Flowers axillary or in terminal botryoid or paniculate inflorescences; bracteoles 2, inserted near middle of pedicel to just below calyx. Calyx 2-lipped. Corolla 2-lipped, purple-blue to white (section Prostanthera), or ± red, sometimes metallic blue-red, rarely yellowish (section Klanderia); tube usually expanded in throat; lower lip usually spreading (particularly section Prostanthera), 3-lobed; upper lip erect or extended forward (section Klanderia), emarginate or 2-lobed. Stamens 4; anthers 2-locular, introrse, with connective often elongated into an appendage. Ovary 4-lobed; style terminal (not gynobasic), but inserted between ovary lobes; stigma 2-fid.
Fruiting calyx often enlarged and frequently conspicuously coloured. Mericarps ± obovoid.
This genus is currently under revision, and several species complexes are unresolved. Natural hybrids occur between several species and most species appear to be capable of hybridizing when in cultivation. Key from: Barry J. Conn and Trevor C. Wilson (2015) Two new species of Prostanthera (Lamiaceae) in New South Wales. Telopea 18: 463-474. The NSW material of Prostanthera melissifolia, typically a Victorian species, either represents a disjunct population, or it is a distinct taxon from the Victorian material and is not included in the key.
| | Key to the species | |
| 1 | Calyx lobes unequal in length; corolla mauve to white, with tube short, broad apically; lower lobe longer and more spreading than the erect upper lobes; fruit enclosed by inward folded lower calyx lobe; upper calyx lobe usually recurved | 2 |
| Calyx lobes ± equal in length; corolla red to pink, or bluish to yellowish green (never mauve to white) with tube long, slightly expanded apically; median upper and lower lobes ± equal; fruit not enclosed by the calyx lobes | 54 |
| 2 | Flowers arranged in bracteose inflorescences (appearing terminal), the floral leaves all or mostly reduced to membranous, usually caducous prophylls | 3 |
| Flowers arranged in leafy botryoids (appearing axillary), with subtending leaves (of flowers) similar to and sometimes smaller than the leaves on the branchlets
Back to 1 | 26 |
| 3 | Leaves with margin entire | 4 |
| Leaves with margin variously toothed
Back to 2 | 16 |
| 4 | Branches glabrous, except for nodes and/or lateral ridges | 5 |
| Branches sparsely to densely hairy
Back to 3 | 6 |
| 5 | Branches with hairs restricted to nodes; leaves narrowly ovate to linear, usually less than 40 mm long, less than 5 mm wide, petiole absent or up to 2 mm long | Prostanthera linearis |
| Branches with hairs restricted to lateral ridges and nodes; leaves ovate, 40–70 mm long, 12–26 mm wide, petiole 5–12 mm long
Back to 4 | Prostanthera petraea |
| 6 | Anther appendages as long as anther locule | 7 |
| Anther appendages absent or less than half the anther locule length
Back to 4 | 8 |
| 7 | Leaf lamina >8 mm wide, length to width ratio <2; leaf margin usually with widely spaced, shallow teeth; flowers clustered in racemiform conflorescences; calyx glabrous | Prostanthera prunelloides |
| Leaf lamina <7 mm wide, length to width ratio >2; leaf margin entire; flowers clustered in dense head-like bracteose botryoidal conflorescences; calyx hairy
Back to 6 | Prostanthera conniana |
| 8 | Leaves with lamina very broadly ovate or almost circular | 9 |
| Leaves with lamina ovate or narrowly ovate
Back to 6 | 10 |
| 9 | Leaves grey-green; lamina very broadly ovate, base truncate; prophylls reduced, soon caducous (in flower); anthers separated during anthesis | Prostanthera cruciflora |
| Leaves dark to light green; lamina almost circular, base cuneate; prophylls conspicuous and persistent; anthers held in pairs within corolla tube
Back to 8 | Prostanthera rotundifolia |
| 10 | Leaf margins flat, leaves glabrous | 11 |
| Leaf margins recurved, leaves hairy
