Key Difference – Liverworts vs Mosses
Liverworts and mosses are two clades that belong to Phylum Bryophyta, which includes the closest living descendants of the land plants; however, there is a distinct difference between these two species.The key difference between liverworts and mosses is that liverworts have either green leafy thallus or foliose with leaf-like structures attached to ‘stems’ whereas mosses have small, leaflike structures arranged spirally or consecutively around the stem like axis attached to the substrate via rhizoids.
Bryophytes are primary green plants with many unspecialized characteristics though they are successful in many ecosystems on Earth. There are about 24,700 species of bryophytes. Bryophytes are also called nontracheophytes since they do not contain tracheid cells that are adapted for conducting water and nutrients. All the other green plants are called tracheophytes. The gametophytes of these plants can photosynthesize and are more visible than sporophytes. Sporophytes are connected with gametophytes and obtain nutrition from them. Like certain tracheophytes, bryophytes require water for their sexual reproduction. Thus, most of these species are mostly found in moist terrestrial habitats. In this article, the difference between liverworts and mosses will be discussed in brief.
What are Liverworts?
Liverworts are simple bryophytes with thin, leathery bodies, they grow in flat, moist terrestrial habitats or surfaces of still water bodies. The body of most liverworts has no true leaf-stem structure, hence it is often called a thallus. The thallus is often subdivided to form lobes, and the lobe size may vary among various species. Some species have ‘leaves’ (not true leaves) attached to ‘stem’ (not a true stem). These ‘leaves’ are a single thick cell and have no cuticle or vascular system. The ‘leaves’ are often divided into two or more lobes and arranged in two rows. Certain liverworts may contain a midrib, and some have pores through which the gas exchange takes place. Unlike stomata in higher plants, these pores cannot close. Some liverworts cannot be resistant to periods of dryness, whereas some are adapted to withstand this situation. Sexual reproduction is similar to mosses. The umbrella-shaped gametangia arise from the gametophyte. Asexual reproduction happens through lens-shaped tissue pieces, which are released from the gametophyte.
What are Mosses?
Moses are complex bryophytes consisting of small, leaflike structures arranged spirally or consecutively around the stem like an axis. Since these leaf-like and stem-like structures do not have a vascular tissue that is generally found in vascular plants, they cannot be considered as true leaves and stems. Mosses have rhizoids that act as roots and enable to them to attach to their substrates. Each rhizoid contains several cells that absorb water. The leaf-like structure is single cell layer thick and have a thickened midrib and flattened blade. Moses have specialized cells in the middle of the gametophyte axis that conduct water. Some mosses also contain food-conducting cells around the water-conducting cell layer. The gametangia of mosses are multicellular and found at the tips of the gametophytes. Female gametangia (archegonia) can be found either on the same plant with male gametangia (antheridia) or separate plants. Antheridium produces several sperms, whereas an archegonium produces a single egg. When sperms are released, they swim with the help of their flagella and reach archegonia. After fertilization and the formation of zygote, it is divided by mitosis and forms the sporophyte. The sporophyte of mosses is a brown stalk with a swollen capsule on top. The leafy gametophyte is photosynthetic, but sporophyte is not and obtains nutrients from the gametophyte.
What is the difference between Liverworts and Mosses?
Characteristics of Liverworts and Mosses:
Structure of the gametophyte:
Liverworts: Liverworts have either green leafy thallus or foliose with ‘leaves’ (not true leaves) attached to ‘stem’ (not a true stem).
Mosses: Mosses have small, leaflike structures arranged spirally or consecutively around the stem like axis attached to the substrate via rhizoids.
Structure of the sporophyte:
Liverworts: Sporophytes are formed within the umbrella-shaped female gametophytes.
Mosses: Sporophytes have a brown stalk with a swollen capsule.
Rhizoids or root-like structure:
Liverworts: Liverworts have a single elongated to cell for the attachment to their substrate.
Mosses: Mosses have multicellular rhizoids.
Liverworts: They are arranged in 2 or 3 rows.
Mosses: Mosses have spiral or whorl arrangement around the axis.Image Courtesy: 1. Marchantia polymorpha HC1 By Holger Casselmann (Own work) [CC BY-SA 3.0], via Wikimedia Commons 2. “Mosses on a tombstone“. Licensed under CC BY 2.0 via Commons