Tag: kingdom plantae

Because Selaginella has both microspores and megaspores, the plant is called as heterosporous. The other fern-allies are homosporous (having only one type/size of spore). This significance of this advance in evolution is important because sexual dimorphism is being expressed much earlier in the life cycle. The organisms to appeared next this are all heterosporous.

A resurrection plant is any poikilohydric plant that can survive extreme dehydration, even over months or years. Selaginella lepidophylla, is known as resurrection plant or birds nest moss as it shows ball like appearance (cespitose habit) in dry season. It is a plant species native to North America, Central and South America, and sold as a novelty.

Heterospory means the production of two spores of different sizes and of two different development patterns. Small spore is called microspore and large spore is called megaspore. Microspore produces the male gametophyte that possesses male sex organs while megaspore produces the female gametophyte that possesses female sex organs. It ultimately leads to seed development. For example, Selaginella, Salvinia, Azolla. Dryopteris and Adiantum are homosporous and haploid spores are produced in each sporangium. 

In Selaginella, trabeculae are endodermal in nature as they develop from the endodermis. In Marsilea, they are cortical. 'soetes' appears to be a typo (likely for 'isoetes'), where trabeculae are sporogenous. In Funaria (moss), trabeculae are amphithecial in nature, developing from the amphithecium layer of the sporangium wall.

The matching of groups to their characteristics is: Psilopsida (rootless), Lycopsida (sporangiophore), Sphenopsida (companion cells - though this is debatable, it is the provided key), and Pteropsida (megaphyllous leaf).

• Spore is uninucleate haploid spherical structure.
• The spore germinates into gametophyte known as prothallus.
• Prothallus has archegonia present on the ventral side.
• Hence, the Prothallus of Dryopteris is a Gametophyte.  It bears archegonia on the ventral side. 
• So, the correct answer is 'Gametophyte, ventral'.

In the life cycle of Dryopteris, the asexual sporophyte is the dominant individual. This is perennial and evergreen and differentiates into rhizome (stem), roots and leaves ( fronds). When the fronds mature these become fertile and are called as sporophylls since they contain sori. In each sorus stalked sporangia is present arising from the placenta, the swollen outgrowth on the divisions of the pinna or leaflets.

The archegonium which develops from a single superficial cell of prothallus is the archegonial initial found just back of the apical meristem. The archegonia  are sessile and embedded. The archegonial initially divides to give 4+4 cells which make up the neck. The neck has a single neck canal cell.

Strobilus is called the fertile branch, because it bears the reproductive structures such as microsporophylls and megasporophylls.

In Dryopteris, the neck consists of a wall or jacket layer of 4 vertical rows of sterile neck cells. The neck cells enclose a central neck canal. They contains a single, long neck canal cells with two nuclei.