Pteris normalis…in a garden centre near you!

In our Winter 2022 IATFG Newsletter, Ben Newell recommended Pteris quadriaurita ‘Tricolor’ as one of his choice terrarium plants. This sparked a correspondence between me and renowned botanist and fern expert, Christopher Fraser-Jenkins. I thought it would be interesting to share Christopher’s comments with you all. P. quadriaurita ‘Tricolor’ is commonly available in garden centres across the UK, mainly due to extensive micro-propagation in Europe by companies such as Vitro Plus in the

Netherlands. It has formed part of my own collection for several years and I had never felt the need to question its name before. But I was fascinated to learn from Christopher that the fern traded as P. quadriaurita ‘Tricolor’ is in fact P. normalis—normally! Here are his comments and conclusions.

It turns out that P. quadriaurita ‘Tricolor’ is, more often than not, a widespread labelling mistake made by nurseries. The Sino-Himalayan species, P. normalis, named in 1824 and from Kathmandu, Nepal, is what is usually misnamed as P. quadriaurita ‘Tricolor’ or P. tricolor in the plant trade. Both P. normalis and P. quadriaurita are both part of the large and complex P. aspericaulis aggregate (group of species). This group is characterised by compound fronds with the lowest few pinnae bearing long basal

pinnules that are themselves divided into lobes. The lowest opposite-pair of pinnae

being the four ‘ears’ of the name ‘quadriaurita’. Most of them have single mucronate points at the ultimate-segment apices. All this group are continually misnamed as P. quadriaurita, but as the late Dr. Trevor Walker showed in 1960 (Figure 1), P. quadriaurita has several teeth at the segment-apices and is confined to Sri Lanka and South India—subsequently understood to be more probably only Sri Lanka (‘The Pteris quadriaurita Complex in Ceylon’, Kew Bulletin, 14:3, 1960, pp. 321–32). The P. aspericaulis

aggregate used to be named after P. quadriaurita until it was realised P. quadriaurita was a rare and restricted species from Sri Lanka of unusual morphology, and the main part of the group was P. aspericaulis and closer relatives like P. normalis.

The genus Pteris in India is complicated. It took many years and detailed collections and study to work them all out. In India it has no less than 60 species, one yet to be named from Bangladesh, and 10 additional subspecies. 32 species are in the P. aspericaulis aggregate. Many previously unknown and overlooked species are now named, including also the three different species formerly lumped together under P. vittata, the Ladder Brake (Fraser-Jenkins, Indian Fern Journal, 39:1, 2021, pp. 1–15). All the compound Pteris

in India were formerly lumped under P. quadriaurita, but almost none of them are really

P. quadriaurita, as Trevor Walker showed. The placing of good species as if a variety or ‘vars.’ of P. quadriaurita or P. aspericalis is also not correct.

The P. aspericaulis aggregate are often pinkish in colour, at least in young fronds and on axes. Completely green plants are also frequent within each species. Occasional variegated plants have also been found in several of the species, with white and/or pinkish stripes. The better pink-coloured, but not variegated ones, with a shorter, wider frond, that are common in the plant trade, belong to P. normalis (Figure 2–3). It has a short, wide frond and very pink younger fronds. The higher Himalayan P. aspericaulis has a much longer frond and has setae above the segments and either pink or green younger fronds. Several photographs of P. normalis,

P. aspericaulis and P. roseolilacina (three coloured species) were included in the plates of my book with the admittedly hardly best-selling title of Taxonomic Revision of Three Hundred Indian Subcontinental Pteridophytes with a Revised Census-List (2008), where Indian Pteris was much revised. A beautifully young, pink-red P. normalis frond is pictured on the cover (Figure 4).

P. normalis is found from Central Nepal eastwards and is quite common. It has few pinnae, up to around seven to nine, a very rough stipe and rachis, a stiff, heavy frond, and the ultimate segments rather gradually sloping to the mucronate point. There are no setae above the ultimate segments (Figure 5), only slightly larger spines above the pinna midribs. A related species, P. dixitii, has setae and more abruptly rounded mucronate segment apices. P. normalis is triploid apomict, as found by Trevor Walker in a research programme with me (a report of diploid apomict also exists, needing clarification). It grows in dense Himalayan forests at upper-mid altitude, around 1500–2000 m—unfortunately also the dense leech zone!

