 Habit. Kakadu National Park. Photo © W.R.Barker |
 Corky trunk. Photo © W.R.Barker |
 Long pedunculate inflorescence. Photo © W.R.Barker |
 Fruits and leaves. Photo © W.R.Barker |
 Young fruits and leaves. Photo © W.R.Barker |
 Fruit. Photo © W.R.Barker |
Synonymy
Hakea arborescens R.Br., Trans. Linn. Soc. London 10: 187 (1810)
T: Carpentaria, South Wellesley Islands, [Qld], Islands a [Sweers], b [Bentinck] and c [Allen], 17–27 Nov. 1802, R.Brown no. 7 [Iter Austral. 3362]; lecto: BM p.p., fide R.M.Barker, Nuytsia 12: 3 (1998); isolecto: B, BM, E, K p.p., MEL 108133 p.p., P, NSW, NY; remaining syn: North coast, s.d., R.Brown s.n.; syn: MEL 108133 p.p., K p.p.; The English Companys Is, Island y1 [Cotton], [N.T.], 20 Feb. 1803, R.Brown s.n.; syn: BM p.p.
Images of the NY Robert Brown type specimens can be seen on the New York Botanical Garden site.
Description
Shrub 2–5 m high, or tree 3–7 m high; bark black or grey, deeply fissured. Branchlets patchily white appressed-pubescent. Leaves flat, linear, narrowly elliptic or narrowly obovate, 5–17 cm long, 1–9 mm wide, initially densely appressed-ferruginous, quickly glabrescent.
Peduncle simple, 4–13 mm long, densely tomentose; rachis 2.5–9 mm long, ferruginous-pubescent. Flowers c. 50–60 per inflorescence, white or yellow; pedicels 3–4.5 mm long, densely white-tomentose. Perianth 2–2.5 mm long, white-tomentose on claw, ferruginous on limb. Pistil 1.5–2.5 mm long; style recurved, rarely ±straight; pollen presenter conical, obliquely inserted.
Fruit obliquely ovate, 3–5.5 cm long, 1.6–3 cm wide, gradually or abruptly attenuate into recurved apiculum to 4 mm long. Seed occupying part of valve, 21–35 mm long, 7.5–13.5 mm wide; wing yellow.
Distribution and ecology
Occurs across northern tropical Australia, north of 21°S in W.A., N.T. and Qld; found on sandstone, quartzite and limestone areas, often from creek banks or low-lying areas, but also from monsoon forest or Eucalyptus woodland.
To plot an up to date distribution map based on herbarium collections for this species see Australia's Virtual Herbarium. Localities outside the native range may represent cultivated or naturalised records.
Flowering time
Flowers Jan.–June, but predominantly in earlier months.
Derivation of name
From arborescens, Latin for becoming tree-like.
Relationships
Part of the Pedunculata Group of Barker et al. (1999), this group of 4 species (H. arborescens, H. pedunculata, H. persiehana and H. stenophylla) is held together morphologically by the possession of a bare peduncle below the rachis. They also have obscurely-veined leaves, oblique or conical pollen presenters, hairy perianths and woody fruits without horns.
While Bentham referred them to the Grevilleoides, presumably because they may sometimes have a corky bark, it seems likely that these will eventually prove to be an artificial group, with H. arborescens and H. persiehana being closely related but probably not close to H. pedunculata and H. stenophylla. Molecular studies by Mast (unpubl.) have already shown the former but the latter two species were not included in the study.
Notes
At least some populations of this species are capable of regenerating after fire according to a note on the specimen George 15330.
Hakea persiehana and H. arborescens are very closely related, differing predominantly in their leaf shape (terete in the former species, flat in the latter), but since no intermediate specimens have been encountered they have been maintained as species. They are unique in Hakea in often having short colourless hairs at the base of the style.
Hakea stenophylla and H. arborescens differ in flower size, branching of the peduncle, and pollen presenter morphology, but unless flowers are present it can be difficult to distinguish them since they overlap in leaf size. Hakea arborescens usually flowers in the earlier months of the year (Jan. & Feb.), although it has been recorded as late as June, while H. stenophylla flowers May–Aug. There appears to be no overlap in distribution, with H. arborescens occurring north of 20°S and H. stenophylla well south of this.
Representative specimens
W.A.: Wolf Creek Crater, A.S.George 15330 (PERTH); 100 km NE of Fitzroy Crossing township, M.Lazarides 6475 (AD, CANB, DNA, NSW). N.T.: 6 km NW of Springvale Stn, M.Lazarides 5065 (AD, BRI, CANB, DNA, MEL, NSW); 0.4 km SW of El Sharana, P.Martensz & R.Schodde AE462 (BRI, CANB, DNA). Qld: Granada, 80 km N of Cloncurry, S.L.Everist 5220 (AD, BRI).
Weblinks
Link to FloraBase treatment of this species for WA.
More photographs of this species can be seen on the Australian National Botanic Gardens site.
Further illustrations
J.A..Young, Hakeas of Western Australia. A Field and Identification Guide 13 (2006)