I have the two books you mention, and I looked through them and got very confused. P. holosericea is in the decaloba subgenus - according to the book, most of these passionvines have a chromosome number of n=6. P. holosericea is the only one mentioned as having a n=7 count. P. holosericea also isn't mentioned as being a parent of a hybrid in any list I can find, but, of course, that doesn't mean a hybrid doesn't exist. It looks to me like you'll have a hard time finding another passi to "mate" with your p. holosericea - without the same chromosome count, it won't happen.
By the way, have you ever found any caterpillars on yours? The information I read about your passi is that it's very hairy, and I've read in another book that some passionvines have recurved hairs that kill caterpillars, so I didn't consider buying it for that reason.
The pictures I've seen of the flower look beautiful, though!
Sherry

Listen to MacDougal. His information is more recent and he's gone through the passiflora species reclassifying them using genetic information as opposed to strictly physical characteristics. However, sometimes even experts can't predict some results, so try them both! You never know what might actually work. Weirder things have crossed that scientists said would never work. (Luther Burbank made lots of experimental crosses like raspberries with strawberries, which never fruited, but spread by both runners and underground stolons.)

Here is a link that might be useful: Luther Burbank

I'm lucky to have 2 things blooming at the same time.
Just like a Dane & a Chihuahua probably not getting together so well, if you try to cross caerulea with herbertiana that's probably not going to work either.
With that said, if holosericea is a decaloba, you may have luck with other decalobas.
The operative word here is *may*.. Even if you have 2 of the same plant (both grown from seed) one or the other (or both) may be infertile.

Try it. If one cross doesn't work, try something else. Keep trying. When I lived in Chico I'd have 3 or 4 blooming each day so every lunch I'd go out there & play Cupid.. Sometimes they worked, sometimes not.
And sometimes when they do work & you plant the seeds & manage to get the prodigy to flower... It's about as unexciting as a mayonnaise sandwich.

But keep trying. Edison said ""We now know a thousand ways not to build a light bulb". (after failing thousands of times to get the filament right) Thus even a failure is a result.