Ed, you asked what is meant by "black-marked". That is a direct quote from Dan Heims and I'm not precisely sure what he means. I can only suppose that the scapes and/or petioles of the plant from Japan had some dark speckles on them.
From the reading I've done, there's some variation in the intensity of red petiole color in native populations of longipes var. latifolia (see Mark Zilis' Field Guide to Hostas, page 183), which is closely related to rupifraga. However, according to Zilis, rupifraga itself (the true form) has green petioles, not red (The Hostapedia, page 800). If that is the case, it indicates that the specimen obtained from Japan by Terra Nova (which was instrumental in the development of 'Purple Heart') was actually longipes var. latifolia, not rupifraga.
This is further supported by W. George Schmid in his most recent "Species Update" posted on the Hosta Library. He says rupifraga is closely related to longipes var. latifolia, but is not identical and should remain classified as a separate taxon. Schmid states that rupifraga, however, has seagreen petioles, not red.
Ed, you mentioned you've seen a rupifraga with very dark scapes. Can you elaborate on that? It sounds like most of the plants sold as rupifraga in the U.S. are actually longipes var. latifolia. Schmid says that the true form of rupifraga has green scapes which are purple-dotted in the lower half.