genus profile

Woodwardia radicans in a garden in London

Tim Pyner surveys Woodwardia chain ferns, a genus of mostly large and in cultivation spectacular species ommonly known as chain most species are colourful, mostly in of elongated segments resembling ferns, Woodwardia are some shades ranging from bronze through a chain of sausages. Cof the most spectacular and to bright red. The young fronds of This article was prompted by imposing ground ferns that can be W. unigemmata and W. prolifera are the realization that two of the grown in temperate gardens. The amongst the most intensely coloured most frequently cultivated species, frond length of European chain fern, of all cultivated ferns. W. radicans and W. unigemmata, have W. radicans, can exceed 3m in its The fertile, spore-bearing fronds few differentiating characters. natural habitats. Ideal growing resemble the sterile fronds in all Without knowing the geographical conditions are not easily replicated species apart from W. areolata. origin of a plant it is sometimes in cultivation but fronds of 2m or Woodwardia radicans and other difficult to decide which species more for this species can be achieved. closely related species usually is being grown. I have therefore The most commonly cultivated produce bulbils or plantlets on checked many herbarium specimens species have erect or shortly the fronds that afford a means at the Natural History Museum creeping rhizomes and leathery, of vegetative propagation. in London, read various papers and winter-green fronds. Two species The name chain fern refers to articles, and visited gardens and fern have far-creeping rhizomes and are the arrangement of the sori. These growers to find reliable characters deciduous, the fronds dying as winter are located close to the midrib of to identify plants grown in British approaches. The young fronds of the frond lobes and are formed and Irish gardens.

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Taxonomy The sori of Woodwardia radicans show Recent molecular studies confirm how the genus got its name of chain fern previous hypotheses based on morphology and cytology that Woodwardia belongs to the family Blechnaceae. Cranfill & Kato (2003) demonstrate that the woodwardioid ferns form a monophyletic clade that forms the sister group to the remainder of the Blechnaceae. They recognize 14 species but separate W. areolata and W. virginica into two segregated genera, Lorinseria and Anchistea, respectively. I am persuaded by their arguments for separating these two genera. They cite unique and aberrant morpholog­ Species in cultivation form huge stands on steep, forested ical characters, unique cytology, a There appear to be eight or possibly mountain slopes. The large fronds long history of separate evolutionary nine species in cultivation in western arch over and downwards, often existence, and geographical isolation Europe. I discuss the European and resulting in the apical bulbil rooting – both occurring in eastern North Asian species first, then the American when it touches the ground. America. However, for practical species. Within these geographical Most clones withstand frosts to reasons I include them here as groupings they are listed in order of -5°c (RHS hardiness rating H3). species of Woodwardia. frequency of cultivation. Occasionally I have come across All photographs by Tim unless Pyner stated otherwise Apart from the enigmatic Mexican healthy plants that have survived species, W. martinezii, the remaining European and temperatures briefly down to -10°c species are placed in three sections. Asian species (H4). As it is generally less hardy Most hardy species are in section These species can be recognized by than W. unigemmata the latter is now Woodwardia, and can for convenience the fact that most produce plantlets more commonly planted. be separated into the Old World and or bulbils on the fronds. The thick rhizome is erect or New World groups. Old World ascending and carries large, arched, species are found from the Himalayas Woodwardia radicans evergreen, bipinnatifid fronds of one eastwards to Japan and Taiwan and The natural range of this species is type, to 2m long, rarely to 3m. These south to islands in Indonesia and the Macaronesia and southern Europe. usually bear one to three large, scaly Philippines. One species, W. radicans, It is found abundantly in the Azores, bulbils in the axils of pinnae near the has a disjunct distribution and is Madeira and high rainfall areas of the frond apex. The stipe (frond stalk) is found in Macaronesia and more Canary Islands. It also occurs rarely up to half as long as the leaf blade. rarely in southern Europe. The New in Portugal, Spain, Italy and also on This species is the most frequently World species range from Canada the islands of Corsica, Sicily and encountered in gardens, although it south to Costa Rica. Species in Crete. It has also been recorded from is being usurped by W. fimbriata, and subtropical areas tend to grow in Algeria, apparently as an introduction. has been grown since the late 18th mountainous regions. It demonstrates a relictual distribut­ century. Several large gardens in Section Japonicae with two or ion, which means it was once more Cornwall, Ireland and Scotland host three species is rarely cultivated. widespread, and shares close spectacular colonies. Neither bulbils or plantlets occur in ancestry with W. unigemmata. The A few cultivars with atypical this section. split between the two species is fronds, such as ‘Burgessiana’, The third section, Chieniopteris, is estimated to have occurred about 13 ‘Cristata’ (syn. ‘Brownii’) and maintained as a separate genus by million years ago (Li et al. 2014). ‘Plumosum McCormack’, have been Chinese botanists. The two small Woodwardia radicans is very described but have not been seen species are attractive but I am not common in parts of the Canarian recently. The cultivar ‘Crispa’ aware of them being in cultivation. and Madeiran archipelagos. It can actually belongs to W. prolifera. ➤

