Fig. 261.
- A, A′. Chrysodium lanzaeanum.
- B, B′. Lygodium Kaulfussi.
- C. Marattia Hookeri.
(After Gardner and Ettingshausen; A, B, ¾ nat. size.)
Lygodium Kaulfussi, Heer. Fig. 261, B, B′.
Fragments of forked pinnules, agreeing very closely in venation and general appearance with recent species of Lygodium, have been identified by Gardner and Ettingshausen[840] from English Eocene beds and by Knowlton from the Miocene beds of the Yellowstone Park[841] as Lygodium Kaulfussi Heer ([fig. 261], B). Despite the absence of sporangia it is probable that these fragments are correctly referred to the Schizaeaceae. The sterile and fertile specimens figured by Heer[842] from Tertiary beds of Switzerland agree very closely with recent examples of Lygodium. Similar though perhaps less convincing evidence of the existence of this family in Europe is furnished by Saporta[843], who described two Eocene species from France.
Gleicheniaceae.
The application by Goeppert[844] and other earlier writers of the generic name Gleichenites to examples of Palaeozoic ferns was not justified by any satisfactory evidence. One of Goeppert’s species, Gleichenites neuropteroides, is identical with Neuropteris heterophylla[845], a plant now included in the Pteridosperms.
The resemblance of sporangia and sori, whether preserved as carbonised impressions or as petrified material, from Carboniferous rocks, to those of recent species of Gleicheniaceae is in many cases at least the result of misinterpretation of deceptive appearances. Williamson[846] drew attention to the Gleichenia-like structure of some sections of sporangia from the English Coal-Measures, but he did not realise the ease with which sections of Marattiaceous sporangia in different planes may be mistaken for those of annulate (leptosporangiate) sporangia. In the regular dichotomous habit of Carboniferous fronds described as species of Diplothmema (Stur) and Mariopteris (Zeiller)[847] we have a close correspondence with the leaves of Gleichenia, but the common occurrence of dichotomous branching among ferns is sufficient reason for regarding this feature as an untrustworthy criterion of relationship. It is, however, interesting to find that in addition to the existence of some Upper Carboniferous ferns with sori like those of recent Gleichenias, the type of stelar anatomy illustrated by Gleichenia dicarpa ([fig. 237], C, p. 310) and other species is characteristic of the primary structure of the stem of the Pteridosperm Heterangium. We find in Carboniferous types undoubted indications of anatomical and other features which in succeeding ages became the marks of Gleicheniaceae.
Some Carboniferous fronds with short and small pinnules of the Pecopteris type, bearing sori composed of a small number of sporangia, have been assigned by Grand’Eury and other authors to the Gleicheniaceae; the same form of sorus is met with also on fronds with Sphenopteroid segments. The former is illustrated by Oligocarpia Gutbieri[848] and the latter by O. Brongniarti described by Stur and by Zeiller[849]. Zeiller has described the circular sori of Oligocarpia ([fig. 270], B) as consisting of three to ten pyriform sporangia borne at the ends of lateral veins and possessing a complete transverse annulus, but Stur[850] believes that the annulus-like appearance is due to the manner of preservation of exannulate sporangia. In this opinion Stur is supported by Solms-Laubach[851] and by Schenk[852]. Despite an agreement between Oligocarpia and Gleichenia, as regards the form of the sori and the number of sporangia, it is not certain that the existence of a typical Gleicheniaceous annulus has been proved to occur in any Palaeozoic sporangia[853].