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Habit and habitat. Photo W.R.Barker

Horizontal root with suckers in situ. Photo W.R.Barker

Horizontal root with new suckers. Photo W.R.Barker

Foliage and inflorescences. Photo W.R.Barker

Inflorescence. Photo W.R.Barker

Note pollen presenter shape. Photo W.R.Barker

Synonymy

Hakea aenigma W.R.Barker & Haegi, J. Adelaide Bot. Gard. 7: 261 (1985)

T: Shackle Rd c. 2.8 km S of Playford Hwy, Kangaroo Is., S.A., 6 Oct. 1982, W.R.Barker 4479 & L.Haegi; holo: AD; iso: CANB, K, MEL, NSW, PERTH.

Description

Rounded bushy shrub, 1.5–2.5 m tall, suckering from horizontal roots. Branchlets densely appressed-pubescent or sometimes patchily glabrescent at flowering. Leaves flat, linear, not twisted, 5–35 cm long, 3–10 mm wide, glabrescent or patchily appressed-pubescent; marginal veins prominent; longitudinal veins prominent, 1–7 above and 4–9 below.

Inflorescence a solitary axillary umbelliform raceme, with 16–33 fully developed but sterile flowers; pedicels cream-white, glabrous. Perianth cream-white. Pistil 4.5–7.2 mm long; gland absent.

Fruit not formed.

Distribution and ecology

Rare and confined to the higher parts of the lateritic plateau system at the west end of Kangaroo Is., S.A. Grows in dense mallee-heath in sandy to clayey loam soil.

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 Sept.–Nov.

Derivation of name

From aenigma, Latin for riddle, a reference to the initial puzzle with respect to the finding of fruits of this species, to its unusual life history and the uncertainty of its origins.

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Relationships

Part of the Conogynoides group recognised by Bentham and characterised by a conical pollen presenter, veined leaves, glabrous perianth and fruits without horns. Barker et al. (1999) recognised a number of informal morphological groups within the section.

 

One of these was the Ulicina group. This group of 21 Hakea species was combined morphologically because they all have simple flat leaves or leaves which are apparently terete but when looked at in cross section are clearly angled; these angled leaves are longitudinally furrowed and often referred to as sulcate. Furthermore the group has inflorescences with 6-80 small flowers (with 3-18 mm long pistils) and erect woody fruits.  

Members of the group are H. aenigma, H. carinata, H. costata, H. cygna, H. dohertyi, H. erecta, H. gilbertii, H. invaginata, H. lehmanniana, H. marginata, H. meisneriana, H. mitchellii, H. myrtoides, H. pycnoneura, H. repullulans, H. rigida, H. scoparia, H. stenocarpa, H. sulcata, H. subsulcata and H. ulicina, mostly from southern WA but also from south-eastern Australia.  

Notes

The closest relative of H. aenigma seems to be H. repullulans , but the two are amply distinct. This remarkable species appears to consist of a single clone which must have spread over its current range, occupying an area of c. 30 km by 15 km, by suckering from vigorous horizontal roots.

 This species is recognised as 'Rare' in J.D.Briggs & J.H.Leigh, Rare or Threatened Australian Plants (1995).

Conservation status

Gazetted as Rare (Schedule 9) under the South Australian National Parks & Wildlife Act 1972.

Representative specimens

S.A.: Flinders Chase Conservation Park, Kangaroo Is., L.Haegi 2287 & W.R.Barker (AD, MEL, MO, PERTH); Waters' mail box near sources of Western R., Kangaroo Is., L.Haegi 2288 & W.R.Barker (AD, BRI, CANB, DNA, NSW, PERTH).

Weblinks

Link to SA eFlora treatment.

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