Question

Selaginella and fern share which of the following characters?
A. Leptosporangiate sporangium
B. Heterospory
C. Absence of ovule
D. Protostele cell

Answer 1

Hint: Selaginella is the vascular plant of the family Selaginellaceae, lesser club mosses or spikemosses. The fern is a member of a group of vascular plants that do not have seeds or flowers and reproduce through spores. By being vascular, i.e., possessing specialised tissues that conduct water and nutrients, and having life cycles in which the dominant period is the sporophyte, they differ from mosses.

Complete Answer:
- Selaginella have scale-leaves containing a ligule and have two varieties of spore, thus differing from Lycopodiaceae. The two varieties of spores produced are microspores and megaspores that constitute male and female spores respectively.
- The submerged leaves of Salvinia bear sori that is surrounded by sporocarps of two types. They are microsporangia that have megaspores and are less in number (approximately 10) and many microsporangia that have 64 microspores in each.
- Both the spores are of different size. Heterospory is the development of spores of two distinct sizes and genders by the sporophytes of land plants. Two kinds of spores, megaspores (large) and microspores (small) are produced by genera like Selaginella (club moss) and Salvinia (floating fern). Since the spores are unequal, it is heterospory.

Thus, option(b) is the correct choice ie., Heterospory.

Additional information:
1. Leptosporangiate Sporangium: These are small specialised sporangia with a small, definite number(<128) of spores that grow from a single initial cell. This frequently arises in a cluster (sorus) often hidden by a tissue flap referred to as an indusium.
2. Protostele cell: A basic, rudimentary arrangement of conducting tissues, consisting of a solid xylem cylinder surrounded by a phloem layer, in the stems and roots of some lower plants.

Note: In Selaginella species, the spores are both pollinated and dispersed by wind. Salviniales are also called watermoss. They are all aquatic ferns and they are distinct from all other ferns by being heterosporous. In heterosporous types, endosporic gametophytes are independent of environmental factors and self-sustaining in food supply. Heterospory causes a dramatic decrease in the size of their gametophytes.