The club mosses (Lycopodium) are vascular plants belonging to the Pteridophyta. They are characterized by presenting the sporophiles (leaves that carry the structures that produce spores) in erect strobili.
The genus Lycopodium belongs to the Lycopodiaceae family and is made up of approximately 40 species. It is almost cosmopolitan and grows in humid places, with a lot of shade and a high content of organic matter .
The stems can be creeping or erect, with dichotomous branching and the vascular tissue located in the center. The leaves are very small, are configured in different ways around the stem and have an unbranched conductive bundle.
Different species of club mosses have been used medicinally. L. clavatum was used to treat kidney stones and other club mosses to heal burns.
The spores of club mosses are known as plant sulfur and were used to make snuffs and the inert coating of pills. They are currently used in homeopathic medicine.
The genus Lycopodium is homosporic (with equal spores) and sexual reproduction is dependent on water. The gametophyte is formed by germination of spores, its development takes several years and is underground and heterotrophic.
The young sporophyte is nutritionally dependent on the gametophyte for approximately four years. Subsequently, the gametophyte dies and the sporophyte becomes fully autotrophic.
Club mosses are part of the oldest vascular plants on the planet. They are characterized by having only tracheids as water conducting elements and an ancestral vascular configuration.
The plants reach a height of up to 30 cm and are herbaceous in consistency. The habit is variable and we can find shrub, climbing and creeping species.
The body of the sporophyte (diploid phase) is differentiated into a shoot (aerial part) with a stem, leaves and a root system. Branching is dichotomous (the apex splits in two to form two branches).
The stems can be prostrate or erect and the leaves are microphilic. Microphiles are very small leaves that have a single vascular bundle (set of xylem and phloem) that does not branch.
In Lycopodium the leaves are small, generally less than 1cm, ovate or lanceolate in shape and leathery in consistency. The configuration of the leaves on the stem can be helical, opposite or whorled, and anisophilia can occur.
The roots branch dichotomously and are adventitious (they do not originate from the embryo). In plants that are erect, they originate at the apex of the stem and grow until they emerge at the base. The roots of creeping plants are produced directly towards the base of the stem.
The strobili (reproductive axes) are erect, simple, or bifurcated. The sporophiles (leaves that bear the sporangia) are ephemeral and have a thin wing at the base. The sporangia (structures that produce spores) are located at the base of the sporophyll and are kidney-shaped.
The spores are small and with a thin cell wall. They can be yellow in color and in some cases have small chlorophyll content. In addition, they present an ornamentation that varies between species, from reticulated to baculada.
The gametophyte can present different forms -obconic, convolute, disk-shaped or carrot-, and is underground.
The stem of the Lycopodium presents a unilayered epidermis (with a single layer of cells). Below the epidermis, several layers of parenchymal cells are configured forming the cortex.
Then there is an endodermis (tissue made up of a layer of cells with thickened walls) and two to three layers of pericycle (tissue that surrounds the conductive tissues). The vascular system is of the plectostela type (xylem plates surrounded by phloem), which is considered primitive within tracheophytes.
The leaves have upper and lower epidermis, and stomata (cells specialized in transpiration and gas exchange) can be on both surfaces. The cells of the mesophyll (tissues between both epidermis) are rounded and with intercellular spaces.
The roots originate from internal tissues of the stem. At the apex there is a caliptra (cap-shaped structure) that protects the meristematic cell (specialized in cell division). Root hairs develop in pairs from cells of the root epidermis.
Lycopodium species generally grow in humid and shady places with acidic or silica-rich soils, and with a high content of organic matter.
The subterranean gametophyte develops in the soil organic matter horizon, at a depth between 1 and 9 cm. The sporophyte generally develops in areas close to the gametophyte.
They are distributed in both temperate and tropical zones. They are found mainly in alpine areas to the north and south of the planet, and in mountains of the tropics.
The genus Lycopodium is homosporic (the sex spores do not differ morphologically). The strobili (cones) are located at the apex of the branches and carry the sporophils.
The sporangia contain sporogenic tissue that is diploid. These cells subsequently divide by meiosis to give rise to haploid spores .
