Short notes on Pyrrosia species ideal for the hothouse and terrarium

Several Pyrrosia species do very well in hothouse or terrarium conditions. In this article I discuss four such species. They are all epiphytes but can adapt to a variety of growing methods.

My own hothouse is essentially like a large warm terrarium. The humidity is above 90 %RH all year and the temperature is around 19–20 °C through the winter. On the hottest days over the summer it occasionally gets to around 28 °C. I must stress that I believe all the species below would be more than happy at slightly lower temperatures, as the survey earlier in this edition may suggest. But these are not like the hardy and borderline-hardy Pyrrosia. I have attempted to over-winter P. nummulariifolia in more basic frost-free conditions with little success. It might be, like other xeric ferns, a dryer

substrate and environment would be needed to take them through a winter at these much lower temperatures.

None of these species have been particularly fussy when it comes to lighting. Within the hothouse, I’ve moved them around several times and they have not been fazed by it. Low to high, indirect light. They have natural light and artificial light. The day length is extended to 12 hours a day using LED flood lights during the winter. In lower light conditions, the fronds will elongate as they reach towards the light, this is particularly noticeable in the smaller species.

I keep the P. longifolia in a terracotta pot and P. confluens in pond plant basket, so they can drain quickly after watering. The P. longifolia stands on capillary matting, whereas the P. confluens hangs on the side of the staging, meaning it is slightly drier. I keep P. nummulariifolia and P. piloselloides similarly, with the addition of a piece of tree fern fibre in the basket to enable them to climb. The P. nummulariifolia has tended to quickly adhere itself onto the capillary matting and romps around the other pots. It seems to enjoy the humidity. All seem to cope well with brief periods of less water, with perhaps the exception of P. nummulariifolia which has less ‘succulent’ like fronds.

All are fertilised regularly. I’ve been using a mixture of orchid fertilisers at a relatively low strength. These tend to have a slightly higher percentage of Potassium—essentially very weak tomato food. It should be noted that my set up allows things to drain freely and I have a tendency to water thoroughly, which probably prevents any build up of salts in the substrate.

The substrate mix I use in the pond basket is around 50% orchid bark, 30% Sylvamix Potting, 10% live or dried moss (sphagnum or forest moss) and usually 10% potting bark. I’m not particularly scientific about the mix, and it’s very much by eye. I don’t tend to use composted bark in the hothouse as I worry it would rot down too quickly in my very damp conditions.

As Peter mentioned in his article, tropical Pyrrosia can be propagated using a variety of

methods. Rhizome cuttings are probably the best options, using the methods described by Evan and Peter. Three of the species discussed below, P. piloselloides, P. longifolia and P. confluens are believed to have the ability for Crassulacean acid metabolism, also known as CAM photosynthesis. This is an adaptation that allows the plant to effectively photosynthesise during the day but only exchange gases at night. This means the stomata on the fronds can be closed during the day, reducing water loss. It’s an adaptation normally associated with arid condition and was first discovered in Crassulaceae. For these tropical rainforest plants it’s likely to help them navigate life as an epiphyte and the lack of a continuous source of water. There is another proposition that this mode of photosynthesis may give these plants an advantage by potentially allowing them to make use of elevated nocturnal CO2 concentrations in the rain forest—in a similar way to how several submerged aquatic plants use CAM photosynthesis.

Pyrrosia nummulariifolia (Creeping Button Fern)

As recommended by Ben Newell in his terrarium article in the IATFG Winter Newsletter 2022, this ‘micro fern’ is perhaps the most readily available tropical Pyrrosia. It is an excellent candidate for terrariums and is generally an easy to grow species if given enough heat and moisture. Once established, it is quick growing and will readily creep on and around hard landscaping, giving the terrarium a natural appearance. It will readily climb onto damp surfaces such as moss-covered bark or slices of tree fern trunk.

P. nummulariifolia originates from China, India and Southeast Asia. In the wild it will grow on trees or rocks, and often in exposed places. The fern has a long creeping rhizome, 0.6–1.6 mm thick. The simple fronds are strongly dimorphic, meaning they are shaped differently depending on whether they are sterile or fertile. Its highly pubescent fronds and rhizome give P. nummulariifolia a fuzzy appearance. The sterile fronds tend to be circular to broadly oblong and have very short stipes, measuring about 1.5–2.5 cm long. Brighter light seems to keep the fronds smaller and rounder. However, the fertile fronds are lanceolate in shape, have longer stipes, and can measure up to 12 cm long. The sporangia completely cover the entire underside of the fertile frond.

