Test: Selaginella - Class 11 MCQ

Selaginella is a pteridophyte. In pteridophytes, sporophyte is the dominant phase.

In Selaginella, each microphyll and sporophyll has a small scale-like outgrowth called a ligule at the base of the upper surface. The plants are heterosporous with spores of two different size classes, known as megaspores and microspores. Under dry conditions, some species of Selaginella can survive dehydration.

The four megaspores derived from a megaspore mother cell may not always be functional. i.e. In S.rupestris single megaspore is functional.

Selaginella oregana , one of the most distinct species in the flora, is easily distinguished by its usually long, epiphytic-pendent stems, slightly loose strobili, and curled branches (in dry specimens). In the flora, S. oregana is most closely related to S. underwoodii.

Microspores of Selaginella are haploid in nature. Each microspore divides by mitosis division and forms a small lens shaped prothallial cell and a large antheridial cell. Subsequesnt division only occur in antheridial cell which result of a 12 celled antheridium in which outer 8 cells form jacket of antheridium and inner 4 cells form primary androgonal cells. Thus mature microgametophyte contains 12 antheridial cells and 1 prothallial cell. 

Rhizophores is a structure of controversial morphological nature. They are leafless and positively geotropic organs that have localised origin and develop from angle meristems. Goebel and Bower considered them as Organs sui generis (i.e.,neither roots or shoots).

Each stele is made up of diarch and exarch xylem in centre. The steles are connected with the cortex by means of many tube-like structures called trabeculae, Monarch which are modified endodermal cells with casparian strips on their lateral walls. The stems contain no pith.

One of the slender, root-like processes formed in Selaginella having prostrate and semiprostrate stems at the branching sites of the stalk. Rhizophores arise in the embryo. In contrast to typical roots, originate exogenously and have no root cap. Upon reaching the ground, rhizophores form several endogenous suckers that penetrate the soil. Rhizophores are considered organs of stem origin.

In Selaginella, each microphyll and sporophyll has a small scale-like outgrowth called a ligule at the base of the upper surface. The plants In leaves are heterosporous with spores of two different size classes, known as megaspores and microspores. Under dry conditions, some species of Selaginella can survive dehydration.

Selaginella produces two types of spores—megaspores and microspores. The dimorphic condition of the spores is known as heterospory. In between the sporophyll and sporangium is present a small membranous structure known as ligule i.e., the sporophyll is similar to a vegetative leaf.

Selaginella is a pteridophyte. It is also known Club moss or spike moss. Its leaves are simple, sessile and microphyllous. They have lateral bigger leaves as well as dorsal small leaves. Each leaf bears a small scale on the basal adaxial surface called ligule. Because of these ligules, leaves of Selaginella are called ligulate.

Selaginella is the only living genus of the order Selaginellales and is commonly known as 'spike moss' or 'small club moss'. It is a large genus comprising of about 700 species distributed all over the world. Abundantly it is found growing in tropical rain forests.

Selaginella shows all the characters like gymnosperms such as they both have vascular tissues, heterospory- the sporangia that generate the male microspores and female megaspores are usually borne on separate cones. The cones of selaginella are called as strobilus which have microsporangia and megasporangia. The sporophylls associated with these two types of sporangia are designated as microsporophylls and megasporophylls respectively. And gymnosperms are flowerless plants that produce cones and seeds.

The male gametophyte gives rise to sperm cells, which are used for fertilization of an egg cell to form a zygote. Megaspores are structures that are part of the alternation of generations in many seedless vascular cryptogams, all gymnosperms and all angiosperms.

The megagametophytes of endosporic plants such as the seed ferns developed within the sporangia of the parent sporophyte, producing a miniature multicellular female gametophyte complete with female sex organs, or archegonia.

A heterosporous life history occurs in some pteridophytes and in all seed plants. It is characterized by morphologically dissimilar spores produced from two types of sporangia: microspores, or male spores, and megaspores (macrospores), or female spores.

The Microspores divides to form a 13 celled non-green, male gametophyte Cone vegetative/prothallial cell + 8 jacket cell + 4 Primary androgenic cells).

In pteridophytes mainly the seed habit has started to originate where after fertilization the zygote is retained inside the mother plant. Lycopodium is a genus of clubmosses, also known as ground pines or creeping cedars, in the family Lycopodiaceae.

Pteridophytes are divided into four classes: Psilopsida, Lycopsida, Sphenopsida and Pteropsida. Selaginella belongs to Lycopsida. Selaginella has small leaves called microphylls. Sporophylls are compactly arranged into structures called strobili or cones. They are heterosporous as they produce two types of spores, macro (large) and micro (small).

In some plants like algae, meiosis occurs at the time of formation of spores where the spores are formed from the zygote and spore mother cells. In such plants, gametes are formed by the mitosis. They fuse to form a diploid zygote which undergoes the meiosis to form haploid spores.

The majority of the pteridophytes produce only one kind of spores in sporangia and the plants are called homosporous. For example, Nephrolepis, Lycopodium, Equisetum and ferns, the condition is said to be homospory.
Heterosporous condition (produce two kinds of spores i.e., megaspore and microspore) is found in Selaginella.

Sometimes plants show vivipary in which the embryo shows up the germination within the seed. In this embryo grows first to break through the seed coat then from the fruit wall it is still attached to the parent plant.

Foot of Selaginella are basically the rhizoids which are roots in lower class of the plant kingdom. They help in absorption of minerals (food) from the surface as well as anchorage. 

Selaginella is commonly known as 'spike moss' or 'club moss'. Mostly the species prefer moist and shady places, but a few species are also found growing in xerophytic conditions on rocks and are sold under the name of resurrection plants.

Selaginella is heterosporous, as it produces two sizes of spores: small spores (termed microspores) that germinate to produce the male gametophyte; and larger spores (megaspores) that germinate to produce the female gametophyte. The microgametophytes produce sperm equipped with flagella that enable them to swim to the eggs generated by a megagametophyte through water, either in the form of dew or rain, in order to achieve fertilization. In contrast to other Pteridophytes, Selaginella have biflagellate gametes, a characteristic feature of Bryophytes.

A distinctive feature of Selaginella stem is the presence of radially elongates endodermal cells, called trabeculae. Due to the presence of trabeculae, the central stele is separated from the cortex by large air spaces.

Homospory the production by various plants (such as the club mosses and horsetails) of asexual spores of only one kind.

Lycopodium is a genus of clubmosses, also known as ground pines or creeping cedar, in the family Lycopodiaceae, a family of fern-allies (see Pteridophyta). They are flowerless, vascular, terrestrial or epiphytic plants, with widely branched, erect, prostrate or creeping stems, with small, simple, needle-like or scale-like leaves that cover the stem and branches thickly. The leaves contain a single, unbranched vascular strand and are microphylls by definition. The kidney-shaped or reniform spore-cases (sporangia) contain spores of one kind only (isosporous, homosporous) and are borne on the upper surface of the leaf blade of specialized leaves (sporophylls) arranged in a cone-like strobilus at the end of upright stems. The club-shaped appearance of these fertile stems gives the clubmosses their common name.