Although not as well-known as our native tree ferns, the king fern is one of the most impressive ferns in the New Zealand flora. Due to its bold, glossy foliage and grand stature (it reaches a height of 3m), this giant has long inspired admiration from native plant enthusiasts. As is sometimes the case with desirable plants, its beauty has worked against it; as unscrupulous collectors are one of the threats that this rare species must contend with.
King fern was only recently shifted from the genus, Marattia, to Ptisana. Hence, we have included the synonym in the title of this plant profile, as most horticulturists will probably know it as Marattia salicina. It is the only member of the Marattiaceae, a primitive family of ferns, to occur within New Zealand. One look at king fern betrays its tropical affiliations, and most of its relatives are found in tropical and sub-tropical forests from Africa to the Pacific. Our native species of Ptisana is also found on other Pacific Islands – including Rarotonga, where the photograph below was taken.
For a species that occupies the shaded understorey of damp forest gullies, P. salicina has a particularly cheerful appearance – due largely to its light green hue and the light-reflecting qualities of its fronds. As noted above, it has been a favourite of many native plant specialists for quite some time. However, it has not yet received the full attention that it deserves as a garden plant, possibly as a result of its slow growth rate and the dearth of plant material traditionally available from nurseries.
Having said that, there is a curious phemonenon in Auckland whereby one often sees isolated specimens of P. salicina standing alone out the southern frontage of old houses – as an indication that this species enjoyed a burst of popularity several decades ago. This also points towards the longevity of this species, as it would seem to have outlasted previous generations of plantings in such cases.
As noted previously, king fern is now rare in the wild, as a result of the depredations of pigs and other herbivores, and unethical collecting by humans. Like many other native plants, it has been shown that populations can rapidly flourish with the removal of the animals that hamper their regeneration – as in the case of the population near Auckland shown in the photographs herein.
With regard to that, this plant is a useful example to illustrate how many rare and threatened species endure in the wild. Animal pests are extremely effective at eliminating populations of plants that they wish to eat. Plants that are desirable to them are termed palatable, and plants that herbivores choose to leave are conversely termed unpalatable. Subequently, much of what one sees in forests that contain pests is simply the unpalatable remainder of what the animals prefer not to eat.
King fern falls into the category of a palatable species, particularly to larger herbivores. Therefore, the plants that survive are those that such animals cannot reach, such as on steep banks (although even those can eventually fall to goats). When animal pests are removed, plants like king fern can recolonise all of the places that they would naturally have inhabited. Regeneration that results from this leads not only to ecological benefits, but makes our natural places more diverse and attractive spaces to be in (the latter is an outcome that is often ignored when discussing conservation objectives).
Ptisana salicina is not just found in New Zealand, but extends towards the tropics, including Norfolk Islands and several Pacific Islands (like the Cook Islands and New Caledonia). Within our shores, it extends from the Far North to a southern limit of Taranaki.
An interesting account of the recent history of lowland forest that king fern inhabits in northern Taranaki was given by the ecologist Geoff Park, in his important book on New Zealand’s lowland ecosystems, ‘Nga Uruora : The Groves of Life’.
It is a fairly easy plant to grow in gardens, as long as it is given a shady position, and soil that is not excessively dry. It is commonly known that king fern drops its enormous fronds when subjected to particularly dry periods. However, well established plants readily recover when moisture once again becomes available, as one often sees in areas of Auckland with volcanic soil. However, bearing that in mind, it is best to provide P. salicina with a situation that has consistent moisture, such as at the shady base of a slope or gully, so that it keeps an even appearance throughout the year. One also needs to consider the size of mature specimens when placing plants, as they can eventually cover a diameter of 3m.
Māori traditionally utilised the bulbous root of P. salicina as a food source, and it is known to have been cultivated for this purpose. The Māori approach to the harvesting of this species was one that current generations should take notice of, as it was restricted by tapu – presumably in recognition of the slow growth rate of the plant1. Aside from this traditional value, the base of the plant also constitutes a distinctive aesthetic feature of the plant – the swollen rounded caudex (which is pictured above) is reminiscent of a famous group of plants with a similarly ancient lineage, the cycads.