Two potential explanations for the origin of the Plagiogyria gene order. Pl, Plagiogyria. The minimal numbers of inversion events compared to the Angiopteris type are provided for each branch. (a), "CE" and "DE" indicate the putative CE and DE inversions as figure 2, respectively. The dashed lines show the hypothetical branches with no experimental evidence. (b), "2 inversions" denotes the two hypothetical inversions that converted the Angiopteris type to the Adiantum type .