Botanical name

Acacia ? rhodophloia x sibirica

Description

Rounded or obconic, spreading shrubs or small trees 1.5-4 (-5) m tall, dividing at or near ground level into 2-6 or more slightly crooked main stems. Bark grey, flakey or exfoliating in a pseudo Minni Ritchi fashion (i.e. peeling in strips that are often slightly recurved at the ends), longitudinally fissured towards base of oldest plants, smooth on upper branches. Branchlets glabrous. New shoots khaki green, glabrous, slightly shiny. Phyllodes linear to narrowly oblong or narrowly elliptic, narrowed at base, (3-) 4-8 (-9) cm long, usually 2-4 (-6) mm wide, coriaceous, sub-rigid, ascending to erect, straight to shallowly incurved, glabrous, dull, green or grey-green to bluish green; parallel longitudinal nerves numerous, the nerves fine, close together and of uniform prominence; apex ending in a hard, non-spiny point. Gland often very obscure, situated on upper margin of phyllode 0-1 mm above the pulvinus. Inflorescences simple, 1 or 2 within axil of phyllodes; peduncles 3-8 (-10) mm long (shorter than the spikes), glabrous or occasionally very sparsely hairy, invested with microscopic red-brown resin hairs when in flower; spikes short, 10-30 mm long (when dry), light golden, the flowers sub- densely arranged. Flowers 5-merous; calyx 1/3-˝ length of corolla, very shortly dissected into triangular lobes, tube ąsparsely hairy at the truncate base. Pods linear to narrowly oblong, flat, scarcely raised over seeds, straight-edged or slightly constricted between the seeds, 4-6 cm long, (4-) 5-6 (-8) mm wide, thinly coriaceous-crustaceous, straight to shallowly curved, glabrous, light brown, with a short basal stalk. Seeds longitudinal to longitudinally oblique in the pods, very dark brown to black, flat, 4-5 mm long, 2.5-3 mm wide; aril presumably white when fresh but drying dull yellow.

Characteristic features

Shrubs or small trees. Bark grey, flakey or exfoliating in a pseudo Minni Ritchi fashion. Branchlets glabrous. Phyllodes linear to narrowly oblong or narrowly elliptic, mostly 4-8 cm long and 2-4 mm wide, coriaceous, sub-rigid, ascending to erect, straight to shallowly incurved, glabrous; parallel longitudinal nerves numerous, fine, close together and of uniform prominence; apex ending in a hard, non-spiny point. Spikes longer than the peduncles, the flowers sub- densely arranged. Calyx 1/3-˝ length of corolla. Pods linear to narrowly oblong, mostly 5-6 mm wide, flat, scarcely raised over seeds, ąstraight -edged. Seeds longitudinal to longitudinally oblique.

Distribution and ecology

This uncommon putative hybrid s confined to the Pilbara region of northwest Western Australia where it occurs at a few localities in the Hamersley Range area between Newman and the general vicinity of Tom Price, and also on Balfour Downs Station (about 150 km northeast of Newman). Grows on in low hilly country in skeletal red-brown loam.

Flowering and fruiting period

Flowering appears to be sporadic and may well occur in response to the incidence and intensity of rainfall. Specimens with flowers have been collected from May to late August, but often only a few flowers (and sometimes also buds) were present on the plants during this period. Pods with mature seeds have been collected in late September.

Variation

Most collections are from the Hamersley Range where phyllodes measure 2-4 (-6) mm wide (suggesting that it is the narrow phyllodes forms of A. sibirica which occur in this area that are implicated in the hybridity). However, the putative A. rhodophloia x sibirica hybrid (growing with the two putative parents) on Balfour Downs Station has phyllodes 8-10 (-13) mm wide which is not surprising because the phyllodes on the adjacent A. sibirica plants measured 5-6 mm wide (and were even wider on the A. rhodophloia plants).

Taxonomy

Some of the plants referred to A. sibirica variant 2 by Maslin (1982) belong to this putative hybrid.

Affinities

It is extremely difficult to recognize this putative hybrid in the absence of knowing its bark characteristics; also, knowing what species it grows with may also aid in its identification. This putative hybrid is always found in association with A. rhodophloia but only rarely is A. sibirica also present in these populations (although it is common in the general area where the hybrid grows). Acacia rhodophloia is most readily recognized by its red Minni Ritchi bark which often extends to the upper branchlets (and therefore may be seen on herbarium specimens), and also its often broad phyllodes (mostly 4-10 mm wide). However, distinguishing the putative hybrid from A. sibirica is more difficult, at least when using dry herbarium material. The most reliable way of distinguishing A. sibirica from the putative hybrid is by its bark which shows no sign of exfoliating in a Minni Ritchi fashion. Collectors often describe the bark of the putative hybrid as being flakey or exfoliating in a pseudo Minni Ritchi fashion (i.e. the individual strips of bark may curl slightly at each end). These are not major differences but experienced collectors are often able to distinguish the two entities in the field. Specimens with linear phyllodes might be confused with A.? adsurgens x rhodophloia which may also have a similar bark. However, A.? adsurgens x rhodophloia is recognized by its peduncles which are about of equal length to the spikes (peduncles clearly shorter than the spikes in A.? rhodophloia x sibirica) and its narrower pods (about 2 mm wide).

Conservation status

There is insufficient information at present concerning this entity to justify including it on the Department of Environment and Conservation's Declared Rare and Priority Flora List.

References

Maslin, B.R. (1982). Studies in the genus Acacia (Leguminosae: Mimosoideae) - 11. Acacia species of the Hamersley Range area, Western Australia. Nuytsia 4(1): 61-103.