Seedless Plant Life Cycles

There are two general types of plants, those that produce seeds and the ones that do not. The non-seed-producing plants are known as seedless plants. They have developed an alternative to seeds for use in propagation. Their life cycle is a little different for seedless plants than for seed-producing plants.

Fern Leaf

Facts

Seedless plants reproduce using spores, and seed-producing plants use seeds to propagate. The seeds house an embryo and nutrients to help the embryo establish itself, whereas spores will house the embryo but very little nutrients. The seedless plant group is divided into four families: psilophyta, or whisk fern; lycophyta, or club moss; sphenophyta, or horsetail; and pterophyta, or fern.

Reproduction

Seedless plants begin life as spores. When the spores are dispersed to a suitable environment, they germinate and form a gametophyte which houses male and/or female sex organs. The gametes, or sex cells, grow inside the sex organs. Fertilization occurs when the sperm joins the egg in the female sex organ of the gametophyte. At this stage, the gametes form a zygote.

Spores

All seedless plants, with the exception of the selaginella club moss and some water ferns, will produce homospores, or spores that are all the same size. Selaginella club moss and the water ferns will produce heterospores, in which a size differential is apparent based on sex.

Homospores are slow-germinating spores and generally measure 20 to 40 microns in diameter. Heterospores have gametophytes that are specialized as either male or female. The male spores are 15 to 35 microns in diameter, while the female spores range in size from 100 to 500 microns in diameter and they are fast-germinating.

Gametophytes

Heterospores produce gametophytes that are either photosynthetic (producing nutrients from sunlight) or mychorrhizal (obtaining nutrients through a fungal association). Homospores produce female gametophytes that use stored nutrients in the spore.

Sporophyte

The zygote, which is the initial cell, will grow into a mature sporophyte with sporangia. The sporophyte is the plant that we see and sporangia are specialized structures to produce spores. Meiosis (cell division) in the sporangia results in the formation of spores. Once the spores are mature, the parent plant releases them for disbursement and the cycle will begin again.

References

• Ohio State University, Horticulture & Crop Science
• Dr. Steven J. Wolf, California State University
• Clinton Community College, State University of New York

Resources

• University of Washington, UW Courses Web Server, Seedless Vascular Plants