Eucalyptus socialis subsp. viridans

Red mallee

Eucalyptus | Symphyomyrtus | Bisectae | Destitutae | Subulatae | Decussatae

Eucalyptus socialis subsp. viridans D.Nicolle, Australian Systematic Botany 18:(6) 505 (2005).

T: South Australia: ca. 4 km NE of Minlaton, on main road to Pt. Vincent, 34° 45' S, 137° 38' E, P.J.Lang 804, 10 April 1977; holo: AD; iso: CANB.

Mallee to 5 m tall. Forming a lignotuber.
Bark usually persistent on lower trunks, grey to brown, loose flaky, shaggy, ribbony; smooth bark on upper trunks and branches grey over cream, rarely yellowy-green.
Branchlets lacking oil glands in the pith.
Juvenile growth (coppice or field seedlings to 50 cm): stem square to rounded in cross-section, non-glaucous; juvenile leaves sessile to shortly petiolate, opposite for few to many pairs becoming sub-opposite then alternate, ovate, 4.5–7 cm long, 2–3 cm wide, usually dull green to grey-green.
Adult leaves alternate, petiole (0.5)1.0–2.5 cm long; blade lanceolate, rarely falcate, 5.5–9.5 cm long, 1–2(2.5) cm wide, base usually tapering to petiole, concolorous, glossy green, side-veins at an acute or wider angle to midrib, densely reticulate, intramarginal vein parallel to and just within margin, oil glands numerous and mostly intersectional.
Inflorescence axillary unbranched, peduncles 0.5–1.3 cm long, buds usually 9 to 13, pedicellate, pedicels 0.2–0.6 cm long. Mature buds ovoid to fusiform (0.8–1.4 cm long, 0.35–0.6 cm wide), scar present, operculum conical to beaked or horn-shaped (0.5–0.9 cm long), stamens irregularly flexed, anthers weakly versatile, globoid to cuboid, dehiscing by broad lateral pores, style long, stigma tapered, locules 3 or 4, the placentae each with 4 vertical ovule rows. Flowers creamy white to pale yellow.
Fruit pedicellate, pedicels 0.2–0.5 cm long, cup-shaped to barrel-shaped to truncate-globose, 0.5–0.9 cm long, 0.5–0.7 cm wide, disc descending, valves 3 or 4, enclosed but surmounted with prominently exserted but easily broken style remnants.
Seeds dull grey to pale brown, 1.5–2.2 mm long, ovoid or flattened-ovoid, dorsal surface smooth, sometimes furrowed, hilum ventral.

Cultivated seedlings (measured at node 10): cotyledons Y-shaped (bisected); stems square in cross-section, sometimes glaucous; leaves opposite, sessile, cordate to ovate, 1.5–3.5 cm long, (0.7)1–2.5 cm wide, amplexicaul or base rounded to tapering, dull grey-green or sometimes slightly glaucous.

Flowering has been recorded in August, October, November and December.

Eucalyptus socialis is a species of mallee widespread in mallee-lands in southern Australia, also in the Great Victoria Desert and in numerous other desert sites north-west to the Pilbara of Western Australia, north and north-east to Central Australia and, disjunctly, in central Queensland. The stems are rough-barked or smooth, the buds are prominently beaked and seedling leaves are sessile and opposite on the square stem.

Eucalyptus socialis belongs 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. socialis is part of the large taxonomic series Subulatae which is further characterised by globoid more or less basifixed anthers, grey smooth seeds with shallow longitudinal furrows, and fruit with fragile, prominently exserted style remnants. Series Subulatae is divided principally into four subseries based on the juvenile leaves: one subseries with spiral, crowded seedling leaf arrangement (subseries Spirales), another with decussate and decurrent seedling leaves (subseries Decurrentes), a third with decussate non-decurrent seedling leaves (subseries Decussatae), and a fourth with disjunct, petiolate seedling leaves (subseries Oleaginae).

Eucalyptus socialis is part of subseries Decussatae along with the following 7 species: E. aspersa, E. dolichocera, E. gillii, E. vokesensis, E. wyolensis, E. yalatensis and E. yumbarrana. Excepting for E. aspersa and E. dolichocera, the geographical range of E. socialis overlaps with that of the other species and often can be found growing quite nearby any of them.

