Hymenophyllaceae.

The frequent use of the generic name Hymenophyllites as a designation of Palaeozoic ferns, more particularly in the older literature, is another instance of the undue importance which palaeobotanists have always been prone to attach to external resemblances of vegetative organs. The fragment of lamina described by Stur for the Culm Measures of Austria as Hymenophyllum waldenburgense[886] has no claim to consideration as evidence of Palaeozoic Hymenophyllaceae. On the other hand, there are a few records of fertile fronds which, though not to be accepted without reserve, are worthy of more careful examination. Some petrified sporangia described by Renault[887] from the Culm of Esnost are referred to Hymenophyllites on account of the position of the annulus, which appears to encircle about two-thirds of the circumference; it is, however, not certain that the annulus is horizontal as in the recent genus.

The Culm species Rhodea patentissima described by Ettingshausen[888] as Hymenophyllites patentissima and subsequently referred by Stur[889] to Rhodea, is regarded by these authors as closely allied to Hymenophyllum simply on the ground of the finely divided and delicate sterile fronds; another species, Rhodea moravica (Ett.), which Ettingshausen referred to Trichomanes, is compared with recent species of that genus. In neither case do we know anything of sporangial characters.

Fig. 270.

(A, B, F, G, after Zeiller; D, after Hooker; E, after Stur.)

A fertile sphenopteroid frond figured by Schimper as Hymenophyllum Weissi[890] from the Coal-Measures of Saarbrücken bears some resemblance to recent Hymenophyllaceae, but the figures are by no means convincing: an examination of the type-specimens in the Strassburg Museum led Solms-Laubach[891] to express dissent from Schimper’s determination. A more satisfactory example is that afforded by the fertile pieces of a frond described by Zeiller[892] from French Coal-Measures as Hymenophyllites quadridactylites (Gutbier). Some of the ultimate segments with a truncated tip are preserved in close association with a group of oval sporangia with a complete transverse annulus ([fig. 270], F, G). The position of the sporangia is such as to suggest their separation from a terminal columnar receptacle like that in Trichomanes and Hymenophyllum. In his account of this species from the Coal-Measures of the Forest of Wyre, Kidston[893] states that Zeiller informed him that he had noticed traces of what appeared to be a columnar receptacle in the French specimens.

The records of Hymenophyllaceae from the Mesozoic and Tertiary formations are not such as need detain us. The facts bearing on the geological history of this family are singularly meagre. There is no evidence which can be adduced in favour of regarding the Hymenophyllaceae as ferns of great antiquity, which played a prominent part in the floras of the past.

It is interesting to find that the genus Ankyropteris[894], one of the Botryopterideae (a group of Palaeozoic Ferns for which I propose the name Coenopterideae), has a morphological character in common with Trichomanes, namely the production of axillary buds: there are also features in the stelar anatomy shared by the Botryopterideae and Hymenophyllaceae[895]. These resemblances, though by no means amounting to proof of near relationship, point to a remote ancestry for certain features retained by existing members of the Hymenophyllaceae.