ID-ing Rhododendron tomentosum vs Rhododendron groenlandicum on iNat?

How does a field botanist distinguish between R. tomentosum and R. groenlandicum? What characteristics must be visible in iNat photos for a reviewer to distinguish between the two? Or is the ID on iNat based purely on geography? Thanks in advance for helpful tips.

from the key at http://floranorthamerica.org/Rhododendron:

  • R. tomentosum:
    Pedicels with at least a few ferruginous, elongated, eglandular hairs, covered with ferruginous, long-crisped, unicellular and/or peltate scales, sometimes also with long-stalked, multicellular, glandular hairs; stamens 10; adaxial leaf surfaces with veins deeply impressed, abaxial with ferruginous, crisped hairs (usually more abundant on midrib, which is usually visible), sometimes forming dense, ± uniform mat; leaf blades ± linear (often much longer than wide); fruits borne on sharply recurved pedicels.

  • R. groenlandicum:
    Pedicels with unicellular and/or glandular-peltate scales and sometimes ferruginous, long-crisped, multicellular hairs; stamens usually 5-10; adaxial leaf surfaces with veins usually not impressed, abaxial with ferruginous, crisped hairs forming usually dense, ± even covering, (usually concealing midvein); leaf blades ovate-lanceolate, sometimes narrowly elliptic to linear; fruits borne on broadly recurved pedicels.

Thank you.