Tag: biology

In selaginella, the sporangia near the apex of a vertically-held strobilus or along the upper side of a horizontally-held strobilus are darker in color and are oval. These contain many very tiny orange spores, the products of meiosis of several sporocytes. These nearly-microscopic spores are called microspores. This makes their sporangium a microsporangium and the sporophyll a microsporophyll. The microsporangia is yellowish brown in color.

The strobili of Selaginella or spike moss is heterosporous. It bears both microsporangium and megasporangium on the axis of the microsporophyll and megasporophyll respectively. The strobili with the sporophylls arranged look like a spike or a cone.

Selaginella rupestris or rock spike moss belongs to the family Selaginellaceae. The plant is heterosporous with the presence of both megaspores and microspores. However, the variation in sporangial distribution pattern in the strobili is related to the number of megaspores per megasporangium. More than often, the megasporangiate has only 1  megaspore per megasporangium.

• The sporangia produce spores by meiosis in spore mother cells. The spores germinate to give rise to inconspicuous, small but multicellular. free-living, mostly photosynthetic thalloid gametophytes called prothallus.
•  These gametophytes bear male and female sex organs called antheridia and archegonia, respectively. 
• The microspore germinates to form the male gametophyte. 
• The first unequal division (1-1) in a microspore results in the formation of a small lenticular prothallial cell (vegetative cell) and a large antheridial initial. The prothallial cell does not divide further. 
• Hence, prothallial cells in the male gametophyte of Selaginella is 1.
• So, the correct answer is '1'.
  

Rhizophores are leafless axial organs, which apices are the only sites for root formation  are unique to the Selaginella genus. Both rhizophores and roots are dichotomously branched, forming a multibranch rhizophore root system.

Selaginella lepidophylla is commonly known as the resurrection plant because it can survive extreme desiccation by curling up and rehydrating when water is available.

Heterospory is the production of two different types of spores by the sporophytes of land plants. Of all the options given in the question Selaginella, Pinus and Cycas all produce micorspores and megaspores for reproduction. However, Pteridium on the other hand is homosporous.

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).

A resurrection plant is any plant that can survive in dehydration conditions. Selaginella lepidophylla is known as resurrection plant. It is a plant species native to North America, Central and South America. The plant is also known as moss for bird's nest due to its appearance on dehydration. 

Selaginella is spike moss or club moss. Peat moss is Sphagnum (Bryophyte).