Heterospory is seen in :

Question

Accepted Answer

The correct option is (2):

The correct answer is *Isoetes*, a genus commonly known as quillworts, because it is a classic example of a heterosporous pteridophyte. The concept of **heterospory** is a major evolutionary milestone in the plant kingdom, defined by the production of two morphologically and physiologically different types of spores: the small, numerous **microspores** and the large, fewer **megaspores**. In *Isoetes*, the microspores develop into the male gametophytes, which produce antheridia (sperm-producing organs), while the megaspores develop into the female gametophytes, which produce archegonia (egg-producing organs). This strict separation of sexes at the gametophyte stage is crucial, as it ensures outcrossing (cross-fertilization) and is a direct prerequisite for the evolution of the seed habit seen in gymnosperms and angiosperms.

The incorrect option is (1):

*Lycopodium* is a genus of clubmosses and is a classic example of a **homosporous** pteridophyte. Homospory refers to the production of only one kind or size of spore. In *Lycopodium*, the single spore type develops into a bisexual gametophyte, which means the gametophyte is capable of producing both male and female sex organs (antheridia and archegonia) on the same thallus. Since *Lycopodium* produces spores that are uniform in size and morphology, it cannot be classified as heterosporous. This life cycle contrasts sharply with that of *Isoetes*.

The incorrect option is (3):

*Equisetum*, or horsetails, is generally considered **homosporous**. Like *Lycopodium*, it produces only one size and type of spore. While the spores and gametophytes of *Equisetum* are all morphologically the same, the gametophytes often develop as functionally separate male or female individuals, a condition sometimes called *incipient heterospory* or *physiological heterospory*. However, because the spores themselves are not dimorphic (different in size) as required by the strict definition of heterospory, *Equisetum* is fundamentally classified as homosporous, making it an incorrect choice for the question.

The incorrect option is (4):

*Pteris* belongs to the group of true ferns (Pteridales), and the vast majority of true ferns, including this genus, are **homosporous**. *Pteris* produces one type of spore which germinates to form a small, photosynthetic, and typically bisexual gametophyte known as a prothallus. This prothallus produces both antheridia and archegonia. While a few rare groups of aquatic ferns exhibit heterospory, *Pteris* is a terrestrial fern that follows the homosporous life cycle, confirming that heterospory is not a characteristic seen in this genus.