Coastal Elymus at Bossington SS84
This is work in progress but designed to make others question what they are seeing and perhaps start to clarify the coastal distribution of Elymus (Couch grasses) in Somerset. At Bossington Beach it’s possible to find Elymus athericus (Sea Couch) fairly easily close to the shingle ridge, one feature that singles it out from E. repens (Common Couch) and E. junceiformis (Sand Couch) (Stace 3 used to be E. juncea) is the ciliate margin on the sheath below the ligule. However the vast majority of the Elymus at Bossington appear to have no visible ciliate margin and it’s easy to pass them by as possibly E. repens? To me the ciliate margin on E. athericus is visible to the naked eye, the possible E. repens even with lens appears to have no ciliate margin.
However taking samples home and at 40X under the microscope a different picture emerges. The first picture is E. athericus with long cilia on margin that are relatively easy to see in field. The last picture is a E. repens taken from into the next field and some 30-50 metres back from the shingle ridge. The middle picture is the vast majority of vouchers taken and the microscope reveals, what eye and lens does not, a short ciliate margin which together with other intermediate characters I am taking as the hybrid Elymus x drucei.
Elymus atherica
Elymus x drucei (atherica x repens)
Elymus repens.
Confirmation of the hybrid is hard, with limited features to go on. The BSBI Grasses handbook relies on the fact that E. x drucei has “hard to find cilia on the margin” is sterile and has intermediate characters. The specimens of putative E. x drucei do appear to be sterile and the only other character that is distinguishable is the leaf ribbing. The leaf ribbing is harder to photograph but E. athericus has nerves less than their own width apart with E. repens more than their own width apart. This is fairly easy to see and indeed E. x drucei has some intermediates but very hard to measure this as a character.
That’s the position at Bossington, I would be very interested to hear from others and have samples from other coastal areas in Somerset.
Graham