The Division Lycopodiophyta (sometimes called Lycophyta or Lycopods) is a tracheophyte subdivision of the Kingdom Plantae. It is the oldest extant (living) vascular plant division at around 410 million years old, and includes some of the most "primitive" extant species. These species reproduce by shedding spores and have macroscopic alternation of generations, although some are homosporous while others are heterosporous. Members of Lycopodiophyta bear a protostele, and the sporophyte generation is dominant. They differ from all other vascular plants in having microphylls, leaves that have only a single vascular trace (vein) rather than the much more complex megaphylls found in ferns and seed plants.
Classification
There are around 1,200 living species divided into three main groups within the Lycopodiophyta, sometimes separated at the level of order and sometimes at the level of class. These are subdivided at the class level here:
*Class Lycopodiopsida – clubmosses and firmosses
Class Isoetopsida – quillworts, scale trees, and spikemosses. The spikemosses are sometimes classified under Selaginellopsida.
Evolution
The members of this division have a long evolutionary history, and
fossils are abundant worldwide, especially in coal
deposits. In fact, most known
genera are
extinct. The
Silurian species
Baragwanathia longifolia represents the earliest identifable Lycopodiophyta, while some
Cooksonia seem to be related.
Fossils ascribed to the Lycopodiophyta first appear in the Silurian period, along with a number of other vascular plants. Phylogenetic analysis places them at the base of the vascular plants; they are distinguished by their microphylls and by transverse dehiscence of their sporangia (as contrasted with longitudinal in other vascular plants). Sporangia of living species are borne on the upper surfaces of microphylls (called sporophylls). In some groups, these sporophylls are clustered into strobili.
During the Carboniferous period, tree-like Lycopodiophyta (such as Lepidodendron) formed huge forests and dominated the land. Unlike modern trees, leaves grew out of the entire surface of the trunk and branches, but would fall off as the plant grew, leaving only a small cluster of leaves at the top. Their remains formed many fossil coal deposits. In Fossil Park, Glasgow, Scotland, fossilized Lycopodiophyta trees can be found in sandstone. The trees are marked with diamond-shaped scars where they once had leaves.
Characteristics
Club-mosses are
homosporous, but spike-mosses and quillworts are
heterosporous, with female spores larger than the male, and gametophytes forming entirely within the spore walls.
The spores of Lycopodiophyta are highly flammable and so have been used in
fireworks. Currently,
huperzine, a chemical isolated from a Chinese clubmoss, is under investigation as a possible treatment for
Alzheimer's disease.
Gallery
References
External links
Introduction to the Lycophyta from the University of California Museum of Paleontology
Lycophytes
Fossil Groves
Paleo Plants
Category:Living fossils
Category:Lycopodiophyta
