Of the different modes of evolution affecting plant diversification — novel genes, expansion

and co-option — the latter holds an especially powerful framework for integrative biology.

Beyond the intricate detail of any particular plant, a large-scale consideration of the plant

tree of life reveals flowing gene histories inside species conduits, morphing and making way

to Darwin’s “endless forms most beautiful” (AU, I changed this, OK?). A concept that was

only tentatively emerging just two decades ago in the animal embryology literature, gene

co-option has exploded into a myriad of examples from nature’s botanical bounty. Gene co-

option — the reuse of existing genes for new developmental functions — is solidifying its

role as a central mechanism driving morphological innovation in plant evolution.

Moreover, mounting evidence points to similar molecular toolkits being recruited

independently across vast evolutionary distances, revealing deep homology of genetic

modules underlying analogous structures. In plants, this phenomenon results in phenotypes

as diverse as stinky flowers, carnivory, sexual deception, amphibious habit, and prickles.

The growing availability of plant genomes and functional model systems across lineages is

uncovering the genetic architecture of landmark developmental innovations in plant

evolution. This holistic view highlights that homologous genes are being repeatedly

tweaked into new networks and repurposed into novel roles, providing renewed support

for a tinkering model of evolution at increasingly larger scales. We present a synthesis of

diverse examples of developmental genes repurposed during land plant under the unifying

theme that gene co-option operates across multiple biological scales, and end with

outstanding questions to further probe the genetic mechanisms underlying co-option across

these expanding scales.