It' a bit more complicated. The following is what I believe this plant represents:
In the early days of Sempervivum taxonomy (mid 1800s), when natural hybrids were found between two species, botanists & taxonomists would give a latinized "group name" for that cross. In some cases, with certain genus of plants, even man-made crosses between two species were frequently given latinized group names. That practice is no longer allowed, there is an International Code of Nomenclature that evolved since the 1700s, with rules for how plants can be named.
International Code of Nomenclature:
https://en.wikipedia.org/wiki/...
The two names "piloseum" and "pilioseum" where never published names, they mostly likely represent spelling corruptions of very old names, there are two old published species names from the mid 1800s that sound similar:
Sempervivum pilosellum &
Sempervivum piliferum. Today both are synonyms of
Sempervivum fauconnettii, a valid species, see this Catalog of Life record for S. fauconnettii, there are 30 synonyms for this accepted species due to the early naming proliferation.
http://www.catalogueoflife.org...
It gets complicated, the name Sempervivum fauconnettii is often written
Sempervivum x fauconnettii, the
"x" denotes a latinized name for a natural hybrid between two species, in this case
arachnoideum x tectorum. Arising from the ashes of nearly two centuries of taxonomic quagmire, a singular
S. fauconnettii is recognized.
Some of these old names have persisted in nurseries and horticulture, often with a misspelling, garbled, or meaningless name. Often these old names get written with single quotation marks and first-letter capitalization, as if a cultivar.
Back to the original question, I believe the names "piloseum" and "pilioseum" probably derived from reference to the old synonym S. pilosellum, with misspelling having crept in.
The NGA Semp DB does not have any hybridizer for their plant record for 'Pilioseum', which signals that it's a name in doubt and came to be from the nursery trade.
Hen and Chicks (Sempervivum 'Pilioseum')
If you have read this far down this post I will give you an acorn:
As a further example of these old persistent synonyms that morphed into cultivar names, here's the record for
Sempervivum x funckii, one that still uses the outdated latinized "group name" and actually cites the cross as natural hybrid of
S. arachnoideum x S. montanum x S. tectorum, named in 1832!
Okay, how many acorns do I need to give away?
Big Groan.
