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Platycerium ridleyi Christ


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This myrmecophyte is one of the world's most striking epiphytic ferns and undoubtedly one of the gems of the genus. Platycerium ridleyi is reportedly extinct in Singapore and is localized in the lowlands of Pensinsular Malaysia and southern Thailand due to habitat loss and over-collection. It is also reported from lowland tropical forests of both Borneo and Sumatra.

The proper binomial for this fern is still unresolved, but presumably prolonged use of this name in horticulture and regional botanical texts will ultimately lead someone to resolve in favor of current combination.

Platycerium ridleyi remains somewhat uncommon in cultivation due to difficulty in propagation since it does not offset and sporelings are challenging to grown on from initial transplant. Some success has been evident in both TC and in vitro germination of spore in SE Asian laboratories. Wild-collected plants still find their way into both local and international trade, but success re-establishing this material remains rather elusive. There have been increasing numbers of spore-grown plants available in the US and EU over the past several years, and prices for smaller plants have dropped to levels where they are generally affordable to the average grower. Specimen-sized plants remain quite costly in the horticultural trade, with prices commonly running into the hundreds of EUR/USD per plant at specialty nurseries in the EU and U.S.

I have found that success with this species hinges largely on cultivation in an environment that provides very high light intensity and excellent ventilation, good water quality and a steady feed of low-dose fertilizer with a skew towards higher N available in non-urea form. While this is a genuinely tropical fern, I have found that it will thrive under conservatory conditions in central Guatemala that regularly experience night-time drops into the 10-11 degree C range (50-53 F) during the winter. In stark contrast to Platycerium madagascariense, P. ridleyi can tolerate fairly long periods of its root ball drying, although some frond wilting and tip burn may be evident following a prolonged drought. I prefer to keep them evenly moist while fronds are developing (particularly the shield fronds) and letting them dry out completely between waterings during the cooler months after the fronds have hardened off.

The plant below was grown on from a 12 cm plantlet diameter acquired in early 2009. For size reference, the fertile frond span in ~85 cm. This individual is very vigorous at this stage of its development and is pushing two new fertile fronds in this image. I would expect it to renew its shield fronds later this summer and expand the diameter of its nest by five or more centimeters.

I find it interesting that both of the Platycerium spp. that are reportedly myrmecophilous share similar nest/shield frond morphology in spite of not being very closely related. Both Platycerium ridleyi and P. madagascariense have handsome, fully enclosed, globular nest fronds that do not function as litter traps like their larger cogeners, and also exhibit distinctive veined "channels" in these fronds, presumably to facilitate movement of ants throughout the root ball. P. ridleyi appears to be unique in the genus in having "pores" (see second image below) evident of larger nests fronds, perhaps to facilitate entry and egress of small ants to the root mass.

The sporangia of Platycerium ridleyi are located on specialized, spoon-shaped extensions on the lower parts of the fertile fronds and plants can produce copious amounts of spore when mature and well-grown.

I highly recommend persons who can avail themselves of the right conditions to try their hand at growing this very striking and rewarding antfern.

J

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