Commelina lukei had been informally recognised as a distinct species for some time, particularly when it was observed in the field because floral characters could be observed. A thorough study of the plant had not been undertaken until the time shortly before the species' publication. Robert B. Faden, the author of the paper describing the species, noted that he realised C. lukei was a new species upon collecting it in 1969, but was unable to distinguish dried herbarium specimens of the plant from the two aforementioned similar species. Eventually Faden noticed that certain specimens had needle-like, acicular hairs along the midvein on the leaves' upper surfaces, while others had mainly or only hook-hairs. Once sorted into two piles based on this character, Faden noticed that the plants with needle-like hairs also had all of their leaves clasping the stem, appendaged seeds, and capsules with a bulging apex, while those with hook-hairs only had leaves towards the tip clasping, unappendaged seeds, and broader capsules lacking an apical bulge. These characters proved sufficient for consistently separating both live and herbarium specimens.
