St. John's-wort identification

St. John's-wort identification. Beginners Guide.

Britain and Ireland have 12 non-shrubby species of St. John's-worts plus a few shrubby species like Tutsan. All have attractive yellow flowers and many are widespread.  

Separation of these 12 species is fairly straightforward in Britain and Ireland. Species that are usually easy to identify as seperate species in Britain may not be so easy in Europe. The best comprehensive and expert guide to 'British and Irish St. John's-worts'  was written by Dr N. K. B. Robson and published by the Wild Flower Society in it's  'A Guide to some difficult plants' reprinted by Summerfield Books in 2006. The strength of this paper is that it gives a European wide perspective, written by the leading expert. 

Following, is my non-expert attempt to produce a set of identification features to separate these 12 species, based on photos I have taken.  The idea is to use it as an addition to your field guide which will include other information like flowering time and distribution maps. It attempts to give more detail than normally possible in a field guide. 

The weasel word 'fairly' appears above because this group of species has pairs that can hybridise. This is especially true of the most common Perforate SJW and the Imperforate SJW and their hybrid know as 'Des Etangs' Hypericum x desetangsii.   David J. Barden wrote an excellent paper on this hybrid, Hypericum maculatum-Hypericum perforatum complex in Cambridgeshire ( V.C. 29) published in Nature in Cambridgeshire Volume 52 2010 and available on their website.

 The key finding for me in this paper, was the range of intermediate plants that David Barden separated into five groups.  It showed me that some plants I had photographed and labelled as pure H. perforatum, were in fact not pure. It is however possible to find populations of Perforate SJW which appear pure and have no aberrant features, the 'perfect perforate'.  

As always, plant ID should be based on a range of features, as no single feature is always 100% reliable.

This Key covers leaves (perforations and black dots), petals and sepals with attention to black glands and stem profile which should be looked at mid-stem, not just at the top. Use of X10 or X15 eyepiece will be expected unless you have very good eyesight. 

Where the ID Key species boxes touch, this indicates that hybridisation can occur.

Finally the exact definition of a gland, is that it has a zone of secretion and this is clearly the case for the stalked glands on the sepals. The black dots on the leaves are also glands but I prefer to call them 'dots' because they just look like dark dots. Perforations which can be dots or lines are a feature of St John's-wort and are also glands. Glands contain hypericin and other chemicals which are an attempt to repel insects. These chemicals have been of medical interest and tend to dominate any web searches for any information regarding St. John's-wort's. 

Peter G. Leonard   May 2022 (Updated September 2022 with changes to Wavy and Toadflax-leaved SJW following visits to Devon and Pembrokeshire) 

To print each page, click to highlight and save to downloads, then print from downloads. One correction needed is the difference in perforations between tetrapterum and undulatum which looking at more plants, does not really hold. See photo below Key. A more important point would be the flowers of tetrapterum are normally very crowded (except in shaded positions) and undulatum are not. The sepal shape and the number of black glands does really seem to work.

Left is Wavy (undulatum), right is Square-stalked (tetragonum).

No difference in perforations that I can see.  The example of Wavy SJW is from a plant grown from seeds given to me at a BSBI Conference but it is possible that these were hybrid plants and the size difference seen on the real undulatum photographed in Wales, is a possibly a useful feature.

Wavy St. John's-wort. Hypericum undulatum

Wavy St. John's-wort.   Hypericum undulatum 

Wavy St. John's-wort was a species I had never seen. It has a distribution in Cornwall and Devon with some in Pembrokeshire and a very few near the coast in Mid-Wales. A trip to Ireland via Fishguard provided a chance see it, although mid-September was getting rather late in the season, some records seemed to suggest this species could still flower through September.

We failed to find any at the first site near Newgale, where we were staying. It was late by the time we arrived and started raining, so it was not a intensive search. The next day we headed off to a site near Carnhedryn;  a large area of rough wet pasture with just a few cattle.

 This provided a suitable habitat and previous records suggested it might be a good place. We only found three plants despite an intensive search but that might have been due to it being late in the season. Later that day a search on the coastal path near Tresinwen also failed to locate any plants. The site looked rather overgrown.

H. undulatum shares some features with H. tetrapterum ( Square-stalked SJW) both having a square stem with wings and these two species can have intermediate forms in the western Mediterranean. This is according to the best article on St. John's-worts, British and Irish St. John's-worts by Dr N. K. B. Robson, published by the Wild Flower Society in 'A Guide to some difficult plants'.

