The aim of this page is to help you decide whether a particular bryophyte is a liverwort, moss or hornwort.
There are three separate pages that go into more detail about MOSS, LIVERWORT and HORNWORT features. This page won't repeat all the detail in those pages but will simply emphasize those features that most easily help you distinguish the three types of bryophytes. This page also will not go into detail about the functions or development of the various structural features. There's more about those topics in the LIFE CYCLE and REPRODUCTION & DISPERSAL pages.
It's always possible, and very easy, to determine whether you have a moss, liverwort or hornwort if sporophytes are present. Remember that a sporophyte consists of a spore capsule, with or without a supporting stalk or seta. If sporophytes are absent you'll naturally need to look at some gametophyte features, the first step being to see whether you have a thallose or a leafy bryophyte. A thallose bryophyte is either a liverwort or a hornwort. A leafy bryophyte is either a moss or a liverwort. In many cases it isn't too hard to determine whether a thallose bryophyte is a hornwort or liverwort or whether a leafy bryophyte is a moss or liverwort. However, there certainly are instances where, in the absence of sporophytes, it can take considerable effort to decide whether you have a moss, liverwort or hornwort.
By the end of this page you should have some idea of when it's easy and when it's difficult to tell whether the bryophyte you're looking at is a moss, liverwort or hornwort. You'll also have seen when a naked eye is sufficient, when you need to use a hand lens and when a microscope is essential.
Incidentally, bryophytes often grow intermingled so you'll sometimes have to check carefully to see which gametophyte a particular sporophyte is attached to.
From what has been said above, you'll understand that sporophytes are very informative and it therefore pays to search carefully for sporophytes, especially for mature sporophytes with open spore capsules. There will be several questions, asking about the sporophyte appearance, and after each question there will be a discussion about the bryophytes that have that particular type of sporophyte.
The bryophyte is a liverwort. A number of complex thallose liverworts produce groups of spore capsules in complex and often somewhat umbrella-like structures called archegoniophores. Here are some examples: Asterella drummondii , Lunularia cruciata , Marchantia and Reboulia hemispherica . Such structures are only found in some genera of complex thallose liverworts. Some liverworts also have their sperm-producing antheridia in complex structures called antheridiophores, which you might initially mistake for archegoniophores. However, you'll never find spore capsules on the undersides of antheridiophores. From one point of view there's no harm done in mistaking a complex antheridiophore for an archegoniophore, since it's only liverworts that have either complex structure.
Now we will look at bryophytes in which the spore capsules are not produced in clusters.
Then the bryophyte is either a liverwort or moss. If the gametophyte is thallose then clearly the bryophyte is a liverwort. If the gametophyte is leafy then some more work is needed before you can decide whether the bryophyte in question is a liverwort or moss.
In the majority of liverworts and mosses the mature sporophyte consists of a single spore capsule held atop a stem which, depending on species, may be fairly short to quite long. If the stem is translucent (and often colourless ) the bryophyte in question is almost certainly a liverwort. Spore capsules of mosses in the genera Sphagnum and Ambuchanania are also supported by translucent stems and in these cases, as in most mosses, the spore capsule opens by means of a well-defined mouth, through which the spores are released. Liverwort spore capsules do not open by means of a well-defined mouth. Instead, in most cases they split open, though in a few genera they break open irregularly. The previous photo showed a group of sporophytes of a leafy liverwort. You'll also find translucent stems in the sporophytes of many thallose liverworts. The photo (right) of the complex thallose liverwort Monoclea forsteri shows a couple of sporophytes with open spore capsules. Initially the capsule is ellipsoid and, when mature, opens along one side to release the spores. This photo shows a group of sporophytes of the simple thallose liverwort Fossombronia intestinalis. In this genus the capsule breaks irregularly.
If the stalk supporting the capsule is opaque and coloured green, brown or red the bryophyte in question is a moss. In mature sporophytes the capsules may be orientated in various ways, depending on species. This photo shows some spore capsules of Polytrichum juniperinum. You can see that the capsules are orientated at right angles to the seta. In this species of Bryum the capsules hang downward from the top of the seta. The capsule of Entosthodon apophysata sit upright at the top of the seta.
In the great majority of moss species the mature spore capsule opens by means of a well-defined mouth. Remember that a liverwort spore capsule never has a well-defined mouth. The mouth may be surrounded by peristome teeth (at times long and hair-like ) or it may be smooth . In some species, such as Polytrichum juniperinum, the tips of the peristome teeth are joined to a white, circular epiphragm . When the spore capsule is still immature it is green and the mouth is covered by a cap called an operculum. Mosses in the genus Andreaea have spore capsules which open by splitting, rather than by means of a mouth. You'll remember that splitting is common in liverwort spore capsules. Capsules that split do so along lines of weakness, or dehiscence lines, that extend from near the base of the spore capsule towards the apex. The base of the capsule is the point at which it is attached to the seta or, where there is no seta, to the gametophyte. The apex is the point directly opposite the base. In a splitting liverwort capsule the dehiscence lines extend all the way to the capsule apex, thereby splitting the capsule into several segments. These segments fold outward and so the capsule opens completely to expose the spores for dispersal. In Andreaea the dehiscence lines stop short of the apex so the capsule doesn't open out. Instead there are several slits in the capsule wall and, depending on the humidity, the slits either open to release spores or close to stop spore release. The accompanying drawing (taken from John Lindley's, The Vegetable Kingdom, published in London in 1853) shows an open Andreaea spore capsule. The genus Andreaea is found in alpine or sub-polar areas where it grows as blackish cushions on exposed rocks. In Australia the greatest diversity of Andreaea species is found in Tasmania.
