The name Callipteridium, created by Weiss[1505] as a sub-genus of Odontopteris, is applied by Zeiller and other authors to a few Upper Carboniferous and Permian species characterised by the occurrence of simply pinnate pinnae on the main rachis between the bipinnate primary pinnae. Single pinnules are borne directly on the rachis of the primary pinnae between the pinnate branches. The form and venation of a typical pinnule are shown in [fig. 366], B. Callipteridium pteridium, originally recorded by Schlotheim as Filicites pteridius[1506], has been fully described by Renault and Zeiller from unusually large specimens found in the Commentry Coal-field[1507]. This species illustrates the peculiar morphological features of the genus. The main rachis of the tripinnate fronds, several metres long, shows a combination of dichotomous and pinnate branching; from the zigzag and forked axis are given off bipinnate pinnae and, between these, shorter pinnate branches. The pinnules closely resemble those of Callipteris conferta but reach a greater length; the pinnules borne on the rachises of the lateral branches differ from the others in their broader base and more triangular lamina.
No fertile specimens have been found. It is probable that Callipteridium was not a true fern, and that White[1508] is correct in including it among the Pteridosperms.
Archaeopteris.
In 1852 Forbes[1509] published a brief description of some supposed fern fronds, found by the Geological Surveyors of Ireland in Upper Devonian rocks of Kilkenny, under the name Cyclopteris hibernica. The Irish specimens were more fully described by Baily[1510] in 1858. Fronds of the same type were referred by other authors to Cyclopteris, Adiantites or Noeggerathia, until Schimper[1511] proposed the generic name Palaeopteris on the ground that the fronds described by Forbes and Baily are distinguished by the nature of their fertile pinnae from the sterile leaves included in Brongniart’s provisional genus Cyclopteris. The earlier use of Palaeopteris by Geinitz for an entirely different plant led Dawson[1512] to institute the genus Archaeopteris. The genus Archaeopteris may be defined as follows:
Fronds bipinnate, reaching a considerable length (90 cm.); the stout rachis bears long linear pinnae; sterile pinnules obovate or cuneate with an entire, lobed, fimbriate, or laciniate lamina traversed by divergent dichotomously branched veins. The fertile pinnae usually occur on the lower part of the rachis; pinnules with a much reduced lamina bear numerous fusiform or oval exannulate sporangia ([fig. 369], A, E, H), sessile or shortly stalked, singly, or in groups of two or three. The base of the petiole is characterised by a pair of partially adnate stipules ([fig. 369], C, D), and single pinnules or scales occur in some species on the rachis between the pinnae and on the petiole.
Fig. 368. Archaeopteris hibernica. (From a specimen in the Science and Art Museum, Dublin. Rather less than ⅙ nat. size.)
Archaeopteris hibernica (Forbes). Figs. [368], [369], A–C.
The specimen from Kilkenny represented in [fig. 368] has a length of over 80 cm. The upper pinnae bear numerous imbricate obovate pinnules ([fig. 369], A, B) with an entire or very slightly fimbriate margin, while on the shorter lower pinnae the ultimate segments are reduced to a slender axis bearing numerous fusiform sporangia, 2–3 mm. in length. Kidston[1513] has pointed out that sporangia occasionally occur on the edge of ordinary pinnules, and he first recognised the stipular nature of the scale-like appendages which Baily noticed on the swollen petiole base (5 cm. broad) of the Irish species ([fig. 369], C). Restorations of Archaeopteris hibernica have been figured by Baily[1514] and by Carruthers[1515], but the description of the fertile pinnae by the latter author requires modification in the light of Kidston’s description of the Dublin specimens.
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