Miniaturization of duckweeds occurred through compression of the angiosperm body plan.

Miniaturization, or an extreme reduction in body size, is present in both the plant and animal kingdoms. In animals, this concept has been studied across a range of systems, where it has been associated with the vestigialization or loss of structures such as the reduction of lungs in miniature frogs1 and the loss of body segments in tardigrades.2 By contrast, the morphological mechanisms underlying plant miniaturization remain poorly understood. The Araceae exhibits a striking evolutionary breadth, encompassing both the smallest flowering plants and some of the largest herbaceous species known, making it an ideal family for exploring the concept of miniaturization. Here, we focus on the rooted species of duckweeds, which measure just a few millimeters and have an aerial body plan consisting of a single, cryptically defined structure, called a frond. Transcriptional dissection of the duckweed frond revealed distinct zones, one with homology to aroid leaf blades and the other with both stems and petioles, indicating that the duckweed frond is a hybrid organ arising from the fusion of stem and leaf parts. The identities of these zones are further supported by patterns of cell division comparable to those in monocot leaves and by secondary cell wall staining consistent with stem tissue. Collectively, our data support the hypothesis that miniaturization in duckweeds has not arisen through the loss of body components,2 as seen in some animal lineages such as tardigrades, but through a restriction in cell division and the fusion of organs.