An erect shrub or subshrub or slender annual herb, 1−2 m high, with few branches. Branchlets densely covered with a very fine indumentum of minute stellate hairs, eventually becoming glabrous or nearly so (glabrescent). Leaves ash-grey or yellowish, stipulate with subulate stipules 2.5−4.0 mm long, petiolate, with petioles 2−10 mm long, densely covered in star-shaped hairs; leaf blade chartaceous, ovate to broadly ovate or ovate-elliptic, 15−35 Í 10−30 mm, densely covered with minute stellate tomentum on both surfaces, margins serrate (sharply toothed), apex rounded or truncate, 5-veined, midrib slightly prominent above, prominently so beneath, with veins inconspicuous above and prominent beneath.

Fig. 2. Leaves of Hibiscus waterbergensis. A. Underside of leaves showing noticeable ventral raised venation and toothed margin (Photo SP Bester). B & C. Upper side of leaves showing indumentum and relative indistinct venation on dorsal side of leaves compared to ventral side (Photo B: SP Bester, C: M Popp).

Flowers grow from the axils of leaves (axillary), are solitary, and bright scarlet−red , with pedicel up to 35 mm long, minutely hairy, articulated near the apex, 7−8 mm long. Epicalyx 7−8, triangular to elongate-triangular, 2.0−2.5 mm long. Calyx 7−8 mm long, with elliptic or lanceolate-elliptic lobes. Petals oblong-elliptic, about 15−20 Í 5−6 mm, externally stellate-pilose, glabrous internally. Staminal tube 5 mm long. Filament parts free, 2.0−4.0 mm long. Style tip deeply 5-lobed, each branch ending in a globose stigmatic surface. Ovary ellipsoid, 4 Í 3 mm, with style branches 1.5−4.0 mm long.

Fig. 3. Floral morphology of Hibiscus waterbergensis. A. Ventral view of flower showing epicalyx (7 or 8 elongate to triangular-elongate lobes – smaller petaloid lobes) and calyx (elliptic or lanceolate elliptic petaloid lobes – larger lobes); B. Side view of staminal tube with numerous anthers fused into a column; also showing 5-branched style tip with hirsute stigmatic surface; C. Side view of branch with pedicel and flower – note the articulation on the pedicel close to the base of the flower; D. Side view of branch with leaf. (Photos SAPlants@Wikicommons)

The peak flowering period is in early summer, from October to December, but plants are very dependent on spring and summer rainfall, so flowering has also been observed from mid-summer to autumn (November to April).

Fruit a sub-globose loculicidal capsule, 12 mm in diam., minutely pubescent. Seeds, kidney-shaped, 2.0−3.0 Í 1.5 mm, densely covered in 2−5 mm long cottony silky hairs.

Fig. 4. Floral morphology of Hibiscus waterbergensis. A. Flower bud with twisted corolla lobes unevenly furnished with stellate hairs; B. Base of flower bud showing the epicalyx (numerous small bractoidal lobes) and calyx (fewer large petaloid lobes); C. Leaf showing extrafloral nectary on base of main vein; D. Fruit in side view; E. Flower and leaf in side view (Photos SAPlants@Wikicommons).

The size of the flowers, them being pendulous and the leaves with the two large patches of extrafloral glands immediately distinguish the Waterberg hibiscus from any of the other red-flowered species found in its natural distribution range.