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hardier than W. radicans and are conclusively. I first became aware undamaged at -10°c (H4), and some of this problem after being asked to can survive lower temperatures. identify woodwardias in a Cornish Woodwardia unigemmata has garden during October 2013. become popular and widespread in Despite my initial confidence I cultivation within the last 40 years. found that I was unable to name It is now much more frequently several with any certainty. planted than W. radicans. The Importantly, it should be noted superior hardiness and colourful new that bulbil number is completely growth combine to make this fern an unreliable for identification ideal subject for gardeners who purposes. Both species can produce require a feature plant that is both one to three plantlets in the upper spectacular and easy to maintain. pinnae axils, and occasionally even A bulbil on the underside of a more; up to seven have been Woodwardia radicans frond Differentiating W. radicans reported in W. unigemmata. and W. unigemmata The intensity of red pigmentation Woodwardia unigemmata The differences between W. radicans in the colourful new fronds is very This is similar to the previous species and W. unigemmata are subtle. useful. Woodwardia unigemmata in overall appearance but the fronds Although the extremes can be told usually has bright reddish or orange are relatively narrow with more apart fairly easily, some plants are new growth, whereas colour is widely spaced pinnae. A large colony almost impossible to identify usually lacking or faint in W. radicans. of this magnificent fern can create an awesome spectacle in spring and summer when a mass of intensely coloured young fronds are unfurling. In the best forms they are a bright red but can vary from orange through to burgundy. As the fronds mature they fade to green but new fronds usually emerge throughout the growing season giving a long period of colour. Woodwardia unigemmata occurs naturally over a vast area of east Asia, The first pinna lobe ofWoodwardia unigemmata arises on the side of from India through China to Japan the pinna facing the apex and Taiwan. Fraser-Jenkins (2008) has shown that W. biserrata, a name that could have usurped The colourful new fronds W. unigemmata, is actually based of Woodwardia unigemmata on a wrongly localised specimen of W. fimbriata and can be disregarded. It has been introduced to cultivation many times from different localities, resulting in variation in frond form and colour intensity. Additionally, several different clones with undulate fronds are in cultivation. There is also some variation in cold hardiness. However, most clones seem to be significantly

