The roots of Psaronius, more especially as regards the stelar structure, are in close agreement with those of Marattiaceae.
The reference to Marattiaceae of the great majority of fertile fern-like fronds from Permian and Carboniferous rocks constituted a strong a priori argument in favour of including Psaronius stems in the same family, especially when it was known that leaves with Marattiaceous synangia were borne by species of this genus. It is, however, well to remember the change in our views as to the dominance of Marattiaceae in Palaeozoic floras consequent on the discovery of the Pteridosperms. The association of fronds bearing Asterotheca and Scolecopteris types of fructification with Psaronius stems recorded by Grand’Eury[1094] is a point in favour of the Marattiaceous affinity of this extinct genus, but it is not impossible that Psaronius stems bore fronds which produced Pteridosperm organs of reproduction. In this connexion the specimen represented in [fig. 297] is of interest, as the fronds (Pecopteris Sterzeli) borne on the Psaronius stems are hardly distinguishable from the seed-bearing leaves known as Pecopteris Pluckeneti.
The position of Psaronius may be best expressed by assigning it to a separate family, the Psaronieae, as advocated by Stenzel, and by regarding it as one of the many instances of a generalised type which in the sum of its characters approaches most nearly to the Marattiaceae.
CHAPTER XXIV.
Ophioglossales (Fossil).
The fossils hitherto classed with the Ophioglossales are not such as afford any satisfactory evidence in regard to the past history or phylogeny of the group. In the generalised class of Palaeozoic ferns, the Botryopterideae, we find certain characters suggesting comparison with recent members of the Ophioglossaceae, but no trustworthy records of these eusporangiate ferns are furnished by the older plant-bearing strata.
Fig. 301. Rhacopteris sp., Ballycastle, Ireland. From a specimen in the Manchester Museum. [M.S.]
The genus Rhacopteris ([fig. 301]), characteristic of the Culm flora, has been compared with Botrychium, but on grounds which are wholly inadequate. The species R. paniculifera Stur[1095] is characterised by a stout rachis bearing two rows of laterally attached rhomboidal or subtriangular segments with a more or less deeply lobed margin and spreading veins. The rachis branches distally into two arms, and these are again symmetrically subdivided into fertile axes bearing clusters of small spherical bodies 1 mm. broad, which Stur speaks of as exannulate sporangia similar to those of Botrychium. He includes the species in the Ophioglossaceae. As Zeiller[1096] pertinently remarks, Rhacopteris differs essentially in habit from any recent member of this family. Rhacopteris also includes species characterised by leaflets deeply dissected into linear segments; an example of this form is represented by Rhacopteris flabellata (Tate) recorded by Kidston[1097] from rocks of Calciferous Sandstone age in Flintshire.