Pyrrosia confluens (Robber Fern)

A slightly larger species, P. confluens is another easy to cultivate species, that seems fairly quick to establish from rhizome cuttings. Its common name, Robber Fern, refers to people mistakingly thinking it was parasitically robbing nutrients from the trees it grew on. Another one of its common names is the Horseshoe Felt Fern, due to its fertile fronds having sporangia arranged in a horseshoe-shape on the back of the leaf-tip. This fern grows readily on slabs of tree fern, or in baskets. If grown in a basket it will quickly begin to tumble over the edge and create an impressive ball. I have found it to be very drought tolerant. Due to its position in the hothouse, it regular gets missed during watering sessions, but it copes fine.

From Australia and some of the surrounding islands, it is generally found on the edge of forests, growing epiphytically. Its rhizome is 1–2 mm thick. P. confluens is similar to P. nummulariifolia in that it has two very distinct frond shapes. The sterile fronds are up to 15 cm long and 2 cm wide. Whereas the fertile fronds are longer at up to 20 cm. Hydathodes can often be seen—these are small pores on the margins of the frond that allow for the secretion of droplets of water.

There is an accepted and described botanical variety referred to as P. confluens var. dielsii (Silvery Felt Fern). This variety is more distinctly dimorphic. The fronds are wider at

the ends, often truncate, and its hydathodes are positioned more marginally than on the straight species.

Pyrrosia piloselloides (Dragon Scale Fern)

Another smaller species, P. piloselloides is a native epiphytic creeping fern. A key difference between P. piloselloides and P. nummulariifolia is that its fronds are generally much more round and fleshy, almost succulent-like. It’s reminiscent of Lepisorus microphyllus (syn. Lemmaphyllum) or even a small Hoya. Not particularly difficult but it is quite slow growing. It prefers to be mounted on bark. It can have a tendency to rot when planted in a basket or pot with compost. It appreciates moisture and high humidity, but it must be free draining—so it adapts well to terrarium conditions as an

epiphyte. As well as having the ability for CAM photosynthesis, the cell walls of this fern are able to fold and shrivel, decreasing the volume of the cell in times of drought.

Widespread across Asia, growing on trees or rocks. Like with most Pyrrosia species, the fronds are covered in pale star-like hairs. It has a rhizome that creeps, about 1 mm thick, and is covered in oval scales with a brown centre and pale hairy margin. It is also dimorphic where the sterile fronds range from oval to circular and narrow linear fertile fronds. The almost circular simple fronds are about 1–7 cm wide, whereas the fertile fronds are more variable and can be up to 25 cm long but only 1.5 cm wide. The sori are produced in a thick continuous band at the margins of the fertile frond, but sometimes are restricted to the tips only.

There is occasionally some variability in the natural frond shape of this fern, that goes beyond the normal sterile and fertile dimorphism. There are a couple of ‘cultivars’ that occasionally circulate. These seem to be stable clones. A fairly common one that circulates has slightly forked fronds, furcated. This was once described botanically as Drymoglossum piloselloides var. platycerioides, though it isn’t considered a botanically

distinct taxa any more.

Pyrrosia longifolia (Long Felt Fern)

This is a very attractive fern. Its longer but stiff fronds make it only suitable for large terrariums or hothouses. One of its common names is the Long Felt Fern. Its

lighter green fronds often seem tinted with silver or white. It’s perfect for hanging

baskets or containers where its long narrow fronds can be appreciated. They thrive in semi-shade and appreciate moist, humid conditions. In the wild, in tropical and subtropical climates, they are usually found as climbers, and can cover trees with their strap-like fronds. It is relatively slow growing and can take a little time to establish.

Originating from China, Australia and Southeast Asia, growing generally epiphytically in forests. This fern has a long, creeping rhizome, that can be nearly 3 mm thick. It has scales on the rhizomes that are appressed, shiny, dark coloured with a smooth margin. The fronds are monomorphic (having only one shape). They gradually narrow at both ends and can be up to 50–80 cm long and up to 0.7–4.5 cm wide. Some sources report fronds 110 cm long. The sori are round and are found near the tips of the fronds on the underside. P. longifolia showing long fronds.