The genus Pyrrosia has many species ranging from frost-tolerant, as described in Remko Beuving’s recent article in the Pteridologist, through to those that do well in hot, humid, terrarium conditions, as discussed by Matthew Reeve. In addition, the genus contains terrestrial, epiphytic and lithophytic species, making the genus an interesting and challenging one for collectors.
Pyrrosia are very adapted to conditions of drought or only intermittent watering. Many have thick fronds for water storage and these are covered in dense stellate hairs (indumentum) to preserve a humid microenvironment around the frond. This indumentum is particularly thick on the underside of the frond around the stomata, where water loss can occur as the plant respires in dry air. In severe drought, many Pyrrosia can go into a period of inactivity with withered fronds that curl upon themselves. They can remain in suspended animation for several months and then the withered fronds can reinflate and come back into life when watered. This ability makes Pyrrosia a very successful genus in tropical monsoon areas.
All Pyrrosia have superficial rhizomes with roots that anchor them to their substrate, be that a tree, rock or forest floor. These rhizomes can be rapidly growing and produce fronds densely, with one or two fronds per centimetre, or sparsely with a frond emerging only every 5–10 cm. This rate of growth and frond distribution needs to be considered when cultivating tropical Pyrrosia, especially if they are for showing.
Often Pyrrosia come to us in pots. It is a natural habit of the plant to course around the perimeter of the pot and then grow over the edge in the search for new areas to root in (Figure 1). If this is allowed to continue for several years and the rhizomes are not successful in finding new root space, then the fronds at the tip of the rhizome can be a considerable distance from the roots supporting them. In time, this results in new fronds being smaller and less able to withstand drought than fronds nearer the root base. So, for the smaller, denser Pyrrosia, growing on a moss-covered piece of bark or tree trunk may provide the best substrate and produce the most naturalistic appearance. Larger species can be grown on wide seed pans, trays (Figure 2), or in
hanging baskets.
Propagation
Large Pyrrosia can be split or a long rhizome can be layered into a new pot adjacent to the main plant. When new growth is seen on the layering, and roots have formed, the rhizome can be divided from the main plant. Most Pyrrosia can be grown from segments of rhizome taken from an established plant without layering. These cuttings will grow most rapidly if they already have some root on them and there is an obvious and undamaged growing point. Pinning the cut rhizome down with wire loops in a moist, light compost of bark and potting compost (50:50) with some chopped sphagnum moss is effective for most species and protection in a large polythene bag or plastic box will ensure high humidity. However, the cuttings must not be soaking wet or the growing tips may rot off. Cuttings without roots or growing tips may become established only after some considerable time, or not at all. I have had such cuttings take months or more than a year to show any activity (Figure 3).
Pyrrosia produce spores and new plants can be grown from these (Figure 4). The spores can be collected by placing a detached fertile frond in a paper envelope and placing it in a warm dry place for a few days. It can be difficult to know when the sori on the frond are about to release their spores due to the heavy indumentum overlying the sori. However, if a frond is watched and taken as soon as spores and empty sporangia are seen on the surfaces beneath it, there will probably be sufficient spores still to be released for collection to be worthwhile. The spores can be sown and sporelings cared for in the same way as for any other fern. It is only when the sporelings are about 3–4 cm high that they begin to have the cultural requirements of the parent plant. At this size care should be taken to keep the sporelings moist but not wet as they are prone to rot otherwise.
Growing on
When a cutting is growing well, or if you have a new plant, it can be replanted in a pot, on bark, in a basket (Figure 5), or on a rock. The compost should be light and well-drained but have some moisture retention. Otherwise, especially in hanging situations, the compost can become so dry that re-wetting is difficult or patchy. In pots, terracotta is probably better than plastic as is allows for better drainage. Also, the Pyrrosia will probably fix itself to the pot as it crawls over the brim, and this can create an attractive display. To this end, tall pots may look better than short ones for large-fronded plants, such as P. lingua and P. angustata, whilst trays or seed pans suit the small-fronded species, P. nummulariifolia, P. piloselloides and P. abbreviata, for example.
