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The Silver tree fern, member of the Cyathacea family, is one of the most distinctive and easily recognised of all the native tree-ferns, the silvery-white underside of the fronds immediately identifying it. Indeed, New Zealand's native emblem, the 'Silver Fern' is derived. The silver tree fern is common in lowland and montane (subalpine) forests throughout the North & South Islands, as far as the Catlin's area in the east and is probably absent from the west. Its alternative name is 'ponga' a Maori native tongue encompassing majority tree fern species within the islands, however over the course of time this has been corrupted to 'punga' or sometimes 'bungie'. The trunk is up to 45 cm in diameter at the base and is fibrous, the upper section marked by the bases of the old frond stalks. The crown exhibits numerous fronds that usually spread horizontally in an umbrella style canopy, and are 2m - 4m long X 60cm - 1.2m wide. The bases of the fronds are covered in a silvery-white, waxy bloom. On the younger plants, the under-surfaces are green, the silvery-white colour not apparent until a certain stage of adulthood has been reached. On fertile fronds, the undersides are dotted numerous brown sori (a cluster of sporangia- any organ, esp in fungi, in which asexual spores are produced - on the under-surface of certain fern leaves). Perhaps most distinctive and easily recognisable are the unfurling fronds, and the spiral-type patterns they manifest throughout the frond (in diminishing patterns) as they open. If the fleshy arm is damaged or pruned when development is at this stage, a resinous, sticky amber coloured sap exudes from the damaged tissue, which jellifies on contact with air.