Answer: Ephedra

Microspores are liberated at the 5-celled stage of male gametophytes specifically in Ephedra among the given gymnosperm options.​

Option Analysis

Pinus

In Pinus, microspores develop into a 4-celled stage before liberation: two small prothallial cells, one generative cell, and one tube cell. Pollination occurs at this 4-celled stage, with winged pollen grains dispersed by wind.

Cycas

Cycas releases microspores at a 3-celled stage: one prothallial cell, one generative cell, and one tube cell. The prothallial cell persists longer, and pollen is unwinged, unlike Pinus.​

Ephedra

Ephedra uniquely liberates microspores at the 5-celled stage. This includes two prothallial cells, a stalk cell, a body cell, and a tube cell, reflecting its advanced Gnetalean features with further divisions before dispersal.​

Ginkgo

Ginkgo microspores are shed at a 3- or 4-celled stage similar to Cycas or Pinus, without reaching five cells prior to liberation. Its pollen lacks wings and develops motile sperm post-pollination.​

Microspores liberated at 5-celled stage of male gametophytes represent a key gymnosperm reproduction feature, distinguishing Ephedra from Pinus, Cycas, and Ginkgo. This 5-celled stage in Ephedra’s pollen development aids wind pollination in arid habitats.​

Gymnosperm Male Gametophyte Stages

Gymnosperms like Pinus, Cycas, Ephedra, and Ginkgo evolve microspores into pollen grains at specific cellular stages before dispersal.

• Pinus: 4-celled (2 prothallial, generative, tube); winged pollen shed pre-pollination.

• Cycas: 3-celled (1 prothallial, generative, tube); unwinged, persists longer.​

• Ephedra: 5-celled (2 prothallial, stalk, body, tube); advanced Gnetophyte trait.​

• Ginkgo: 3/4-celled; motile multiflagellate sperm post-liberation.​