Lycopods sentence example
Hooker enumerated twenty-one species of flowering plants, and seven of ferns, lycopods, and Characeae; at least seventyfour species of mosses, twenty-five of Hepaticae, and sixty-one of lichens are known, and there are probably many more.
Sphenophyllum was a slender climbing plant with whorls of leaves, which was probably related both to the calamites and the lycopods.
The long linear leaves of some species of Podocarpus, in which the lamina is traversed by a single vein, recall the pinnae of Cycas; the branches of some Dacrydiums and other forms closely resemble those of lycopods; these superficial resemblances, both between different genera of conifers and between conifers and other plants, coupled with the usual occurrence of fossil coniferous twigs without cones attached to them, render the determination of extinct types a very unsatisfactory and frequently an impossible task.
A highly specialized means of vegetative reproduction is seen in the tubers of Phylloglossum and the embryos of some Lycopods.
Independently of introduced plants, fifty-five species have been collected in the group, twenty-nine being flowering plants and twenty-six ferns and lycopods.Advertisement
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.
The best known of the Palaeozoic Lycopods were trees, reaching loo ft.
Broadly speaking, the Palaeozoic Lycopods, whatever their dimensions, show a general agreement in habit and structure with our living forms, though often attaining a much higher grade of organization.
We will first take the arborescent Lycopods, as in every respect the more important group. They may all be classed under the one family Lepidodendreae, which is here taken to include Sigillaria.
Some analogy among recent Lycopods is afforded by the stem of Isoetes, and by the base of the stem in Selaginella spinosa; in the fossils the process was of a more normal type, but some of its details need further investigation.Advertisement
Lepidocarpon affords a striking instance of homoplastic modification, for there i s no reason to suppose that the Lycopods were on the line of descent of any existing Spermophyta.
The discovery of Sigillariostrobus, which was the fructification of Subsigillariae as well as of the ribbed species, has finally determined the question of the affinities of the genus, once keenly discussed; Sigillaria is now clearly proved to have been a genus of heterosporous Lycopods, with the closest affinities to Lepidodendron.
The morphology of Stigmaria has been much discussed; possibly the main axes, which do not agree perfectly either with rhizomes or roots, may best be regarded as comparable with the rhizophores of Selaginellae; they have also been compared with the embryonic stem, or protocorm, of certain species of Lycopodium; the homologies of the appendages with the roots of recent Lycopods appear manifest.
Under this name are included the fossil Lycopods of herbaceous habit, which occur occasionally, from the Devonian onwards.
One such plant, Miadesmia, has already been referred to, as one of the seed-bearing Lycopods.Advertisement
The evidence for terrestrial Silurian vegetation is still dubious; apart from some obscure North American specimens, the true nature of which is not established, Potonie has described well-characterized Pteridophytes (such as the fern-like Sphenopteridium and Bothrodendron among Lycopods) from supposed Silurian strata in North Germany; the horizon, however, appears to be open to much doubt, and the specimens agree so nearly with some from the Lower Carboniferous as to render their Silurian age difficult of credence.
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.
Bothrodendron still survives, but Lepidodendron, Lepidophloios, and the ribbed Sigillariae are the characteristic Lycopods.
The Upper Coal Measures (Stephanian) are characterized among the Calamarieae, now more than ever abundant, by the prevalence of the Calamodendreae; new species of Sphenophyllum make their appearance; among the Lycopods, Lepidodendron and its immediate allies diminish, and smooth-barked Sigillariae are the characteristic representatives.
Starting with the Permo-Carboniferous vegetation, and omitting for the moment the Glossopteris flora, we find a comparatively homogeneous flora of wide geographical range, consisting to a large extent of arborescent lycopods, calamites, and other vascular cryptogams, plants which occupied a place comparable with that of Gymnosperms and Angiosperms in our modern forests; with these were other types of the greatest phylogenetic importance, which serve as finger-posts pointing to lines of evolution of which we have but the faintest signs among existing plants.Advertisement
Selaginella - A few hardy kinds of this large family of Lycopods are valuable for carpeting the fernery or clothing shady spots in the rock garden.