Flowers axillary, solitary [paired in some non-N.S.W. species], mostly bisexual. Spines basically arranged alternately to the perianth segments with a pair of spines opposite the radicular bulge, one or more of the spines reduced, absent or modified (e.g. into tubercles). Stamens 5. Styles 2.
Fruiting perianth becoming thickened and hardened, either readily disarticulating or remaining firmly attached to the branch and the whole plant, or section of it, being dispersed. The upper perianth often remaining distinct and termed the 'limb'. Seed vertical to horizontal, released by the breakdown of the woody perianth.
| | Key to the species | |
| 1 | Fruiting perianth bordered by a narrow rim or wing more or less broken up into 5–15 spines or teeth | 2 |
| Fruiting perianth without a narrow rim or wing, spines 2–6 | 3 |
| 2 | Spines or teeth 8–15; lower fruiting perianth almost globose | Sclerolaena stelligera |
| Spines or teeth 5; lower fruiting perianth hemispherical
Back to 1 | Sclerolaena brachyptera |
| 3 | Spines usually 2 or 3 | 4 |
| Spines mostly 4–6
Back to 1 | 21 |
| 4 | Spines 2 (sometimes 3 or 4 in Sclerolaena decurrens) | 5 |
| Spines usually 3 (sometimes 4 in Sclerolaena ventricosa and S. andersonii, 4–6 in S. lanicuspis)
Back to 3 | 14 |
| 5 | Base of fruit deeply hollowed | 6 |
| Base of fruit not or slightly hollowed
Back to 4 | 10 |
| 6 | Fruiting perianth silky-villous | Sclerolaena eriacantha |
| Fruiting perianth tomentose, pubescent or glabrous, never silky-villous
Back to 5 | 7 |
| 7 | Spines erect, parallel, equal | Sclerolaena parallelicuspis |
| Spines divergent
Back to 6 | 8 |
| 8 | Tubercle large, much more conspicuous than the spines, spines to 1 mm long or often reduced | Sclerolaena uniflora |
| Tubercle small or the same size as the spines, spines c. 2–5 mm long, not reduced
Back to 7 | 9 |
| 9 | Fruiting perianth thick-walled, not constricted in middle | Sclerolaena diacantha |
| Fruiting perianth thin-walled, more or less constricted in middle
Back to 8 | Sclerolaena constricta |
| 10 | Perianth globose or almost so, 5 mm or more long | Sclerolaena bicornis |
| Perianth not globose, if almost so then less than 5 mm long
Back to 5 | 11 |
| 11 | Spines not in same vertical plane, limb not very conspicuous | Sclerolaena obliquicuspis |
| Spines in same vertical plane
Back to 10 | 12 |
| 12 | Upper perianth (limb) as long as lower fruiting perianth | 13 |
| Upper perianth (limb) shorter than lower perianth but conspicuous; fruiting perianth not ribbed
Back to 11 | Sclerolaena patenticuspis |
| 13 | Fruiting perianth tomentose, not ribbed | Sclerolaena limbata |
| Fruiting perianth glabrous, ribbed
Back to 12 | Sclerolaena decurrens |
| 14 | Fruiting perianth hairy | 15 |
| Fruiting perianth glabrous
Back to 4 | 16 |
| 15 | Fruiting perianth villous with long silky hairs, not swollen in lower part | Sclerolaena lanicuspis |
| Fruiting perianth tomentose, swollen in lower part
Back to 14 | Sclerolaena ventricosa |
| 16 | Spines spreading or recurved | 17 |
| Spines more or less diverging upwards
Back to 14 | 19 |
| 17 | Spines usually recurved; fruiting perianth cylindrical, c. twice as long as broad | Sclerolaena articulata |
| Spines more or less spreading, perianth c. as long as broad
Back to 16 | 18 |
| 18 | Main spines arranged with 1 abaxial and 2 lateral in line; stamens 3 | Sclerolaena divaricata |
| Main spines arranged with 1 abaxial, 1 lateral, and 1 somewhat adaxial or curved around branch; stamens usually 5
Back to 17 | Sclerolaena cuneata |
| 19 | Fruiting perianth conical, base expanded | Sclerolaena tricuspis |
| Fruiting perianth not conical, base not expanded
Back to 16 | 20 |
| 20 | Fruiting perianth laterally attached, much longer than the limb | Sclerolaena glabra |