When the spores are mature, the sporangia open and the spores are released. It can take several years for club moss spores to form the gametophyte .
The germination of the spore begins with the formation of six to eight cells. Later, the spore goes to rest for up to a year and for its development it requires the presence of a fungus. If infection with the soil fungus does not occur, the gametophyte does not continue to grow.
Once the fungus has infected the gametophyte tissues, the formation of the sexual structures can take up to fifteen years.
Antheridia, archegonia and fertilization
The Lycopodium gametophyte is bisexual. Male and female gametes are produced at the apex of this structure.
The antheridia (male structures) are globose and produce large amounts of sporogenous tissue. This tissue will form numerous biflagellate male gametes (anterozoids).
Archegonia (female part) have an elongated neck, which opens when the structure is mature. At the base of the archegonium the female gamete is located.
The fertilization of club mosses is dependent on water. The biflagellate male gametes travel in the water until they reach the archegonium.
The anterozoids (male gametes) are considered to be attracted to the female gamete by chemotacticism. The anterozoid enters the archegonium through the neck, swims to the female gamete, and later they fuse.
Once fertilization occurs, a zygote (diploid) forms that rapidly begins to divide to give rise to the embryo. Once the embryo develops, it forms the young sporophytes, which can be attached to the gametophyte for several years.
The haploid (gametophyte) and diploid (sporophyte) phases of Lycopodium have different forms of nutrition. They can be heterotrophic or autotrophic in different stages of development.
As mentioned above, the clubmoss gametophyte is associated with endophytic (internal) fungi that infect rhizoids. The gametophyte, being underground, does not present chlorophyll and is therefore heterotrophic.
The Lycopodium gametophyte obtains the necessary nutrients from the fungi that infect its tissues. Connections are established between the cells of the fungus and the plant through which nutrients are transported.
It has been observed that a network of mycelia can form in the soil connecting different gametophytes.
When the embryo begins to develop, it forms a foot that is connected to the gametophyte. This structure works for the absorption of nutrients and is known as haustorium.
For about the first four years of the sporophyte’s life, it remains attached to the gametophyte. This phenomenon is known as matrotrophy, which involves the nutritional dependence of the sporophyte.
The sporophyte uses the gametophyte as a carbon source, but does not establish a direct relationship with soil fungi. In the area of contact between both phases, cells specialized in the conduction of substances are observed.
When the gametophyte decomposes, the roots of the sporophyte come into contact with the soil. At this time they may or may not develop symbiotic relationships with soil fungi.
From this moment on, the plant becomes totally autotrophic. The green parts that contain chlorophyll photosynthesize to obtain their carbon source.
The roots in contact with the soil, absorb the water and the nutrients necessary for the development of the plant.
Phylogeny and taxonomy
The genus Lycopodium belongs to the Lycopodiaceae family of the Pteridophytas. This is the oldest group of vascular plants on the planet and is believed to have originated in the Devonian about 400 million years ago.
The taxonomy of the Lycopodiaceae has been complex. For a long time, the genus Lycopodium was considered to include almost all species in the family.
Lycopodium was described by Linnaeus in 1753 in his Species Plantarum . Subsequently, the gender was segregated into different groups. Currently, the different researchers differ in recognizing 10 to 4 genera.
Lycopodium , strictly speaking, is made up of about 40 species and has been divided into 9 sections. These differ in growth habit, the presence or absence of anisophilia, the shape of the sporophils and gametophytes, among others.
From the phylogenetic point of view, the genus Lycopodium is a sister group to Lycopodiella , from which it differs by its erect strobilus.
Several species of Lycopodium have been used medicinally, mainly because of their high alkaloid content.
L. clavatum has been used in Europe as a medicinal product since the 16th century, when it was macerated in wine to treat stones. Later, in the seventeenth century, the spores were known as plant sulfur or club moss powder.
This powder was used for the preparation of snuff (snuff) and other medicinal powders. Another use given to the spores of some Lycopodium species was as an inert coating for pills.
Some club mosses have also been used to treat skin burns, muscle aches, and as a pain reliever for rheumatic pain. It is currently used for the preparation of various homeopathic treatments.
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