Poa infirma – March 2020

This one is by way of thank you to Clive for all his expertise and skills in the determination.

Just before lockdown in early March I was meeting friends from Wales at Taunton Racecourse; part of my mind was considering the possibility of Poa infirma in the car park or various rings and the track itself. Hence in pocket the GPS, camera and note book.

In deepest darkest Taunton, taking the turn outside Sainsbury’s towards the racecourse the traffic island had a very characteristic strip of light green.

You can clearly see the lighter green strip on the right of the picture? Now there are other reasons for a light green strip, water logging, herbicide drift, and just plain old fashioned moss. Clearly this had to be investigated and there was parking to spare although I have some sort of recollection that double yellow lines have an important meaning. The ensuing horns seemed to stop when I held up my GPS and notebook for some reason. Samples secured, I was reasonably certain they were Poa infirma but had a look at them the next day under the microscope to measure the anthers. This was where my confusion started as the anthers were a fraction on the large size for P infirma being over just over 0.6mm. Poa infirma is usually found to have anthers in the range 0.15-0.4mm and P annua 0.6-1.1 (BSBI Grasses of the British Isles by Tom Cope and Alan Gray). In practice the difference between the two is usually very clear even in the field. P. infirma anthers very difficult to see and require a lens, P annua visible to naked eye and much longer than wide.

These despite being over 0.6mm were not P annua anthers.

This is your typical size and shape of P infirma anther from previous years recording.

This was the anther from Taunton specimens, clearly shape of infirma but on large size. A call to Clive who has previously recorded the hybrid and he was only too willing to help. Clive found much deflated pollen that did not stain with aceto-orcein and some full pollen that did stain. Given the presence of sterile pollen and size of anthers the conclusion was made that this is the hybrid between annua and infirma.

It’s perhaps interesting to note that locally to me Poa infirma is very easy to find throughout Minehead but despite taking multiple samples there has not been any suggestion of a hybrid.

My thanks again to Clive, his experience with the hybrid he found in Wiltshire and his expertise in extracting pollen from the anther and staining techniques were essential.

The best picture of Poa infirma for those who have yet to see it are by Fred on the Somerset Rare Plant Register where it remains at the moment although it is now Not Scarce in VC5 and VC6 from diligent searching in last few years by many Somerset botanists.

This is the BSBI map for current distribution of Poa infirma, very hard to say how overlooked it remains in VC5 but certainly much better recorded than even a few years ago.

Best wishes