Eucalyptus thamnoides subsp. megista

Eucalyptus | Symphyomyrtus | Bisectae | Glandulosae | Erectae | Pedicellatae

Eucalyptus thamnoides subsp. megista Brooker & Hopper, Nuytsia 14: 354 (2002).

T: Norman Rd., Corackerup Creek Nature Reserve, east side of road, 8 Apr. 1995, M.I.H.Brooker 12212 W; holo: CANB; iso: AD, NSW, PERTH.

Mallee to 4 m tall. Forming a lignotuber.
Bark smooth throughout, grey shedding to pinkish brown or coppery, rarely with up to 0.3 m of long-flaky grey-brown rough bark.
Branchlets have oil glands in the pith.
Juvenile growth (coppice or field seedlings to 50 cm): stems rounded in cross-section; juvenile leaves always petiolate, alternate, ovate-lanceolate, 6–10 cm long, 2–6 cm wide, dull, grey-green.
Adult leaves alternate, petioles 1–2 cm long; blade lanceolate, 5–12.5 cm long, (0.8)1–2.2 cm wide, base tapering to petiole, margin entire, apex finely pointed, glossy, green, side-veins at an acute or wider angle to midrib, reticulation sparse to moderate and clear, intramarginal vein present, oil glands numerous, ± round, island and intersectional.
Inflorescence axillary unbranched, spreading to pendulous, peduncles narrowly to broadly flattened, 0.8–3.5 cm long, buds 7, pedicellate (pedicels 0.3–0.7 cm long). Mature buds stubby to slightly elongated, 1.4–2.3 cm long, 0.4–0.7 cm wide, swollen at or just below the join, scar present (outer operculum shed early), inner operculum horn-shaped but usually blunt, ca 1–2 times the length of the hypanthium, stamens erect, anthers oblong, versatile, dorsifixed, dehiscing by longitudinal slits, style long and straight, stigma blunt, locules 4, the placentae each with 4 vertical rows of ovules. Flowers cream to pale lemon.
Fruit pedicellate (pedicels 0.3–1), cupular to campanulate or obconical, 0.7–1.3 cm long, 0.8–1 cm wide, disc level at first then descending, valves 4, usually held at rim level.
Seeds blackish brown, 1–2 mm long, ovoid to flattened-ovoid, dorsal surface shallowly and clearly reticulate, hilum ventral.

Cultivated seedlings (measured at node 10): cotyledons Y-shaped (bisected); stems rounded in cross-section; leaves always petiolate, opposite for 2 to 4 nodes then alternate, usually ovate, rarely deltoid, 4.5–7 cm long, 2–4.5 cm wide, dull, green to blue-green.

Flowering has been recorded in March, April, May, June, July, August, September, October and November.

A mallee species endemic to Western Australia, found from west of Quairading south to the Stirling Ranges and east almost to Hopetoun, on sandy-clay or gravelly soils, not on breakaways. Bark is smooth throughout, (rarely with a very short stocking of rough bark), and crown leaves glossy green with some reticulate venation visible.

Eucalyptus thamnoides belongs in Eucalyptus subgenus Symphyomyrtus section Bisectae subsection Glandulosae because the buds have an operculum scar, cotyledons are bisected and branchlets have oil glands in the pith. Within this large subsection (ca 80 species), E. thamnoides is closely related to a group of mallets and mallees (series Erectae subseries Pedicellatae) recognised by the glossy green leaf surface, leaves with many oil glands but not obscuring the secondary venation, peduncles long and flattened or terete, inflorescences spreading to pendulous and buds with operculum longer than the hypanthium (base) and erect stamens arising from a narrow staminophore.

Eucalyptus thamnoides differs from the closely related species E. astringens only in its mallee (not mallet) habit and in habitat preference. Both species have stubby buds with the operculum only one to two times the length of the hypanthium, and campanulate fruit. Other closely related species, viz. the rough-butted tree of freshwater creeks and depressions E. occidentalis, rough-barked mallee E. aspratilis, smooth-barked mallee E. sporadica and usually rough-butted tree of saline sites E. sargentii subsp. sargentii, all have more slender buds with elongated opercula. (The other 3 species in subseries Pedicellatae, E. sargentii, E. diminuta and E. stowardii all have more or less terete peduncles that don't widen apically).

There are two weakly separated subspecies:

E. thamnoides subsp. thamnoides
This has smaller buds and fruit (fruit 0.6–0.8 cm diameter) than subsp. megista, and occurs south from Gnowangerup to the Stirling Ranges and east to Needilup and Jerramungup.

E. thamnoides subsp. megista
This has fruits from 0.8–1 cm diameter and occurs from near Quairading south to Cranbrook and extending in an arc east to Corackerup and Hopetoun, including Fitzgerald River National Park. It is absent from the Stirling Ranges. Mallees from near Bremer Bay to Boxwood Hill may have some basal rough bark but otherwise match this subspecies. (Herbarium specimens annotated with the manuscript names "E. astringens subsp. oligocorma" and "E. oligocorma" are now correctly E. thamnoides subsp. megista).

E. thamnoides subsp. thamnoides and subsp. megista have only been recently described. More field investigation is required to clarify their overlapping distributions, especially in the area immediately north of the Stirling Ranges east to Needilup. Further work may indeed show the two subspecies are not really distinct.

Eucalyptus thamnoides: Greek thamnos, shrub or bush, referring to the mallee, not mallet, habit, with regard to its relationship to E. astringens.

subsp. megista: Greek megistos, largest, referring to the size of the fruits relative to subsp. thamnoides.