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We have two large Banksia marginata trees in our garden, and whenever I have had to dig near them I've noticed that the soil near the roots is cemented into pithy lumps, having almost the consistency of polyurethane foam.

I have several brick paths made from house bricks laid directly on soil. The tree roots periodically upset these, and when this happens I take up the bricks in the affected area, remove all the roots, re-level the soil and replace the bricks. I was doing this the other day in an area near one of the Banksia trees, and noticed that in several places the bricks were separated by mats of white pithy material, which looked almost like thick blotting paper.

I mentioned this one day when we were talking about symbiotic fungi at the Herbarium, and they told me that banksias are unique among Australian plants. Whereas most Australian plants rely on symbiotic fungi to extract nutrients from the notoriously deficient Australian soils, banksias have developed their own network of microfine roots to do the same job.

These photos are of one of these mats. It can be seen that the pithy material consists of a mass of roots (almost certainly from the banksia), and each root has a fringe of microfine hairs.

Most of the pithy material in the vicinity is a dirty pinkish brown, but the material in this pad is a fresh almost creamy white. I suspect that I may have taken up this area relatively recently, and that the pad has formed in a gap left between the bricks which had not been filled with dirt when the bricks were replaced.


Fungal mat 15.9.06

The pink rectangle marks the location of the RH image.

 

Enlarged image of part of mat


 

 

 © Roger Riordan 2004-2019

Banksia Roots