Interestingly, until recently no one knew what this fern was as David Don’s types were kept in unincorporated boxes in the British Museum. Alison Paul (Senior Curator of

Pteridophytes at the Natural History Museum) worked her magic and managed to process and incorporate about 200 years of huge and important backlog collections from all over the world, kept safely for the future in hundreds of boxes. I worked on typifying and revising Don’s Nepalese ferns there and it became clear that P. normalis was the species I, and others before me, had mistakenly been calling P. oppositipinnata (syn. P. asperula). Though also pink, P. oppositipinnata is a clearly distinct Philippine species.

P. aspericaulis has many more pinnae than P. normalis, up to 18 pairs (Figure 6). It is found throughout the Himalaya, from Pakistan eastwards and is very common (Figure 7 & 8). It is diploid sexual and has a comparatively less rough, matt stipe and rachis, a normal herbaceous frond and the ultimate segments quite abruptly sloping to the rounded and mucronate point (Figure 9). There are several setae above the ultimate segment midrib, towards the tip (Figure 10). P. aspericaulis occupies a rather higher altitude forest zone, about 1800–3200 m.

Another fern close to P. normalis, is a diploid sexual species we described as P. scabririgens, with a very rough, dark grey (fuscous) stipe and rachis, a rigid frond and obviously narrower, strongly mucronate ultimate segments. It is likely to have been involved in the ancestry of P. normalis and occurs from east Nepal eastwards, very common around Kalimpong, Darjeeling, where the young fronds are beautifully pink, sticking out in small masses from roadsides (Figure 11).

P. roseolilacina is another much rarer, upper-mid altitude species (although common in Southwest China) with dark-pink young fronds. It occurs sporadically from Central Nepal eastwards, including at the back of the well-known Nagarjun mountain, visited by Wallich in 1820, and just at the back of my former flat in Kathmandu. It has few pinnae (from three to a maximum ten) and a slightly stiff frond, the stipe is merely matt, not asperous (Figure 12), and it has a long apical part to the whole frond, like a pinna. The ultimate segments are abruptly rounded to a non-mucronate or very weakly mucronate apex. There are three or four very distinctive purple stiff setae just below the segment apex, with the uppermost being a pair that are widely apart, towards the margin, unlike in the other species (Figure 13 & 14). Pinna costae and often pinnule midribs are usually purplish, but can also be green in some plants. P. roseolilacina is triploid apomict, like P. normalis, but very different in morphology.

P. normalis, P. aspericaulis and sometimes P. roseolilacina and P. dixitii are the ones seen in cultivation and all have pink young fronds (Figure 15 & 16). However, if you search for ‘Pteris tricolor’ on Google the images that appear on the first page at least are all P. normalis. It is owing to the nice gradation of colour in growing fronds, bright-pink, to yellow, to green, that P. normalis is often sold as P. tricolor. However, the true P. tricolor is a very distinct species. P. tricolor is very rare in northeast India, less so in north Myanmar, Southwest China and Southeast Tibet. It is truly spectacular, though delicate and not so easy to grow.

In a recent article, Dr. B. S. Kholia, of the Botanical Survey of India wrote: ‘P. tricolor is one of the topmost species for priority of conservation in India’ (‘Commercialization—a suggested approach for conserving a threatened fern, Pteris tricolor’, Current Science, 116:11, 2019, pp. 1790–2). P. tricolor is both a threatened and high-conservation-priority species, and, importantly, a species of high horticultural value and economic

potential. During the 1860s, it was sold at 6–15 shillings per plant in the European markets.

Although the plant is considered difficult to cultivate there is evidence from the literature and old catalogues that it was widely cultivated invarious nurseries and fern houses in Europe before the First World War when many gardens had to be turned into vegetable patches. Real P. tricolor is a good species, not just a ‘var.’ of something. The pinna-costae are bright red, with a broad band of bright white on either side, with some narrow, red veinlets running into it, then an abrupt transition to bright green for all the upper halves of segments (Figures 17, 18 & 19). It also happens to be the only one, as far as we know, to have such a colour pattern, which is useful. P. tricolor really is a tricoloured fern and easily the most spectacular variegated fern of all, arguably much better than the south-Indian P. argyrea which only has a white band (though some plants of that don’t) and no central red colour.

