Duckweed on the loose?

January 2nd 2018

Most botanists when visiting Assynt tend, predictably, to make for the limestone, hills or coast.  However, for us locals, engaged in the ‘serious’ business of recording, it is the relatively built-up areas that tend to yield the longest lists.  Gardens and ‘waste ground’ can often house species that are found across much of the British Isles, but may be rare up here, and occasionally there are real surprises.

There was one such surprise on 8th October 2017, when Gwen Richards and I were recording the 1km square NC 0822, which stretches west from Inverpark to Baddidarrach.  At the bottom of Inverpark there is an area of no-man’s land where people tend to deposit their garden rubbish, but which abuts onto an unspoilt stretch of saltmarsh and other coastal vegetation.  Slithering down a bank, through a sallow thicket, we came across a pool just above high tide mark completely carpeted with a tiny floating plant which was instantly recognizable as one of the duckweeds Lemna spp.

No species of duckweed had been recorded from the North-west Highlands until 2014, when I happened upon two in a garden pond at Drumbeg (NC1232) belonging to the late Teresa Weinburg, ivy-leaved L. trisulca and fat L. gibba.  I have since found the latter species in other garden ponds at Clachtoll, Kinlochbervie and Rhue near Ullapool.

Duckweeds are not the most charismatic of plants.  Four of the five species now found in the British Isles consist just of rounded floating fronds adhering in small groups, with few distinguishing characters.  However past experience did enable me to identify the Inverpark example as fat duckweed, probably the first time it has been found ‘in the wild’ north of the Central Belt.  It must have escaped, or been accidentally transferred, from someone’s garden pond, and seems to be thriving.

Ian Evans

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