Bryophytes - Definition, Types and Examples

For a plant to survive, it will need to both get nutrients from its environment and transport them throughout their organism. Most plants do this through a vascular system, i.e. a complex system of tubes which sends minerals and other nutrients to fulfill its vital functions, including metabolism and reproduction. Most of the plants on Earth are vascular, providing the majority of its biomass and food^[1].

A minority of plants are bryophytes or non-vascular plants. They can be found in a wide range of habitats, being very adaptable to even inhospitable environments. Since they do not have a vascular system, they are unable to reach a large size, so all bryophytes are relatively small plants. However, they can spread over large surfaces. Although they are non-vascular plants, bryophytes do have the following characteristics:

• Multicellular: they are made up of more than one cell, so they are relatively complex organisms even without a vascular system.
• Chlorophyll: like vascular plants, bryophytes contains chlorophyll which allows them to carry out the process of photosynthesis.

Bryophytes are green plants. Although they may be very small and do not contain veins, they also have leaves and stems. They do not have flowers. Various different shades of green are present in bryophytes, ranging from very light to very dark. We will explain more about the characteristics of bryophyte plants in the next section below.

Bryophytes and Bryophyta

There is some confusion over the use of the terms bryophyte and Bryophyta. In terms of taxonomic categorization, Bryophyta is a division of land plants (Embryophyta) which officially only contains the non-vascular plants we call mosses. However, some botanists have proposed that we also include the plants known as liverworts and hornworts.

This means some may only consider mosses to be true bryophytes since they make up the official taxonomic group Bryophyta. Others may include liverworts and hornworts as types of bryophytes since they are non-vascular plants which fit the same description.

One of the reasons for differing opinions is the debate over whether they form a monophyletic group, i.e. they are descended from a common ancestor. A lack of data or different interpretations of data foster this debate. IN terms of this article, we are referring to bryophyte plants as those which include mosses, liverworts and hornworts.

One of the reasons we can group together certain plants as bryophytes is because they share some important characteristics. These are related to their organic structure, habitat and method of reproduction. We better understand these non-vascular plants by looking at the main characteristics of bryophytic plants:

• Habitat: the ecosystems which are home to bryophytes are incredibly varied, most so than vascular plants. Although they generally prefer humid environments, they can also be found in dry deserts. Vascular plants need soil, water or similar substrates for their roots to anchor themselves and take up nutrients for transportation. As non-vascular plants, bryophytes do not have this need so they can grow on surfaces such as rocks and the bark of trees. They absorb water from their environment like a sponge, but this moisture can come from various sources. Learn more about plants which do not require much water with our article on types of xerophyte plants.
  
  
• Vegetative structure: since they do not have a vascular system or flowers, they are considered relatively simple organisms. Their structure is fairly homogenous. Although they cannot grow to be tall, they can be very wide and cover a large surface. This can be seen in mosses which cover the forest floor, for example. Their leaves are small and difficult to differentiate. Not all non-flowering plants are bryophytes, as you can see in our article on different cryptogamic plants.
  
  
• Reproduction: bryophytes can reproduce both sexually and asexually.

Reproduction of bryophyte plants

• Sexual reproduction: the plant produces the male gametes that will fertilize the female gamete. The union of both gametes will give rise to the sporophyte, which will germinate in new plants.
  
  
• Asexual reproduction: in this form of reproduction any part of the plant can give rise to a new one. The buds that we can find in this type of plant, when they come into contact with a suitable surface for their development, give rise to a plant identical to its parent.

As we have already explained, some only consider mosses to be by bryophytic plants. Here we provide all the types of bryophyte which we can find in nature according to their broader definition.

Mosses

Of the taxonomic division Bryophyta, mosses are usually found forming dense blankets across various surfaces. Although they may look one giant plant, they are actually individual plants which grow in clumps. Each plant has tiny structures with function similar to those of roots in vascular plants as they allow them to affix to a surface. These are known as rhizoids and they have an appearance similar to that of very fine hairs.

The presence of bryophytes helps prevent erosion of the soil in which they are found. The soils which mosses cover tend to be rocky or stony, but not exclusively so. Large populations of these types of bryophyte plants are generally a good indicator of an ecosystem's health.

Liverworts

These are plants form the division Marchantiophyta, of which there are around 9,000 individual species. They are so called due to the appearance of their leaves which are a similar shape to the human liver. They develop in shady and cool areas, occupying large tracts of land.

As with all types of bryophyte, liverworts are small, but they can spread over a large area when in clumps. Their life cycle starts from the germination of a haploid spore. They are also a plant which exhibits a type of symbiosis in nature. This is because they can live with certain types of fungi and provide mutual benefit for survival.

Hornworts

These bryophytic plants make up the division Anthocerotophyta. They are also very small and have a simple structure. There are much fewer hornwort species that liverworts. They are so called due to the horn-shaped structure of their leaves.

As they are non-flowering plants, bryophytes reproduce either sexually or asexually using spores. Learn more about this general process with our guide to sporulation in biology.

We have already explained the types of bryophytes, but within these broad categories are many individual species. We take a look at some of these individual species of bryophytic plants according to their type:

Mosses

With around 12,000 known species, mosses are the most populous type of bryophyte. Some emblematic species include:

• Common haircap (Polytrichum commune)
• Goblin gold (Schistostega pennata)
• Glittering woodmoss (Hylocomium splendens)
• Tree climacium moss (Climacium dendroides)
• Grey-cushioned grimmia (Grimmia pulvinata)
• Archidiaceae (Archidium)
• Broom forkmoss (Dicranum scoparium)
• Woodsy thyme-moss (Plagiomnium cuspidatum)

Liverworts

With around 9,000 individual species, there are still many different types of liverworts which can be found across the world. They include:

• Bolander's asterella (Asterella bolanderi)
  
• Campbell's liverwort (Geothallus tuberosus)
• Great scented liverwort (Conocephalum conicum)
• Common liverwort (Marchantia polymorpha)
• Neohodgosonia mirabilis

Hornworts

There are significantly fewer liverwort species. Some estimates put them as much as 900, but others only account for around 100 individual species. They include:

• Field hornwort (Anthoceros agrestis)
• Anthoceros aethyopicus
• Anthoceros affinis
• Anthoceros agrestis
• Anthoceros alpinus

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