Reproducing by Spores
Most vascular plants have flowers. Once pollinated, flowers produce seeds. Seedless vascular plants have roots, stems and leaves, but they do not produce flowers or seeds; they reproduce through spores that blow in the wind. Seedless vascular plants have two separate reproductive phases: the sporophyte phase and the gametophyte phase. They alternate, each producing the other.
Seeds vs. Spores
The seed protects the zygote, the first cell of life. Seeds store energy, allowing them to remain dormant while they wait for the right conditions to grow. Seedless vascular plants, the earliest form of plant life, release spores into the air where they are carried by the wind. Spores do not store energy. They need moist soil or water in order to develop.
Two Phases of the Life Cycle
The dominant phase, the sporophyte, the visible plant, produces spores. Under the right conditions, these spores develop into the second phase, the gametophyte, which can be as small as a few cells. The gametophyte produces antheridia, male sperm, and archegonia, female eggs.
The sporophyte uses special structures called sporangia to produce spores by meiosis. In meiosis, a parent cell divides into four cells. Each of these cells contains half of the genetic material of its parent. The sporophyte has reproductive structures called strobili which produce spores that become a gametophyte.
The Gametophyte Phase
The sperm produced by the gametophyte have tails. They swim. That is why they need moisture or water to reproduce. The male sperm and female eggs combine to form a zygote, the first cell of a new saprophyte. The grown plant, a mature sporophyte, releases spores and begins the process anew.
Individual sporophytes have evolved to continue the life cycle in different ways. Most seedless plants spread by horizontal or vertical rhizomes or stems that grow along the ground or up a tree or other host. Many plants in the Phylum Lycophytra, that includes club mosses, spike mosses and quillwarts, are epiphytes, meaning that they grow on other plants without harming them. Quillworts are aquatic, meaning they live in rivers, ponds or lakes. The whisk fern has special rhizoids, branching fibers or filaments that spread through the soil; they use these rhizoids to anchor themselves and obtain nutrients.