Eucalyptus opimiflora

Northern silver mallee

Eucalyptus | Symphyomyrtus | Bisectae | Destitutae | Falcatae | Rugatae

Eucalyptus opimiflora D.Nicolle & M.E.French, Nuytsia 12: 424 (2012).

T: Western Australia: north-east of Badgingarra (near old town site), 28 October 2000, D. Nicolle 3515 & M.E.French ; holo: PERTH; iso: AD, CANB.

Mallee to 7 m tall. Forming a lignotuber.
Bark smooth throughout, creamy brown, grey and pale silver grey.
Branchlets lacking oil glands in the pith.
Juvenile stems rounded in cross-section; juvenile leaves always petiolate, opposite for lowest node only then alternate, elliptic lower down then ovate higher up stem, no measurements available, green to grey-green, dull.
Adult leaves alternate, petiole 1–1.8 cm long; blade lanceolate to falcate, 5.5–12 cm long, 0.8–2 cm wide, base tapering to petiole, margin entire, apex pointed, concolorous, green or slightly grey-green, usually glossy but sometimes only weakly so, side-veins about 45° to midrib, reticulation dense, intramarginal vein close to margin, oil glands absent or obscure.
Inflorescence axillary unbranched, peduncles erect to spreading, 0.7–1.6 cm long, buds 7 to 15, pedicellate (pedicels 0.1–0.6 cm long). Mature buds ovoid but slightly constricted at join with hypanthium (1–1.5(1.7) cm long, 0.4–0.7 cm wide), hypanthium ribbed or virtually smooth, scar present (outer operculum shed early), operculum conical and smooth, stamens inflexed, anthers cuboid, versatile, sub-basifixed, dehiscing by longitudinal slits, style long and straight, stigma more or less blunt, locules 3 or 4, the placentae each with 4 vertical rows of ovules. Flowers creamy white.
Fruit pedicellate (pedicels 0.1–0.6 cm long), more or less obconical to truncate-globose, ribbed, almost smooth, 0.5–0.8 cm long, 0.7–1 cm wide, rim thick, disc descending obliquely, valves 3 or 4, slender and prominently exserted but fragile.
Seeds grey-brown to brown, 1.5–2.3 mm long, ovoid or flattened-ovoid, dorsal surface smooth, hilum ventral.

Cultivated seedling: cotyledons Y-shaped (bisected); stems rounded in cross-section; leaves opposite for ca 11 to 12 nodes then alternate, sessile and linear at lowest node then becoming petiolate and elliptical then ovate after alternation, 2.5–3.5 cm long, 1.5–3.5 cm wide, base tapering, margin entire, apex rounded to acute, green to grey-green, dull.

Flowering has been recorded in June and November.

A mallee endemic to Western Australia, restricted to the northern and central wheatbelt and adjacent sub-coastal sandplains from south-east of Geraldton to Eneabba, Badgingarra, Moora, Calingiri and near Cunderdin, on white or yellow sandy soil. The bark is smooth, crown glossy green, umbels erect to weakly spreading, and has ovoid more or less ribbed buds on short slender pedicels.

In the classification of Brooker (2000) the more recently published Eucalyptus opimiflora would belong in Eucalyptus subgenus Symphyomyrtus section Bisectae subsection Destitutae because buds have two opercula, cotyledons are Y-shaped and branchlets lack oil glands in the pith. Within this subsection  E. opimiflora belongs to a group of species and subspecies characterised by down-turned or spreading inflorescences with pedicellate ovoid buds with a conical to beaked operculum, flattened to truncate globose fruits with exserted fragile valves, and adult leaves that are green, densely reticulate and have numerous intersectional oil glands. This group is series Falcatae subseries Rugatae and has been considerably modified since Brooker's published classification. The species now included in subseries Rugatae are: the mallets E. falcata, E. ornata, E. purpurata, E. recta, E. rugulata and the recently described E. annettae, and the mallees E. dorrienii, E. petrensis, E. opimiflora, E. ecostata, plus E. goniantha (with 2 subspecies), E. semiglobosa, E. notactites, and E. kessellii (with 2 subspecies) .

Within subseries Rugatae the mallee E. opimiflora differs from the mallet species mentioned above by its profoundly different growth habit.

Of the mallee species in subseries Rugatae, E. petrensis, a sprawling mallee, differs from E. opimiflora in having consistently unribbed buds, a more beaked operculum and a restricted habitat on outcropping coastal limestone from Seabird south to Mandurah. In the southern wheatbelt and adjacent foothills the mallee E. dorrienii occurs usually on rising ground and differs from E. opimiflora by its distinctly pendulous umbels on longer slender peduncles, longer pedicels with more dilated hypanthia on the ribbed ovoid buds. Further south-east E. ecostata also has pendulous umbels, and further differs in its buds that are scarcely ribbed or are unribbed and have an elongated conical operculum.

The remaining mallee species in subseries Rugatae all occur in southern coastal or subcoastal areas, and differ from E. opimiflora thus: E. goniantha (squared branchlets, flat peduncles, stout cream ovoid buds which are weakly ribbed or not ribbed, in 7s or 9s), E. notactites (squared or winged branchlets, flat peduncles, stout cream ovoid buds weakly ribbed, in 7s up to 19s), E. kessellii (broad flat short peduncles, stout cream ovoid ribbed buds in 3s or 7s), E. semiglobosa (pendulous umbels on slender scarcely flattened peduncles, cream rounded buds with rounded short operculum, not or weakly ribbed, in 7s, 9s or 11s).

Eucalyptus opimiflora: from Latin, opimus meaning fat, and -flora after Flōra the goddess of flowers.