From what little I know of plant biology/nomenclature, this plant shouldn't
exist as a distinct species.

It is not a distinct species; it is a hybrid. The full name is xPyracomeles
vilmorinii. (The "x" in front of the name is actually a times sign.) I found a
complete entry in the Hillier manual. The parents are Pyracantha
crenato-serrata x Osteomeles anthyllidifolia var. subrotunda. The leaves follow
the habit of the Osteomeles parent, being partly pinnate & partly lobed. Also
according to Hillier, it does have fruits. Apparently some specimens do, &
perhaps some are sterile. It originated in cultivation somewhere in France
before 1922. It is listed on the Web as being hardy in Zones 6 to 9. It is also
reported to be resistant to salt spray and air pollution. Apparently there are
no named cultivars. It must be fairly easy to grow from seed, or difficult from
cuttings.

Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)