B. Phyllotheca.
The generic name Phyllotheca was proposed by Brongniart[545] in 1828 for some small fossil stems from the Hawkesbury river, near Port Jackson, Australia. The stems of this genus are divided into nodes and internodes and possess leaf-sheaths as in Equisetum, but Phyllotheca differs from other Equisetaceous plants in the form of the leaves and in the character of its sporophylls. We may define the genus as follows:—
Plants resembling in habit the recent Equisetums. Stems simple or branched, divided into distinct nodes and internodes, the latter marked by longitudinal ridges and grooves; from the nodes are given off leaf-sheaths consisting of linear-lanceolate uninerved segments coherent basally, but having the form of free narrow teeth for the greater part of their length. The long free teeth are usually spread out in the form of a cup and not adpressed to the stem, the tips of the teeth are often incurved.
The sporangia are borne on peltate sporangiophores attached to the stem between whorls of sterile leaves.
Our knowledge of Phyllotheca is unfortunately far from complete. The chief characteristic of the vegetative shoots consists in the cup-like leaf-sheaths; these are divided up into several linear segments, which differ from the teeth of an Equisetum leaf-sheath in their greater length and in their more open and spreading habit of growth. The large loose sheaths of the fertile shoots of some recent Horse-tails bear a certain resemblance to the sheaths of Phyllotheca. The diagnosis of the fertile shoots is founded principally on some Permian specimens of the genus described by Schmalhausen from Russia[546] and redescribed more recently by Solms-Laubach[547]. Prof. Zeiller[548] has, however, lately received some examples of Phyllotheca from the Coal-Measures of Asia Minor which bear strobili like those of the genus Annularia, a type which is dealt with in the succeeding chapter. A description of a few species will serve to illustrate the features usually associated with this generic type, as well as to emphasize the unsatisfactory state of our knowledge as to the real significance of such supposed generic characteristics.
There are a few fossil stems from Permian rocks of Siberia, from Jurassic strata in Italy, and from Lower Mesozoic and Permo-Carboniferous beds in South America, South Africa, India and Australia which do not conform in all points to the usually accepted definition of Equisetites, and so justify their inclusion in an allied genus. On the other hand there are numerous instances of stems or branches which have been referred to Phyllotheca on insufficient grounds. Our knowledge of this Equisetaceous plant has recently been extended by Zeiller[549], who has recorded its occurrence in the Coal-Measures of Asia Minor associated with typical Upper Carboniferous plants. The same author[550] has also brought forward good evidence for the Permian age of the beds in Siberia and Altai, where Phyllotheca has long been known. It is true that Zigno’s species of the genus occurs in Italian Jurassic rocks, but on the whole it would seem that this genus is rather a Permian than a Jurassic type. The species which Zeiller describes under the name Phyllotheca Rallii from the Coal-Measures of Herakleion (Asia Minor) shows some points of contact with Annularia. It is much to be desired, however, that we might learn more as to the reproductive organs of this member of the Equisetales; until we possess a closer acquaintance with the fructification we cannot hope to arrive at any satisfactory conclusion as to the exact position of the genus among the Calamarian and Equisetaceous forms. M. Zeiller[551] informs me that his specimens of P. Rallii, which are to be fully described in a forthcoming work, include fossil strobili resembling those of Annularia radiata. The verticils of linear leaves fused basally into a sheath agree in appearance with the star-like leaves of Annularia, but in Phyllotheca Rallii the segments appear to spread in all directions and are not extended in one plane as in the typical Annularia[552].
1. Phyllotheca deliquescens (Göpp.).
In an account of some fossil plants collected by Tchikatcheff in Altai, Göppert[553] describes and figures two imperfect stems of an Equisetum-like plant. Owing to the apparent absence of nodal lines on the surface of the stem the generic name Anarthrocanna is proposed for the fossils; and the manner in which the main axis appears to break up into slender branches suggested the specific name deliquescens. Schmalhausen[554] afterwards recognised the generic identity of Göppert’s fragments with the Indian and Australian stems referred to the genus Phyllotheca by McCoy[555] and Bunbury[556].
We may define the species as follows:—
Stem reaching a diameter of 2–3 cm. with internodes as much as 4 cm. long, the surface of which is traversed by longitudinal ridges and grooves which are continuous and not alternate at the nodes. Branches arise in verticils from the nodes. The leaves have the form of funnel-shaped sheaths split up into narrow and spreading linear segments, each of which is traversed by a median vein. The fertile shoot terminates in a loose strobilus bearing alternating whorls of sterile bracts and sporangiophores.