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The other is more involved. By choosing an appropriate set of criteria
which is applied to *all* the species in a genus, the entire concept of
a key is instantly changed. You see, suppose I wished to key out the
non-anthocyanin-free _Sarracenia_ (recognizing no taxa beyond species).
And suppose my criteria was as follows (using 1=yes)
10000 Flowers are red
01000 phyllodia formed
00100 phyllodia sharply recurved
00010 distinct white fenestrations on upper pitcher
00001 tall erect tubular pitcher on mature plant
Then I would classify the 8 species of _Sarracenia_ as...
00001=S.alata
00011=S.minor
01001=S.flava
01101=S.oreophila
10000=S.purpurea
10010=S.psittacina
10001=S.rubra
11011=S.leucophylla
This method is interesting in that we see things we might not have noticed
before. That is, S.minor is remarkably similar to S.alata on my scheme,
while S.leucophylla is equally distinct from S.alata and S.purpurea.
I suppose you could go nuts and use the *not* operator to take the inverse
of a species, and in fact I see that not-S.oreophila is S.psittacina.
This is very silly, although not too unrelated to cladistics?
The main difference is that while normal botanical keys have the most important
distinctions keyed out first, and then you look at the details, this system
has no required order. Of course, it means all features must be examined. There
are strengths and weaknesses to this method, I guess.
Barry