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''Sphaeropteris excelsa'',
synonym A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are al ...
''Cyathea brownii'', commonly known as the Norfolk tree fern or smooth tree fern, is probably the largest
fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes exce ...
species in the world. It is
endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...
to
Norfolk Island Norfolk Island (, ; Norfuk: ''Norf'k Ailen'') is an external territory of Australia located in the Pacific Ocean between New Zealand and New Caledonia, directly east of Australia's Evans Head and about from Lord Howe Island. Together wit ...
, in the
Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the conti ...
near
Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
and
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island coun ...
. It is named after the botanist Robert Brown (1773-1858).


Description

In its natural habitat, ''Sphaeropteris excelsa'' is reported to reach or more in height. The broad, lance shaped, bipinnate-pinnatifid to tripinnate
frond A frond is a large, divided leaf. In both common usage and botanical nomenclature, the leaves of ferns are referred to as fronds and some botanists restrict the term to this group. Other botanists allow the term frond to also apply to the lar ...
s can reach ) 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.


Habitat

''Sphaeropteris excelsa'' occurs naturally in
subtropical The subtropical zones or subtropics are geographical and climate zones to the north and south of the tropics. Geographically part of the temperate zones of both hemispheres, they cover the middle latitudes from to approximately 35° north a ...
rainforest Rainforests are characterized by a closed and continuous tree canopy, moisture-dependent vegetation, the presence of epiphytes and lianas and the absence of wildfire. Rainforest can be classified as tropical rainforest or temperate rainfores ...
s on Norfolk Island. Average daytime temperatures reach around during the summer months falling to around during the winter. The highest temperatures likely to be experienced in this environment are around , the lowest around 6 °C. Relative humidity is fairly consistent at levels between 70 and 80% throughout the year. Yearly rainfall is approximately . ;Conservation The once extensive forests of
Norfolk Island Norfolk Island (, ; Norfuk: ''Norf'k Ailen'') is an external territory of Australia located in the Pacific Ocean between New Zealand and New Caledonia, directly east of Australia's Evans Head and about from Lord Howe Island. Together wit ...
are now reduced to a single small forested area which has been designated part of a
national park A national park is a natural park in use for conservation purposes, created and protected by national governments. Often it is a reserve of natural, semi-natural, or developed land that a sovereign state declares or owns. Although individual ...
. ''Sphaeropteris excelsa'' is protected within this park. It is available in cultivation in many countries and though rare is not considered endangered.


Cultivation

''Sphaeropteris excelsa'' is cultivated as an
ornamental tree Ornamental plants or garden plants are plants that are primarily grown for their beauty but also for qualities such as scent or how they shape physical space. Many flowering plants and garden varieties tend to be specially bred cultivars that ...
. 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. ''Sphaeropteris excelsa'' requires high humidity and either high rainfall or frequent watering. During the summer months even a very young pot grown plant can consume of water per day. ''Sphaeropteris excelsa'' 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 Britain most often refers to: * The United Kingdom, a sovereign state in Europe comprising the island of Great Britain, the north-eastern part of the island of Ireland and many smaller islands * Great Britain, the largest island in the United King ...
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. It is easily grown from spore and can be very fast growing when young.


References

{{Taxonbar, from1=Q17188525, from2=Q1998991 excelsa Ferns of Australia Flora of Norfolk Island Endemic flora of Australia Garden plants of Australia Ornamental trees