I just finished updating and verifying my
transcription of some of the herbal section, and
ran this count on unique characters. Some folios
hit 24 characters, but if wierdos were removed
(those that appear only once and are very likely
an embellishment or mistake for a known
character), we have a high-end count of 23
characters for the herbal section. It's still
possible that the actual count is 24, since these
passages are generally very short.
This count is in line with a western latin
alphabet or table. Many tables exist from the
15th and 16th centuries that place Greek, Hebrew
and Latin alphabets against each other in
sequences of 23. English and Latin had no J, no
Y, and no Z, and the alphabet is extended to 24 by
the addition of the "Y", taken from the Greek
alphabet.