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the pinnae axils of W. radicans and W. unigemmata. Plantlets occur in both species, sometimes completely covering the frond surface. It is now known that W. orientalis is a fertile allotetraploid species derived from a sterile hybrid between diploid W. prolifera and a second, as yet uncertain, species (Takamiya et al. 1992). Most plants in cultivation appear to be W. prolifera. True W. orientalis is possibly grown and I am currently searching fern collections for plants that may be it. Woodwardia prolifera is a large plant that can have fronds more than 2m in length. The young fronds vary in colour, sometimes green but often very intensely coloured carmine or Woodwardia radicans (left) orange, frequently more colourful and W. unigemmata (right) than those of W. unigemmata. When the fronds are covered in tiny However, many plants of W. radicans rather technical distinction, it does plantlets, W. prolifera is easily have some trace of colour, and occas­ prove reliable in the majority of distinguishable from W. unigemmata. ionally a pale orange colouration. cases. It is important to check for Even when they have dropped, small Of course, unfurling frond colour presence of a vein in the lobe, as scars remain on the frond surface. is no help during winter or when occasionally an unveined lobe can be When well-grown the pinnae and young fronds are lacking. The fronds present in W. unigemmata that can be pinna lobes of W. prolifera are of W. radicans are often appear more misleading. Several fronds on a plant characteristically narrow and foliose or leafy, with broader pinnae should be checked, as aberrant attenuated. Another important and lobes that are more densely fronds can be present. difference is that two or three basi­ arranged on the frond. However, this Despite this, knowledge of the scopic pinna lobes adjacent to the can vary and both species can look geographical origin of a particular rachis are not developed. However, very similar. Good illustrations of plant is the most helpful and reliable both these characters may be less frond silhouettes can be found in aid to identification. prominent in small or young plants. Hoshizaki & Moran (2001). Woodwardia prolifera does not The most reliable differentiating Woodwardia orientalis & appear to be as hardy as W. unigemm­ character is found in the vascular W. prolifera ata. However, it has a similar wide structure of the pinnae. In W. radicans These two species are similar in geographic range and I have noted the basal pinna lobes are usually overall appearance to W. radicans. some variation in cold tolerance, catadromous, i.e. the first lobe arises Until recently, W. prolifera was but is best treated as an H3 plant. basiscopically (on the side of the considered to be a variety of A cultivar, W. prolifera ‘Crispa’, is pinna that faces the base of the W. orientalis. In western horticulture rarely encountered. It is a rather frond). In W. unigemmata the vein a lack of understanding of the scruffy plant with malformed, branching is anadromous i.e. the first characters used for separating the depauperate fronds that may appeal lobe arises acroscopically (on the side species has lead to confusion to lovers of curiosities. Spore and of the pinna that faces the apex of regarding the correct name. stomata measurements indicate that the frond). The latter species Both species produce tiny it belongs to W. prolifera. It appears therefore has pinnae that appear plantlets on the upper surface of the to be relatively hardy and has to lack a basally projecting lobe frond that are very different from survived temperatures of -10°c adjacent to the rachis. Although a the larger, scaly bulbils produced in in my Essex garden. ➤

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Fronds of Woodwardia prolifera showing remnants The pinna lobes of Woodwardia prolifera are drawn out into a of spring colour long tip and the basal basiscopic lobes are missing

The pinna lobes of Woodwardia orientalis are not drawn out Woodwardia prolifera usually carries plantlets on the upper into a long tip like those of W. prolifera surface of older fronds

As is frequently the case with polyploid ferns, true W. orientalis is a smaller plant than its diploid parent. The fronds typically reach 1m in length. The pinna lobes are relatively broad and are acute to acuminate and rarely attenuated. Only the first basiscopic pinna lobes are missing. In 2014 I encountered W. orientalis growing wild in Japan and noted its strong resemblance to young plants of W. prolifera. There are significant differences in spore size that should help detect this plant in cultivation. There are also small differences in average stomata guard cell length that may prove helpful when identifying young plants. In Japan, W. prolifera tends to occur in coastal Woodwardia japonica in a garden in Belgium locations whereas W. orientalis grows inland at moderate altitudes, so it

