Spinifex sericeus  R.Br. 1810

pronounced: SPIN-ih-fecks sir-ee-KEE-uss

(Poaceae – the grass family)

common names:  Beach Spinifex, Coastal Spinifex

Spinifex Spinifex sericeusmale beach spinifex Spinifex sericeusfemale beach spinifexis derived from the Latin spina, a thorn, and the root of facere, to make; sericeus is Latin for silky. This plant, and not the porcupine grass (Triodia scariosa) locally known as spinifex, is the true spinifex, and it was great to see it appear in two separate locations, one male and one female, on Picnic Bay beach in December, 2014. It became quite well established by the end of winter 2016, and the plants should greatly assist with beach stabilization.

Spinifex sericeusmale flowering Spinifex sericeusfemale flowering Beach spinifex is an important pioneer species which colonizes coastal dunes, being able to grow in bare sand and binding the loose sand with its horizontal runners. It can form dense mats.

This is a dioecious perennial grass native to Australia and New Zealand. It has branched stolons and rhizomes extending up to several metres, as far as 20 m when conditions are favourable. New nodes are formed at intervals of 10 – 15 cm. Roots emerge from these, and, where there is sufficient space, a discrete plant will eventually form and become independent of the original stolon.

Spinifex sericeusfemale inflorescence Spinifex sericeusmale inflorescence The leaves, usually less than 1 cm wide and up to 30 or 40 cm long, have a ligule of a rim of dense hairs; the blades are limp, flat and densely silky. The layer of fine hairs on the leaves slows down air movement, assisting the plant to reduce water loss from the leaves.

 

Beach spinifex can grow to about 50 cm tall, but is more frequently found 30 – 40 cm high.

Spinifex sericeusmale inflorescence detail Spinifex sericeusfemale inflorescence detail The male inflorescence is an orange-brown terminal cluster of spiky racemes subtended by silky-hairy bracts; the rachis is bare in the lower part and prolonged as a stout bristle beyond the spikelets. The female inflorescence detaches at maturity, a globose seed head of sessile racemes up to 20 cm in diameter, each raceme reduced to a single spikelet enclosed by large silky-hairy bracts, the rachis extending into a stout bristle 5 – 10 cm long, giving the cluster a spiky appearance. After detaching, the female flower-head becomes a tumbleweed that can be seen rolling along the beach driven by the wind, and will often become caught in other vegetation. Male and female plants usually form colonies of equal size. Flowers of both genders begin to appear in spring when pollination occurs.

Spinifex sericeusmature male inflorescence Spinifex sericeusseeds The female inflorescence examined provided only a very few viable seeds. This may mean that propagation by seed dispersal may not be as important to this species as the spreading by runners. It should be noted, however, that the clump of spinifex first noted in 2014 has now, by 2017, spread considerably.

Spinifex sericeusseed detail There is a floral smut, Ustilago spinificis , that can infect both the male and female flowers, and can wipe out whole colonies of coastal spinifex. I suspect that is the explanation for the scarcity of this plant on our local beaches. Infected flowers have a swelling above the base of each flower spike.

Photographs taken in Picnic Bay 2014-2017

Page last updated 18th September 2017

 

 

 

 

 

 

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