>Can someone tell me what makes a new name a valid name?
The rules that have to be obeyed for a plant name to become valid are
summarized in the ICBN (International Code of Botanical Nomenclature).
These (rather numerous) rules are aiming at stability and reliability of
names. (The rules themselves are not overly stable but it is at least hoped
that the emerging nomenclature will become rather stable some fine
day...;-))
>Must specimens be depositied in a herbarium, in order to be valid?
Yes, all scientific plant names at the rank of species or below must be
based on durable specimens (nomenclatural types) which should be kept at
responsible/ durable institutions.
Furthermore, a name of a taxon new to science must be validated by an
effectively published description or diagnosis in Latin (the protologue),
rendering identification of the type specimen (and other specimens
belonging to the taxon) with the name possible. Scientific plant names are
Latin (irrespective of origin).
The names "N.mikei" and "N.xiphioides" apparently lack both, protologue and
type designation (at least in the sphere of cps, where "N." is supposed to
mean _Nepenthes_). Thus, they are nomina nuda ("naked" names) and plainly
invalid, i.e. these should not be used.
Besides scientific nomenclature which applies to naturally occurring taxa,
there is a separate nomenclature for cultivated plants following different
rules (International Code for the Nomenclature of Cultivated Plants,
ICNCP). These cultivated varieties or culivars have to result from some
kind of breeding. Names of these plants consist of the scientific name(s)
of the wild plants they were bred from (e.g. a bastard formula) and an
appended cultivar name which *must not* be Latin (in order to prevent
confusion with scientific names).
Cultivars must be represented by living clones of the plant (=one
individual) originally selected and described (not necessarily in Latin but
also to be published effectively). Thus, the existence of a cultivar and
its name ends with the life of its last clone whereas scientific names last
"forever" (or until the next taxonomic revision ;-)).
At least _Drosera rotundifolia_ L. and _Pinguicula vulgaris_ L. retained
these names unchanged since May 1st, 1753 ("Species Plantarum", 1.Ed. by
Carolus LINNAEUS, the beginning of modern scientific plant nomenclature).
Kind regards
Jan