Moss represents a primitive type of plants that are classified under phylum Bryophyta. Its close relatives are liverworts and hornworts. Mosses grow in dense green clumps or mats in damp or shady locations. They possess simple leaves attached to a stem that may be or may not be branched. Thin, hair-like rhizoids attach the plant to the substrate. Most mosses are non-vascular plants but, some may develop a primitive vascular system. They absorb water directly from their body surface. Mosses are photosynthetic plants and only grow in the presence of water. They arrest their metabolism when water is not available. Mosses are important as their adaptation from aquatic habitats to the land emphasizes the origination of vascular land plants.
Key Areas Covered
Key Terms: Differentiation of Plant Body, Moss, Photosynthesis, Sexual Reproduction, Spores, Thick Cell Wall
What is Moss
A moss is a primitive type of land plants classified under phylum Bryophyta. It is a non-vascular and non-flowering plant. Mosses undergo alterations of generations with a prominent gametophyte. The sporophyte of mosses appears on the gametophyte. It is composed of a spore-producing capsule held by a stalk. Spores germinate, producing a protonema, which is a filamentous structure. The stems of protonema develop into gametophytes. The lifecycle of a moss is shown in figure 1.
How Does Moss Adapt to its Environment
Mosses represent one of the most primitive plants on the land. This means the first entities that evolved from aquatic environments to terrestrial environments are ancestors of mosses. They are evolved from the algae that lived in the sea and freshwater. Mosses, liverworts, and hornworts descend from the first plants that spread onto the bare rock and soil. In order to survive on the land, mosses develop several adaptations. Those adaptations are listed below.
- Mosses have developed leaf-, stem-, and root-like structures, apart from the thallus of algae. They develop specialized structures for a particular function. Generally, leaves are specialized for photosynthesis; stems are specialized for support as well as transport; roots are specialized for support and absorption of water. The leaf-like structures of mosses are simple and one-cell thick. The stems hold the plant against the ground. The root-like structures of mosses are called rhizoids and they attach the plant to the substrate.
- Each cell of the moss is surrounded by a thick cell wall, providing support to the plant as in higher plants.
- The absorption of water mainly occurs through the body surface of the plant. Water diffuses from cell to cell. However, they have developed special storage areas for both water and nutrients. Some mosses have developed primitive types of vascular systems, allowing the efficient transfer of water and nutrients throughout the plant.
- Mosses have chlorophyll for photosynthesis. Hence, they produce their own food.
- Mosses asexually reproduce through spores. A spore consists of a single reproductive cell covered by a protective, hard, and watertight covering. It is transmitted through the air. The production of this type of spores by mosses is an adaptation for the life on land.
However, water plays a role in determining the size of the plant and the sexual reproduction. Since mosses lack a developed vascular system, the plants cannot grow tall. The general height of mosses is 0.4-4 inches. The limited size of the mosses is also affected by the absence of supportive cells as in higher plants. Water also reduces the sexual reproduction of mosses as fertilization of gametes depends on water. Hence, mosses wait for favorable conditions to undergo sexual reproduction.
Mosses are a type of primitive plants on the land. Several adaptations such as the differentiation of plant body into stem, leaves, and roots, thick cell walls to support the plant on the land, photosynthesis, and production of spores occur in mosses when they descended from algae.
1. Proctor, M. C. F. “Mosses and Alternative Adaptation to Life on Land.” New Phytologist, vol. 148, no. 1, 2000, pp. 1–3., doi:10.1111/j.1469-8137.2000.00751.x.