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Eucalyptus arachnaea Brooker & Hopper, Nuytsia
8:68 (1991) subsp. arachnaea.
E. redunca Schauer var. melanophloia Benth.,
Fl. Austral. 3: 253 (1867).
T: Cheeanga Thicket, Murchison River, Western Australia, Oldfield
s.n.; holo: K; iso: NSW.
Mallee to 5 m tall. Forming a lignotuber.
Bark rough, grey-black for up to 2.5 m of trunks, tightly
fibrous and fissured to flaky, smooth above, grey and yellowish
brown.
Branchlets with pith oil glands at the nodes.
Juvenile growth (coppice
or field seedlings to 50 cm): stems triangular in cross-section
when young, soon rounded, warty; juvenile leaves always petiolate,
opposite for ca 3 nodes then alternate, ovate, 5.5-9 cm long, 3-5.5
cm wide, base tapered or truncate to rounded, blue-green to slightly
glaucous.
Adult leaves alternate, petioles 0.8-2 cm long;
blade lanceolate, 6-12 cm long,
1-2.2 cm wide, base tapering to petiole, margin entire apex pointed,
concolorous, very glossy, green, side-veins
greater than 45° to midrib,
reticulation moderate to dense, intramarginal vein remote from margin,
oil glands mostly island.
Inflorescences axillary unbranched, peduncles widening apically,
0.8-1.8 cm long; buds 11 to 15, pedicellate, elongated-fusiform,
scar present, operculum horn-shaped, three to four times the length
of the hypanthium and narrower than it at the join, a few outer
stamens erect, most deflexed to varying extent, anthers oblong,
versatile, dorsifixed, dehiscing by longitudinal slits, style long
and straight, stigma more or less tapered, locules 3, the placentae
each with 4 vertical rows of ovules; flowers creamy white.
Fruit pedicellate, cylindrical to obconical, 0.4-0.5 cm wide,
disc descending vertically, valves 3, near rim level or tips scarcely
exserted.
Seed straw-coloured, 0.8-1.2 mm, sub-spherical, surface smooth,
hilum ventral/terminal.
Cultivated seedling (scored at ca node 10): cotyledons Y-shaped
(bisected); stems more or less
rounded in cross-section, slightly warty; leaves always petiolate,
opposite for 3 or 4 nodes then alternate, ovate, 5-8 cm long, 2-5
cm wide, green, slightly glossy by node 10; earliest leaves with
warts on leaf margin but smooth by node 5.
NOTES
Eucalyptus arachnaea (Latin, arachnaeus, spidery,
referring to the bud clusters).
A mallee or mallet endemic to Western Australia, widespread in subcoastal
areas from north of Murchison River south-east to Wagin, usually
on low hilly country. Bark rough on lower part of stems, dark grey
to grey-black. Adult leaves are glossy green. Inflorescences are
distinct in the many slender buds forming a spidery cluster.
Eucalyptus arachnaea belongs to Eucalyptus subgenus
Symphyomyrtus section Bisectae subsection Glandulosae
because the cotyledons are bisected, buds have an operculum scar
and the branchlets have oil glands in the pith. Within this subsection
E. arachnaea is one of a group of 7 species that form series
Levispermae subseries Phaenophylla characterized by
having smooth sub-spherical seed, a peduncle that widens apically,
buds that are narrowly fusiform with some stamens erect and others
variably deflexed, and glossy green leaves.
The rough bark, very elongated buds (to 1.8 cm long) with operculum
recurved at the tip and narrower than the hypanthium at the join
and the seedling leaves with warty margins distinguish E. arachnaea
from other glossy-leaved species.
There are two subspecies:
subsp. arachnaea
The more widespread mallee form which occurs over the whole of the
species' distribution apart from the most inland sites.
subsp. arrecta (Latin, arrectus, upright, referring
to the tree form compared with the typical mallee form).
The mallet form that is only known from west of Morawa, south-east
of Geraldton, in relatively high, stony, hilly country where it
forms small pure stands emergent from the more dominant lower mallee
scrub of the area.
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