Cromwell Bottom – Basic Fern Identification

Cromwell Bottom – Basic Fern Identification

Saturday 14th September 2024

Leader: Laurence Sutton

Number of attendees: 16

Laurence used the new cabin at Cromwell Bottom Local Nature Reserve to give a brief but informative presentation on common ferns and features to use to identify them. Laurence had brought a car full of samples to examine, including some that do not grow at Cromwell Bottom. The group examined some of these before and after the walk. Then we had a walk around the reserve to find some of the ones that do grow there.

One of our first stops was to look at Dryopteris affinis (Scaly Male-fern). Scaly Male-ferns typically have a dark patch on the underside of the frond at the junction of the costa and rachis, but Laurence cautioned that a dark patch can develop late in the season on Dryopteris filix-mas (Male-fern).

There are two sub-species of Scaly Male-fern at this site and there was an example of each growing close to each other (there is ongoing work into whether these are subspecies or species but Stace’s New Flora of the British Isles (2019) classes them as subspecies). Laurence pointed out the differences between the two; Dryopteris affinis ssp. affinis (often referred to as Golden Scaly Male-fern) is more robust and thicker to the feel and grows more upright whereas Dryopteris affinis ssp. borreri (often referred to as Borrer's Scaly Male-fern) tends to curve out and down. The best check is to find mature indusia on the underside of the fronds; Golden Scaly Male-fern indusia split radially whereas Borrer's Scaly Male-fern indusia shrivel into a narrow cone and look like a pie crust.

There is an abundance of Dryopteris dilatata (Broad Buckler-fern) at Cromwell Bottom as the reserve is largely wooded and Broad Buckler-fern is a woodland species. Laurence showed us what to look for; the lowest pair of pinnae are slightly shorter than the one above and the scales on the stipe have a dark stripe down the centre of them. Later in the walk we were able to compare this to Dryopteris carthusiana (Narrow Buckler-fern). This latter species has creeping rhizomes which separate the fronds a little, making the plant seem more spread-out, rather than in an exact shuttlecock form; also, there is no stripe on the scales.

We were able to see the differences between the common Athyrium filix-femina (Lady-fern) and Dryopteris filix-mas (Male-fern). Lady-fern has a more delicate appearance (it was possibly considered ‘lady-like’ to the Victorians who named it).

The final fern of note is Polystichum setiferum (Soft Shield-fern). These grow in a very upright manner and taper in at top and bottom, and so are widest in the middle. They also have a distinctive pinnule shape with the lowest part having a ‘thumb’ that sits horizontal with the costa.

Much other information was passed on by Laurence and other knowledgeable members in the group. Many thanks to Laurence for a very interesting and informative session, and to Andrew for recording.

Text by Ian D

Photographs by Ian and Sky (with additional photos by Susan, not taken on this meeting)