For plants growing on bark, the compost should be covered in moss or coarse bark flakes and held onto the base with nylon thread or fine wire. Plants grown like this need humidity and spraying on a regular basis.
Liquid fertiliser can be used either on the compost or as a foliar feed. Cork bark slabs can often be obtained from garden centres or from reptile shops. These shops can often supply dried sphagnum in compressed form as well.
Hanging baskets suit Pyrrosia very well and have the advantage that they can be hung outside in the summer and brought in when winter approaches. The baskets should be lined with a material, such as thin coir matting, that allows free drainage but which holds the compost securely.
The compost should be light, such as potting compost and bark at a ratio of 50:50 with added chopped sphagnum moss for water retention. Perlite can be used for the same purpose but is unattractive in my view.
Some Pyrrosia can be grown on rocks, although the weight of these can make a display unwieldy. Light-weight artificial rock, such as the sintered porcelain aggregates used for koi carp filters, are more manageable and look naturalistic if rubbed with compost and soaked in water to encourage mosses and algae.
Watering
Whilst Pyrrosia can tolerate drought, it doesn’t mean that they enjoy it! To keep them healthy it is best to water them regularly every few days but let them drain. Having said that, if you are going away and no-one can help in watering, I have found that standing the terracotta pots in a couple of centimetres of water will cause no damage for a few weeks, especially if they are placed outside, the weather is warm, and there is free air-movement. As always, rainwater is ideal, but any water is better than no water. Liquid fertiliser can encourage growth and should be with a high nitrogen compound used at half the recommended strength for other plants.
Pyrrosia to grow indoors
Small-leaved varieties such as P. nummulariifolia, P. piloselloides (Figure 6), P. abbreviata, P. lanceolata and many others will all grow well in a domestic living room in a bright place. They will tolerate some direct sun if kept well-watered. If they are kept in a darker site, they will tend to produce larger, less hairy fronds that are more green than grey.
Larger fronded species include P. angustata, with fronds of more than 60 cm and P. lingua and its many cultivars. The Japanese have specialised in growing cultivars with striped, crested and crisped forms, some of which are very attractive, P. lingua ‘Ogon Nishiki’ for example (Figure 7). The variegated cultivars require quite high light-levels to maintain this feature, otherwise they will revert to the green form.
In the glasshouse
Many Pyrrosia will tolerate a winter minimum of 10 °C, certainly all of the P. lingua cultivars that I have grown. They may well tolerate much less than this if you are prepared to risk it, as discussed by Remko Beuving. Certainly, P. elaeagnifolia will tolerate a mild winter outside but does much better in a 10 °C greenhouse, as does
P. calvata and P. subfurfuracea, the species discussed in Evan Sharp’s article. Some Pyrrosia are truly tropical and need a winter minimum of 18–20 °C. P. glabra (syn. P. nuda) is such a plant, as is P. longifolia, P. linearifolia and P. confluens. A terrarium provides an ideal environment for some Pyrrosia.
Pests and diseases
The genus Pyrrosia is fairly resistant to pests although young Pyrrosia fronds can be infested with aphids despite the protective indumentum. Scale insect seems not to be too common in the indoor species, although fern scale, Pinnaspis aspidistrae, with its tiny white male forms, can be a problem. This is best dealt with by removing badly infested fronds and treating the plant both topically and systemically with Acetamiprid (Bug Clear™ Ultra: Vine Weevil Killer).
Pyrrosia as show plants
For display purposes, Pyrrosia can be extremely attractive, especially in their grey and variegated forms. They are not too brittle for handling and are easy to transport. They are also able to resist the variable and dry conditions of a show hall or marquee, although misting benefits them. The many species and cultivars illustrated in this article demonstrate the variety of the genus and novel methods of support, such as growing on pieces of bark, can enhance these attractive features (Figure 8).
PETER BLAKE
Peter became interested in tropical ferns whilst making regular trips to India in the 1990s and 2000s. He retired from the NHS in 2012 and was able to develop his interest in growing tropical ferns from spores. He now lives in Norwich where he can provide much more space for their culture. He maintains a particular interest in the ferns of South India and Sri Lanka.
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