Remains of early Triassic floras have been found at a few locali ties in Europe, notably in the Vosges district, on the northern edge of the Eifel, and elsewhere. Characteristic genera are Pleuromeia, Schizoneura, Voltzia, Albertia, Pelourdea, Neuropteridium, Equi setites and a few examples of Cycadean plants. Pleuromeia is rep resented by stems, occasionally reaching a length of 2 metres or more, with spirally disposed leaf-scars similar to those on some species of the older genus Sigillaria. On the upper region of the stem were overlapping, short and broad scales bearing seed-like reproductive organs. The lobed and swollen base of the stem bearing numerous rootlets suggests comparison with the living quillworts (Isoetes). We may picture the plant as a compara tively low unbranched shrub bearing needle-like leaves and at a higher level shorter and broader fertile scales, growing probably among sand dunes in arid regions. It is one of the rare links discovered in Mesozoic floras with the tree-like lycopodiaceous plants of the Coal age. Along with species of Schizoneura occur large stems of Equisetites differing in their ampler proportions and possibly in structure from modern horsetails. Voltzia is a conifer resembling in its foliage-shoots and in the structure of the wood species of Araucaria, e.g., the Norfolk Island pine, Araucaria ex celsa, but in some respects differing from all recent conifers nota bly in the structure of the female shoots. Albertia with its broader leaves recalling those of Agathis—the genus which includes the kauri pine of New Zealand—may also be related to the Araucarias. In Arizona over many square miles of country petrified trunks of trees, some probably goof t. in length, have been laid bare by the denudation of early Triassic rocks ; many of the stems are Arau carian or have Araucarian characters. Specimens of ribbon-like leaves have been described from Triassic beds as species of Y uc cites, Bambusium, etc., because of their similarity to the leaves of Yucca and bamboos. It has been proposed to refer them to the non-committal genus Pelourdea. The probability is that these leaves were borne by plants descended from Cordaites or other Palaeozoic gymnosperms.
Reference has already been made to the fern-like fronds of Neuropteridium (Gondwanidium) as fossils characteristic of the Glossopteris flora; the name Neuropteridium is applied also to some Triassic leaves (fig. i 1) which are probably not directly related to the southern and older examples. The occurrence of a few fronds such as Dioonites and Zarnites in earlier Triassic floras prepares us for the rapid development of the Cycadophyta in the Rhaetic and Jurassic floras. It is, however, important to note that these generic names, suggested by the resemblance of the fossil leaves to those of the living Mexican and American Cycads Zamia and Dioon, should not be regarded as evidence of close affinity of the extinct to the living forms.
The much greater abundance and variety of plants in later as compared with the earlier Triassic floras affords evidence of ameli oration in the physical environment. Collections made from the Richmond coal field in Virginia and from Upper Triassic beds in Austria and Switzerland enable us to follow the main lines along which the plant world was developing. Among equisetaceous types
attention may be called to the genus Neocalamites which is not always readily distinguishable from Schizoneura. It is character ized by long linear leaves springing in circles from the nodal joints and free to the base instead of being united into a sheath as in Equisetum. Neocalamites was a very widely distributed Triassic genus; it is recorded from Tongking, from South Africa and Australia, as well as from northern localities. A notable feature of the Keuper floras is the abundance of ferns; Macrotaeniopteris, characterized by simple banana-like fronds reaching a length of a metre and a breadth of i7cm., is probably a fern though no spo rangia have been discovered. Fronds often described as species of Acrostichites, an unfortunate name because of its implication of relationship to the living genus Acrostichum, are in some in stances at least members of the Osmundaceae, a family which has been traced as far back as the Permian period. Clathropteris platyphylla, with its large fronds divided into spreading lobes like the segments of a horse chestnut leaf and its approximately rec tangular meshes of slender veins on either side of a central rib, is one of many ferns in Mesozoic floras agreeing closely with the Indian and Malayan species of the genus Dipteris. The family Marattiaceae, now characteristic of the Tropics, was also repre sented by Pseudodanaeopsis, Marattiopsis and other genera closely resembling recent tropical species. These and other ferns are a few of many Triassic genera which give a modern aspect to the earlier Mesozoic floras.
Another distinguishing feature of the later Triassic floras is the abundance of the Cycadophyta as illustrated by such genera as Sp/ienozamites with its handsome fronds bearing two rows of large truncate segments, Pterophyllum and Pseudoctenis with fronds similar to those of several existing cycads in the form of the leaf lets. It must be remembered that the term Cycadophyta is used in a comprehensive sense embracing not only the living cycads, represented by a comparatively small number of species and genera for the most part tropical in range, but also an extinct group, the Bennettitales. The Bennettitales reached their maxi mum development in the Jurassic period and in the early days of the Cretaceous period when they were represented by a large number of types : in the form and structure of the stem and in their large palm-like leaves many of them must have borne a striking resemblance to modern cycads, but in the structure of the reproductive organs they differed in many characters from all ex isting cycads (see p. 86). The point which concerns us at the moment is that the much greater wealth of cycadean plants in the later Triassic floras than in the earlier floras of the same period prepares us for their further increase in Rhaetic and Jurassic floras. Similarly the occurrence in some Triassic beds of the genus Thinnfeldia (fig. 4), which is probably a pteridosperm, character ized by fern-like fronds with leathery leaflets, is another example of the appearance of a new type which played a conspicuous part in Triassic, Rhaetic and Jurassic floras in almost all regions of the world.