Phylox series

The  was, according to the TARDIS information system, the planet on which the city of Castrovalva was located.

Exactly what was meant by the word series in an astronomical context was unknown. The Index File noted that "Castrovalva [was] the central habitation of the planet that forms the ". 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 instructed Adric to place this false entry into the Index File, the information was entirely suspect. The may have never existed. (TV: Castrovalva)