The exquisite, original coloured print of P. tricolor was made in 1859 by J. J. Linden, a famous Belgian botanist and horticulturalist in Bruxelles (Figure 20). He, by great good luck, discovered it growing by chance among orchids he was sent, probably from Myanmar. Linden realised P. tricolor was an absolute gold-medal winner, which it then proceeded to actually win. It is reproduced on the front cover of one of my books, The First Botanical Collectors in Nepal (2006) (Figure 21). The illustration is magnificent and

true to life. It always has a short, wide frond, with few pinnae, often just three or four, a thinly herbaceous texture, and non-apiculate ultimate segments with prominent pink-red subapical setae on the top surface.

About ten years ago Henry's Plant Farm, USA, used to list the real thing, and kindly sent me some baby plantlets they had raised from spores, but they are not listing it at

the current time. Hopefully it will still turn up occasionally in commerce—after sifting through all the P. normalis substitutes, nice though those may be!

Incidentally it is worth pointing out that most coloured, variegated ferns do also have normal, green forms, and people often don’t realise they can be the same species. Correspondingly, people sometimes think that any variegated or coloured fern should be P. tricolor. But to recognise the species underlying the colours, one needs to go by number of pinnae, whether the pinnule-apices are mucronate or not, and whether setae are present or not, plus of course cytology—despite chromosome-counters

being on the verge of extinction themselves nowadays! I’m suspicious that

a fern named by me in 2009, P. mawsmaiensis from limestone-cave country in the Khasi Hills, could perhaps merely be the normal green form of P. tricolor. I will synonymise it if so, but one needs to compare them side by side, particularly the seta arrangement, and I no longer have any P. tricolor or P. mawsmaiensis to grow in my little Portuguese garden.

Another fern worth noting in this discussion is P. blumeana, which occurs at low altitude in both north-east (rare) and south India. A one-off, faintly tricolorous nineteenth-century collection of it from the Khasi Hills was again confused with P. tricolor. Professor S. C. Verma, of Panjab University, found P. blumeana to be diploid sexual. P. tricolor remains of unknown cytotype. P. blumeana has a very long lamina with 15–18 plus pinnae, like P. aspericaulis. But unlike the latter, P. blumeana has very narrow segments without apical mucros and bearing very long, thin white, partially deciduous setae above the midrib of the ultimate segments (on the top surface). The variegated plant, as well as the normal green one, is not in cultivation and only one variegated herbarium-specimen exists, in Sir William Hooker’s herbarium at Kew. But interestingly it seems that P. blumeana is another species that can have a variegated pinna with a pale stripe along the middle of each pinna, but very rarely so.

Another little species, P. subquinata, common among calcareous rocks in Nepal, is normally green, but there are some populations from Sikkim eastwards, first

collected by Sir Joseph Hooker, which are really beautiful, miniature plants with a strong white stripe along the middle of the pinnae. I have named this naturally occurring cultivar as ‘White Hooker’ and have found it in Sikkim, Bhutan and the Khasi Hills (Figure 22). Unfortunately the species is really hard to cultivate as it doesn’t transplant (many Pteris are a bit tricky in this respect), but spores grown on limestone can take. It would be perfect for a tufa block, bell-jar fernarium along with the exquisite miniature species from Myanmar, Adiantum parishii, with tufts of low penny-like fronds an inch high, also pink when young. Well one can but dream!

CHRISTOPHER FRASER-JENKINS

Christopher is a very well-known expert on the ferns of the Indian subcontinent. He has written widely on the taxonomic, cytological and molecular-cladonomiic studies of the Indian pteridophytes and recently published the three-volume An Annotated Checklist of Indian Pteridophytes (2021). He has worked closely with other Indian pteridologists and more widely internationally. He has always been a ready source of advice on the identification of ferns, and he is an Honorary Member of the BPS. He currently lives in Portugal having moved from Nepal.