Wednesday, September 06, 2006

The Water fern and Duck weed association

Kingdom: Plantae
Division: Pteridophyta
Class: Pteridopsida
Order: Marsileales
Family: Azollaceae
Genus: Azolla
Species: A.filiconoides

Kingdom: Plantae
Class: Liliopsida
Order: Alismatales
Family: Araceae
Genus: Lemna
Spcies: L.minor

The Azola water fern and duck weed Lemna minor are in no way related as can be seen above. L. minor is related to the arum lilly and the water fern to the tree fern so how far apart could they be.However they have both solved their problems the same way and often live in close association, so much so that they both seem to share the same species of mycorrhiza. It appears to be an Ectomycorrhiza association with a mantel hypha sheath, a Hartig net and external hypha.I have not been able to discover any reference to the micorrhiza in any of the numerous descriptions of duck weed on the internet.None of the drawings or photos of roots show mycorrhiza.

Micorrhizas perform the task of making phosphate available to plants but it has been discovered that in fact in L. minor the roots
do not take up nutrients at all. Roots are for keeping the plant upright in the water, and by entwining with other roots as the top photo shows and keep the plants together to form a mat on the surface of the water.The nutrients are taken in through the bottom side of the leaflets. Whether this holds for the water fern as well I do not know.

L.minor is very widespread through many countries and is very invasive but not necessarily always a problem.

Another curious thing is that there are structures attached to the roots like long root hairs,these are shown in the bottom photo.


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