In article ,
Rusty_Hinge wrote:

One of the disagreements between horticulturalists and
botanists was whether Malus and Pyrus should be one genus or two.
The former claimed two, because they are graft-incompatible.

I don't know where the Craetagus/Pyracantha/etc. group fits in; it
might be closer to Pyrus.

Might Pyracantha/Pyrus be a clue?

No. Pyrus comes from the latin for a pear, and pyracantha from
the Greek for fire+thorn. Yes, I had to look those up :-)


Regards,
Nick Maclaren.