Fig. 258. Fertile pinnae of Cladophlebis denticulata. (From a Yorkshire specimen in the Sedgwick Museum, Cambridge.)
Schizaeaceae.
Evidence bearing on the existence of this family in Carboniferous floras is by no means decisive. The generic name Aneimites proposed by Dawson[822] for some Devonian Canadian plants resembling species of the recent genus Aneimia, and adopted by White[823] for a species from the Pottsville beds of Virginia, is misleading. The Canadian plants give no indication of the nature of the reproductive organs, and the fronds described by White are, as he shows, those of a Pteridosperm and bore seeds.
An examination of the suspiciously diagrammatic drawings published by Corda[824] of the small fertile pinnules of a Carboniferous fern from Bohemia, which he named Senftenbergia elegans, leads us to conclude that the sporangia are almost certainly those of a Schizaeaceous species. The small linear pinnules bear two rows of sessile sporangia, singly as in recent Schizaeaceae and not in sori, characterised by 4–5 rows of regular annular cells ([fig. 270], A) surrounding the apex. It has already been pointed out that the apical annulus of recent Schizaeaceae, though normally one row deep, may consist in part at least of two rows. Zeiller[825] examined specimens of Corda’s species and decided in favour of a Schizaeaceous affinity; he describes the sporangia as 0·85–0·95 mm. in length, with 3 to 5 and occasionally only two rows of cells in the apical annulus. Zeiller’s figures ([fig. 270], A) confirm the impression that Corda’s drawings are more beautiful than accurate. Stur[826], on the other hand, who first pointed out that the type-specimens of Senftenbergia came from the Radnitz beds of Bohemia and not from the Coal-Measures, convinced himself that the sporangia have no true annulus ([fig. 270], E). He describes them as characterised by a comparatively strong wall and by the presence of a band of narrow vertical cells marking the line of dehiscence, features which lead him to assign the plant to the Marattiales, a group which seems to have exercised a dominating influence over his judgment. In a later publication Zeiller[827] replies to Stur’s criticism but adheres to his original opinion. Solms-Laubach[828], while expressing himself in favour of Marattiaceous affinity, recognises that Zeiller’s arguments cannot be set aside.
The question must remain open until further evidence is forthcoming; but it would seem that this Carboniferous type, not as yet recognised in Britain, possessed sporangia having a distinct resemblance to those of the Schizaeaceae, though this similarity does not amount to proof of the existence of the family in the Palaeozoic era.
Palaeozoic floras may be described as rich in generalised types, types foreshadowing lines of evolution, which in the course of ages led to a sorting and a redistribution of characters. It may be that Senftenbergia is one of these generalised types.
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It is not until we ascend the geological series as far as the older Jurassic rocks that we meet with a type which can with confidence be classed with the Schizaeaceae, as least so far as sporangial characters are concerned. The species Klukia exilis is selected as the best known and most widely-spread representative of Jurassic Schizaeaceae.
Klukia exilis (Phillips)[829]. Fig. 259.
The generic name Klukia was proposed by Raciborski[830] for a species originally described by Phillips[831] from the Inferior Oolite of the Yorkshire coast as Pecopteris exilis. Bunbury’s[832] discovery (supplemented by additional evidence obtained by Raciborski) of well-preserved sporangia justified the substitution of a distinctive designation for the provisional term Pecopteris.