 In the UK hybrids have been found although they are very rare.

Wavy SJW hiding in long grass. 13Sept21 

Wavy SJW- top view of flower showing the usual yellow and black anthers.

The good news was that the odd flower was still showing petals so I could see the main characteristic of this species, the red undersides of the yellow petals. See photo below.

Note the sepal like bracts (with a thick main vein) just below the flower where the second stalk breaks off the to the left. This is also present on the bud on the left and made photographing the sepals difficult.

Although several species of St. John's-worts can have red on the underside of the petals, which give the unopened buds a red look, none have the extent of red which Wavy SJW exhibits, as shown below. This and the square stem are good features to identify this species. The petals are showing none or maybe just one black dot near the margin suggesting that black dots are few. 

Wavy SJW 13th Sept 2021

The sepals are showing some black glands either on the margin or just inside it. Two stalked glands can be seen on the right example. The sepals are showing pale perforations forming lines of paler green plus some signs of veins. 

Sepals are both pointed with a distinct tip and oval in shape, with the widest point in the middle. They are also quite wide. Compare with Square-stalked SJW below.

Square-stalked SJW sepals. Narrower and very pointed with a more tapering shape. Same pale perforation lines and veins just visible and just a few black glands.  A maximum of three glands is suggested in the literature for Square-stalked SJW , whereas Wavy SJW has three plus.

Wavy SJW different plant showing wide sepals.

A different example shows sepals with more black glands on the surface. Note the oval shape, where the widest point is about half way on the sepal on the middle bud. Some tips have been lost on the sepals on the open flower. 

 Wavy SJW showing sepals and bracts. 13 Sept 21

Here again there is a sepal like bract getting in the way and hiding one of the sepals on the open flower. 

The shape of these sepals is still wide and oval and they do not just taper down from a wide base as in Square-stalked SJW. 

Stem.

Wavy SJW square stem.

Stem shape  at mid level shows a square stem with wings. Sometimes these wings have black edges.

This is similar to Square-stalked SJW which can have slightly larger wings apparently.

Wavy SJW Leaf.

Leaf showing wavy edge, a feature that was not as easy to see on these late season plants, partly due to the lack of lower leaves at this late date. The leaf is sessile but not clasping. It has many quite prominent perforations and some net veins can be seen between the major veins. It also has black dots mainly along the edge.

Wavy SJW leaf showing net veins.

Some comparison shots of Square-stalked SJW.

Flowers

Square-stalked SJW flowers. 

Flowers are crowded at the top of plant. Petals are pale yellow with no or very limited red.

Sepals are tapering and pointed and can have a few black glands, if any. 

Square-stalked SJW. 

Stem is square and winged.  The leaf is sessile but not clasping. It has many quite prominent perforations and some net veins can be seen between the major veins. It also has black dots mainly along the edge. All similar to Wavy SJW except the perforations are smaller and denser but this difference is tiny and may be too subject to variation.

Detail of leaf of Square-stalked SJW showing density of perforations.

Detail of leaf section of Wavy SJW showing lower density and slightly larger size perforations .

 Conclusion.

The combination of lots of red on the petals, less crowded flowers and a wavy edge to some of the leaves, especially lower down, separate Wavy St. John's-Wort from Square-stalked SJW. The size of the leaf perforations and density are also a feature, with Square-stalked having smaller and denser perforations but as the photos show above, this is a subtle difference and may not be reliable.

The literature suggests that the winged square stems have more prominent wings in Square-stalked but this is hard to judge and there may be some overlap in this feature. On the sample of only three plants,  it is hard to judge the sepal shape but it does appear that the sepals are more oval in shape than most Square-stalked SJW .

Separation of these two closely related species is therefore fairly straightforward however, finding a hybrid between them would be quite difficult and would require very close inspection. We are fortunate that flowers in Britain have the prominent red flushing because plants in for example Portugal, have just yellow petals. 

The literature suggests that the flower diameter is 12-20mm for Wavy SJW and 9-13mm for Square-stalked SJW. A featureI did not check on my visit.

Peter Leonard

Rampton , Cambridgeshire.

15 March 2022

Square-stalked SJW leaf showing small and dense perforations.

Wavy SJW leaf showing slightly less dense perforations.

Note the wavy edge to these leaves especially near the base of the leaf. Not easy to see. 

Rosa agrestis. Small-leaved Rose in Cambridgeshire.

 Rosa agrestis Small-leaved Rose in Cambridgeshire.

