And Tropicos may list only 'wild taxa'?
Probably.

Although IPNI is the best we have got, there are quite a few names not
listed by IPNI.
I thought IPNI is supposed to include everything in IK.

Of course if this 1980 publication were to happen today a proposal to
conserve Larix xeurolepis would be the thing to do
Why?

Since the two species do not naturally meet it is not a natural hybrid!
That explains it. So what do you call the name Larix xmarschlinsii?


Iris,
Central NY, Zone 5a, Sunset Zone 40
"The trouble with people is not that they don't know but that they know so much
that ain't so."
Josh Billings (Henry Wheeler Shaw), 1818-1885