Only Clement of Alexandria could have been the source for the List of the Apostles because the List of the Apostles identifies Clement as an "apostle" and only Clement from among the Church Fathers is identified as acknowledging Mark's "apostlehood." In the last post from Stahlin the reference:
In Cod. Ottob. 167, fol. 147v (Pseudo-Dorotheus), according to Schermann, op. cit., it reads: “These are among the disciples of the Savior, as Clement relates in the fifth [book] of the Hypotyposeis, and as many of the apostles as I know: Paul, Barnabas, Mark, Titus, Timothy, Luke, and Silvanus."
Again, identifying Mark as an "apostle" is unique. Clement also calls Barnabas an apostle in his other writings. The likelihood that another Clement - i.e. Clement of Rome - was responsible for this "Mark the apostle" reference is unlikely. The Christians of Egypt at the time of Clement, no less the Christians of Egypt today, identify Mark as an apostle.