Cyathea brownii

Norfolk tree fern
Scientific classification
Kingdom:	Plantae
Division:	Pteridophyta
Class:	Pteridopsida
Order:	Cyatheales
Family:	Cyatheaceae
Genus:	Cyathea
Subgenus:	Sphaeropteris
Section:	Sphaeropteris
Species:	C. brownii
Binomial name
Cyathea brownii Domin, 1929
Synonyms
Alsophila excelsa R. Brown ex Endlicher, 1833 Sphaeropteris excelsa (R. Brown ex Endlicher) Tryon, 1970

Cyathea brownii, commonly known as the Norfolk tree fern or smooth tree fern, is probably the largest tree fern species in the world. An endemic of Norfolk Island, in the wild it is reported to reach 20 m (67 ft) or more in height. The broad, lance shaped, bipinnate-pinnatifid to tripinnate fronds can reach 5 m (17 ft.) in length. Stipe is long and has a line of white, stitch like dashes along its length. Rachis and stipe are covered in white-brown and darker orange-brown scales. The trunk can become smooth with age and may display oval scars left from fallen fronds. It is named after the botanist Robert Brown (1773-1858).

Habitat and distribution

World distribution of Cyathea brownii

Cyathea brownii is endemic to Norfolk Island in the Pacific Ocean close to Australia and New Zealand.

Cyathea brownii occurs naturally in subtropical rainforest on Norfolk Island. Average daytime temperatures reach around 23 °C during the summer months falling to around 17 °C during the winter. The highest temperatures likely to be experienced in this environment are around 29 °C, the lowest around 6 °C. Relative humidity is fairly consistent at levels between 70 and 80% throughout the year. Yearly rainfall is approximately 1200 mm.

Conservation

The once extensive forests of Norfolk Island are now reduced to a single small forested area which has been designated part of a national park. Cyathea brownii is protected within this park. It is available in cultivation in many countries and though rare is not considered endangered.

Cultivation

Cyathea brownii is easily grown from spore and can be very fast growing when young. It requires a neutral to slightly acidic soil rich in organic matter. The soil must be moisture retentive but well drained. The tree fern will suffer if left to stand in waterlogged soil. Cyathea brownii requires high humidity and either high rainfall or frequent watering. During the summer months even a very young pot grown plant can consume half a litre of water per day. Cyathea brownii requires good light but does best when shaded during the hottest parts of the day. It responds well to fertilization but can be intolerant of some commercial fertilizers producing malformed fronds and a larger but weaker plant. It is able to withstand only light frosts. Larger plants may survive overnight temperatures as low as minus three degrees Celsius. In countries such as Britain it is best grown in a conservatory. Its large size however often makes this impractical. A beautiful and rewarding plant but in colder regions it is strictly for the more dedicated of enthusiasts.

References

• Braggins, John E. & Large, Mark F. 2004. Tree Ferns. Timber Press, Inc. ISBN 0-88192-630-2
• Rickard, Martin. 2003. The Plantfinder's Guide To Garden Ferns. Timber Press, Inc. ISBN 0-88192-567-5
• Bureau of Meteorology, Australian Government.