Non Vascular Plants
Non-vascular plants are typically small due to the lack of a vascular system, which is responsible for transporting gases, water, and other compounds. Examples of non-vascular plants include algae, liverworts, hornworts, and mosses. Reproduction in these plants occurs through spore production, instead of seeds; therefore, they do not produce wood, flowers, or fruits.
Non-vascular plants, also referred to as lower plants, lack specialized vascular tissues such as xylem and phloem. To compensate for this, they have developed specialized tissues to conduct water and other essential substances. These tissues lack lignin, making them not true vascular tissues. Non-vascular plants are usually found inhabiting moist and damp areas, in water, bogs, swampy and shady regions. As a result of the absence of xylem and phloem, these plants are considered to be primitive with primitive parts.
Structure of Non-Vascular Plants:
The absence of vascular tissues makes mosses relatively simpler and shorter. Mosses lack the tissues found in the least specialised form of plants, such as stems, leaves, and true roots. Instead, they are supported by rhizoids, which are hair-like structures, and absorb minerals and water through osmosis and diffusion. As mosses do not have true leaves, they are also not subject to excessive water loss through transpiration.
The weak stem is composed of simple tissues which is not capable of holding the plants as seen in vascular plants. Here, the gametophyte generation is dominant with haploid gametophyte. The gametophytes give rise to sporophytes of the plants and depend on the gametophytes for minerals and water. Often, these plants serve as pioneer species which mostly do not require much water and nutrients to survive. They can thrive on barren lands.
The evolutionary process is marked by the first appearance of primitive plants, which are divided into two main groups: bryophytes and algae.
Bryophytes are composed of plants such as liverworts and most mosses found in shady regions. These plants feed on decaying and dead plants. There are three main divisions of bryophytes:
Liverworts (Marchantiophyta) are typically small, non-vascular plants that measure less than 4 inches in height. They possess lobed, ribbon or leaf-like photosynthetic tissues instead of leaves, and lack stems. Rhizoids of these plants are extremely fine. Often, they are found growing in colonies which form a carpet-like structure on the ground.
Mosses (Bryophyta) are larger, coarser non-vascular plants that can be found in dense clumps, allowing them to retain moisture. They possess multicellular rhizoids, which are more like roots, and have small photosynthetic structures resembling leaves surrounding a stem-like structure found at the centre.
Hornworts (Anthocerotophyta) are small non-vascular plants that are similar in size to liverworts. They possess fine and thin rhizoids that do not have a stem, and have tiny, pointed and long horns that emerge several inches above the gametophytes of the plant.
The haploid gametophytes are the primary plants in all bryophytes. They are the only diploid portion associated with sporophytes, which consist of a sporangium and stalk. These plants do not have lignified tissue for conduction, and therefore cannot grow as tall as vascular species.
Non-vascular Plants - Characteristics
Non-vascular plants are plants that lack a vascular system, which is composed of specialized tissues that transport water, nutrients, and other materials throughout the plant. Characteristics of non-vascular plants include:
- Small size
- Lack of true leaves, stems, and roots
- Reproduce by spores instead of seeds
- Absorb water and nutrients through their body surface
- Slow growth rate
Typically, the stature of these plants is short and they lack vascular tissues, true roots, leaves, seeds and flowers. Rhizoids, which can be compared to roots, anchor to the ground and absorb water and minerals. Moisture is favourable for their reproduction, as sperms produced by the male gametophytes swim through dew or rainwater to reach an egg produced by female gametophytes. As a result of the meiosis of the diploid sporophyte generation, haploid spores are produced. In order for these spores to disperse, moisture is necessary.
Non-vascular Plants - Examples
- Mosses
- Liverworts
- Hornworts
Moss - With heights ranging from a foot tall to microscopic, these plants are commonly found in dark and swampy areas, as well as forest floors and woodlands. Globally, there are close to 12,000 species of moss, which have adapted to colonize habitats ranging from deserts to cold arctic regions. However, due to the lack of vascular tissues, mosses are unable to transport minerals and water to the top of the plant, limiting their growth.
Liverworts are primitive non-vascular plants which grow in small, leaf-like structures. They are usually found in swampy, shady, and damp areas near the ground, and are widely distributed, particularly in tropical areas. The gametophytic structure of this plant is the thallus, which possesses specialized structures to support the sporophytic phase.
