Acacias of Australia

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Acacia trachycarpa E.Pritz. x Acacia tumida var. pilbarensis M.W.McDonald




Confined to the Pilbara region of north-western W.A. where it is scattered and relatively infrequent in areas N of the Fortescue R.


Shrub or tree 2–5 (–6) high. Bark grey, normally pseudo ‘Minni Ritchi’ towards base of main stems (i.e. grey and exfoliating in ±oblong, short strips which are mostly very slightly recurved at the ends). Branchlets normally glabrous. Stipules persistent, triangular, 0.5–1 mm long, dark brown. Phyllodes broadly linear to narrow elliptic, not rigid, upper margin flat and c. twice width of lower margin, 6–13 (–15) cm long, 4–7 (–10) mm wide, normally glabrous; longitudinal nerves numerous, fine, close together but not touching (0.2–0.3 mm apart), sometimes sparingly anastomosing, central nerve the most pronounced. Inflorescences a mixture of axillary spikes and short racemes 1–20 (–35) mm long; peduncles (2–) 6–12 (–14) mm long; spikes 15–25 mm long, golden, showy. Flowers 5-merous; calyx dissected for about ½–¾ its length, shortly villous. Pods (few seen) ±narrowly oblong, flat, variably constricted between the seeds, 2–10 cm long, 9–11 mm wide, thinly coriaceous, straight to strongly curved, reticulately nerved, glabrous, pale brown. Seeds longitudinal, oblong to elliptic, 7 mm long, dark brown, with a narrow band of verriculose tissue bordering the pleurogram; aril dull yellow and waxy textured.


Flowers May–July.


It grows mostly in (often stony) sand along watercourses.


W.A.: 6 miles [10 km] N of Fortescue R. crossing, [old] North West Coastal Hwy, B.R.Maslin 2758 (CANB, K, PERTH); 11.65 km WSW of Mt Sabine, Millstream–Chichester Natl Park, Hamersley Ra., site 1149, M.E.Trudgen 18347 (PERTH).


This putative hybrid has occasionally been used for amenity planting in Karratha and Dampier where it develops as a handsome tree to 6 m tall with a bushy growth form.

The putative hybrid status of this entity has been determined from field observations and from examination of herbarium material; it is recognized in the field by its pseudo ‘Minni Ritchi’ bark which distinguishes it from both putative parents. It is intermediate between the parents in phyllode width and inflorescence structure, fide B.R.Maslin et al., Wattles of the Pilbara CD-ROM (2010) for discussion. Some specimens resemble A. eriopoda ´ tumida var. pilbarensis which occurs in the vicinity of Nullagine.

Plants described here as A. trachycarpa × tumida var. pilbarensis were erroneously referred to A. ancistrocarpa × trachycarpa by B.R.Maslin, Nuytsia : 4: 405–407 (1983) and noted under A. ancistrocarpa by NSW, Fl. Australia 11B: 246 (2001).

FOA Reference

Flora of Australia Project