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10.5.3.3. Alternate reproduction in plants

Alternate reproduction in seedless plants

Seedless plants, such as mosses and ferns, have alternating reproduction in which a phase of asexual reproduction (by spores) alternates with another of sexual reproduction (by gametes) .

Alternate reproduction in mosses (bryophytes)

Bryophytes do  not have flowers. Its reproduction is alternating , where an alternation of generations occurs:

  • Sporophyte: It is a stage in which the plant reproduces by means of spores. The spores are in capsules (sporangia), covered by a cap, and supported by a long filament that comes out of the thallus.
  • Gametophyte: it is a stage in which the plant produces, in the false leaves, sexual gametes (male and female). The male gamete has a flagellum that allows it to swim, if there is sufficient humidity, until it reaches and fertilizes the female gamete, forming the zygote that will originate the sporophyte. The sporophyte lives on the gametophyte, and consists of a stem ending in a capsule inside which the spores will form and mature and, when they fall on moist soil, they will germinate to give rise to a new gametophyte.

Alternate reproduction in ferns (pteridophytes)

Pteridophytes also reproduce by alternation of generations:

  • Sporophyte stage. It is the best known phase. The plant consists of an underground stem, called a rhizome, from which the roots emerge  through which they absorb water and mineral salts (crude sap) and the leaves, called fronds, through which they capture carbon dioxide and where the photosynthesis. Thus, it manufactures the organic matter (produced sap) that it will transport to the rest of the plant. When spring arrives, on the underside (lower part) of the fronds, structures called sori are observed,which are groups of sporangia where the spores originate . The spores, when they fall to the ground, form a new plant, the prothallus.
  • Gametophyte stage. The prothallus is the gametophyte, a very short phase in which sexual reproduction occurs. In the prothallus, the female and male gametes (flagellates) are formed, which need water to meet and for fertilization to occur, which will give rise to a new sporophyte or fern.