E. socialis is most closely related to E. gillii, a species occurring in the northern Flinders Ranges of South Australia extending east into the Fowlers Gap area of New South Wales. E. gillii is considered by some botanists as a neotenous variant of E. socialis, differing from it by its crown of glaucous, sessile, cordate to ovate, juvenile leaves. E. yalatensis occurs within the southern range of E. socialis, crossing the Nullarbor Plain from Balladonia and Toolinna in Western Australia to the Eyre Peninsula and, disjunctly, Tailem Bend in South Australia, and differs from E. socialis its low spreading habit, small buds with a pointy operculum (no beak), small obconical fruit and in never being glaucous. E. yumbarrana, a South Australian endemic species related to and occurring within the range of E. socialis in the desert country north-west of Ceduna, differs in having thicker glossy adult leaves, buds with the operculum slightly wider than the hypanthium at the join and slightly larger fruit.

In the area of the Great Victoria Desert north-west of Ooldea two species closely related to E. socialis occur, E. vokesensis and E. wyolensis. Both are heavily glaucous on the new branchlets, buds and fruit. E. vokesensis has petiolate adult leaves forming the crown whilst E. wyolensis has a crown of sessile opposite large juvenile leaves; both species have buds larger than those of typical E. socialis.

The remaining two species in subseries Decussates, E. aspersa and E. dolichocera, are found immediately east and northeast of Perth, Western Australia. E. aspersa is a mallee occurring sporadically as understory in Jarrah forests in the Darling Range and differs from E. socialis in having smaller leaves, buds and fruit and in being non-glaucous. E. dolichocera occurs in the wheatbelt and is a large mallee with obvious rough bark, pendulous bud clusters, buds with prominently beaked operculum and is never glaucous.

Eucalyptus socialis has three subspecies:

E. socialis subsp. socialis
Very widespread, in New South Wales, Victoria, South Australia, extending to the Pilbara in Western Australia and to Central Australia, and, disjunctly, in central Queensland (sporadically from west of Winton and Longreach to north-east of Aramac). Subsp. socialis may be glaucous or not so, but always has dull leaves. Distinguished from subsp. viridans by these dull green adult leaves and from subsp. victoriensis by its smaller buds and fruit.

E. socialis subsp. victoriensis
A mallee from the southern part of the Great Victoria Desert, extending from Forrest Lakes in Western Australia near the border with South Australia, south-east to the Gawler Ranges and north-western Eyre Peninsula, particularly on dune crests or in swales between dunes. It has large buds with the operculum slightly wider than the hypanthium at the join, large fruit (0.7–1 cm wide) and has coarse, usually dull, rarely slightly glossy, adult leaves.

E. socialis subsp. viridans
It occurs in South Australia from the eastern side of the Eyre Peninsula through the Yorke Peninsula to the southern Murray Mallee, possibly extending into the western parts of Victoria. It is distinguished from subsp. socialis and subsp. victoriensis by its glossy adult leaves. It has been confused with E. peninsularis, a distantly related species endemic to the Eyre Peninsula, which can be easily identified by its decurrent juvenile leaves, pendulous prominently beaked buds and strongly urn-shaped fruit. In the absence of buds and juvenile leaves specimens of subsp. viridans have been misidentified as E. oleosa subsp. oleosa.

The taxonomy of E. socialis and related species is somewhat complex, not least due to the remote occurrences of some forms. The name E. eucentrica was published in 1991 by L.A.S. Johnson & K.D. Hill to account for plants occurring in the Great Victoria Desert, the Pilbara, Central Australia and Queensland, that had coarser leaves, larger buds that were often glaucous and yellow flowers, compared with more typical E. socialis. Relatively large-leaved E. eucentrica  was regarded by Johnson & Hill as smaller than the non-glaucous glossy leaved E. yumbarrana. Nicolle (2005) re-classified E. eucentrica at subspecies level i.e. E. socialis subsp. eucentrica, differing from  subsp. socialis by the glaucous branchlets and buds and the creamy yellow flowers. Nicolle also regards the subsp. eucentrica as occurring from the Pilbara east to the Simpson Desert and disjunctly in central Queensland, but occurring in South Australia only in the far-north-west, not in the Great Victoria Desert. Observations in the field and herbarium by the authors of EUCLID show that the variation in glaucescence is pronounced with non-glaucous and glaucous plants with similar sized leaves and buds growing side by side in some areas; degrees of glaucescence from none to slight to pronounced also occur within populations. For this reason we include Nicolle's subsp. eucentrica in subsp. socialis. Bud dimensions also suggest subsp. eucentrica is better placed in subsp. socialis than in subsp. victoriensis.

Eucalyptus socialis: Latin socialis, friendly, referring to its occurrence with several other species.

subsp. viridans: Latin viridis, green, referring to the seedling and adult leaf colour.