Sphenopteris.
Sphenopteris is one of the many generic names which we owe to Brongniart[1404]. It is the generic designation used for a great number of Palaeozoic and later fronds, most of which are those of true ferns while some Palaeozoic species are undoubted Pteridosperms. The genus, which is purely provisional, includes members of widely different families possessing pinnules of the same general type, such as is represented in some recent species of Davallia, Asplenium, and other ferns.
The fronds of Sphenopteris may be bipinnate, tripinnate, or quadripinnate; the rachis may be dichotomously branched or the branching may be of the pinnate type characteristic of most recent ferns. The pinnules are small; they vary considerably in shape even in a single frond, but the chief characteristics are: the lobed lamina, contracted and often wedge-shaped at the base ([fig. 352]), the dichotomously branched veins radiating from the base or given off from a median rib at an acute angle. The lamina may be divided into a few bluntly rounded lobes ([fig. 352], C) or deeply dissected into linear or cuneate segments ([fig. 352], A, B, E).
Examples of Sphenopteroid leaves have already been described under the genera Coniopteris, Onychiopsis, Ruffordia, etc. Among the numerous examples of Sphenopteris species from the Carboniferous rocks mention may be made of Sphenopteris obtusiloba Brogn.[1405] ([fig. 352], A–C), which occurs in the Middle and Lower Coal-Measures of Britain[1406]. This type is characterised by the almost orbicular, oval or triangular pinnules which may reach a length of 15 mm.; they are occasionally entire, but more usually divided into 3 to 5 rounded lobes. The forked veins radiate from the base of the pinnule. The rachis may be dichotomously branched. Fructification unknown.
The species S. furcata Brongn.[1407], characteristic of the Middle and Lower Coal-Measures of Britain ([fig. 352], E), is referred to under Stur’s genus Diplotmema[1408] in which it is included by some authors solely because of the dichotomous habit of branching of the pinnae.
The pinna represented in [fig. 353] illustrates a similar type of pinnule. This species, which is very common in the Calciferous Sandstone of Scotland, was described by Lindley and Hutton as Sphenopteris affinis[1409].
The fronds of Sphenopteris affinis were discovered by Mr Peach[1410] in a fertile condition, but he regarded the reproductive organs as those of a plant parasitic on the Sphenopteris fronds. Kidston[1411] substituted Stur’s genus Calymmatotheca for Sphenopteris on the ground that the sporangia figured by Peach under the name Staphylopteris Peachii bear a close resemblance to the organs which Stur described as valves of an indusium in his species Calymmatotheca Stangeri[1412]. An examination of Stur’s specimens by Miss Benson[1413] and by Prof. Oliver and Dr Scott has confirmed Stur’s interpretation of the appendages at the tips of the fertile pinnae as valves of an indusial or cupular structure. The superficially similar bodies on the fertile pinnae of S. affinis are however true sporangia, and cannot legitimately be included in the genus Calymmatotheca as described by Stur. For this reason Miss Benson institutes a new genus Telangium, the type-species of which, T. Scotti from the Lower Coal-Measures of Lancashire, is based on petrified material. The Scotch species Sphenopteris affinis (= Calymmatotheca affinis of Kidston) is also transferred to Telangium; the sporangia are considered by Miss Benson to be microsporangia. This with other species is no doubt correctly included in the Pteridosperms. A complete frond of Sphenopteris affinis, showing a regular dichotomy of the main axes, is represented by an admirable drawing in Hugh Miller’s Testimony of the Rocks[1414].
Fig. 353. Sphenopteris affinis, Lind. and Hutt. From the Calciferous Sandstone of Burdiehouse (Scotland). (Sedgwick Museum, Cambridge.) M.S.
Some of the Palaeozoic species of Sphenopteris probably represent the fronds of true ferns, but others are known to have been borne by Pteridosperms. S. Hoeninghausi ([fig. 290], C, p. 399) is the foliage of Lyginodendron, and Scott[1415] speaks of three species, S. dissecta, S. elegans, and S. Linkii as the leaves of Heterangium. Grand’Eury[1416] has recorded the occurrence in French Coal-Measures of seeds in association with other Sphenopteroid fronds.