Prototaxites: Fungal Obelisks or World’s Oldest Carpet?

By Nathan Smith

A long time ago in a galaxy far far aw…..well actually in our galaxy, indeed on our planet, there existed tree-like organisms up to 8.8m tall (that’s approximately 4.5 doors tall or, for a more enjoyable measurement, roughly the size of two T-Rexs standing one on top of the other with the one on top wearing a party hat) and 1.36m wide. Found between 420 and 370 million years ago, its internal structure consisted of tiny intertwining tubes less than 50 micrometres in diameter.

Prototaxites_Dawson1888Prototaxites existed well before the developments of trees; its surrounding environment consisted of mats of moss and liverworts, populated by giant invertebrates, such as an ancient form of scorpion that could reach up to a metre long. The historical views of these structures are that they are the fossilised remains of huge external fungal structures; organic statues standing defiant in an otherwise flat landscape.  There are also suggestions that these giant structures may have had algal symbionts, and therefore should be classified as a lichen. Amongst other things, this suggestion would give good reason for why such structures became ‘extinct’ —this being that they were outcompeted by the emergence of vascular land plants in terms of being able to access the light they required.

But maybe Prototaxites aren’t fungi. Maybe they aren’t even a unique organism. There is an alternative theory; one that suggests that these giant structures weren’t signs of fungal domination but rather the results of an epic battle between nature and itself. Specifically, it suggests that the giant structures are the result of mats of liverworts being pulled up from the ground and rolled up by means of wind, water, or gravity, with algae and fungi possibly being caught up in the mix. Its evidence for this suggestion comes from the similarity in microstructure between fossilised Prototaxites and artificially created liverwort rolls, the paper being published in the American Journal of Botany in 2009.

Whether tree-like fungi or sections of liverwort torn out of the ground, Prototaxites remain a fossilised oddity of a time long since forgotten.

Three in the bed make for a hot relationship

By Nathan Smith

A plant, a fungus, and a virus live together in an environment inhospitable to each partner on their own. This isn’t an absurdist sitcom that’s been written whilst high in the garden, but a genuine biological phenomenon.

The plant, a type of grass known as Panic Grass (Dichanthelium lanuginosum), can grow at temperatures of up to 65C (for a point of comparison, the lethal temperature for humans is about 40C). It is found growing in Yellowstone National Park but only when it has a fungal symbiont Curvularia protuberata and this in turn is ‘infected’ with Curvularia thermal tolerance virus (CThTV).

Yellowstone_Nationalpark3

Too close for comfort? Not for Panic Grass, found near geysers in Yellowstone National Park in the United States

The ecological love-triangle was shown to be necessary for the plant-partner’s survival. This was done by infecting the plant with a ‘cured’ fungus (one that lacks the virus) and comparing it to a plant with both fungus and virus and a plant with no symbionts. The plants were then treated to growing conditions of 65C for 10hrs and 37C for 14hrs. At the end of the treatment, only plants with both partners remained healthy. Furthermore, all plants with both symbionts remained alive whereas the majority of the plants with only the fungus or nothing at all died before the experiment was completed.

However, panic grass isn’t that important or useful to us. It’s not eaten, nor is it cultured to produce fibre or biofuels. So is there any point to this knowledge? Well, the tri-kingdom system can be translated into more economically important crops. It has been shown that the fungal symbiont can colonise the roots of tomato plants and provide protection against higher temperatures, though not to the same extent as is provided to panic grass. It also suggests that the adaption to this system is widespread in nature, as panic grass and tomatoes diverged relatively early in the evolution of plants.

This certainly is hot stuff!