In June 2020 Joe Sharman (of Monksilver Nursery at Cottenham)  brought Alan Leslie ( author of Flora of Cambridgeshire) a specimen of an unusual rose he had collected  from near Knapwell Wood. Alan recognised it as a probable R. agrestis and this was confirmed by a visit to the site and subsequent confirmation by the BSBI rose expert Roger Maskew. This was the first record for Cambridgeshire. I had been attempting to take photos of all the wild roses found in Cambridgeshire, so this proved an added bonus as this was not a species I had considered as a remote possibility. There is only one other dot on the BSBI map in East Anglia and that is near Norwich.

R. agrestis is a very rare rose with just a scattering of records in Southern Britain and slightly more in the centre of Ireland.

This blog contains some photographs of the excellent find by Joe and Alan.

R. agrestis belongs in the Section Caninae because it has the peculiar canina meiosis where four fifths of the inheritable characteristics come from the seed parent. All roses in the section caninae are all unbalanced polyploids. R. agrestis is in sub-section Rubigineae with R. micrantha and R. rubiginosa.   

R. agrestis Knapwell Wood, 15th June 2020

At first sight the flower could be passed over as just another Dog Rose.

R. agrestis.

The stigma cluster is quite large nearly covering the disc and with few hairs if any. The disc is slightly convex. Again this could be within the variation of a Dog Rose R.canina.

R. agrestis, 15th June 2020 Sepals and pedicel.

The pedicel (stalk just below the flower and hypanthium) has no glandular hairs being clean, again just like a Dog Rose R. canina. The sepals have an upper surface covered in cobwebby hairs which is a feature shared with many other roses. The sepals are long and pinnate with edges showing the red tips of the glandular hairs. Sepals are reflexed at flowering stage. Again there is nothing here to separate it from a Dog Rose R. canina although the number of red tipped glandular very stalked hairs on the sepals is a bit unusual for a R. canina.

R. agrestis Underside of leaf. 15th June 2020

Leaflet shape has narrow base (cuneate) which is not normal in Dog Rose and the stem between the leaflets ( petiole and rachis) are covered in stalked glandular hairs and no simple hairs. Hard to see in this photo but the leaflets have scattered clear glands all over the lower surface. Time to take a more detailed look as these glands are not consistent with a Dog Rose.

R. agrestis Underside of leaflet. 15thJune2020

The underside of the leaflet is covered with clear stalked glandular hairs and although there is some variation in the size of these glandular tips they are in the range 0.1-0.12 mm diameter for the larger, which is similar to those seen on R. rubiginosa and R. micrantha.

R. agrestis 22nd Aug 2020, Leaf upper-side somewhat shiny. The lower leaflets are often smaller and reflexed.

R. agrestis Leaf upper side, new growth May 2021

R. agrestis Leaflet edge showing glandular edge. 22th Aug 2020

A close view of the leaflet edge shows a uniserrate edge with glandular hairs on both sides of the teeth which give it a multi-serrate look. The teeth tips have red hydathodes which are different to the glandular hairs in that they are solid and hard and pointed, not rounded. The glandular hairs are not really forming on distinct secondary-tips. Exact shape of leaflet edge does change depending on what part of the leaflet you look at and sometimes the glandular hairs do sit on secondary tips, as shown below on a new leaflet taken in May 2021.

New growth, May 2021. Multiserrate edge.

R. agrestis Stipule at base of leaf. 15th Jun 2020

Stipule is quite narrow with stalked glandular hairs on the edge and also some on lower surface. The glandular hairs on the leaf stem (petiole) are often on a short stalk and the rachis and petiole lack any white simple hairs. 

R. agrestis 15th Jun 2020. Stipule and young prickles.

R agrestis. 15th Jun 2020 Base of terminal leaflet.

Not all leaflets will be as extreme as this example but the narrow cuneate base is a key feature of R. agrestis. Note also the stalked glandular hairs on the rachis with no simple white hairs.

A new word to learn....

R. agrestis. 15th Jun 2020. Leaflet veins highlighted to show semi-craspedodromus pattern.

One of the important features in separating roses in the fossil record is the semi-craspedodromus pattern shown in some roses species. This is not a term I had come across before, so had to look it up. 

