Lycopodiophyta
Encyclopedia
The Division Lycopodiophyta (sometimes called Lycophyta or Lycopods) is a tracheophyte
subdivision of the Kingdom Plant
ae. 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 spore
s 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 microphyll
s, leaves that have only a single vascular trace (vein) rather than the much more complex megaphylls found in fern
s and seed plants.
, and Selaginellales); in addition there are extinct groups. There is some variation in how the extant orders are grouped into classes: they may be put into a single class; they may be put into two classes, with the Isoetales and Selaginellales combined into one class; or they may be put into three classes, one order in each. The system which uses two classes for extant species is:
s 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 microphyll
s 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 sporophyll
s). In some groups, these sporophylls are clustered into strobili
.
During the Carboniferous Period
, tree-like Lycopodiophyta (such as Lepidodendron
) formed huge forests that dominated the landscape. The complex ecology of these tropical rainforests collapsed during the mid Pennsylvanian
due to a change in climate.
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.
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
.
Vascular plant
Vascular plants are those plants that have lignified tissues for conducting water, minerals, and photosynthetic products through the plant. Vascular plants include the clubmosses, Equisetum, ferns, gymnosperms and angiosperms...
subdivision of the Kingdom Plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
ae. It is the oldest extant (living) vascular plant
Vascular plant
Vascular plants are those plants that have lignified tissues for conducting water, minerals, and photosynthetic products through the plant. Vascular plants include the clubmosses, Equisetum, ferns, gymnosperms and angiosperms...
division at around 410 million years old, and includes some of the most "primitive" extant species. These species reproduce by shedding spore
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
s and have macroscopic alternation of generations
Alternation of generations
Alternation of generations is a term primarily used in describing the life cycle of plants . A multicellular sporophyte, which is diploid with 2N paired chromosomes , alternates with a multicellular gametophyte, which is haploid with N unpaired chromosomes...
, although some are homosporous while others are heterosporous. Members of Lycopodiophyta bear a protostele, and the sporophyte
Sporophyte
All land plants, and some algae, have life cycles in which a haploid gametophyte generation alternates with a diploid sporophyte, the generation of a plant or algae that has a double set of chromosomes. A multicellular sporophyte generation or phase is present in the life cycle of all land plants...
generation is dominant. They differ from all other vascular plants in having microphyll
Microphyll
The terminology of fossil plants is in places a little confusing. In the discipline's 200+ year history, certain concepts have become entrenched, even though improved understanding has threatened the foundations upon which they are based...
s, leaves that have only a single vascular trace (vein) rather than the much more complex megaphylls found in fern
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s and seed plants.
Classification
There are around 1,200 living (extant) species of Lycopodiophyta which are generally divided into three orders (Lycopodiales, IsoetalesIsoetales
Isoetales, also written Isoëtales, is an order of plants in the class Isoetopsida. There are about 140-150 living species, all classified in the genus Isoëtes , with a cosmopolitan distribution but often scarce to rare. Living species are mostly aquatic or semi-aquatic in clear ponds and...
, and Selaginellales); in addition there are extinct groups. There is some variation in how the extant orders are grouped into classes: they may be put into a single class; they may be put into two classes, with the Isoetales and Selaginellales combined into one class; or they may be put into three classes, one order in each. The system which uses two classes for extant species is:
- Class LycopodiopsidaLycopodiopsidaLycopodiopsida is a class of plants often loosely grouped as the fern allies. Traditionally the group included not only the clubmosses and firmosses, but also the spikemosses and the quillworts...
– clubmosses and firmosses - Class IsoetopsidaIsoetopsidaThe Isoetopsida is a class of the Lycopodiophyta. All living plants belong to the genus Selaginella in the Selaginellales or to Isoetes in the order Isoetales. In the past, members of this group have sometimes been placed in the class Isoetopsida, sometimes in the Selaginellopsida or Lycopodiopsida...
– quillworts, scale trees, and spikemosses - Class † ZosterophyllopsidaZosterophyllopsidaThe Zosterophylls are a group of extinct plants. The taxon was first established by Banks in 1968 as the subdivision Zosterophyllophytina; they have since also been treated as the division Zosterophyllophyta and the class Zosterophyllopsida. They were among the first vascular plants in the fossil...
– extinct zosterophylls.
Evolution
The members of this division have a long evolutionary history, and fossilFossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s are abundant worldwide, especially in coal deposits. In fact, most known genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
are extinct
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...
. The Silurian
Silurian
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...
species Baragwanathia longifolia represents the earliest identifable Lycopodiophyta, while some Cooksonia
Cooksonia
Cooksonia is an extinct grouping of primitive land plants. The earliest Cooksonia date from the middle of the Silurian ; the group continues to be an important component of the flora until the Early Devonian, a total time span of...
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 microphyll
Microphyll
The terminology of fossil plants is in places a little confusing. In the discipline's 200+ year history, certain concepts have become entrenched, even though improved understanding has threatened the foundations upon which they are based...
s 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 sporophyll
Sporophyll
A sporophyll is a leaf that bears sporangia. Both microphylls and megaphylls can be sporophylls. In heterosporous plants, sporophylls bear either megasporangia , or microsporangia...
s). In some groups, these sporophylls are clustered into strobili
Strobilus
A strobilus is a structure present on many land plant species consisting of sporangia-bearing structures densely aggregated along a stem. Strobili are often called cones, but many botanists restrict the use of the term cone to the woody seed strobili of conifers...
.
During the Carboniferous Period
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
, tree-like Lycopodiophyta (such as Lepidodendron
Lepidodendron
Lepidodendron is an extinct genus of primitive, vascular, arborescent plant related to the Lycopsids . It was part of the coal forest flora. They sometimes reached heights of over , and the trunks were often over in diameter, and thrived during the Carboniferous period...
) formed huge forests that dominated the landscape. The complex ecology of these tropical rainforests collapsed during the mid Pennsylvanian
Pennsylvanian
The Pennsylvanian is, in the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period. It lasted from roughly . As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain...
due to a change in climate.
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
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...
deposits. In Fossil Park, Glasgow
Glasgow
Glasgow is the largest city in Scotland and third most populous in the United Kingdom. The city is situated on the River Clyde in the country's west central lowlands...
, Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
, fossilized Lycopodiophyta trees can be found in sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
. 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
Fireworks
Fireworks are a class of explosive pyrotechnic devices used for aesthetic and entertainment purposes. The most common use of a firework is as part of a fireworks display. A fireworks event is a display of the effects produced by firework devices...
. Currently, huperzine, a chemical isolated from a Chinese clubmoss, is under investigation as a possible treatment for Alzheimer's disease
Alzheimer's disease
Alzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death...
.
External links
- Introduction to the Lycophyta from the University of California Museum of Paleontology
- Lycophytes
- Fossil Groves
- Paleo Plants