Roots to simplicity: when evolution removes a key organ.

The evolution of roots was an instrumental event in the colonisation of land by vascular plants. Roots have undergone extensive radiation and can take many diverse forms including taproots, fibrous roots, and adventitious roots. This includes specialist root types, such as pneumatophores in mangroves, that have allowed species to occupy new ecological niches. In some cases, the relationship between roots and soil has been broken, rendering roots unnecessary and ultimately resulting in loss of this organ in some species. We identify several ecological niches/life habits in which rootless vascular plants have evolved: aquatic environments, canopies, arid environments, and carnivory. Many of these plants are challenging to cultivate in a laboratory environment. The exception to this is duckweeds, which we propose as a powerful experimental model for studying organ loss in plants.