Although quite subtle and not present in every part of the leaflets, overall these leaflets show this semi-craspedodromus pattern with the loops before the veins make it to the leaflet edges. In a craspedodromus leaf the veins all end up going directly to the leaf margin. Some may split on the way. The semi-craspedodromus venation is present in all the section caninae roses and many others, so it is not a useful ID feature but it would be an interesting find if you found a rose that did not have his feature. An example would be Rosa stellata which has leaves like a gooseberry, but it is not hardy in the UK coming from the deserts of Texas to Arizona. 

Craspedodromus leaf venation      Semi-craspedodromus leaf venation

R.agrestis 15th Jun 2020. Stem prickle.

The BSBI Rose handbook No7 shows the prickles having a very stout base whereas the prickles photographed were a more ordinary shape. However the shape of prickles is quite variable depending on what part of the stem you look at. These prickles are not very hooked.  

R. agrestis 15th Jun 2020 Near Knapwell Wood, Cambridgeshire.

Finally a photo of the largest, possibly the original, plant in this group of about ten plants.

All these section Caninae roses are species derived from hybrids from their past evolution which continue to hybridise now. To identify a rare rose like R. agrestis, I am very grateful that Alan Leslie took a sample and sent it to BSBI rose expert Roger Maskew to be confirmed. 

Peter Leonard

Rampton, Cambridgeshire.

6th May 2021

Ref:- 

 G. G. Graham and A.L. Primavesi.(1993) Roses of Great Britain and Ireland, BSBI handbook No 7 . 

 Leslie, A.C. (2019). Flora of Cambridgeshire. RHS, London.

Postscript. Additional sites seen in 2021.

The nearest agrestis site to Cambridge is at Wymondley near Hitchin. This population was found on the banks of the Wymondley Grid Station back in 1986 and was confirmed by A.L. Primavesi  in 1994.  Alan and I visited this site on 12th July 2021 and a large number of bushes was found. They showed the same key features as the Knapwell plants but had a more greyish leaf colour.  

Wymondley Grid Station  Hertfordshire. 12th July 2021
Note the rose in the picture was not identified as it was inside a perimeter fence.

R. agrestis Wymondley Grid Station 12th July 2021

Leaflet shape showing pointed apex and well spaced leaflets. Petiole and rachis showing lots of glandular hairs.

R. agrestis Wymondley Grid Station 12th July 2021

The above photo shows the slightly greyish leaflet colour of all the plants at this site.

New Norfolk site.

On 27th July 2021, I visited Snettisham RSPB  reserve in Norfolk to see the Western Sandpiper and having obtained distant views, walked south on the footpath to find two bushes which fitted Rosa agrestis.  A sample was taken and this was later confirmed by Mr Maskew as R. agrestis. First record for West Norfolk.

R. agrestis Snettisham RSPB. 27th July 2021

R. agrestis. 27th July 21. Photo showing smooth pedicel, hypanthium and sepals.

R. agrestis. 27th July 2021. Rachis showing glandular hairs plus some simple hairs.

The observations from these two addition sites is that the Wymondley plants had a greyish look unlike the Knapwell plants; the Snettishham plants had additional simple hairs on the petiole/rachis which the Wymondley and Knapwell plants did not have. One has to conclude that within, what is regarded as a species, there is some variation of quite important features. 

Essex Botany No 13 Autumn 2021 reported six bushes of Rosa agrestis had been found on scrubbing saline pastures on Oozedam Farm at Stanford-le-Hope VC18 growing on mud-flat deposits. 

'It's possible that there is sufficient marine shell material in the mud to provide the calcareous substrate which is supposed to need.'

This is the first record for Essex. It might be worth searching for more coastal sites in East Anglia?

Peter Leonard

23rd Feb 2022

Final update 2023. The Knapwell Wood records, following a search of the area by Alan Leslie has been found to have spread from a planted original plant nearby. It would appear that somewhere is a nursery that is carefully propagating wild roses species for sale and this will contaminate the distribution mapping. 

Lanceolate Spleenwort in West Cork

Lanceolate Spleenwort in West Cork.

A search for new ferns while on a winter break in West Cork, December 2021.

 Two possible targets were Irish Spleenwort (Asplenium onopteris) and Lanceolate Spleenwort (Asplenum obovatum).  Both are rarely recorded, especially Irish Spleenwort which has no recent records in County Cork.

Both species hybridise with the variable Black Spleenwort (Asplenium adiantum-nigrum) so some care would be needed in identification, especially as I have no previous experience. A site near Bandon, Keye's Bridge, was checked for Irish Spleenwort, where it had been seen in the past but only Black Spleenwort was found. About ten quite large plants were seen. One possibly might have been showing some intermediate characterises of Irish Spleenwort but more likely was just variation. 