| Fruiting perianth attached basally, c. as long as the limb
Back to 19 | Sclerolaena decurrens |
| 21 | Spines usually 4 (2–5 in Sclerolaena decurrens, 4–6 in S. lanicuspis) | 22 |
| Spines 5 or 6
Back to 3 | 28 |
| 22 | Plant hairy | 23 |
| Plant glabrous
Back to 21 | 25 |
| 23 | Fruiting perianth ribbed, glabrous | Sclerolaena decurrens |
| Fruiting perianth not ribbed, hairy
Back to 22 | 24 |
| 24 | Upper perianth (limb) as long as lower fruiting perianth | Sclerolaena limbata |
| Upper perianth (limb) shorter than lower perianth and covered by long silky hairs
Back to 23 | Sclerolaena lanicuspis |
| 25 | Limb recurved | Sclerolaena divaricata |
| Limb erect
Back to 22 | 26 |
| 26 | Fruiting perianth conical, spines more than 10 mm long | Sclerolaena longicuspis |
| Fruiting perianth not conical, spines 10 mm long or less
Back to 25 | 27 |
| 27 | Spines irregularly spaced, usually divergent to horizontal | Sclerolaena glabra |
| Spines more or less equally spaced, divergent, erect
Back to 26 | Sclerolaena tetracuspis |
| 28 | Spines 5 (sometimes 6 in Sclerolaena lanicuspis and S. convexula) | 29 |
| Spines 6
Back to 21 | 41 |
| 29 | Plants hairy | 30 |
| Plant glabrous or almost so
Back to 28 | 38 |
| 30 | Fruiting perianth urn-shaped; spines recurved | Sclerolaena blackiana |
| Fruiting perianth not urn-shaped; spines more or less recurved
Back to 29 | 31 |
| 31 | Limb erect, conspicuous | 32 |
| Limb recurved, inconspicuous
Back to 30 | 33 |
| 32 | Fruiting perianth hairy | Sclerolaena lanicuspis |
| Fruiting perianth glabrous
Back to 31 | Sclerolaena decurrens |
| 33 | Leaves obovate to oblanceolate or linear-lanceolate | 34 |
| Leaves linear to semiterete
Back to 31 | 35 |
| 34 | Leaves glabrous above, dark green | Sclerolaena muricata |
| Leaves hairy all over
Back to 33 | Sclerolaena birchii |
| 35 | Fruiting perianth much longer than broad | Sclerolaena tubata |
| Fruiting perianth c. as long as broad
Back to 33 | 36 |
| 36 | Fruiting perianth globose, summit convex | 46 |
| Fruiting perianth not globose, summit flat
Back to 35 | 37 |
| 37 | Fruiting perianth attached basally; leaves terete | Sclerolaena johnsonii |
| Fruiting perianth attached laterally, leaves flat to semiterete
Back to 36 | Sclerolaena muricata |
| 38 | Fruiting perianth much longer than broad | 39 |
| Fruiting perianth c. as long as broad
Back to 29 | 40 |
| 39 | Fruiting perianth attached basally | Sclerolaena tubata |
| Fruiting perianth attached laterally
Back to 38 | Sclerolaena intricata |
| 40 | Fruiting perianth attached basally; leaves terete, pale green | Sclerolaena johnsonii |
| Fruiting perianth attached obliquely; leaves flat to semiterete, dark, glaucous
Back to 38 | Sclerolaena muricata |
| 41 | Perianth 2-spurred at base, glabrous | Sclerolaena calcarata |
| Fruiting perianth not spurred at base, glabrous or hairy
Back to 28 | 42 |
| 42 | Fruiting perianth urn-shaped | Sclerolaena anisacanthoides |
| Fruiting perianth not urn-shaped
Back to 41 | 43 |
| 43 | Spines c. 1 mm long | Sclerolaena parviflora |
| Spines 2 mm or longer
Back to 42 | 44 |
| 44 | Fruiting perianth covered with long silky hairs | Sclerolaena lanicuspis |
| Fruiting perianth loosely hairy
Back to 43 | 45 |
| 45 | Spines mostly 5, but occasional fruit with 6 spines; fruit mostly 2.5 mm wide; longer spines mostly less than 3 mm long and 0.5 mm or less in diam | Sclerolaena convexula |
| Spines 6; fruit 3 mm or more wide at the widest point; longer spines mostly more than 3 mm long and 0.5 mm or more in diam
Back to 44 | Sclerolaena napiformis |
| 46 | The three longest spines on fruiting body mostly <3 mm long | Sclerolaena convexula |
| The three longest spines on fruiting body mostly >5 mm long
Back to 36 | Sclerolaena deserticola |
