forest on the eastern slopes of the Serra do Mar in the Brazilian states of São Paulo and Santa Catarina, at 650 to 1,200 m (2,130 to 3,940 ft) above sea level.

[23] Although some of its morphological traits, such as the very large pads, are suggestive of arboreal (tree-dwelling) habits, most specimens were collected in pitfall traps on the ground.

[3] The range of Drymoreomys albimaculatus is relatively large and the species occurs in several protected areas, but it has only been found in seven localities and its habitat is threatened by deforestation and fragmentation.