Differences Between Moss Stems and Fern Stems

Plant Evolution

• Fern and moss plants represent two stages within the plant evolution process. Mosses belong to the Bryophyte plant division. These plants must live in or near a water supply in order to survive. Ferns exist as land-based plants, which consist of several divisions of plants. One prominent difference between ferns and mosses appears as the presence of stems in fern plants and the lack of stem structures in moss plants. As plants evolved from water-based environments to land-based environments, plant bodies developed a more complex structure for surviving on land. In effect, the development of stem structures played a significant role in allowing plants to survive on land.

Conductive Structures

• The key distinguishing feature between fern and moss stems appears as a specialized type of plant material known as vascular tissue. Vascular tissue consists of two channels of cell tissues -- known as xylem and phloem -- that run the length of the stem. Xylem cells transport water and nutrients from the root of the plant up into stem and leaf structures. Phloem cells transport needed sugar supplies throughout the plant structure. As plants requiring a nearby water source, mosses use a more primitive water-nutrient transport system, so actual, full-grown stem structures do not exist on most moss plants. As land-based plants, ferns require this specialized tissue in order to take root and survive in soil environments.

Protective Coverings

• The vascular tissue found in fern stems consists of a reinforcing material known as lignin. Lignin is a tough, wood-like material that provides structural support for the stem and plant body. The outside of a fern’s stem has an additional layer of cells known as the epidermis. This layer helps to protect the cells that produce food for the plant. In the case of moss plant varieties, primitive, stem-like structures known as shoots extend from the base of the plant root and also from the base of the plant body. These shoot structures allow some moss plant varieties to live on land if there’s a nearby water source. Since mosses tend to grow close to the ground, these plants lack the protective and structural materials found in fern plant stems.

Pressure Gradients

• The different types of materials found in fern and moss stems give rise to different methods for moving water and nutrient materials through the plant body. The xylem cell materials found in vascular tissue consist of large cell bodies that have thick cell walls. These features enable fern plant stems to create pressure gradients, or forces within the vascular tissue. In effect, fern stems use these pressurized forces to work against the effects of gravity and move water up through stem and leaf structures. While moss shoots lack the structural features found in fern stems, the shoot system does create an absorption effect that moves water and nutrients throughout the plant body. This accounts for why moss plants grow short and close to the ground.