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16. Juncus filiformis



Juncus filiformis aka ‘Thread Rush’ occurs in just one place in Ireland, and that is on Lough Allen! We have sought it in several locations around Lough Allen since being informed of its presence in one small spot. Our experience with that other exotic, Spiranthes romanzoffiana, leads us to look for the habitat — find the right habitat and you will find the fauna or flora? Not so in the case of Thread Rush...

Habit and Habitat.

LEFT shows the locality for this rare species. It is a habitat common to many shores of Lough Allen. This photograph was taken in October in mild and dry weather so there is much vegetation on the shore. The Rush grows in a small area behind the rocks.



The growing ‘habit’ of this plant is quite distinctive. Firstly it grows largely in sand with a thin cover on it. All the stems emerge from the ground in a straight line of up to 15cm. They are emerging from a single rootstock. This is common to other rushes but this species does it very noticeably. The lower part of the stem is red, then green and ridged, and then brown as the stems tend to die off above the fruiting body.




Stems and Fruit

In a young plant the bright green stalk are strikingly vertical. As they get older the fall away from one another like the supports of a fan. On LEFT, at the bottom of the picture, you can see a row of at least 4 stems gently spread apart. As the heads develop in the Autumn this is obvious. In the Spring the sharp fresh rows of bright green stalks emerging from the water like they are standing to attention, make this species somewhat recognisable. It is amazing to think of this delicate species surviving in a small patch the size of an urban garden. Plus the fact that in the Winter of 2013/14 they were submerged for months.



These two images are from October 2013 when the fruits were maturing. Definitive identification of the species can be made on the basis of these fruits. Juncus filiformis has very rounded fruits a small ‘bud’ at the tip which eventually breaks apart to release the seeds. The flowering head on the LEFT is covered in seeds. The Image on the RIGHT shows a capsules (or fruits) mostly intact but starting to burst open and release the seeds




Distribution and Occurrence.

Thread Rush is widely distributed in both the New and the Old World and seems to be spreading in Britain and now occurring here. The specimen on the LEFT was found after stormy conditions in the Spring had eased and this shore was exposed again. It was hanging on by a thread! Most of the other Thread Rushes in the area were intact in a slightly clayey bank which had not been broken up. Perhaps if sections like this drifted away from the site they might root elsewhere. So far, we have looked in many such suitable habitats but strangely it has not be re-located yet!

(Anatomy) RIGHT

This picture is reproduced courtesy of WikiMedia Commons (many thanks!) and shows the characteristic features of a plant in the way that only a good sketch can do. (I wish my wife would start to produce such work!!!)

The painting is by Jacob Sturm from 1792

It effectively shows the detail we have shown in our photographs apart from the ribbing on the stem which is characteristic of the species.

 ‘a’ shows the reddish coloured roots with flowering stems arising from it in precise order.

 ‘d’ refers to the structure of the flower with 6 Tepals (combined petals/sepals and the remnants of a stigma withering on top of the ripening fruit.

 ‘e’ is a mature capsule with its little topknot holding it all together.



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If you have any interesting records of animals or plants from the Lough Allen basin, we will be very pleased to reproduce them here.