Back to 8 | 14 |
| 11 | Calyx densely hairy; leaves with lamina narrowly ovate | Prostanthera discolor |
| Calyx glabrous or almost so; leaves with lamina ovate
Back to 10 | 12 |
| 12 | Largest Leaves at least 2.5 cm long | Prostanthera ovalifolia |
| Largest leaves less than 2.5 cm long
Back to 11 | 13 |
| 13 | Indumentum consisting of short, curled hairs | Prostanthera cineolifera |
| Indumentum consisting of short, straight hairs
Back to 12 | Prostanthera lanceolata |
| 14 | Leaves 8–13 mm long, ovate but appearing rhombic when margins become excessively recurved after drying | Prostanthera stricta |
| Leaves 10–30 mm long, narrow ovate to ovate, but never ovate when shorter than 15 mm long
Back to 10 | 15 |
| 15 | Leaves 1.5–6 mm wide, margins often strongly revolute | Prostanthera hirtula |
| Leaves 6–10 mm wide, margins weakly recurved
Back to 14 | Prostanthera makinsonii |
| 16 | Leaves flat | 17 |
| Leaves with margin recurved or revolute
Back to 3 | 24 |
| 17 | Leaves deeply toothed with teeth rounded and directed forward; branches and leaves moderately to densely covered with distinct, long (1–1.5 mm long), ± spreading hairs | Prostanthera askania |
| Leaves shortly toothed; branches and/or leaves glabrous or if hairy then hairs short (less than 1 mm long) and curled
Back to 16 | 18 |
| 18 | Flowers white, or with pale wash of mauve, spots in throat of corolla, inside and outside of corolla hairy, anther appendage at least as long as anther locule | 19 |
| Flowers deep mauve, corolla markings absent, inside corolla not hairy, anther appendage shorter than locule or absent
Back to 17 | 20 |
| 19 | Petiole 4–8 mm long, lamina width 20–30 mm | Prostanthera lasianthos |
| Petiole 2–5 mm long, lamina width 4–5 mm
Back to 18 | Prostanthera tallowa |
| 20 | Leaves with lamina almost circular, base cuneate | Prostanthera rotundifolia |
| Leaves with lamina ovate to narrowly ovate
Back to 18 | 21 |
| 21 | Leaves with usually 3 teeth on each side of margin, older branches sometimes inserted at 90 degree angle | Prostanthera incisa |
| Leaves entire or with teeth, older branches inserted at less than 90 degree angle
Back to 20 | 22 |
| 22 | Calyx densely hairy; leaves with lamina narrowly ovate to oblong | Prostanthera discolor |
| Calyx glabrous or almost so; leaves with lamina ovate
Back to 21 | 23 |
| 23 | Branchlets hairy or with hairs at least restricted to decussate grooves | Prostanthera ovalifolia |
| Branchlets glabrous
Back to 22 | Prostanthera caerulea |
| 24 | Leaves glabrous, except for a few short stiff hairs near margin leaf margins | Prostanthera denticulata |
| Leaves hairy on both surfaces, margins crenate
Back to 16 | 25 |
| 25 | Leaves c. 5(–7) mm long, with short, stiff hairs | Prostanthera violacea |
| Leaves (8–) c. 10 mm long, finely and densely hairy
Back to 24 | Prostanthera incana |
| 26 | Leaves convex or with margin recurved to revolute | 27 |
| Leaves flat or margin conduplicate or incurved
Back to 2 | 43 |
| 27 | Leaves ± terete, oblong, linear, or deeply 3- or 5-fid (in Prostanthera staurophylla) with lobes linear | 28 |
| Leaves narrowly ovate to broadly ovate, ± circular or obovate, never lobed
Back to 26 | 34 |
| 28 | Leaves ± terete; margin entire or deeply 3- or 5-fid and lobes 3–5 mm long; prophylls not persistent, c. 0.5 mm long; branches densely covered with shortly curled hairs | 29 |
| Leaves oblong, narrowly oblong or linear; margin entire; prophylls persistent, at least 1.6 mm long; branches glabrous between nodes or sparsely to densely covered with ± straight, spreading to appressed hairs
Back to 27 | 30 |
| 29 | Adult leaves grey-green, strongly revolute such that lamina appears subterete, 5–16 mm long; margin entire or deeply 2- or 3-fid, densely covered with sessile glands; branches densely covered with sessile glands; anther appendage absent or minute | Prostanthera teretifolia |