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Woodwardia fimbriata is slow-growing but tolerant of a wide range of conditions The sori of Woodwardia fimbriata may prove to be more hardy. It is a elongated and pointed. However, natural distribution ranges from handsome species that would be further research will be required to British Columbia south to Baja useful for smaller gardens. establish its true identity. California, mostly in coastal areas. In cultivation I have rarely seen Woodwardia japonica American species fronds exceeding 100cm, although This large species has distinctive None of the New World species they reach 2m long in habitat and pinnae that narrow towards their produce plantlets or bulbils, and only there are reports of fronds reaching bases and are symmetrically lobed one is commonly grown. Hoshizaki 3m (Taylor 1973). They tend to be each side of the pinna midrib. & Moran (2001) give excellent held in an upright position, are The unfurling fronds are brightly illustrations of all the cultivated relatively narrow and the lower coloured. Neither bulbils or American species. pinnae are usually shorter than those plantlets are produced. above, giving the frond an elliptic or Although grown in the 19th century Woodwardia fimbriata oblanceolate outline. The lower it apparently disappeared from This species is now the most widely surface of the frond is covered with cultivation. Rush (1984) records that available chain fern in UK nurseries minute, sessile, yellowish glands that he was cultivating plants but one in and garden centres. It is remarkable can be easily seen using a hand lens, his garden had not survived. I was that Rush (1984) had no reports of it even on dried fronds. This is an therefore surprised to see a healthy being in cultivation. Rickard (2000) important character used to separate plant when visiting the magnificent had it in cultivation but it was then W. fimbriata from the next species. garden of Koen van den Berg in rarely seen and apparently difficult The new growth is green. Belgium. He had obtained it from a to propagate. Chinese nursery as an unidentified Since then it has entered the Woodwardia spinulosa Woodwardia species. Van den Berg market of mass-produced ferns and This species is closely related to has raised young plants from spores can be found on the fern benches of W. fimbriata. It is native to mount­ and kindly gave a plant to me, so most garden centres. Even so, it is ainous areas of Central America, hopefully it will become re- not a fern that is easily grown. It from north Mexico south to Costa established in British gardens. seems difficult to get established Rica. It differs from W. fimbriata in An additional species, W. magnifica, and is then slow-growing. However, frond shape, being widest near the is recognized in China (Wang et al. I have seen well-grown plants in base, the spreading frond posture, 2013) although western botanists gardens in counties as climatically absence of yellowish glands, and do not consider it to be distinct. different as Dorset and Suffolk, so it presence of small, dissected scales However, a recent study (Li et al. obviously tolerates a wide range of on the frond lower surface. 2014) hints that species status may conditions once settled in. It is apparently cultivated in be more appropriate. There is a It seems to require high humidity, North America but is rarely possibility that van den Berg’s plant warm summers and mild winters to mentioned in British literature. belongs to this segregate species as thrive and is unlikely to survive However, Rickard (2000) mentions the pinna lobes are particularly temperatures below -10°c. Its growing a plant that survived ➤

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The distinctive pattern of sori Woodwardia semicordata in on Woodwardia semicordata a garden in Scotland many years in central England. I have Asia. A very attractive fern, it would perhaps through apogamy. yet to see this species in cultivation. be a valuable addition to gardens. Hoshizaki & Moran (2001) also Although W. martinezii is alleged to noted that the plant in cultivation in Woodwardia semicordata be in cultivation, this is incorrect and North America is W. semicordata, but & W. martinezii it has probably never been introduced. confusion has persisted. For example, Woodwardia martinezii is a small The fern grown as that species is the plant captioned as W. martinezii species endemic to a limited area of W. semicordata, which occurs in in Olsen (2007) is misidentified. I Mexico. It has a creeping rhizome, mountainous areas of Mexico. It was have seen plants in several Scottish short, triangular fronds on relatively first described as a hybrid between gardens, including Royal Botanic long stipes, and long sori that occur W. martinezii and W. spinulosa (Mickel Garden Edinburgh’s Benmore and alongside all the major veins of the & Beitel 1988). Later, Mickel & Logan gardens, labelled as W. martin­ frond. It is taxonomically rather Smith (2004) treated it as a species, ezii; they are all W. semicordata. isolated, with its closest relations in as some forms produce fertile spores, Woodwardia semicordata is another references handsome fern, with fronds resembling those of W. spinulosa but Cranfill, R & Kato, M (2003) New York Botanic Garden, New York Phylogenetics, Biogeography and Mickel, JT & Smith, AR (2004) the sori towards the frond apex Classification of the Woodwardioid Ferns The Pteridophytes of Mexico. New York occur adjacent to the major veins, (Blechnaceae). In: Chandra, S & Botanical Garden, New York as in W. martinezii. The rhizome Srivastava, M (eds.) Pteridology in the Olsen, S (2007) Encyclopedia of Garden resembles that of W. martinezii and is New Millenium. Kluwer Academic Ferns. Timber Press, Oregon Press, Netherlands Rickard, M (2000) The Plantfinder’s Woodwardia virginica is a wetland Fraser-Jenkins, CR (2008) Guide to Garden Ferns, David & species from North America Taxonomic Revision of Three Hundred Charles, Devon Indian Subcontinental Pteridophytes with Rush, R (1984) A Guide to Hardy a Revised Census List – A New Picture of Ferns. British Pteridological Society, Fern Taxonomy and Nomenclature in the London Indian subcontinent. Bishen Singh Takamiya, M, Osato, K & Ono, K Mahendra Pal Singh, India (1992) Karyomorphological studies Hoshizaki, BJ &Moran, RC (2001) in Woodwardia sensu lato of Japan. Fern Grower’s Manual. Timber Press, Bot. Mag. (Tokyo) 105(2): 247–263 Oregon Taylor, TMC (1973) The Ferns and Li, C, Lu, S, Ma, J, Gai,Y & Yang, Q Fern-allies of British Columbia. KM (2014) Phylogeographic history of the MacDonald, British Columbia, Canada woodwardioid ferns, including species Wang, F, Xing, F & Kato, M (2013) from the Himalayas. Palaeoworld Blechnaceae. In: Flora of China http://dx.doi.org/10.1016/j.palwor. Editorial Committee (eds) Flora of 2014.10.004 China. Vol 2–3 (Lycopodiaceae through Mickel, JT & Beitel, JM (1988) The Polypodiaceae). Science Press, Beijing & Pteridophyte Flora of Oaxaca, Mexico, Missouri Botanic Garden Press, St Louis Glen Mittelhauser / Maine Natural History Observatory History / Maine Natural Glen Mittelhauser

