>Hmm, I had not thought of this... Fungi though, are often placed in their own
>kingdom, no?
Yes. And this is probably the best solution.
> And lichens are usually labelled as cryptogams, even though they
>are a combination of a fungus (kingdom Fungi) and an alga (kingdom Protista)!
This can only rely on their (very) superficial similarity with mosses.
Well, cyanobacteria (procaryotes!) have also been classified as algae etc.
in the past.
Anyway, cryptogams (all "plants" which are not phanerogams) have not always
been a clearly defined taxon, and in the broadest (historical) sense the
group is obviously paraphyletic. I just want to stress that fungi (and also
lichens) should not be classified as plants as long as any distinction
between animals and plants is retained (the inclusion of fungi and
exclusion of animals would make "plants sensu lato" a paraphyletic group).
Kind regards
Jan