Wednesday, 28 September 2022

Toadflax-leaved St. John's-wort. Hypericum linariifolium.

Toadflax-leaved St. John's-wort.  Hypericum linariifolium. 

Toadflax-leaved SJW underside of flower showing sepals.

This rare St. John's-wort might be called narrow-leaved St John's-wort since this is its main feature difference, compared with other species of SJW.

 In my previous blog on SJW ID features I had to use photos from Northern Portugal since I had not seen this species in the UK.  This is not ideal as some features might be slightly different, so I decided to visit the Teign Valley in Devon to update my photos.

I had a tip off that a site close to Fingle Bridge on the upper path to Castle Drogo had a good population but this was back in 2017. In fact the BSBI database had no records in the Teign Valley since 2017.

The site was visited on the 19th July 2022. The valley side is mainly wooded but the grid reference aligned with a clear area. No plants were found but the area was very dry.

The next day I went to Dunsford Wood which has the most records on the BSBI database. This site is slightly downstream of the Fingle Bridge site but is similar in being a wooded steep valley with occasional rocky outcrops which are free of tree cover.  Several sites were checked but no plants were found. A final area just upstream of Dunsford Wood was checked and I climbed up a steep wooded slope to a clear area.

Again this site was very dry, even the heather was struggling to flower.

Rocky outcrop being suitable habitat.

This site was my lucky break. Three plants were found and one was in full flower.

Toadflax-leaved St. John's-wort. 20July2022

The above photo shows the main feature of the narrow leaves. The main stem is upright but other stems were prostrate. One plant was looking very dry and had no open flowers.

The narrow leaves were about 1-1.5cm long and had a prominent pale central vein.

Close up views of a backlit leaf shows prominent central vein and thiner secondary veins which run up the leaf. The leaves have black glands (dots) mainly on the margin but also some on the inner parts. No perforations were seen but according the the literature some can occasionally occur. The stem can be seen as round in section.The leaves are sessile and have no petiole.

The only other St. John's-wort with narrow leaves is the Irish SJW but this has no black dots anywhere.

Underside of flower. Teign Valley, Devon. 20July2022
The length of the sepals were about half the petal length, much longer than the plants I had seen in Portugal. The sepals in both countries have very long stalks tipped with the black glands. The length of these stalks seems to vary from long to extremely long as shown in above photo. Based on a limited sample of plants this would appear to be a distinctive feature. The sepals also have black lines (glands), present in both countries and the petals have lots of black glands on the margin.

This flower also has two sepal like bracts just below the sepals, a feature which seems to be common in many SJW's. The above flower is not showing any red lines on the petals which may have faded out as in bud, the petals can look red. You can just see two-three yellow anthers poking out from behind the petals.

Toadflax-leaved SJW Northern Portugal. 2017

Toadflax-leaved SJW, 20Jul 2022. Teign Valley, Devon

Final shot showing top view of flowers.


I was very lucky to find any plants this year. The preferred habitat of the rocky outcrops was very dry. Maybe in a wetter year more plants would have been showing, however with no BSBI Database records from the Teign Valley since 2017, it is possible than this species is becoming less frequent. It should be well adapted to dry conditions since its range is more southerly in Europe (France and Iberian Peninsula) and Britain is at its northern limit. 

Dr Robson in his article 'British and Irish St. John's-worts' published in ' A Guide To Some Difficult Plants' by the Wild Flower Society suggests that plants on mainland Britain, seem to be pure without any signs of hybridisation with Trailing SJW (Hypericum humifusum).  Plants on the Channel Islands and a previous population on Cape Cornwall (now extinct), had either been thought to be a form called var. approximatum or possible the result of hybridisation. More recent informatiom from the 'Hybrid Flora of the British Isles', 2015 by Stace, Preston and Pearman show hybrids have been recorded from Pembrokeshire and the Lleyn peninsula, Caernarfonshire. 

Peter G. Leonard

July 2022


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