Croton magneticus  Airy Shaw 1980

pronounced: KROH-tun mag-NET-ik-uss

(Euphorbiaceae – the spurge family)

common name:  Magnetic Island Croton

Croton croton magneticusCroton magneticus croton magneticusmottled bark comes from the Greek κροτων (kroton), a tick. And yes, magneticus is botanical Latin for ‘from Magnetic Island’. This plant occurs in north-east Queensland between Greenvale in the north to near Collinsville in the south. It grows in deciduous vine thickets on soils derived from sandstone, granite or acid agglomerate substrates. It is noted to be rare to occasional on Gloucester Island and Mount Stuart, frequent to common on Magnetic Island, Mt Abbot and Mt Blackjack.

This is a deciduous small tree or shrub that grows up to 5 m high. The bark is a distinctive mottled grey. The young shoots are densely covered with ginger-coloured to silvery stellate hairs. The leaves are obovate, elliptic or ovate-elliptic in outline, 2–11.5 cm long by 1.2–6 cm wide, alternately arranged along the branchlets. There are 5–9 lateral veins on either side of the midrib. The upper surfaces of the leaves are hairless or with scattered stellate hairs; the lower leaf surface is silvery with scattered to dense stellate hairs. The leaf margins are minutely and shallowly toothed with 8–24 acute or rounded teeth.

croton magneticus in budin bud croton magneticus male flowersmale flowersThe inflorescences are terminal racemes, up to 8 cm long and bearing mostly separate male and female flowers 3–5 mm long. There are 6–10 female flowers at the base of the raceme for about a third of its length, and the remaining flowers are all male. The orange-yellow fruiting capsules are round, measuring about 8 mm in diameter, and densely covered with stellate hairs. The mature capsules split to release usually 3 seeds. There is a similar plant, Croton arnhemicus, that grows in the same area as Croton magneticus, and is distinguished by the 3–5 veins that arise from the base of the leaf.

croton magneticus developing fruitdeveloping fruits croton magneticus mature fruitmature fruit The species is listed as vulnerable. The main threat in the past has been the destruction of habitat by land clearing. This threat has now lessened, as the 11 populations known to remain on leasehold or freehold land are in areas of remnant vegetation that are now protected from broad-scale clearing. The main potential threats include inappropriate fire regimes and the invasion of the species habitat by exotic species such as lantana (Lantana camara) and rubber vine (Cryptostegia grandiflora). The lantana invasion has the added disadvantage of alteringthe fuel characteristics and flammability of the relatively fire-sensitive deciduous vine thicket communities. Infrastructure development may also destroy plants, or disturb or fragment the remaining habitat.

The plants photographed are by the side of the road to the old Arcadia jetty, near the shelter. There is also a group of the plants on the headland between Arthur and Florence Bays, near the lookout. They have also been sighted between Radical and Balding Bays, between White Lady Bay and Horseshoe Bay, and at the end of West Point. In the Gustav Creek area of Nelly Bay, Croton magneticus has been found in both vine forest and mixed deciduous woodland. I should be very interested to hear of any other sightings of this plant.

Photographs taken in Geoffrey Bay, 2010, 2012

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