And Tropicos may list only 'wild taxa'?

Iris Cohen schreef
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.

+ + +
IPNI does include everything in the IK, as well as from some other indexes.
However the IK is far from complete. For the regular heavy user it is not at
all uncommon to find something that is not in the IK
+ + +

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

+ + +
There are a lot of people fed up with name changes for nomenclatural
reasons. There was so much pressure that in 1988 even the Americans
relented, and it became possible to conserve names of species.
Since Larix x eurolepis is a name of a taxon of considerable economic
importance it would have been a shoo-in to be conserved.
+ + +

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
+ + +
The name of a hybrid?
PvR