Allocasuarina decussata

Allocasuarina decussata, commonly known as karri oak[2] or karri she-oak,[3] is a medium-sized tree, or more rarely a shrub, that is endemic to the south west of Western Australia. It is an understory tree in karri forest but also occurs as a stunted shrub in places like Bluff Knoll in the Stirling Range.

Karri she-oak
Allocasuarina decussata.JPG
A. decussata, foliage and cones
Allocasuarina decussata - Flickr - Kevin Thiele.jpg
A. decussata, cone detail
Scientific classification edit
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Rosids
Order: Fagales
Family: Casuarinaceae
Genus: Allocasuarina
A. decussata
Binomial name
Allocasuarina decussata
Occurrence data from AVH

Casuarina decussata Benth.


Karri oak usually grows as a medium tree 8–15 m (26–49 ft) high, although in harsh, exposed situations in places like the top of Bluff Knoll it is a stunted shrub or poorly-formed tree in shrubland. As with other members of the family Casuarinaceae, the foliage consists of wiry green branchlets called cladodes with rings of minute leaf scales. In this species, the branchlets are about 140 mm (5.5 in) long, roughly square or X-shaped in cross section, with four scale-teeth in each ring. The rings of scale-leaves are 7–9 mm (0.28–0.35 in) apart. Separate male and female flowers form on the same individual plant. The fruiting structure is a woody cone, shaped like a short cylinder with its diameter roughly equal to or slightly greater than its length. The fruit is a winged samara 7–9 mm (0.28–0.35 in) long.[4] It often grows in association with Acacia pentadenia[2] and Asplenium aethiopicum often grows as an epiphyte on its branches.[4]


This species was first formally described in 1873 by George Bentham Flora Australiensis from specimens collected by James Drummond near Cape Riche, Western Australia. Bentham gave it the name Casuarina decussata.[5][6] In 1982, Lawrie Johnson moved it to its current genus Allocasuarina in his revision of the she-oaks.[7] It is closely related to A. torulosa of New South Wales and Queensland.[2]

Bark of a young A. decussata in the Walpole-Nornalup National Park.

The specific epithet (decussata) is a Latin word meaning "like the letter X" or "the Roman numeral ten".[8]

Distribution and habitatEdit

Karri oak is restricted to the southwest of Western Australia in the Esperance Plains, Jarrah Forest and Warren biogeographical regions. It grows on loam in the karri forest but also found on much poorer soils in the Stirling Range.[3]

Cultivation and usesEdit

Karri oak is not known in cultivation and there is only limited availability of timber because most trees are in national parks but its pale reddish-brown heartwood has distinctive rays that potentially make it useful as a craft wood.[2]


  1. ^ a b "Allocasuarina decussata". Australian Plant Census. Retrieved 7 January 2020.
  2. ^ a b c d "Karri oak". Forest products commission Western Australia. Retrieved 29 January 2015.
  3. ^ a b "Allocasuarina decussata (Benth.) L.A.S.Johnson". FloraBase. Western Australian Government Department of Parks and Wildlife.
  4. ^ a b Wilson, Karen Louise; Johnson, Lawrence A.S. (1989). Flora of Australia (Volume 3) (PDF). Canberra: Australian Government Publishing Service. pp. 142–143. Retrieved 7 January 2020.
  5. ^ "Casuarina decussata". APNI. Retrieved 7 January 2020.
  6. ^ "Flora australiensis:a description of the plants of the Australian territory /by George Bentham, assisted by Ferdinand Mueller". Biodiversity Heritage Library. pp. 200–201. Retrieved 30 January 2015.
  7. ^ "Allocasuarina decussata". APNI. Retrieved 7 January 2020.
  8. ^ Brown, Roland Wilbur (1956). The Composition of Scientific Words. Washington, D.C.: Smithsonian Institution Press. p. 255.