Tag: kingdom plantae

In older plants, the branches bear reproductive structures at their tips. They are called as strobilus or spondiferous spike. The arrangement of micro and megasporophylls in the strobili of different species is variable. The strobili of S.oregana are among the longest in the flora and they often show several novel features. In S.kraussiana, there is only one megasporangium at the base and the rest of the sporophylls bear microsporangia.

Selaginella and Salvinia are considered the first plants to exhibit a significant step toward the evolution of seed habit because embryo develops in female gametophyte which is retained on parent sporophyte. It occurs because Selaginella and Salvinia both are heterosporous, i.e., these plants produce two kinds of spores, macro (large) and micro (small) spores. In the heterosporous species, the female gametophyte remains on the parent sporophytes for variable periods. The development of the zygotes into young embryos takes place within the female gametophytes. This event is a precursor to the seed habit (tendency towards seed formation) considered an important step in evolution. Hence, heterospory leads to seed habits in plants.

The presence of Ligule - a small tongue shaped appendage on the adaxial side of the leaf near the leaf base is a distinctive feature of the Selaginella. This consists of elongated secretory cells the glossopodium which tends to keep the sporangium wet. Another distinctive feature is the cones or strobilus on which the sporophylls are present.

Dryopteris Filix-mas (Linn.) is commonly known as male-shield fern, because they have a shield-shaped protective covering for their spore containing structures. 

Heterospory is a phenomenon in which two kinds of spores are borne by the same plant. These spores differ in size. The smaller one is known as microspore and the larger one is known as megaspore. The microspore germinates to form the male gametophyte and the megaspore germinates to form the female gametophyte. Heterospory evolved first in pteridophytes such as Selaginella and Salvinia. Hence option B is correct.

Under dry conditions, the xerophytic species of Selaginella roll into brown balls but remain uprooted. This phenomenon is called as a cespitose habit. But during moist conditions, the brown balls become green and unroll again. Therefore, these plants are called as resurrection plants. e.g. Selaginella lepidophylla and Selaginella bryopteris.

Peritichious flagellation is found in Escherichia coli where the flagella are projecting in all directions;
The living fossil plant is the Ginkgo biloba.Largest perennial alga is the Macrocystis pyrifera.
Smallest flowering plant is Wolffia arrhiza and belongs to the genus WolffiaRhizophore - the downward-growing leafless dichotomous shoots is a characteristic feature of the genus Selaginella. Thus, the correct answer is option D.

Selaginella bryopteris, known commonly as sanjeevini and sanjivani booti. It is used medicinally in India. The rare life saving herb Sanjeevani known to have been brought by Lord Hanuman to save Lord Laxman. The Hindu mythology Sanjeevani is described as a magical plant which can wake dead people to the life, or which lends immortality. In the high, hostile peaks of the Himalayas where sustaining life is a challenge in itself, scientists say they have found a wonder herb that can regulate the immune system, help adapt to the mountain environment and, above all, protect from radioactivity.

In majority of the pteridophytes, all the spores are of similar kinds, such plants are called as homosporous. Genera like Selaginella and Salvinia which produce two kinds of spores, macro (large) and micro (small) spores, are known as heterosporous. The megaspores and microspores germinate and give rise to female and male gametophytes, respectively. The female, gametophytes in these plants are retained on the parent sporophytes for variable periods. The development of the zygotes into young embryos take place within the female gametophytes. This event is a precursor to the seed habit considered an important step in evolution.

The antherozoid of Lycopodium is pear shaped with two flagella at the anterior end. The biflagellate antherozoids of Lycopodium resemble more to the antherozoids of Bryophytes, rather than those of vascular plants.