Saturday 7 December 2019

Maidenhair Spleenwort ferns thrive on lime in old wall mortar

Maidenhair Spleenwort is a very common and widespread fern
Maidenhair Spleenwort is a very common and widespread fern

Jim Hurley - Nature Trail

Science Week, Climate Change Week and ever more so RTÉ's excellent 'On Climate' series across television, radio and online, together with dedicated news features about climate change, brought us new, interesting and inspiring content.

I had my own possible reminder of the topic while sweeping up what must be getting close to the last of the autumn leaves.

The wind helped by gathering the leaves into piles and as I lifted a pile for transfer to the waiting wheelbarrow, I spotted that daffodils shoots concealed beneath were several centimetres tall. The tips of the shoots were pearly white, but the bases sported the rich dark green that is so familiar when the plants are in full bloom. Daffodils emerging in mid-November is a new departure in my neck of the woods.

As many trees and shrubs continue to lose their leaves for the winter and as many plants die off after their first experience of recent sharp frosts, mosses and some ferns come into their own.

Bracken is a fern that dies off in the autumn and this year there was a fine display of seasonal colour as the dark green fronds faded to pale green and progressed through a series of shades of yellows and oranges before turning the rich autumn colour named after the common fern: 'bracken brown'.

One fern that is very common and widespread and that stays winter-green is Maidenhair Spleenwort. It grow on old walls. The 'old' part is important. More modern walls have cement joints, but many old walls have lime mortar joints and it is in that medium that the lime-loving ferns thrive.

Lime mortar is weaker, softer and more porous than cement mortar, so it protects walls from cracking. It also crumbles and stays moist and it is these two characteristics that make it attractive to Maidenhair Spleenwort.

The delicate Maidenhair Spleenwort is very obvious at present growing in wiry tufts in every part of Ireland and is worth a second look as it is an attractive little plant. Its distribution ranges from the most remote rural areas to the centres of busy towns and cities wherever old mortared walls can be found.

The leaves in ferns are called fronds and the finger-long fronds of Maidenhair Spleenwort are evergreen unlike those of Bracken. Each frond is divided into several pairs of opposite oval leaflets called pinnae. As shown above, the fronds are widest at or above their middle and taper to both ends.

The Argus