Inflorescence terminal or in the upper leaf axils; flowers in compact cymose clusters. Calyx 2-lipped; lower lip ± equally 4-lobed (with 2 lateral lobes and 1 median lobe pair), with lobes ± triangular, acute or acuminate; upper lip a single broad lobe scarcely longer than the lower lip. Corolla 2-lipped; tube variously bent to straight, longer than calyx, swollen at the base or produced into a spur on the upper side; lower lip entire; upper lip 3- or 4-lobed. Stamens 4, fertile; anthers ± circular, medifixed. Ovary deeply 4-lobed; style gynobasic; stigma 2-fid.
| | Key to the species | |
| 1 | Bracts not forming an imbricate crown-like covering at the apex of the inflorescence; leaves non-aromatic or pleasantly aromatic; pedicels spreading to ascending; mature calyx glabrous in throat | 2 |
| Bracts forming a conspicuous imbricate crown-like covering at the apex of the inflorescence; leaves strongly and unpleasantly aromatic when crushed; pedicels erect and appressed to the inflorescence axis; mature calyx densely hairy in throat. ('Plectranthus caninus group') | 11 |
| 2 | Bracts persistent at least until the fruiting stage; corolla white, sometimes pale mauve, with purple markings or freely speckled with purplish spots | 3 |
| Bracts soon caducous (in P. alloplectus, often persistent in flower, but not persistent in fruit); corolla more or less violet-blue
Back to 1 | 5 |
| 3 | Branches more or less glabrous to shortly hairy, with white, antrorse hairs; margins of leaves with 3–6 pairs of teeth | Plectranthus verticillatus |
| Branches densely covered with long hairs; margins of leaves with 7–15 pairs of teeth
Back to 2 | 4 |
| 4 | Upper calyx lobe erect; branches densely covered with maroon-purple multicelled hairs, hence branches purplish | Plectranthus ciliatus |
| Upper calyx lobe horizontal; branches densely covered with white multicelled hairs
Back to 3 | Plectranthus amboinicus |
| 5 | Leaves with margins finely crenate; lamina lanceolate to ovate (length to breadth ratio 2.2–4.2); bracts usually persistent in flower; stamens and style well-exserted by 1.5–4.5 mm beyond the lower corolla lip | Plectranthus alloplectus |
| Leaves with margins crenate to more or less toothed; lamina usually ovate to broad-ovate (length to breadth ratio mostly 1–2); bracts soon caducous; stamens and style scarcely, if at all, exceeding the lower corolla lip
Back to 2 | 6 |
| 6 | Branches sparsely covered with antrorse hairs | Plectranthus apreptus |
| Branches moderately to densely covered with spreading or more or less appressed and retrorse hairs, hairs never antrorse
Back to 5 | 7 |
| 7 | Margins of leaves with 10–23 pairs of teeth; lamina always densely hairy | 8 |
| Margins of leaves with 4–9 pairs of teeth, if 10–12 pairs of teeth then leaves sparsely hairy
Back to 6 | 9 |
| 8 | Hairs of branches of 2 types, always with gland-tipped more or less spreading hairs, and usually with spreading multicelled hairs | Plectranthus graveolens |
| Hairs of branches appressed and retrorse or branches more or less glabrous
Back to 7 | Plectranthus argentatus |
| 9 | Branches moderately to densely covered with long, more or less spreading multicelled hairs and glands absent | Plectranthus cremnus |
| Branches sparsely to densely covered with short, more or less appressed, retrorse hairs and glands always present
Back to 7 | 10 |
| 10 | Branches densely covered with shortly, more or less appressed retrorse hairs; lamina densely hairy, sessile glands not prominent | Plectranthus suaveolens |
| Branches sparsely covered with short retrorse hairs; lamina sparsely covered with antrorse hairs and sessile glands prominent
Back to 9 | Plectranthus parviflorus |
| 11 | Annual herb; inflorescence with short internodes such that flowers and fruits densely clustered; corolla 8–10 mm long | Plectranthus caninus |
| Perennial herb; inflorescence lax basally with at least 1 or 2 spaced fruiting whorls below the flowers; corolla at least 12 mm long
Back to 1 | 12 |
| 12 | Inflorescence 7–15 cm long, with 5–12 spaced fruiting whorls below the flowers; corolla 12–20 mm long | Plectranthus neochilus |
| Inflorescence usually 3–5 cm long, with 1 or 2, rarely more, spaced fruiting whorls below the flowers; corolla 20–25 mm long
Back to 11 | Plectranthus ornatus |
