Great moments in plant evolution

Just as dinosaurs can be regarded as protobirds (1) and synapsids as protomammals (2), understanding the evolution of plants depends on extinct fossil groups, such as those linking spore and seed plants. A profound paleobotanical surprise in 1904 was discovery of pteridosperms, commonly called seed ferns, because of their unexpected combination of seeds and fern-like leaves (3). Another paleobotanical surprise in 1960 was discovery of progymnosperms, spore plants with woody anatomy comparable to modern conifer trees (4, 5). Now, Wang et al. (6) in PNAS report a Chinese Permian (298 Ma) fossil plant, Paratinga wuhaia. These permineralized fossils convincingly expand the progymnosperm clade to include the enigmatic Noeggerathiales, variously regarded as leptosporangiate or eusporangiate ferns, sphenopsids, cycads, or possible progymnosperms (7). The insight comes from permineralized fossils, sometimes mistakenly called petrified, or, literally, turned to stone. In contrast to petrified limb casts, permineralized plants retain original cell walls infiltrated by colloidal silica, revealing details of histology and reproduction in thin sections and acetate peels. Paratingia bore numerous (perhaps as … [↵][1]1Email: gregr{at}uoregon.edu. [1]: #xref-corresp-1-1