| Adult leaves lime- to dark green, oblong or linear, if lobed, then lobes linear, never terete-like, 2–9 mm long, deeply (2–)3(–7)-fid, with scattered glandular hairs adaxially; branches densely covered with podiate glandular hairs; anther appendage present
Back to 28 | Prostanthera staurophylla |
| 30 | Branches 4-ridged (often winged), glabrous, except for nodes | 31 |
| Branches not 4-ridged, hairy throughout
Back to 28 | 32 |
| 31 | Nodes and bases of short shoot distinctly hairy; flower approximately 4 times longer than pedicel; prophylls opposite; adaxial calyx lobe apiculate and approximately equal in size to abaxial calyx lobe | Prostanthera linearis |
| Nodes with a few short hairs present; pedicels as long as or up to 2 times as long as the flower; prophylls ± subopposite; adaxial calyx lobe rounded, shorter than abaxial calyx lobe
Back to 30 | Prostanthera elisabethae |
| 32 | Leaves with apex acute; calyx lower lip often retuse with two sharp points, calyx glabrous | Prostanthera scutellarioides |
| Leaves with apex obtuse; calyx lower lip rounded and hirsute or with at least a few sparse hairs
Back to 30 | 33 |
| 33 | Leaves evenly covered with short straight hairs and margin shortly (often indistinctly) lobed to bluntly toothed; hairs suberect to spreading, not appressed; anther appendage absent | Prostanthera stenophylla |
| Leaves with only a few hairs or glabrous and with margin entire; hairs appressed, antrorse, short; anther appendage present
Back to 32 | Prostanthera saxicola |
| 34 | Leaves wrinkled with margin crenate | Prostanthera rugosa |
| Leaves ± smooth with margin entire
Back to 27 | 35 |
| 35 | Spines present, weakly erect or prostrate shrubs | Prostanthera sejuncta |
| Spines absent, open erect shrubs
Back to 34 | 36 |
| 36 | Leaves ± circular, usually appearing angular-ovate (rhombic) | Prostanthera rhombea |
| Leaves narrowly ovate to ovate or obovate, if broadly ovate then usually appearing narrowly ovate because margin revolute (in Prostanthera decussata)
Back to 35 | 37 |
| 37 | Leaves glabrous | 38 |
| Leaves hairy, at least with a few short tooth-like hairs near margin
Back to 36 | 39 |
| 38 | Leaves obovate, 4–6.5 mm long; prophylls not persistent, 3–3.5 mm long; strongly aromatic shrub; branches densely covered with short, ± spreading hairs | Prostanthera cuneata |
| Leaves narrowly ovate, 5–15 mm long; prophylls persistent, 2.5 mm long; slightly aromatic; branches sparsely covered with short, appressed hairs between ridges
Back to 37 | Prostanthera phylicifolia |
| 39 | Leaves often with upper surface almost glabrous, having a few tooth-like hairs | 40 |
| Leaves with upper surface moderately to densely hairy
Back to 37 | 41 |
| 40 | Leaves hairy, at least with a few short tooth-like hairs near margin; branches densely covered with short to long spreading to antrorse hairs; corolla without markings in throat | Prostanthera decussata |
| Leaves with upper surface almost glabrous, having a few tooth-like hairs; branches predominantly glandular, usually sparsely to moderately covered with short, ± antrorse hairs; corolla throat with dark purple spots
Back to 39 | Prostanthera howelliae |
| 41 | Anther appendage absent, dark mauve markings in corolla, leaves grey-green, never toothed (if missing spots and not grey-green= P. rhombea) | Prostanthera granitica |
| Anther appendage about as long as locule, lower inside corolla throat white covered with orange markings; leaves green, sometimes toothed
Back to 39 | 42 |
| 42 | Branchlets, leaves and calyces scabrous hirsute; leaves narrowly ovate to narrowly elliptic, up to 8 mm long; prophylls up to 2.5 mm long | Prostanthera marifolia |
