>Suppose a name and description is published for Drosera rotundifolium L.,
>and this is pretty obviously a misspelling of D. rotundifolia L. Is the
>former name considered a nomen illigitimum?
No. The wrong Latin termination is an orthographic error because _Drosera_
is female. If the name was otherwise legitimate, only the suffix had to be
corrected, but type, status, author, and original publication date remained
unaltered (If the name was *cited* as "Drosera rotundifolium L.", it was a
wrong citation because LINNAEUS' name was _D.rotundifolia_, actually).
>Suppose the spelling change was done to provide a proper latin suffix?
The proper suffix is "-a", not "-um". Even if LINNAEUS had written
"rotundifolium" (which he has *not*), the name would have to be cited as if
LINNAEUS had written "rotundifolia" (which he *has*, actually).
A name is not illegitimate just because of orthographic errors (wrong
terminations are considered orthographic errors even if they are in fact
grammatical errors).
>If a Drosera rotundifolia (Walter) Engelm. & Coult. is described in a flora,
>would this also be a nomen illigitimum, or something else?
Here we have to distinguish principally two cases:
1. WALTER's "Taxon rotundifolium" (let us call the basionym of the new
combination like this for the sake of convenience) is based on the type of
_Drosera rotundifolia_ L. (at the times of WALTER, there were no stringent
rules for basionym citation, so that it would have to be assumed that
WALTER *meant* to derive his new combination from the Linnean name). Then,
the author citation is wrong because the basionym was indeed _Drosera
rotundifolia_ L. for both combinations. The name published by ENGELM. &
COULT. must be cited as _Drosera rotundifolia_ L., that by WALTER is "Taxon
rotundifolium" (L.) WALT. (being a nomenclatural synonym of _D.r._ L.).
BTW, "T.r." WALT. is automatically illegitimate because _D.rotundifolia_ is
the type species of the genus _Drosera_ L. (which has been published
earlier than "Taxon" in any event because it did appear in "Species
Plantarum", 1753), and all segregates from the Genus _Drosera_ which
include its type species *must* be called _Drosera_, again.
2. WALTER did not mean the Linnean plant exactly (irrespective of
taxonomic considerations), i.e. he described his "Taxon rotundifolium"
after a specimen different from LINNAEUS' type of _Drosera
rotundifolia_. In this case we have two possibilities:
2.1. The plants of WALTER and LINNAEUS do belong to the same taxon (at
least in the opinion of ENGELM. & COULT.). Then, "Taxon rotundifolium"
WALT. is a taxonomic synonym of _Drosera rotundifolia_ L., and Drosera
rotundifolia (WALT.) ENGELM. & COULT. is an (illegitimate) later homonym
(and at the same time a taxonomic synonym) of _D.rotundifolia_ L..
2.2. The plants do belong to different taxa of (or within) _Drosera_ (at
least in the opinion of ENGELM. & COULT.). Then, "Taxon rotundifolium"
WALT. is a taxonomic synonym of a species of _Drosera_ L., and Drosera
rotundifolia auct. non L.: (WALT.) ENGELM. & COULT. is an (illegitimate)
later homonym (but not a synonym) of _D.rotundifolia_ L.. This means two
further possibilities are left:
2.2.1. A valid name for "T.r." WALT. does exist in _Drosera_ already.
Fine, we use this name, and "T.r." WALT. and Drosera rotundifolia auct.
non L.: (WALT.) ENGELM. & COULT. are synonyms thereof (taxonomic if
types are different, nomenclatural if types are identical).
2.2.2. A valid name for it does not exist in _Drosera_. BINGO! You can give
the plant a new name of your choice within _Drosera_ (it should be a
legitimate one, however) because a nomen novum is needed. If WALTER was
kind enough to write a protologue for his "Taxon r." already, you do not
even need to do so. Just cite his protologue and type material, express
your sincere regrets (...;-)) that no valid name is available yet, list the
synonyms, and get the whole stuff published effectively (please send me a
reprint!).
A rather long answer to a short question (you did not really expect a short
answer from me, did you?).
Kind regards
Jan
PS: Do you write a monograph on _D.rotundifolia_? Wolfram Diester has done
so, already, and it will (hopefully) appear soon in the cp database!