Going back to your roots
Lycophyte (a group of plants more commonly known as clubmosses) roots are interesting because evidence suggests that, despite their similar appearance, they evolved independently of those in other vascular plants (euphyllophytes). To get to the bottom of this, you have to look at the differences in the ways that their roots branch. In a recent Tansley insight, Alexander (Sandy) Hetherington and Liam Dolan describe a new framework for examining the differences.
Euphyllophyte and lycophyte roots branch in very different ways. Euphyllophyte roots branch laterally, with new roots emerging at a distance behind the root tip. By contrast, lycophyte roots branch via a form of splitting called exogenous dichotomous branching – where the parent root meristem splits into two.
The image on the cover of New Phytologist 215:2 is a scanning electron micrograph (SEM) image of a root of Phlegmariurus squarrosus, an epiphytic lycophyte. The root has recently branched via dichotomous branching, and now there are two daughter roots of roughly equal size – another characteristic that sets lycophyte roots apart from their euphyllophyte cousins.
For their Tansley insight, Hetherington and Dolan reviewed existing research on the roots of living and fossil lycophytes and proposed a new framework for describing the rooting structures of these ancient plants: highly conserved roots, and highly disparate structures from which roots develop.
The cover image was key for the research behind the Tansley insight because it conveyed many of the key features of the highly conserved root anatomy of lycophytes, particularly the dichotomous branching described above. The image is a guide for what to look for when examining the fossil record and, while fossil roots are rarely preserved with the level of detail visible here, it highlights the key features.
A final fascinating fact about the roots of Phlegmariurus squarrosus, says author Sandy Hetherington, is that the roots actually originate within the shoots, close to the tips, growing through the cortex of the plant stem before emerging at the base of the plant. The majority of the plant’s root system is therefore hidden within the shoots themselves.
In more than one sense, these roots go back further than you think.
Read the paper:
Hetherington, A. J. and Dolan, L. (2017) The evolution of lycopsid rooting structures: conservatism and disparity. New Phytologist, 215: 538–544. doi: 10.1111/nph.14324
What to read next:
- Behind the Cover: New Phytologist 215:1
- An interview with Etienne Laliberte, winner of the New Phytologist Tansley Medal 2016
- A radical role in lateral root development