Water lilies, loss of woodiness, and model systems

The delicate necklace of threaded petals from the tomb of Rameses II, midnineteenth century glass houses built for the newly discovered Victoria amazonica , and Monet’s giant canvases in the Musee de l'Orangerie all testify to a deep human attraction to water lilies: beguiling plants with showy flowers that seem to arise nymph-like out of the mud. Like orchids, cacti, succulents, and carnivorous plants, water lilies have a dedicated band of horticulturalists devoted to growing and exploring their endless variety. The late nineteenth century craze for water lilies that attracted Monet was fueled by one such enthusiast, Joseph Bory Latour-Marliac (1), who developed hardy water lily cultivars with dazzling new flower colors ranging from “delicate yellow to fuscia and deep red.” Nymphaea thermarum , the focus of the recent paper by Povilus et al. (2), is another unusual water lily variant. The smallest water lily known, N. thermarum was discovered and described in the late 1980s (3). Endemic to hot spring lakes in the Albertine Rift Valley of Rwanda, now, just a few decades after its discovery, it appears to be extinct in the wild (4, 5). Crucially, as recognized by Povilus et al. (2), it has a small genome, only about three times larger than that of the botanical model of choice, Arabidopsis. Povilus et al. (2) provide initial documentation of that genome and use it to explore the genomic correlates and evolutionary significance of an unusual water lily trait, the complete loss of the vascular cambium that is responsible for the formation of woody tissues in almost all seed plants. Part of the interest in water lilies for Povilus et al. (2), and for contemporary plant science, flows from the phylogenetic position of water lilies in flowering plant (angiosperm) evolution. It has long been suspected that … [↵][1]1To whom correspondence may be addressed. Email: peter.crane{at}yale.edu. [1]: #xref-corresp-1-1