Further to my previous post I have now measured spores and stomata guard cells of both species. Usually tetraploids will have larger spores and guard cells than diploids and this has proved the case here. Despite the small sample i.e. 1 plant of each species, the differences are so marked that I am confident that a wider sample will give similiar results. The increase in size for spore measurements was around 15% and for guard cell length about 20% for the tetraploid W. orientalis. W. prolifera
Spore length = 75-78 microns
Guard Cell length = 37-40 microns
Spore length = 88-90 microns
Guard Cell length = 50-55 microns
The 2 species can be difficult to separate when young or poorly grown. However, the differences in these measurements are such that small or non-fertile plants of either species should be reliably identified.
I will now be checking possible candidates for true W. orientalis whenever I encounter them.
Update December 2014. I have recently measured guard cells from some different plants of W. prolifera and the sizes are more varied ranging from 35-51 microns. As it stands there is an difference in mean length but I will need more measurements of W. orientalis to confirm my earlier confidence that these will prove to be a reliable character. Current measurements indicate a mean lengths of below 50 microns for W. prolifera and exceeding 50 microns for W. orientalis.
Further spore measurements for W. prolifera also show increased variation ranging from 65-80 microns, still substantially smaller than in the tetraploid species.
The fern known as Woodwardia orientalis in cultivation actually comprises two closely related species. True Woodwardia orientalis is an allotetraploid species derived from a hybrid between W. prolifera and an unknown second parent. Woodwardia prolifera is a diploid species that has been known under the names W. orientalis var. prolifera or var. formosana. The latter name is frequently used for cultivated plants.
Horticultural literature usually separates Woodwardia orientalis and its varieties from other Woodwardia species by the characteristic plantlets or propagules scattered over the upper surface of the frond. Other bulbiferous species have larger plantlets restricted to the upper rachis. The var. formosana is often characterised by having many more bulbils than the nominate variety, however this is not correct.
During my ongoing research into Woodwardia in cultivation I have been trying to work out if one or both species are grown. I have also been puzzled about the actual differences between the 2 species. Herbarium specimens often comprise small fronds or frond portions and although the 2 species appear to be morphologically distinct when mature, small fronds are alarmingly similiar.
My participation in the recent BPS trip to Japan gave me the opportunity to examine mature specimens.
I saw Woodwardia orientalis growing in a couple of natural sites. Mature fronds are relatively small, mostly less than 1 metre in length. The pinnae lobes are rather broad and abruptly tapered. One or 2 basal basiscopic pinnae lobes are absent.
Woodwardia orientalis growing wild in Japan
Woodwardia orientalis-frond showing pinnae and lobes.
I only saw Woodwardia prolifera in Kyoto Botanic Garden. It is a much larger plant with fronds 1.5 – 2 metres in length. The pinnae lobes are narrow, acuminate or caudate and 2 or 3 basal basiscopic pinnae lobes are absent.
Woodwardia prolifera. Large plant growing in Kyoto Botanic Garden
Woodwardia prolifera – frond showing pinnae and lobes
Both species had small plantlets on their fronds although most had fallen when observed (late October, early November).
Despite their variability I now believe that most or all plants in cultivation in the UK (also Netherlands and Belgium), judged on their overall morphology, are W. prolifera. I will be investigating ways to identify the 2 species more reliably. Spore size may be one method to tell the species apart but information is currently lacking. It is quite possible that true W. orientalis is lurking in some collections. I would be very interested if anyone believes they may have the true species in cultivation.
Horticulturalists and botanists have for some time had conflicting views in regard to the correct name of this commonly cultivated species of Blechnum originating from temperate South America. Botanists call the plant Blechnum cordatum while gardeners insist that the correct name is Blechnum chilense and that B. cordatum is a different, tropical species differing in many ways from the cold-hardy cultivated plants. It is a member of a difficult group that botanists treat in a variety of ways, mostly as a single variable species.
Part of the confusion results from the ambiguous collection details recorded on the type specimen of Lomaria cordata (= B. cordatum). This specimen resembles the plants cultivated as Blechnum chilense. The type locality is given as Perou-Concepcion. However the collector, Joseph Dombey, did not visit this area but did travel from Peru to Concepcion in Chile where he apparently collected the type specimen.
As the type of Lomaria cordata (published 1811) was collected in Chile, where it is the only member of the complex, the correct name under the rules of priority is Blechnum cordatum. The basionym of B. chilense, Lomaria chilensis, was not published until 1824.
I am sure that the complex includes more than a single species, however we will have to wait until detailed molecular, cytological and morphological studies have been carried out before a more complete understanding is achieved.
Meanwhile, irksome as it is to gardeners, it does appear that botanists are correct on this occasion and the name that should be used is Blechnum cordatum.
Usual form found in UK gardens
Different form with less undulate pinnae seen in Belgium
Following a recent visit to Scotland I have now seen supposed Woodwardia martinezii growing in the Fernery at Benmore and in the garden at Logan Botanic Garden. They are both labelled as this species but both are clearly W. semicordata. Alastair Wardlaw also has a very well grown plant in his garden in Glasgow which he obtained as W. martinezii but again is W. semicordata.
Martin Rickard has kindly supplied me with a frond from his plant of ‘W. martinezii’. This too proved to be W. semicordata.
I therefore conclude that all plants currently being grown as W. martinezii are W. semicordata, unless someone can show me the true plant.
Now, can anybody show me the remaining Mexican species, Woodwardia spinulosa? Is it still in cultivation? Or is that incorrectly named too?
