The Index File noted that "Castrovalva [was] the central habitation of the planet that forms the Andromedan Phylox Series". This begged the unanswered question of how a single object made a series.
However, the Index File was, at the time that Nyssa and Tegan consulted it about the Phylox Series, compromised. Because the Master instructed Adric to place this false entry into the Index File, the information was entirely suspect. The Andromedan Phylox Series may have never existed. (TV: Castrovalva)