 The new book on ferns, 'Britain's Ferns' by James Merryweather, uses photos taken in Corfu which shows plants of Irish Spleenwort which are more similar to Black Spleenwort than those seen in Ireland. The Irish plants are more extreme in their fine dissection. 

The Keye's Bridge visit did allow me to get more familiar with Black Spleenwort. These were large plants that had fronds with pinna over 20cm of rachis.

Black Spleenwort at Keye's Bridge.  19Dec2021

Black Spleenwort, large frond. 19Dec2021

The two lowest pinna have pinnules that are divided into pinnulets so this large frond is tripinnate.

Smaller fronds are only just bipinnate but all are triangular in outline.

A bit of detail.

Black Spleenwort. Keye's Bridge.  Linear sori are long. 19Dec2021

The sori are covered by a hinged indusia which is at least four time as long as wide, on the longer ones. They are also starting towards the inner side of the pinnulet. 

Black Spleenwort indusia is long and thin and they start near the base of the pinnule/pinnulet.
The one highlighted is measured as six times as long as wide although the ones further out are much shorter. The indusia are hinged along one long edge and cover the sori. 

Black Spleenwort. 27th Dec2021

Notice the stem , called the stipe below the lowest pinna, is dark brown. This dark shinny brown colour goes all the way round the stipe until just below the lowest pinna then fades out to green on the upper side but continues on the back of the frond as a tapering brown line that eventually thins out at least half way up the rachis. See photo below.

Black Spleenwort 27Dec2021. Brown strip tapers out on underside of rachis. 

Why are these features important?  The new target species, Lanceolate Spleenwort, has short indusia.

The shinny red-brown stem ascends the stipe/rachis higher in Irish Spleenwort according to some literature but I have yet to see that feature or the species, to see if it holds true. 

The search for Lanceolate Spleenwort started with research into the British Pteridological Society Bulletin ( Vol 7, 2010 No3 page 198-204), where I found a society visit to West Cork back in 2009. They had found an 'easy to access' colony of Lanceolate Spleenwort on the Kilcatherine area of the Beara Peninsula, not far form where we were staying. There was even a photo showing members taking pictures of Asplenium obvatum subsp. lanceolatum on the wall of a small outbuilding beside the road.

A bit more research using street view on google maps located the outbuilding was still present and that ferns could still be seen growing on it.  It seemed likely that this would be a good place to check out.

On the 31st December I drove to Kilcatherine and found the stone outbuilding. 

It looks as if nothing has changed since 2009. The ferns were still growing on about ten clumps high on the wall. The house has been done up but that's about it. I took photos.

The first thing to say is that these clumps of ferns looked similar to Black Spleenwort but were somewhat different. Late December is probably not the best time of year and they were a bit bashed up but the fronds which stayed close to the wall were still in good condition and even at a distance looked different. Something about the way the terminal pinnae stick out with a clear gap between them and form a ladder each side of the rachis was unlike the Black Spleenwort I had seen earlier that day. Out on the end of the Beara, all these plants are small and the fronds are typically not more than 7cm long compared with the 20cm of the more inland Black Spleenwort (Keye's Bridge, Bandon).  

Lanceolate Spleenwort, 31Dec2021, 

Lanceolate Spleenwort. Detail of frond showing ladder of pinna on each side of the rachis.

Another characteristic which the above photo shows, is that the pinnules on the lower pinna are cut back to the pinna stem making this a bipinnate frond. This is not a useful distinction as the small Black Spleenwort are also often bipinnate ( pinnate to bipinnate to tripinnate). What is slightly more interesting is that the pinnules are rounded (obovate) and have points, like little hands with tiny short fingers.

Shape:

 The most important difference as stated on page 36 of 'Britain's Ferns' is

                                       Lanceolate  Spleenwort                                 Black Spleenwort
Fronds-                          Ovate-lanceolate in outline narrowing             Triangular in outline. broadest
                                       at the base. Basal pinna weakly inflexed.         at the base. 

Pinna -                           lanceolate shape                                               triangular shape
Pinnules-                       obovate shape                                                   lanceolate shape

(Note Obovate , egg-shaped with the broadest part near the apex.)

My photos did not support the pinna shapes as stated above. Maybe this is due to small plant size.

I could see that the Lanceolate Spleenwort has fronds that are not triangular. The pinnae were often triangular in the sense that the pinnules get larger towards the base on the pinna, not lanceolate. These pinnules were rounded/obovate. 

