‘Norfolk Island Tree Fern’
The name Cyathea brownii derives from:
Cyathea – from the Greek ‘kyatheion’ meaning little cup, referring to the structure that holds the spores.
brownii – the species was named after Robert Brown (1773–1858), a Scottish botanist who travelled aboard the Investigator on a voyage to Australia in 1801. Brown is noted for his pioneering use of the microscope.
Common names include the ‘Norfolk Island tree fern’, ‘Norfolk tree fern’, ‘smooth tree fern’.
Cyathea brownii is only found growing in the wild on Norfolk Island one of Australia’s external territories in the South Pacific. In the wild the species is found growing amoungst Cyathea australis in the Norfolk Island National Park. The fern is now rarely found outside of the national park following land clearance. Prior to European colonisation, most of Norfolk Island was covered with subtropical rain forest. Today there is only (5km²) of rainforest left on the island, this was declared the Norfolk Island National Park in 1986. This ensures protection of the habitat of Cyathea brownii.
Cyathea brownii is very closely related to Cyathea cooperi although differs slightly in appearance. The hairs covering the stipes on Cyathea brownii are a sandy colour and dense whereas with Cyathea cooperi the hairs go from dark at the base to a lighter brown. The other difference is that Cyathea brownii grows to be a lot bigger, possibly the largest tree ferns species in the world. Botanists think that the reason for these subtle differences are down to evolution.
The evolution of this species and many other on the island are derived from the chance dispersal of seeds, pollen and spores across huge expanses of ocean. Once on the island species have evolved into unique, or endemic, forms due to isolation from other populations and having different evolutionary pressures.
According to the Bureau of Meteorology the islands average maximum temperatures range from 18C to 19C in winter to between 23C and 25C in summer. The average minimum temperatures range from 13C to 15C in the winter and between 18C and 20C in the summer. The lowest ever recorded temperature was 6°C. The annual mean rainfall is 1312mm meaning that the island has a very pleasant sub-tropical climate.
In its natural habitat the species has a very stable climate but it is capable of withstanding a degree or two of frost however it will not tolerate prolonged or hard frosts.
Cyathea brownii is a very fast growing tree fern which can grow to a height of 24m (78ft) although in cultivation 12-15m is more realistic. The stipes and upper trunk are covered densely in sandy brown scales. The elegant arching frond can reach up to 5m (16ft) in length. This plant is easily grown from spore and will quickly grow into a specimen plant within 3-5 years. If you live in an area which doesn’t experience more than a few degrees frost or temperatures much in excess of 30°C (86°F) then this fern is well worth trying from spore.
Cyathea brownii should be planted in a semi-shaded position out of strong midday sunshine and chilling winds. The plant will become more tolerant as it matures. You will also need to consider the eventual size of the species when planting as they quickly form a trunk and do not like to be moved.
Cyathea brownii will need lots of water. Young plants can consume 1-2 litres a day so make sure it is a position where you can access the plant to water it every day. Drainage is important as the plant will not tolerate being waterlogged. Therefore getting the soil drainage correct is the key. A good humus open compost with lots of organic matter and high in nutrients is best.
Dig a hole 1m in diameter and 60-80cm in depth and fill this with drainage material like rubble and then cover in gravel to stop the top soil washing through. Then fill the whole with your compost securing the plant whilst trying not to compact the compost to much. To achieve this you may want to stake the plant if it is trunked to provide extra stability whilst the plant establishes its root system.
This species is difficult to grow in colder climates as the speed at which it grows means within a few years it become difficult to protect over winter in a greenhouse or conservatory.
Family Name: Cyatheaceae.
Common Name: Norfolk Island tree fern, Norfolk tree fern, smooth tree fern.
Position: semi shaded.
Soil: Humus-rich, fast draining, neutral to acid soil.
Growth Rate: very fast.
Eventual spread: 10m
Max Height: 15m (cultivated)
Hardiness: Half Hardy – down to -2°C.
Summer tips: Keep plants moist, without waterlogging.