| Branchlets, leaves and calyces densely and softly hairy; leaves broadly ovate, often cordate, 6–13 mm long; prophylls 2–5.5 mm long
Back to 41 | Prostanthera densa |
| 43 | Branchlets, leaves and calyces with glandular hairs | Prostanthera cryptandroides |
| Branchlets, leaves and calyces without glandular hairs
Back to 26 | 44 |
| 44 | Branchlets, leaves and calyces glabrous | Prostanthera striatiflora |
| Branchlets, leaves or calyces hairy
Back to 43 | 45 |
| 45 | Leaves narrowly obovate (often appearing almost linear) or linear, conduplicate or incurved, usually appearing ± terete | 46 |
| Leaves ± flat or slightly channelled above; margin slightly incurved or slightly recurved
Back to 44 | 47 |
| 46 | Erect shrub 1–4 m high; adaxial calyx lobe 3–5 mm long; corolla 14–18 mm long; anther appendage c. 1.5 mm long; leaf lamina 10–50 mm long, 0.5–2 mm wide | Prostanthera nivea |
| Low spreading, decumbent or sub-prostrate, or weakly erect subshrub, 0.1–0.3 m high; adaxial calyx lobe 1.5–1.8 mm long; corolla 8–12 mm long; anther appendage 0.5–0.7 mm long; leaf lamina 8–16 mm long, 1–4 mm wide (note: elliptic to narrowly elliptic leaves are also present on young plants or near the base of older plants)
Back to 45 | Prostanthera junonis |
| 47 | Branchlets moderately to densely hairy, with hairs patent or slightly spreading | Prostanthera makinsonii |
| Branchlets appearing sparsely hairy or with hairs restricted to opposite decussate bands
Back to 45 | 48 |
| 48 | Branchlets with opposite decussate bands of hairs (often superficially appearing glabrous) | 49 |
| Branchlets sparsely hairy with appressed hairs, or if almost glabrous then hairs restricted to nodes
Back to 47 | 52 |
| 49 | Leaves obovate to ± spathulate; calyx with inner surface glabrous and outer surface densely hairy | Prostanthera palustris |
| Leaves linear, ovate, elliptic, or narrowly obovate; calyx variously hairy or glabrous throughout
Back to 48 | 50 |
| 50 | Strongly aromatic shrub; leaves with margin dentate to deeply dissected | Prostanthera incisa |
| Non-aromatic or faintly aromatic shrub; leaves with margin entire
Back to 49 | 51 |
| 51 | Erect shrub to 2 m high; calyx with outer surface glabrous or almost so; anther appendages absent | Prostanthera hindii |
| Low spreading, decumbent, weak subshrub, erect when young 0.1–0.3 m high; calyx with outer surface sparsely to densely hairy, especially on abaxial surface of tube and abaxial lobe (distinct anther appendages almost as long as the locule)
Back to 50 | Prostanthera junonis |
| 52 | Leaves (5–)6–10 mm wide, fresh leaves aromatic when crushed | Prostanthera gilesii |
| Leaves less than 5 mm wide, not aromatic when crushed
Back to 48 | 53 |
| 53 | Leaves up to 15 mm long, branches lacking ridges | Prostanthera saxicola |
| Leaves 15–45 mm long, branches distinctly 4-ridged
Back to 52 | Prostanthera linearis |
| 54 | Prophylls inserted at base or on lower half of pedicel | Prostanthera ringens |
| Prophylls inserted at base of calyx or on upper half of pedicel
Back to 1 | 55 |
| 55 | Leaves with lamina ± terete | Prostanthera aspalathoides |
| Leaves with lamina ovate to narrowly ovate, sometimes ± circular, never terete or linear-obovate
Back to 54 | 56 |
| 56 | Branches 4-angular and 4-ridged, ridges fused to base of petiole | Prostanthera porcata |
| Branches ± terete, ridges absent
Back to 55 | 57 |
| 57 | Leaves with lamina less than 5 mm long; petiole absent or to 0.5 mm long; venation not visible | Prostanthera serpyllifolia |
| Leaves with lamina more than 10 mm long; petiole more than 1.5 mm long; venation visible, often faint
Back to 56 | 58 |
| 58 | Prophylls 10–18 mm long; inner surface of calyx lobes hairy; leaves non-aromatic | Prostanthera monticola |
| Prophylls 4–6.5 mm long; inner surface of calyx lobes glabrous; leaves aromatic
Back to 57 | Prostanthera walteri |
