This is one of the most commonly collected species of Psychotria in Madagascar, and quite distinctive. It is characterized by dense velvety pubsecence that becomes ferrugineous when dry; thick-textured, elliptic to obovate leaves that are obtuse or rounded to truncate or retuse at the apex and markedly bullulate, with the higher-order venation closely reticulated and prominent on the lower surface; well developed, calyptrate, caducous stipules; fasciculate or sessile inflorescences with several well developed peduncles or rays and reduced bracts; truncate glabrous calyx limbs ca. 2 mm long; tubular yellow corollas; and smooth ellipsoid fruits ca. 5 mm long. The obovate bullulate leaves with pubescence on the undersides are distinctive. The calyptrate stipules are unusual in Psychotria of Madagascar.

Psychotria macrochlamys has been confused with a number of other Psychotria species in Madagascar with obovate leaves and ferrugineous pubescence. In particular it has been confused with Cremocarpon trichanthum, which can be separated by its triangular, generally persistent stipules ca. 5 mm long, single peduncle, and short white corollas. Psychotria macrochlamys is also sometimes confused with Psychotria parkeri, which is similar in general aspect however is glabrous, has elliptic leaves that are obtuse to acute at the apex and most often smooth (though sometimes weakly bullulate), shorter though apparently also calyptrate stipules, a single peduncle, and a shorter calyx limb.