> Why isn't there a genus _Lentibularia_ in the Lentibulariaceae?
The question is wrong. In fact, there is a genus Lentibularia
Seguier, based on Lentibularia major Gilib. (=_Utricularia vulgaris_
L., the type of the earlier, valid genus _Utricularia_ L.).
see (once again...):
http://www.hpl.hp.com/bot/cp_home
find "all, incl. synonyms"
search "Lentibularia"
Therefore, Lentibularia is a superfluous later homonym of
_Utricularia_. However, the first valid name for the family
containing _Utricularia_ & al. was derived from the generic name
Lentibularia (NB: it is not illegitimate to use superfluous names as
basionyms for taxa at other ranks; the names thus formed are valid if
legitimate). Therefore, e.g. Utriculariaceae is a later superfluous
homonym of Lentibulariaceae (as a Botanist, you should not be
surprised: cf. also Caprifoliaceae/_Lonicera_, Aquifoliaceae/_Ilex_,
Ebenaceae/_Diospyros_, Theaceae/_Camellia_, Fabaceae/_Vicia_,
Onagraceae/_Oenothera_, Balsaminaceae/_Impatiens_, Grossulariaceae/
_Ribes_, Caryophyllaceae/_Dianthus_, Himantandraceae/... if you
don't know this one look it up in a dictionary, it is really funny!).
Kind regards
Jan