In addition to genera founded on true synangia or groups of free or partially united sporangia, the literature of Palaeozoic ferns contains several generic names applied to sporangia which occur singly on Sphenopteroid or Pecopteroid pinnules. The following may serve as examples; but it should be stated that these will probably be transferred eventually to the Pteridosperms. It is, however, immaterial whether they are dealt with here or in the chapter devoted to the seed-bearing “ferns.”
Dactylotheca.
Zeiller[1014] created this genus for fertile fronds of Pecopteris dentata Brongn. (= P. plumosa Artis[1015]), a common British species in the Upper and Middle Coal-Measures. Stur[1016] included P. dentata in his list of species of Senftenbergia, the genus to which reference was made under the Schizaeaceae.
Pecopteris (Dactylotheca) plumosa (Artis). Figs. [290], E, [292], [293].
| 1825. | Filicites plumosus, Artis, Antedil. Phyt. p. 17, Pl. XVII. |
| 1828. | Pecopteris plumosa, Brongniart, Hist. vég. foss. p. 348, Pls. CXXI. CXXII. |
| — | P. dentata, Brongniart, ibid. Pls. CXXIII. CXXIV. |
| — | P. delicatulus, Brongniart, ibid. Pl. CXVI. fig. 6. |
| 1832. | Sphenopteris caudata, Lindley and Hutton, Foss. Flor. Vol. I. Pl. XLVIII.; Vol. II. Pl. CXXXVIII. |
| 1834. | Pecopteris serra, Lindley and Hutton, ibid. Vol. II. Pl. CVII. |
| 1834. | Schizopteris adnascens, Lindley and Hutton, ibid. Vol. I. Pls. C. CI. |
| 1836. | Aspidites caudatus, Goeppert, Syst. fil. foss. p. 363. |
| 1838. | Steffensia silesiaca, Presl, in Sternberg, Flor. Vorwelt, Vers. II. p. 122. |
| 1869. | Pecopteris silesiacus, Schimper, Trait. pal. vég. Vol. I. p. 517. |
| — | Cyathocarpus dentatus, Weiss, Flora der jüngst. Stk. und Roth. p. 86. |
| 1877. | Senftenbergia plumosa, Stur, Culm Flora, II. p. 187 (293). |
| — | S. dentata, ibid. |
| 1886. | Dactylotheca plumosa, Kidston, Cat. Palaeozoic Plants, p. 128. |
| 1888. | Dactylotheca dentata, Zeiller, Flor. Valenc. Pls. XXVI.–XXVIII. |
For a fuller synonymy reference should be made to Kidston’s account of this species[1017], from which the above list is compiled. The large fronds of this species are tri- or quadripinnate. The pinnules vary much in shape and size and in degree of lobing, according to their position on the frond ([fig. 293]). The primary pinnae are subtended by two Aphlebiae ([fig. 293], A) appressed to the rachis, like the delicate leaves of the recent fern Teratophyllum aculeatum (see [page 301]). The sporangia (0·5–0·65) are oval and exannulate and are attached parallel to the lateral veins; they may occupy the whole of the space between the midrib and the edge of the pinnules. This species occurs in the Upper, Middle, and Lower Coal-Measures of Britain, reaching its maximum in the Upper Coal-Measures. The aphlebiae undoubtedly served to protect the young fronds, as shown by a specimen figured by Kidston ([fig. 293], B); they may also have served other purposes, as suggested by the above comparison with Teratophyllum, in the mature frond. Lindley and Hutton regarded the aphlebiae as leaves of a fern climbing up the rachis; which they named Schizopteris adnascens, a confusion similar to that already mentioned in the description of Hemitelia capensis (see p. 304).
Fig. 292. Dactylotheca plumosa. (After Kidston. Slightly reduced.)
Fig. 293. Dactylotheca plumosa: A. Rachis with Aphlebiae. B, a, young pinnae circinately folded. (After Kidston. A, B, ⅘ nat. size.)