Rudolf Schmid-Höllinger reported observing upper pitchers of N. rhombicaulis on Mount Pangulubao in 1993. He published his findings the following year in the Carnivorous Plant Newsletter. Charles Clarke also reported finding one small upper pitcher in 1995. Prior to this, it was thought that the upper stem of N. rhombicaulis was only used for climbing and did not produce pitchers. However, doubts have been raised about the identity of the upper pitchers observed by Schmid-Höllinger.