Prometheum systematics

Prometheum (A.Berger) H.Ohba (J. Fac. Sci. Univ. Tokyo, Bot. 12(4): 168 (1978))
is a small genus formerly included in Rosularia.
According to Mr.Urs Eggli: Illustrated handbook of succulent plants:Crassulaceae, there are 8 species in genus:

P. aizoon (Fenzl) 't Hart (in H. 't Hart & U. Eggli (eds.), Evol. & Syst. Crassulac. 170 (1995))
P. chrysanthum (Boiss.) 't Hart (in H. 't Hart & U. Eggli (eds.), Evol. & Syst. Crassulac. 170 (1995))
P. muratdaghense (Kit Tan) 't Hart (Succulenta 78(5): 236 (1999))
P. pilosum (M.Bieb.) H.Ohba (J. Fac. Sci. Univ. Tokyo, Bot. 12(4): 169 (1978))
P. rechingeri (C.-A.Jansson) 't Hart (in H. 't Hart & U. Eggli (eds.), Evol. & Syst. Crassulac. 170 (1995))
P. sempervivoides (M.Bieb.) H.Ohba (J. Fac. Sci. Univ. Tokyo, Bot. 12(4): 169 (1978))
P. serpentinicum (Werderm.) 't Hart (in H. 't Hart & U. Eggli (eds.), Evol. & Syst. Crassulac. 170 (1995))
P. serpentinicum (Werderm.) 't Hart var. giganteum (Eggli) 't Hart (Succulenta 78(5): 236 (1999))
P. serpentinicum (Werderm.) 't Hart var. serpentinicum
P. tymphaeum (Quézel & Contandr.) 't Hart (in H. 't Hart & U. Eggli (eds.), Evol. & Syst. Crassulac. 170 (1995))

also according to The International Plant Names Index (www.ipni.org) one more subspecies is mentioned:
P. chrysanthum (Boiss.) 't Hart subsp. uludaghense Kaynak, Yılmaz & Daşkın (Ann. Bot. Fenn. 46(5): 456 (- 458; fig. 1, map). 2009 [30 Oct 2009])
and a great article about the description: http://www.sekj.org/PDF/anb46-free/anb46-456.pdf

Sources:
1. Urs Eggli: Illustrated handbook of succulent plants:Crassulaceae

2. The International Plant Names Index:
http://www.ipni.org/ipni/advPlantNameSearch.do;jsessionid=68E584FD3495028DCAF04805D65C595E?find_family=&find_genus=Prometheum&find_species=&find_infrafamily=&find_infragenus=&find_infraspecies=&find_authorAbbrev=&find_includePublicationAuthors=on&find_includePublicationAuthors=off&find_includeBasionymAuthors=on&find_includeBasionymAuthors=off&find_publicationTitle=&find_isAPNIRecord=on&find_isAPNIRecord=false&find_isGCIRecord=on&find_isGCIRecord=false&find_isIKRecord=on&find_isIKRecord=false&find_rankToReturn=all&output_format=normal&find_sortByFamily=on&find_sortByFamily=off&query_type=by_query&back_page=plantsearch

3. http://www.sekj.org/PDF/anb46-free/anb46-456.pdf

There are more synonyms for almost every species of Prometheum but many of those synonyms are historical and they include
genera Sedum, Ubilicus, Cotyledon, Pseudorosularia...
I won't write all the synonyms, but only the ones that are still today oftenly used and mistaken.

Most of the names include name Rosularia for the species from genus Prometheum. That is understandable if
we know that this was one genus until recently.
Name Sedum is today still oftenly used for some species from this genus.

P. aizoon (Fenzl) 't Hart (in H. 't Hart & U. Eggli (eds.), Evol. & Syst. Crassulac. 170 (1995))
= Rosularia aizoon A.Berger (Nat. Pflanzenfam., ed. 2 [Engler & Prantl] xviii a. 466 (1930))
= Rosularia pallida (Schott & Kotschy) Stapf (Bot. Mag. 149: sub t. 8985, in obs. 1923 )
= Rosularia tauricola Kit Tan (Notes Roy. Bot. Gard. Edinburgh 45(2): 365. 1989 [1988 publ. 1989])

P. chrysanthum (Boiss.) 't Hart (in H. 't Hart & U. Eggli (eds.), Evol. & Syst. Crassulac. 170 (1995))
= Rosularia chrysantha (Boiss.) Takht. (Izvest. Acad. Sci. Armen. SSR vi. No. 5, 67 (1953))

