This species is charcterized by medium-sized,. somewhat stiff-textured leaves, subsessile to shortly pedicellate 4-merous flowers, a dentate calyx limb 0.7-1 mm long, and hite to cream-colored corollas with the tube 21-35 mm long. Anunciação (2004) noted that the seeds are spongy. Steyermark separatedt this species in part based on details of pubescence, but also noted (1972: 278) variation in the presence of pubescence on various stsructures. This species is similar to Ferdinandiusa sprucei., with elongated capsules,. and these seem difficult to separate in bud. 

Ferdinandusa rudgeoides was described based on two specimens, a Spruce collection from the Rio Negro in northern Brazil and a Schomburgk specimen supposedly from Guyana, but Steyermark (1972: 278) noted that the Schomburgk specimen was also collected in Brazil along the Rio Negro. Anunciação (2004) included Ferdinandusa duckei within the circumscription of Ferdinandusa rudgeoides; the only distinction Steyermark noted between these was a corolla tube 5 mm long longer in Ferdinandusa duckei, but additional specimens document longer  corollas lengths in Ferdinandusa rudgeoides now.