Warszewiczia longistamina was separated in its protologue from Warszewiczia schwackei based on the relative length of the corolla tube vs. the lobes, the relatively length of the corolla and filaments, different lengths of the calyx limbs, relatively different sizes of the disk in relation to the calyx limb, and details of the pubescence. Both of these species were described based on a single specimen. These first two characters vary size in Warszewiczia according to the phase of the flower (pistillate vs. staminate), thus are probably related to the phase of the flowers studied rather than species-level differences. The Peruvian plants of Warszewiczia schwackei show a full range of pubescence that unites the two forms Schumann described. Thus Warszewiczia longistamina is likely either a synonym of Warszewiczias schwackei, or a regional form that maybe usefully regarded as an infraspecific taxon. The status of this name cannot be conclusively evaluated until more material from the southern Amazon drainage in Brazil has been studied.These two names were described together; the name Warszewiczia schwackei has been widely used in floras and catalogues for several countries, while Warszewiczia longistaminea has not been recognized since the time of its description, so if these names are synonymized, Warszewiczia schwackei would be the preferable name to adopt for this species.
These plants were reviewed in detail by Delprete (2010), who recognized both of these species and reported both of them from Goiás, with Warszewiczia longistaminea known only from the type specimen. Delprete separated these species only by filament length, 2.5--3 mm long in Warszewiczia longistaminea vs. 0.8--2 mm long in Warszewiczia schwackei. He commented (p. 1384) that pubescence characters of leaves and corollas that were used by previous authors to separate these species actually show continuous variation, and that these species are very possibly not distinct. The name Elaeagia subspicata Standl. has also been used for this species, and was cited as a synonym by Delprete (2010: 1383). However the type specimen of Standley's name actually is Bathysa bathysoides; this species has been confusd with Warszewiczia elata, see comments under that species, and Warszewiczia elata and Warszewiczia schwackei have been frequently confused in herbarium identifications and this confusion seems to have extended to Warszewiczia longistaminea.