| 1 | Leaves densely dark-dotted on underside. Stipules intrapetiolarly connate |
| 1' | Leaves not densely dark-dotted on underside, sometimes pitted on the underside where hairs have been. Stipules connate or free |
| 2 | Leaves without basal glands. Petals 6-7.5 mm long |
| 2' | Leaves with 2 basal glands, usually on petiole, rarely in margin. Petals up to 4 mm long |
| 3 | Basal glands on the petiole |
| 3' | Basal glands on the leaf surface, sometimes in a contraction of the leaf-base, sometimes absent |
| 4 | Racemes without leaves on the basal part of the rachis |
| 4' | Racemes with 2 leaves under the flowers |
| 5 | Leaves with 2 or more basal glands and with usually many additional glands in two rows parallel with the midrib. Petals 3-8 times as long as sepals. |
| 5' | Additional glands, when present, not distinctly in two rows parallel with the midrib. Petals at most twice as long as sepals |
| 6 | Basal leaf-glands deeply hollowed, distinctly bulging above |
| 6' | Basal leaf-glands flat or only slightly hollowed and hardly bulging above, or in all leaves absent |
| 7 | Racemes solitary and simple. Basal leaf-glands in blade proper |
| 7' | Racemes in bundles (short shoots without or with terminal bud) or truly compound. Basal glands sometimes in contraction of the leaf-base |
| 8 | Stipules free |
| 8' | Stipules with the bases of their midribs intrapetiolarly connate |
| 9 | Stamens 50 or more |
| 9' | Stamens not more than c. 50 |
| 10 | Ovary densely hairy |
| 10' | Ovary glabrous or with few hairs |
| 11 | Stamens 20-40 |
| 11' | Stamens 50-85 |
| 12 | Stamens 50 or more. Inflorescences 3.5-11 cm long |
| 12' | Stamens not more than 50 |
| 13 | Leaves with 5-9 pairs of nerves. Inflorescences up to 1.5(-4) cm long. Ovary densely hairy |
| 13' | Leaves with 8-12 pairs of nerves. Inflorescences up to 3.5 cm long. Ovary sparsely hairy to glabrous. See alse Prunus A with inflorescences up to 10 cm long |
| 14 | Racemes in bundles (short shoots with or without terminal bud) or truly compound |
| 14' | Racemes solitary and simple |
| 15 | Stipules intrapetiolarly connate. Inflorescence a compound raceme, 5-10 cm long, with 1-5 laterals. Stamens 50-80. Ovary glabrous or with few hairs |
| 15' | Stipules free |
| 16 | Ovary glabrous or with few hairs. Basal leaf-glands absent. Stipules usually with one large, hollowed gland outside. Stamens 15-40 |
| 16' | Ovary densely hairy |
| 17 | Perianth differentiated as triangular sepals and elliptic to obovate petals. Stamens 35-45 |
| 17' | Perianth segments subequal |
| 18 | Stamens 10-20 |
| 18' | Stamens 10-50(-60) |
| 19 | Ovary densely hairy |
| 19' | Ovary glabrous or with few hairs. N.B.: Ovary unknown in Prunus D, fruits sparsely hairy. |
| 20 | Stipules intrapetiolarly connate |
| 20' | Stipules free |
| 21 | Racemes short (-1 cm), peduncle almost none, pedicels up to 2 mm |
| 21' | Racemes and pedicels longer |
| 22 | Leaves thin-papyraceous |
| 22' | Leaves coriaceous, stiff |
| 23 | Leaves usually with 2 basal glands. Stipules with 1-3 flat or pustular glands on the outside. Racemes with up to 6 flowers. Flowers small (hypanthium 1.5 mm long, perianth segments less than 1 mm long) |
| 23' | Leaves usually without basal glands. Stipules with glands in margin but not on surface. Racemes with up to 10 flowers. Flowers slightly larger (hypanthium 2-3 mm, perianth segments 1-1.5 mm long) |
| 24 | Leaves herbaceous or papyraceous |
| 24' | Leaves coriaceous, often hard and thick |
| 25 | Racemes short, never over 5 cm long |
| 25' | Racemes (at least some) longer than 5 cm |
| 26 | Leaves thin-herbaceous to papyraceous |
| 26' | Leaves herbaceous |
| 27 | Perianth segments subequal, 7-15 |
| 27' | Perianth differentiated as sepals and petals. N.B.: See also the insufficientiy known P. odorata. |
| 28 | Leaves herbaceous to papyraceous |
| 28' | Leaves coriaceous, stiff |
| 29 | Racemes up to 3 cm long |
| 29' | Racemes longer than 3 cm |
| 30 | Leaves papyraceous |
| 30' | Leaves herbaceous |
| 31 | Perianth segments subequal |
| 31' | Perianth differentiated as sepals and petals, but equal in size |
| 32 | Leaves hairy when young, indumentum still present when mature. Stipules often connate |
| 32' | Leaves glabrous or practically so when mature |
| 33 | Stipules often connate. Racemes up to c. 30 cm long. |
| 33' | Stipules free. Racemes not longer than 10 cm |
| 34 | Racemes shorter than 3 cm |
| 34' | Racemes longer than 3 cm |
