Saturday 31 October 2020

An astonishing find in Breckland

You know how sometimes you're out plant-hunting and you think you've found a rare plant? But 99 times out of a hundred it turns out to be something less amazing that's maybe looking a bit unusual? Read on to find out why it's always worth taking a closer look...

The mystery umbellifer in flower
Image: P. Stroh

First BSBI member Ian (mainly a birder but also a pretty good botanist) sets the scene:   

"In late June this year I was contacted by a council Planning & Countryside Officer, who asked me to look at an umbellifer that one of his volunteers had found at a site where the council had undertaken some work to create a wild flower meadow. Much of the area had been flooded over winter and was still damp/marshy in places.

"I had a look at the site a few days later and easily found the umbellifer which was frequent across the site and was certainly intriguing! It seemed to key out to and to best fit the description for Creeping Marshwort Helosciadium repens but, as that species is currently known from just one native site in Oxfordshire, logically it couldn’t possibly be that, could it? Moreover, some of the measurements were marginal and therefore it seemed more plausible that the plant would be some sort of hybrid. Following some consultation with others (who only saw photos) I reported back to the Council Officer that this seemed most likely, possibly even a cross genera hybrid between Berula and Apium/Helosciadium, which would be interesting in itself. However, the plants were at an early growth stage, and I determined to come back at a later date.

The mystery umbellifer in fruit and
with 3-7 bracts below the flower:
a mystery no more?
Image: P. Stroh
"Most of my spare time during July and August focused on surveys of other rare plants for the Breckland Flora Group and quadrat surveys on the BTO’s Nunnery Lakes reserve, and I didn’t return to the umbellifer site until late August. By that time, many of the plants were in fruit, and the tiny nagging voice I had earlier had at the back of my mind suddenly became very loud!

"A few measurements still seemed marginal, however, and given its rarity I still couldn’t believe that the plant would really turn out to be H. repens. I posted some pictures on Twitter to obtain some more opinions, without mentioning a possible ID. This prompted a quick and excited response with a number of Twitter experts suggesting it looked good for H. repens, and I subsequently contacted Pete Stroh, BSBI's England Officer who alerted Fred Rumsey at the Natural History Museum. After seeing the photos, both Fred and Pete came to see the plant in situ the following day".

Pete takes up the story….. 

"After meeting up with Ian, we strolled down to the site. Creeping Marshwort has a very distinctive ‘sickly green’ look to the leaves, and so my hopes were raised when we started looking around at the locally abundant, very neat-looking umbellifer. Several times over the years I’ve been excited about a possible find of this nationally rare species, only to find out after closer examination that it was the stunted growth form of Fool’s Watercress, an apt name all things considered. 

The damp meadow, with
Creeping Marshwort frequent
across the site
Image: P Stroh
"But this did appear to be different, and examination of the number of bracts (at least three, sometimes four or five), and the fruit shape (short and fat), as well as the shape of the basal leaves (as broad as long, more-or-less) raised excitement levels. Fred appeared out of the ether about 10 minutes after me and Ian arrived on site, and after examining some plants, had no doubt that they were Creeping Marshwort. In fact, he was pretty sure before getting to Thetford, based on the photos that Ian had posted on Twitter. No plants of Fool’s Watercress were present, which made the job of searching for a possible hybrid fairly redundant. 

"Wandering around, it was clear the plant was everywhere, and almost certainly must have arisen from the seed bank. It’s a quite amazing find, and credit must be given to the sharp-eyed volunteer who alerted Mark Webster, the Countryside & Planning Officer for Thetford Town Council. Mark organised the removal of topsoil for the specific purpose of seeing what would appear, wild flower meadow creation without resorting to imported seeds – how very refreshing!

"Now the task will be to ensure that the species persists, although given the enthusiasm of Mark, the fact that that the seeds are clearly very long-lived in the soil, and that hundreds of plants were in fruit, all the signs are that with a bit of disturbance now and again, and a few tweaks with mowing regimes, this second extant native site for Creeping Marshwort will remain the best example of wild flower meadow creation I have seen".

So a new dot has now appeared on the BSBI distribution map for Creeping Marshwort and it looks as though the next step will be for Pete to update the Species Account for this rare plant.

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