Hi Chris:
AmphibiaWeb has some interesting information about X. muelleri:
AmphibiaWeb - Xenopus muelleri
Would love to see pictures of your frogs
In the wild, there are two distinct species groups: muelleri "east" and muelleri "west". Both ranges are discontinuous, meaning that the groups are geographically separated. Some scientists think that muelleri "west" (from western Africa) should be a distinct species, Xenopus alboventralis, while muelleri "east" (from eastern, central and southern Africa) retain the current scientific name. The species list from the web site you mentioned is a bit outdated. There are now 18 species of Xenopus and 2 species of Silurana (sister taxon to Xenopus). All of the X. laevis subspecies have been moved to species level or merged into X. laevis. Thanks to DNA analysis, I believe there will be several new species described soon.