There are more than 600 Cyathea species, a genus of evergreen tree ferns found throughout the tropics. They look like single-stemmed palms, with a crown of graceful fronds (up to six metres long) at the top of a trunk, which can be over 20 metres high. In their native tropical forests, tree ferns tend to occupy the understorey layer. Tree ferns are sometimes referred to as ancient ferns since rich fossil deposits have been found containing tree ferns.
Tree ferns have a few, short roots at the base of the trunk for anchorage, but most of the roots descend from the crown of fronds, covering the trunk with a mass of aerial roots. It is important to keep the trunk regularly misted, especially in the summer, both outside and under glass, to replicate the cloud forest from which many Cyathea species come. A characteristic of cyatheas is the occurrence of old frond scars on the trunks. Many species have brown trunks but some have black trunks, such as in Cyathea medullaris, a tall, elegant tree fern, native of New Zealand and parts of Australia.
The majority of cyatheas need protection when grown in the UK; Cornwall is perhaps an exception, where it is possible to grow Cyathea australis outside. Young plants can make good pot plants, but do need to be kept watered.
As with all ferns, reproduction in cyatheas is by spores, not seed. Spores are produced in structures (sori) on the underside of the fronds. The arrangement and shape of the sori helps identify different tree ferns, together with characteristics such as frond shape and structure. At Oxford Botanic Garden, cyatheas, and other ferns, are grown from spores sown upon a damp, sterilised, peaty medium. Once sown, the pot is covered with a sheet of glass or plastic to create the necessary humid environment, and placed in a warm, shady spot in a glasshouse.
The soft, trunk pith of some species of Cyathea is baked and roasted for eating, whilst the characteristic dense hairs found on the leaf stalks are used to stuff pillows. However, both of these practices come with a warning; many ferns contain carcinogenic chemicals. Furthermore, the hairs can be intensely irritating to the skin and throat, so care should be taken when handling specimen plants. The trunks are used for buildings, growing orchids on and packing material. Some natural tree fern populations are declining.
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