Eucalyptus | Symphyomyrtus | Bisectae | Hadrotes | Lehmannianae | Liberae
Bark smooth throughout, mottled dark grey, light greeny grey and orange.
Branchlets lacking oil glands in the pith.
Juvenile growth (coppice or field seedlings to 50 cm): stems rounded in cross-section; juvenile leaves always petiolate, alternate, deltoid to ovate, 3.5–8 cm long, 2.5–6 cm wide, green.
Adult leaves alternate, petioles 0.7–1.7 cm long; blade lanceolate, 6–10(11) cm long, 1–2.5 cm wide, base tapering to petiole, margin entire, apex pointed and with a black warty mucro, glossy, green, concolorous, side-veins at an acute or wider angle to midrib, reticulation moderate to dense, intramarginal vein remote from margin, oil glands obscure.
Inflorescence axillary unbranched, peduncles spreading or down-turned, strap-like, 2.3–5 cm long, buds 3 or 7, sessile to subsessile. Mature buds elongated (3–6 cm long, 0.5–1.6 cm wide), operculum scar present (outer operculum lost early), operculum ca 3 times as long as the hypanthium, dilated basally, with many large warts, stamens erect, anthers narrowly oblong, versatile, dorsifixed, dehiscing by longitudinal slits, style long and straight, stigma tapered to rounded, locules 3, the placentae each with 6 vertical rows of ovules (2 extra partial rows sometimes present medially). Flowers yellowish green.
Fruit on spreading to down-turned peduncles, sessile, campanulate to obconical, 1.8–2.7 cm long, 2.3–3.5 cm wide, dehiscing by elliptical holes initially formed when the 3 valves split along the sutures but remain connected by the style base (this connection soon weathers and the holes coalesce), disc covering the valves, striate.
Seeds black, 1.5–4 mm long, ovoid to angularly so, dorsal surface shallowly reticulate, margin not or scarcely flanged, hilum ventral.
Cultivated seedlings (measured at node 10): cotyledons Y-shaped (bisected), robust; stems rounded in cross-section, scabrid; leaves always petiolate, opposite for 2 or 4 nodes then alternate, broadly ovate, 3.5–8 cm long, 2.5–7.5 cm wide, margin undulate, slightly discolorous, green, scabrid for at least 11 nodes. Scabridity is due to bristle-glands.
Flowering has been recorded in January, June and November.
A mallet endemic to Western Australia and found only in the far south in the Ravensthorpe Range and the Whoogarup Range. The bark is smooth and adult leaves glossy green with the large buds and fruit easily visible in the crowns; buds are very large (3-6 cm long) with long yellow-green stamens.
Eucalyptus megacornuta belongs in Eucalyptus subgenus Symphyomyrtus section Bisectae subsection Hadrotes because the cotyledons are coarsely bisected, buds have an operculum scar, a long (inner) operculum and erect stamens, fruit are large, thick-rimmed and held rigidly. There are 12 species in subsection Hadrotes, two species (E. macrandra, E. cornuta ) have oil glands in the pith whilst 10 species lack these oil glands. Together these 10 species form series Lehmannianae, a group further characterised by having scabrid seedlings and fruit with exserted valves that remain fused at their tips after seed is shed, a feature shared with the more distantly related E. cornuta.
Of the ten species in series Lehmannianae four, E. newbeyi, E. burdettiana, E. talyuberlup, and E. megacornuta, have buds and fruit in each umbel basally free (subseries Liberae) whilst the other six species, E. lehmannii, E. conferruminata, E. arborella, E. mcquoidii, E. sinuosa and E. retusa have the buds (and fruit) in each axillary cluster fused basally (subseries Conjunctae). The scabridity of the seedling leaves of these ten species is due to emergent multicellular oil glands.
E. megacornuta and E. newbeyi are both mallets (non-lignotuberous), the former with extremely warty large buds and the latter with long smooth buds (5.2-6 cm long). E. newbeyi has a restricted coastal distribution in the Beaufort Inlet area and in Fitzgerald River National Park. The other two species in series Liberae , E. burdettiana, with almost parallel-sided, slightly warty opercula, and E. talyuberlup, with smooth opercula, are both mallees (lignotuberous).
E. megacornuta is an attractive ornamental with gross, warty opercula and beautiful yellow-green balls of flowers.