P. muratdaghense (Kit Tan) 't Hart (Succulenta 78(5): 236 (1999))
= Rosularia muratdaghensis Kit Tan (Notes Roy. Bot. Gard. Edinburgh 45(2): 367. 1989 [1988 publ. 1989])

P. pilosum (M.Bieb.) H.Ohba (J. Fac. Sci. Univ. Tokyo, Bot. 12(4): 169 (1978))
= Rosularia pilosa (M.Bieb.) Boriss. (Fl. URSS ix. 117 (1939))
= Sedum pilosum M. von Bieberstein (Fl. Taur.-Caucas. 1: 352. 1808) - this name is still very often in culture

P. rechingeri (C.-A.Jansson) 't Hart (in H. 't Hart & U. Eggli (eds.), Evol. & Syst. Crassulac. 170 (1995))
= Rosularia rechingeri C.-A.Jansson (Acta Horti Gothob. xxviii. 182 (1966))

P. sempervivoides (M.Bieb.) H.Ohba (J. Fac. Sci. Univ. Tokyo, Bot. 12(4): 169 (1978))
= Sedum sempervivoides Fisch. ex M.Bieb. (Fl. Taur.-Caucas. 3: 313. [Dec 1819 or early 1820]) - mostly used name in culture
= Rosularia sempervivoides (Fisch. ex M.Bieb.) Boriss. (Fl. URSS ix. 118 (1939))

P. serpentinicum (Werderm.) 't Hart (in H. 't Hart & U. Eggli (eds.), Evol. & Syst. Crassulac. 170 (1995))
= Rosularia serpentinica (Werderm.) Muirhead (Fl. Turkey 4: 222 (1972))

P. serpentinicum (Werderm.) 't Hart var. serpentinicum
= Rosularia serpentinica (Werderm.) Muirhead var. serpentinica

P. serpentinicum (Werderm.) 't Hart var. giganteum (Eggli) 't Hart (Succulenta 78(5): 236 (1999))
= Rosularia serpentinica (Werderm.) Muirhead var. gigantea Eggli (Kakt. And. Sukk. 386: 137 (1987))

P. tymphaeum (Quézel & Contandr.) 't Hart (in H. 't Hart & U. Eggli (eds.), Evol. & Syst. Crassulac. 170 (1995))
= Sedum tymphaeum Quézel & Contandr. (Candollea xx. 62 (1965) (tympheum), designat. typi omissa; et in Taxon, xvi.240 (1967), cum typo.)
- some other sources treat this synonym as an accepted name ( http://www.theplantlist.org/tpl/record/kew-2488997)
but Mr. Eggli explains that this species can hybridize with P. pilosum and P. sempervivoides


Sources:
1. Urs Eggli: Illustrated handbook of succulent plants:Crassulaceae

2. http://www.ipni.org/ipni/advPlantNameSearch.do;jsessionid=68E584FD3495028DCAF04805D65C595E?find_family=&find_genus=Rosularia&find_species=&find_infrafamily=&find_infragenus=&find_infraspecies=&find_authorAbbrev=&find_includePublicationAuthors=on&find_includePublicationAuthors=off&find_includeBasionymAuthors=on&find_includeBasionymAuthors=off&find_publicationTitle=&find_isAPNIRecord=on&find_isAPNIRecord=false&find_isGCIRecord=on&find_isGCIRecord=false&find_isIKRecord=on&find_isIKRecord=false&find_rankToReturn=all&output_format=normal&find_sortByFamily=on&find_sortByFamily=off&query_type=by_query&back_page=plantsearch

3. http://www.theplantlist.org/tpl/search?q=Prometheum

In some global name lists
http://www.tropicos.org/NameSearch.aspx?name=Prometheum&commonname=
http://www.theplantlist.org/tpl/search?q=Prometheum
http://gni.globalnames.org/name_strings?commit=Search&page=2&search_term=Prometheum

I've found 2 more names:
Prometheum silvana F. Barros & Cath.
Prometheum sincorana V.P. Castro & Campacci

This was very strange because I couldn't find any more explanations or descriptions about those species.

For both species I've found orchid with similar name and with the same authors
who described this species. These orchids are named:
Promenaea silvana F.Barros & Cath
Promenaea sincorana P.Castro & Campacci

so I would say that this ''new Prometheum species'' are created as a mistake in writing.

Prometheum silvana F. Barros & Cath (Crassulaceae) = Promenaea silvana F.Barros & Cath (Orchidaceae)
Prometheum sincorana V.P. Castro & Campacci (Crassulaceae) = Promenaea sincorana P.Castro & Campacci (Orchidaceae)