Q37.Heterospory is not found in
(A) Pinus
(B) Cycas
(C) Selaginella
(D) Pteridium
The correct answer is (D) Pteridium.
Heterospory involves producing two spore types—microspores (male) and megaspores (female)—a key evolutionary step toward seed plants. Pteridium, a homosporous fern, produces only one spore type.
Option Analysis
Pinus (A)
Pinus, a gymnosperm (conifer), exhibits heterospory with microspores in pollen cones and megaspores in ovulate cones, leading to separate male and female gametophytes.
Cycas (B)
Cycas, another gymnosperm (cycad), shows heterospory by producing microspores (pollen) and megaspores within ovules, supporting its seed-forming reproduction.
Selaginella (C)
Selaginella, a pteridophyte (spike moss), is a classic heterosporous example, producing microspores and larger megaspores in separate sporangia on the same plant.
Pteridium (D)
Pteridium (bracken fern), a pteridophyte, is homosporous, releasing only one uniform spore type that develops into bisexual gametophytes—thus lacking heterospory.
Introduction to Heterospory
Heterospory is not found in plants like Pteridium that produce a single spore type, while Pinus, Cycas, and Selaginella exhibit this trait with distinct microspores and megaspores for specialized reproduction.
Gymnosperms: Pinus and Cycas
Gymnosperms such as Pinus and Cycas display heterospory essential for seed production—microspores form pollen grains, megaspores develop within ovules.
Heterosporous Pteridophyte: Selaginella
Selaginella represents advanced pteridophytes with heterospory, where microsporangia yield small microspores and megasporangia produce retained megaspores.
Homosporous Fern: Pteridium
Pteridium produces identical spores that germinate into prothalli bearing both antheridia and archegonia, lacking the dimorphism of heterospory.
Exam Context
This question tests knowledge of reproductive strategies in plant groups, emphasizing heterospory’s role in Selaginella and seed plants versus homospory in ferns like Pteridium.