Frond of Lanceolate Spleenwort, Asplenium obvatum subsp. lanceolatum   Kilcatherine, Beara.

The main point is that the frond is not triangular with the lowest pinnae being slightly smaller than the next pair up. I would consider the pinnae to be triangular rather than lanceolate. Maybe larger plants show a lanceolate shape as stated in 'Britain's Ferns'. The lower pinnae are clearly supporting separate (stalked) pinnules (example highlighted in blue), which are quite rounded in shape.  The terminal pinnae are stalked.

The pinnae start off being opposite and become more and more alternate as you go up the rachis. Some fronds had opposite pinnae all the way up but others were alternate for most of the way up. Lots of variation on this feature and it is probably not that useful.  I have yet to see a Black Spleenwort with opposite pinnae going all the way up the rachis. 

Lanceolate Spleenwort. Kilcatherine, Beara.

Another frond which again is lanceolate in outline - certainly not triangular. Pinnae shape not as open on this frond but pinnules are still rounded. Ultimate segments near the apex are stalked.

Lanceolate Spleenwort, Kilcatherine, Beara.

Although the tip of the frond is rather damaged this frond displays the ladder effect of the pinnae sticking out at right angles in a line. Black Spleenwort tends to have more upswept pinnae but this is a marginal feature.

 

Lanceolate Spleenwort. Detail of pinnule showing the serrated outer margin with sharp tips.

Black Spleenwort. Detail showing similar sharp tips which is not always present on some plants. 

Black Spleenwort showing triangular frond outline despite some damage.
Note the terminal segments are wide based rather than stalked at least on smaller fronds, whereas on Lanceolate Spleenwort these terminal segments are more stalked. There is variation as some Black Spleenwort also can have stalked terminal segments.

Black Spleenwort , typical small frond from West Beara. 

Lanceolate Spleenwort. 

The above photo shows the short indusia which are at most, three times as long as wide in Lanceolate Spleenwort.  They also start towards the margin rather than at the base. The tiny hair like scales that are present on the rachis and underside of the pinnules, a feature that Black Spleenwort can also have.

Lanceolate Spleenwort. A more mature frond showing indusia and sori.

The shape and position of the of the indusia are useful in separation of Lanceolate and Black Spleenwort. The above photo shows very short indusia at most three times as long as wide, plus the starting point is further out from the base in comparison to Black Spleenwort.

I made a second trip back to Kilcatherine to double check I really had found Lanceolate Spleenwort and to exclude the possibility that some were hybrids. Black Spleenwort is quite a common plant in the area. More photos were taken and in the end I was happy.

 Something in the shape of the fronds is different even before you look at the outline shape, but is hard to put into words that do not fall foul of the variation between fronds. Size of fronds makes a big difference and all the Black Spleenwort I found this far west, are small. Getting very familiar with Black Spleenwort would seem important before looking for the rare species and I am only starting on this journey.

The good news was that on the 4th Jan on a walk out the road on Dursey Island, I was looking at the Black Spleenwort in the roadside bank when I spotted something different, a Lanceolate Spleenwort growing in a crack between stones in the bank.  A new record for Dursey Island.

Lanceolate Spleenwort, 4th Jan 2022. Dursey Island.

Lanceolate Spleenwort is called Aspenium billotii in  C.N. Page, The Ferns of Britain and Ireland but the scientific name has been updated to A. obovatum.  Two sub-species are known, subspecies obovatum is found in SW Europe and Mediteranean but has not been recorded in the British Isles. It is a diploid whereas A. obovatum subsp. lanceolatum is a autotetraploid. ( ref Plant Crib 1998, BSBI) The Plant Crib has an interesting table to separate Black and Lanceolate Spleenwort including  a comment on habit. 

Black Spleenwort is a plant rarely with a well-formed rosette , with few leaves whereas Lanceolate usually forming a compact rosette of many (15+) leaves amongst old persistent leaves and petioles. I did not count the number of fronds but I think my photos did show these features. Indusia length is noted as 1-3mm in Black Spleenwort and 1-2mm in Lanceolate which does not sound much of a difference but together with the position actually quite a useful ID feature. 

Resources

Page, C. N. (1982) The Ferns of Britain and Ireland.   Cambridge University Press.

Merryweather, J (2020) Britain's Ferns. Princeton University Press.

Peter Leonard

Rampton, Cambridgeshire. 13th January 2022