The only explicit reconstruction regarding the evolution of morphological traits in Osmundaceae can be found in Miller's groundbreaking work. Notable is that Permian rhizomes of both families in the Osmundales, the extinct Guaireaceae and the Osmundaceae including the extant species, show already relatively complex stele anatomies in comparison to the surviving members of the group. The rhizome fossil record also indicates several independent radiations of likely arborescent lineages, the Guaireaceae and Thamnopterioideae in the Permian, "Osmundacaulis" in the Triassic, and "Plenasium" (subgenus "Aurealcaulis") in the late Cretaceous to Paleogene. As already noted by Miller, highly derived forms not directly related to the extant species and genera, can be found in the Jurassic and Cretaceous, such as "Millerocaulis (Osmundacaulis) kolbii". Another general trend is that the Permian Osmundales were much larger than their modern counterparts. Today, the widespread species of Osmundaceae are rhizomatous with small, low-dissected steles.