W. semicordata in Alastair Wardlaw’s garden
W. semicordata in Benmore Fernery labelled as W. martinezii
The genus Woodwardia is found mainly in Eastern Asia and North America. Currently 14 or 15 species are recognised of which 4 are found in Mexico. One of these, W. fimbriata, is mainly distributed in the western American states northwards to British Columbia in Canada. It reaches southwards into north-western Mexico.
The other 3 species are W. spinulosa, W. martinezii and W. semicordata. The former is the most widespread species and also occurs in some central American countries to the south of Mexico. It is closely related to W. fimbriata.
W. semicordata is believed to have arisen as a hybrid between W. martinezii and W. spinulosa. These form a species complex and both sterile and fertile forms of W. semicordata have been found.
The purpose of this note is to draw attention to a discrepancy regarding the identity of the species in cultivation. W. fimbriata is commonly cultivated on both sides of the Atlantic and is not considered further here.
According to Hoshizaki and Moran (Fern Grower’s Manual 2001) W. spinulosa and W. semicordata are cultivated in the USA. The illustrations (frond silhouettes) are clearly correct. The very distinctive W. martinezii is stated not to be in cultivation.
Martin Rickard (Plantfinders Guide to Garden Ferns 2000) claims to have grown both W. martinezii and W. spinulosa outside for many years in Central England. They are not illustrated but the brief description of W. martinezii casts doubt on its correct identity.
Sue Olsen (Encyclopedia of Garden Ferns 2007) includes both W. martinezii and W. spinulosa and states that the former is not cultivated in the USA but is grown in the UK and Europe. However the description of W. martinezii is rather ambiguous but the plant in the photo is clearly misidentified and although it cannot be positively named it can be dismissed as W. martinezii.
W. semicordata was first named and described as a hybrid by John Mickel and Joe Beitel in the Pteridophyte Flora of Oaxaca, Mexico (1988). Later, Mickel and Alan Smith (The Pteridophytes of Mexico 2004) changed its status to a full species as some populations were found to be fertile, either through chromosome doubling or apogamy.
It is of interest that Rolla and Alice Tryon (Ferns and Allied Plants 1982) illustrate W. martinezii with photos and a frond silhouette. The latter appears to be correctly named but the habitat photo is almost certainly W. semicordata.
W. martineziiis a relatively small fern with a long-creeping rhizome. The lamina is broadly triangular with 1 or few free pairs of pinnae. Distinctively, the sori occur along the costae, costules and upper part of the rachis.
W. spinulosa has a short rhizome and fronds more typical of Woodwardia. There are 4-5 (or more?) free pairs of pinnae and sori along the costules only.
W. semicordata is somewhat intermediate with the habit of W. spinulosa but sori along the upper parts of the costae as well as the costules.
None of the Mexican species have bulbils on the fronds.
I strongly suspect that what is grown in UK and Europe as W. martinezii has been misidentifiedand is most likely to be W. semicordata.
At the 2014 AGM I asked if any members were growing Mexican Woodwardias and Andrew Leonard said he thought he was. I have now seen his plant and can confirm that it is Woodwardia semicordata.
I would be very interested to hear of any Mexican Woodwardia being grown by members and would particularly welcome any confirmation that true W. martinezii is in cultivation.
I have added the 2014 update to the Ferns in Members Garden page. There have been relatively few losses since the previous list was drawn up, these mainly due to poor cultivation rather than adverse weather conditions.
There is a substantial increase in numbers to the list because I have included a lot of species that were not ready to be moved into the garden at the time. Many of these are now planted out in borders or in sinks and troughs. Most of these have yet to endure a hard winter although many were outside sheltered against the house wall during the last very mild winter. Therefore the numbers may reduce if next winter is cold. I do keep spares of some species if grown from spores but some plants are single crowns and these may be given some protection during very cold snaps if particularly rare or desirable.
On the whole the ferns are left unprotected apart from some xerics that may have temporary protection during very wet or snowy spells. These tend to be damaged or killed if left wet or with snow in the crown. If it is dry but cold the covers come off.
Experimenting with supposedly tender ferns can be frustrating at times but on the whole is very rewarding with many surviving and thriving in the garden.
I have tried to be as accurate and up-to-date with names as possible. Fern classification is going through an exciting period and several names for a species are available. I have sometimes made a decision that on reflection I may not be happy with and will change the name at some time in the future. I have included relevant synonyms where I feel they may be useful.
I have also remarked upon species that have been supplied under the wrong name in case others may also have the plant. Some species are also not definitely identified and I have noted where there is doubt.
Further research may reveal that other names are not correct and these will be updated and explained in due course.
Please contact me if you have any queries about fern names or wish to discuss or dispute those I have used.
Of particular interest to me is the classification and taxonomy of ferns. This interest leads onto nomenclature and use of correct names in horticulture. I have recently researched into so-called Dryopteris labordei and this has been published in the latest Pteridologist (Vol.6 Pt1). Prior to this I have written about hardy Blechnum in cultivation (Plantsman n.s Vol 11 Pt 1(2012)). Since the latter article has been published more information has come to light and I intend to write some follow-up articles in the not too distant future.
My interest in Blechnaceae is continuing and I am currently researching into Woodwardia and Doodia. Both these genera have species that are circulating under wrong or outdated names. This has come about through research not being disseminated among horticulturalists and also a lack of interest in taxonomy by many growers. Botanists are invariably helpful when contacted but much of their research seems to be hidden from interested amateurs.
I intend to share the results of some of my investigations as well as some questions that are proving difficult to answer on this blog .