The vascular supply of the leaf (leaf-trace) consists of a single strand only in the haplostelic and some of the more primitive siphonostelic forms. In the microphyllous groups Leaf.trace of Pteridophytes (Lycopodiales and Equisetales) in and Petlolar which the leaves are small relatively to the stem, the Strands, single bundle destined for each leaf is a small strand whose departure causes no disturbance in the cauline stele.
the Equisetales (Horse-tails), the Lycopodiales (Club mosses), the Filicales (Ferns) and Cycadofilices, the Sphenophyllales and Cordaitales.
The Sphenophyllales are only known in a fossil state, while the Equisetales, Lycopodiales and Filicales include both living and extinct representatives.
Our knowledge of the extinct Equisetales, full as it is with respect to certain types, does not suffice for a strictly phylogenetic classification of the group. The usual subdivision is into Equisetaceae including Equisetum and Equisetites (with which Phyllotheca and Schizoneura may be provisionally associated), and Calamariaceae, including Calamites and Archaeocalamites.
In general appearance the species of Sphenophyllum (the remains of Cheirostrobus known do not allow of any idea of its habit being formed) present some resemblances to the Equisetales.
The anatomy of the stem is thus very unlike that characteristic of the Equisetales, and presents essential points of resemblance to the Lycopodiales and especially to the Psilotales.
The general morphology of the cones, on the other hand, suggests some affinity with the Equisetales.
A consideration of the characters of both shows that the Psilotales are the nearest living representatives of the Sphenophyllales, while resemblances suggesting actual relationship exist between this group and the Equisetales and Lycopodiales.
In the earliest land vegetations of which we have any sufficient record specialized forms of Equisetales, Lycopodiales, Sphenophyllales and Filicales existed, so that we are reduced to hypotheses founded on the careful comparison of the recent and extinct members of these groups.
The study of the Sphenophyllales, however, as has been pointed out above, appears to indicate that the Equisetales and Lycopodiales may be traced back to a common ancestry.
In addition to the three classes, Equisetales, Lycopodiales and Filicales, under which recent Pteridophytes naturally group themselves, a fourth class, Sphenophyllales, existed in Palaeozoic times, clearly related to the Horsetails and more remotely to the Ferns and perhaps the Club-mosses, but with peculiarities of its own demanding an independent position.
Dawsoni in the fact that each sporangiophore bears two sporangia, attached to a distal expansion approaching the peltate scale of the Equisetales.
The Sphenophyllales as a whole are best regarded as a synthetic group, combining certain characters of the Ferns and Lycopods with those of the Equisetales, while showing marked peculiarities of their own.
Professor Nathorst has described a remarkable Devonian plant, Pseudobornia ursina (from Bear Island, in the Arctic Ocean), which shows affinity both with the Equisetales and Sphenophyllales.
Among Devonian plants, Equisetales, including not only Archaeocalamites, but forms referred to Asterophyllites and Annularia, occur; Sphenophyllum is known from Devonian strata in North America and Bear Island, and Pseudobornia from the latter; Lycopods are represented by Bothrodendron and Lepidodendron; a typical Lepidostrobus, with structure preserved, has lately been found in the Upper Devonian of Kentucky.
2) and Phyllotheca among the Equisetales, Naeggerathiopsis and Euryphyllum, probably members of the Cordaitales (q.v.
Of other Equisetales there are Schizoneura and Phyllotheca; the former first appears in Lower Gondwana rocks as a member of the Glossopteris flora, migrating at a later epoch into Europe, where it is represented by a Triassic species.
Equisetales, Sphenophyllales, Lycopodiales (see Pteridophyta).
The most important and best known of the extinct Equisetales are, however, the Calamites (see Palaeobotany: Palaeozoic).
The word usage examples above have been gathered from various sources to reflect current and historial usage. They do not represent the opinions of YourDictionary.com.