190 September 2015 PlantsmanThe prostrate and creeping. Therefore it briefly coloured on unfurling. The raised position or bank from where is easily divided, which may explain rhizomes are horizontal and very the heavy fronds can hang down is its relative frequency in gardens. As robust and strong-growing. ideal. If space is available magnificent yet it is unclear whether sterile, fertile I have found this species difficult colonies can develop. If planted in a or both forms are in cultivation. to keep alive as it is a true aquatic border the fronds tend to flop. The fern. Young plants grow quite well in New World species related to Woodwardia areolata moist garden soil but mostly die over W. fimbriata have more upright This species differs substantially winter. I suspect that the rhizomes fronds and are better suited to from other Woodwardia. The are tender and deep water protects confined spaces. rhizome is slender, horizontal and them from severe frost. If ideal creeping, forming colonies. The conditions are available it should Propagation fronds are deciduous, thin-textured be an attractive plant for a large Propagation of the bulbiferous and pinnatifid, with the fertile ones bog garden. I have not yet seen species, W. prolifera, W. radicans and being contracted and skeletonized. W. virginica established in a UK W. unigemmata, can easily be done by New growth is quite colourful. garden although it is occasionally pegging down fronds and allowing Although naturally a marsh or bog offered by fern suppliers. the bulbils or plantlets to root before plant and preferring constant severing them from the frond. The moisture, it will grow under normal Cultivation bulbils or plantlets can also be garden conditions although stature is In the wild chain ferns are found removed and rooted separately but reduced and growth is less vigorous. most frequently in areas of high require high humidity for success. It originates from eastern North rainfall and humidity with relatively Woodwardia areolata, W. semicordata America ranging from southeast mild winters. Soil should ideally be and W. virginica possess creeping Canada south to the Gulf of Mexico. acidic to neutral. Continuous rhizomes and these can be easily It is probably the most cold-hardy moisture is beneficial, although most divided. species. It appears to be rarely species are tolerant of limited dry All species can be grown from cultivated in the UK but is attractive periods. Woodwardia virginica and, to spores and most seem to be relatively and deserves to be better known. a lesser extent W. areolata, are from easy to raise by this method. marshy habitats and require Woodwardia virginica permanent moisture for successful Conclusion Another deciduous species from establishment. For terrestrial species I hope this article will help gardeners eastern North America, in this the a site sheltered from strong or cold establish the identities of chain ferns fertile fronds resemble the sterile winds is preferable. in their gardens and encourage more ones; they are fully pinnate and For the Old World species, a to be grown. Confirmation that W. spinulosa is still in cultivation would be welcome, as would information on W. harlandii, W. kempii and W. martinezii, the three other temperate species that may demonstrate cold hardiness

Tim Pyner is interested in ferns and trialling tender plants outdoors. email: [email protected]

acknowledgements Thanks to Martin Rickard for advice and information, Alison Paul for help when visiting the herbarium of the The sterile fronds of Woodwardia Natural History Museum, and Koen areolata, but with the red stipes of van den Berg for his hospitality and two unfurling fertile fronds on the left generosity when visiting his garden.

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