Question

The smallest antheridia in vascular plants, producing the smallest member of sperms are found in-
A. Equisetum
B. Isoetes
C. Lycopodium
D. Selaginella

Answer 1

Antheridia is the male sex organ of the plantd or smaller organisms like algae, ferns, mosses. They generally work as to hold the sperm cells in bryophytes or non flowering plants.

Complete answer:
Equisetum which is also known as the horsetail belongs to the horsetail family, order Equisetales and class Equisetopsida. It is a perennial herb which grows on moisture containing soils. They reproduce by the help of spores. It is called the living fossil because it is the only vascular plant of this class known which is still alive from 100 million of years or more. The leaves of the Equisetum are reduced and its microphylls are single, non vascular and non branching. These are generally homosporous and have smaller spores. These spores have elaters which are moisture sensitive. Equisetum is considered to have the smallest antheridia.
On observing the other options-
Isoetes are called quillworts due to their appearance and belong to the family Isoetaceae and class Lycopods. The roots of these plants are swollen at the base which are attached as clusters to form bulblike underground rhizomes.
Lycopodium belongs to the family Lycopodiaceae and class clubmosses. These are pteridophytes and also known as creeping cedars. These are flowerless, vascular epiphytes having antheridia and archegonia in the same plant. They have spiny and reduced leaves.
Selaginella belongs to the family Selaginellaceae and class Lycopodiopsida. They have scales like microphylls and are heterosporous. Selaginella is also known as spike moss.

Note: Angiospermic plants are the last stage of evolutionary changes. These are the flowering plants which are of terrestrial habitat. They contain a large number of genus or varieties.