| 1 | Leaves spirally arranged or partly (sub)opposite, sometimes subverticillate |
| 1' | Leaves distichous |
| 2 | Leafy twigs and lower surface of the lamina (at least partly) with (dark) brown hairs |
| 2' | Leafy twigs and lamina beneath with whitish hairs or indumentum absent |
| 3 | Stipules almost subulate and finely striate, often subpersistent, at least at the apices of leafy twigs |
| 3' | Stipules subovate to lanceolate and chartaceous, not striate, caducous |
| 4 | Base of the lamina cordate to subcordate |
| 4' | Base of the lamina cuneate to rounded |
| 5 | Stipules up to 1(-1.2) cm long; lamina often shorter than 10 cm |
| 5' | Stipules usually 1-2(-2.7) cm long; lamina often longer than 2 cm |
| 6 | Epidermis of the petiole persistent; waxy glands in the axils of both basal lateral veins |
| 6' | Epidermis of the petiole flaking off; waxy glands usually only in the axil of one of the basal lateral veins (or if in both, then unequal in size) |
| 7 | Stipules dark brown when dry; base of the lamina ± distinctly inequilateral and one side ± clearly decurrent and often slightly to clearly (minutely) auricled; often additional waxy glands in the axils of the 2nd to 4th pairs of lateral veins or the single waxy gland in such positions and not in the axils of the basal lateral veins |
| 7' | Stipules greenish to pale brown when dry; base of the lamina slightly or not unilaterally decurrent and the waxy glands, 1 (or 2), in the axils of the basal lateral veins |
| 8 | Leafy twigs and petioles entirely glabrous; epidermis of the petioles of the youngest leaves usually not yet flaking off |
| 8' | Leafy twigs and petioles minutely and sparsely hairy; epidermis of the petioles of the youngest leaves already flaking off |
