Unless we have a knowledgeable fern-loving friend who gives us a fern with a hand-on-heart assurance about its name, most of us are obliged to buy our plants and trust that the vendor has got the correct name. While this is a fairly widespread difficulty when buying hardy ferns for the garden from garden centres and non-specialist nurseries, the problem intensifies when buying tropicals, which usually involves an online purchase which allows no chance of inspecting what we are buying and we are stuck with whatever name it is sold under. Of course our own knowledge and experience will grow and with reading, discussion and cautious Google searches we can often discover the true botanical name and if necessary rectify any wrong label. Luckily there are a few reliable companies run by specialists with pteridological expertise; but there are others that are not. For a few years now a very attractive exotic fern has been marketed as a species of Dictyophyllum. While I cannot profess to know what this fern really is, I can certainly say it is not a Dictyophyllum, which is a genus only known from Antarctic fossils dated as Middle Jurassic—wouldn’t we all love to have one?
However aware we are of this problem, we all too easily buy things in the hope that the name is right—especially when it’s a plant we’ve read about and want to grow. Some ten or so years ago I saw an advert for Aglaomorpha brooksii (now a synonym of Drynaria brooksii). I already grew one or two other related species and a fascination with the group was developing, and has never left me. So I went ahead and bought it on spec, and have been growing it ever since. And based on the overall frond shape I had been firm in my belief that the ‘brooksii’ species name was right.
Drynaria brooksii is an epiphyte native to Malaysia, where it is restricted to the northern parts of Borneo. It has large leathery pinnatifid fronds that grow out from a surface-hugging rhizome, 3 cm in diameter, and densely covered in scales. The fronds can grow to over a meter long, and if extending sideways in several directions can—as I have found—be a decided obstacle in a small greenhouse. The fern I had bought as D. brooksii was better behaved and did not grow nearly so large and its fronds tended to grow upwards and never projected sideways. The space problems were however noted with another Drynaria that I acquired as a 7.5 cm bit of rhizome on a visit to Sarawak
(Borneo). Other than the fact that the rhizome was certainly part of a Drynaria, I had no idea which one it would prove to be. I planted it pinned down onto the surface of a pot of peat and within a few weeks it produced an exciting new crozier. Even though it was in an unheated greenhouse it appeared to be thriving and soon put out a second large frond. Later when it was placed in a warmer greenhouse, its growth recognised no boundaries—although, as noted above, it soon created some for me. These were resolved to some extent by placing its now very large pot on a raised plinth, so that the
fronds could be ducked under. In the fourth year of my having it, this hitherto unidentified Drynaria revealed itself clearly as brooksii when an emerging new frond turned out to be fertile.
Fertile fronds of Drynaria that were once placed in the Aglaomorpha genus fall into two types. In what may be called Type 1 the sori occur on the underside of pinnae that are not very obviously different in shape from non-fertile pinnae. In Type 2 the sori occur on a distal set of pinnae that form a sort of ‘tassel’ of considerably narrowed pinnae. Although this very marked dimorphism is mostly found in Philippine and New Guinea
species, it also appears in species elsewhere. In Borneo only D. brooksii and D. drynarioides have it, and in the latter, which compared to brooksii has a much wider distribution, the fertile pinnae are much more constricted. The photograph (Figure 1) shows the tassel of sporing pinnae on my Borneo plant; and this should be compared with the wider green non-fertile pinnae lower down on the same frond.
The Drynaria bought as brooksii (which from now on I shall call ‘mystery’) had never produced a fertile frond of any sort until this year; but now it has, and it is certainly not like the brooksii of Borneo origin. A photograph of it (Figure 2) shows the sori, which occur on pinnae that on the upper surface look just like sterile pinnae. The sori occur in varying numbers and are arranged in lines between the secondary veins.
There is one other obvious difference in the two ferns. Both have very scaly rhizomes, and the scales of both are tapering; but those on the Borneo plant are an opaque dark brown with a lighter translucent margin, and they are about 2 cm long, whereas those on the ‘mystery’ plant are a uniform pale ginger and about half that length. In terms of general shape the fronds of both ferns are fairly similar, though the pinnae of the ‘mystery’ plant are rather wider and glossier. Under ×10 magnification one can observe a brown coloured membranous rim which runs along the edge of each pinnatifid lobe and so surrounds the entire frond.
Having read the foregoing, Peter Blake suggested that the mystery fern might possibly be D. roosii (syn D. fortunei). This was an attractive idea and one well worth investigating. Of the Drynaria of Type 1, that is those whose sporing fronds are not of the tassel variety, there is a strong similarity between such fertile fronds in D. roosii and our ‘mystery’. This is apparent in comparing the frond of Figure 2 with a fertile frond of
D. roosii, shown in Figure 3. The colour and form of the rhizome scales also compares favourably. However, not all the morphology supports an identification as D. roosii. The maximum length recorded by Roos for the foliage fronds is 55 cm (M. C. Roos, Phylogenetic Systematics of the Drynarioideae (Polypodiaceae), Universiteitsdrukkerij, 1985, p. 287). The longest frond of ‘mystery’ at 80 cm exceeds this.
Moreover the consistent frond shape or overall contour of ‘mystery’ is obovate with the greatest width occurring at about 55 cm on that same fertile frond, whereas Roos describes it as elliptic to ovate. The greatest discrepancy is seen in nest fronds. These seem to occur very regularly in D. roosii (Figure 4), but I have yet to see any on ‘mystery’, which behaves rather more like D. coronans (Figure 5) in frequently producing widely-flared frond bases (Figure 6). I have never seen this in D. roosii nor seen any report of it.
There is another Drynaria sometimes offered in garden centres under the name ‘Snake
Fern’. Valdy Pierozynski and I both grow this plant and he has mooted the possibility that Snake Fern could be a form of D. coronans. The relevance here is that while it was
still a juvenile I remember that ‘mystery’ looked very like these Snake Ferns, so it is certainly possible that they are the same. But as yet mine has shown neither nest
fronds nor flared bases. Like D. roosii the fertile fronds of D. coronans are of Type 1 though the soral patterns are distinct: compare Figure 2 and Figure 7. All the fronds produced on my Snake Fern to date have been sterile, so the soral pattern has yet to be observed.
It will appear therefore that I have not been able to pin down the identity of this ‘mystery’ trade plant. There remains the possibility of course that it is hybrid, and if so, could well prove sterile. This year it will be possible to check this out when some of the spore is sown. I hope to report in due course—so watch this space!
DICK HAYWARD
Dick lives in North Wales just a few miles from Snowdon. From an early age ferns fascinated him and when he retired from teaching Linguistics at the School of Oriental and African Studies in 2002, he bought Rickard's Hardy Ferns and for five years ran a specialist fern nursery on a one-time hill farm just south of Bangor. Aiming to enlarge the range of ferns available at the nursery he made spore-collecting trips to Taiwan,
Chile, South Africa and Sarawak (Borneo), and in the course of this discovered tropical epiphytes which have continued as a passion long after selling on the nursery.
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