Plant roots evolved at least twice, and step by step

The discover of a unique rooting anatomy from 407m years ago supports theory roots evolved at least twice, and step by step

Susannah Lydon

@susieoftraken
Thu 23 Aug 2018 07.02 EDT

Most of us do not spend much time contemplating plant roots. Not only do they suffer from the wider issue of plant blindness, but they are also the bit of the plant that is not visible. In terms of getting people excited about plant science, it’s a tough gig. This is a shame, because plant roots are critical to all of our lives: no roots means no food. Roots provide anchorage, and allow plants to gain water and nutrients from the soil. They also form a key symbiotic relationship with mycorrhizal fungi, which provide minerals from the soil in return for a steady supply of carbs from the plant.

In the modern world, we can easily divide plants into the ones that have roots and the ones that don’t. The flowering plants (angiosperms) and the other vascular plant groups (conifers and other seed plants, ferns, horsetails and clubmosses) all have a recognisable root, defined by having a meristem of rapidly-dividing, undifferentiated cells, and by having a root cap, which protects the apex of the growing root and which is where the plant perceives gravity.

The other, non-vascular, land plants – mosses and liverworts - lack the plumbing to move water and food around their bodies, and also lack true roots. These plants do have rhizoids, which are simple, hair-like structures, analogous to the root hairs on the surface of a flowering plant root. Rhizoids are used for water transport, and some may be involved in nutrient transport, but they aren’t fully-functioning roots.

We know that rhizoids have been around for a very long time. The Rhynie Chert is an amazing window into the past. It preserves a 407m-year-old hydrothermal wetlands ecosystem in astonishing, cellular detail. Most of the early land plants found in the Rhynie Chert have rhizoids, but until now nothing anything like a true root organ had been recognised.

More:
https://www.theguardian.com/science/2018/aug/23/lost-worlds-revisited-the-hidden-life-of-plant-roots