The bryophyte is a hornwort. A hornwort sporophyte is an opaque, tapering horn-like or needle-like structure. The whole structure is a spore capsule that tapers evenly to the apex. There is no seta. The hornwort capsule is initially green and as spores mature it turns brown. The spores near the apex mature earliest, so that is the area where the colour change first occurs and the brown colouration then spreads downwards as the spores lower down mature. As the spores mature the capsule opens by means of one or two lengthwise slits .
The bryophyte is a liverwort or moss. There are a number of mosses and liverworts in which the mature sporophytes have no setae, or setae so short as to be hard to detect. It is also worth noting that in liverworts in which the fully mature spore capsules are held on noticeable setae, the setae extend only once the spore capsules are mature. In such species you may see numerous mature, but unopened, spore capsules seemingly seated directly on the gametophytes, as shown in this photo . As noted earlier, in the majority of mosses the spore capsule opens by means of a well-defined mouth. That's never the case in liverworts, in which the capsules mostly split open completely along dehiscence lines. The differences between splitting in the capsules of liverworts and those of the moss genus Andreaea have been explained above. In a few mosses and liverworts capsules disintegrate and you may need to look at gametophyte features to help you decide whether you have a moss or liverwort. Gametophyte features are dealt with below in the section headed "If sporophytes are absent".
So far we've been looking at thallose liverworts in which sporophytes are outgrowths from the gametophyte. The complex thallose genus Riccia is different in that the spore capsules are embedded within the thallus and the spores are exposed for dispersal by disintegration of the overlying thallus. Don't mistake the surface gemma cups of the thallose liverwort Marchantia for embedded spore capsules. The gemma cups are involved in VEGETATIVE REPRODUCTION.
The first thing to do is to see whether you have a thallose or a leafy bryophyte. The almost leathery thallus of a robust thallose bryophyte is fairly easy to pick. Similarly, in some leafy species the leaves-on-stems growth habit is very easy to see. The following photographs show such a pair.
However, sometimes it's more difficult. Several of the simple thallose liverworts, with very flimsy thalli, are superficially somewhat leaf-like. This is a photo of the simple thallose liverwort Symphyogyna podophylla. The thallus is very thin and you might think that the photo is showing a close-up view of a few leaves. Here is Hymenophyton flabellatum, another thallose liverwort. Initially you might think you're seeing a fanned-out array of leaves atop a stem. In this liverwort the thalli are somewhat strap-like, but they fork from time to time, thereby giving that fanned-out look.
In some leafy bryophytes the leaves are very small. Hence, there are times when you will need to use a hand lens magnifying at least 10 times and look carefully to see whether you have a leaves-on-stems growth form or not. It can also be very hard to make out any details in dry plants. In leafy bryophytes the leaves typically fold or curl inwards as the plant dries and thallose bryophytes may also close up as conditions become dry. So, two basic rules of bryophyte gametophyte examination are: use a hand lens and look at moist specimens. The specimens should be moist, so that the gametophytes are fully open, but not waterlogged. If there's too much water the effects of refraction and reflection will make it difficult to see the necessary detail.
Some complex thallose liverworts may produce substantial non-sporophyte structures which are also helpful in distinguishing them from hornworts. These raised, star-like pads are the sperm-producing antheridiophores of the thallose liverwort Marchantia berteroana. Gemma cups produce tiny, disc-like vegetative propagules called gemmae, which are discussed in the VEGETATIVE REPRODUCTION page. In Marchantia the gemma cups are circular and in Lunularia they are semi-circular . Hornworts never produce such structures.
In the absence of any surface structures, it becomes more difficult to distinguish hornworts from liverworts. We'll finish this section about thallose bryophytes by listing some features you can use. Hornworts never have the extensive tissue differentiation shown by the complex thallose liverworts. Hence if the thallus is quite thick and dotted with the white specks that indicate air pores , the bryophyte is a liverwort. Hornworts form symbiotic associations with cyanobacteria, which take up residence in internal cavities within the hornwort thallus. In the accompanying photograph of Dendroceros crispatus you can see such cyanobacterial cavities as darker dots in the rather thin thallus. You'd generally need a hand lens to see those dots. Without the cyanobacterial colonies this hornwort could easily be mistaken for a simple thallose liverwort. Hornworts generally have just one or two large chloroplasts per cell whereas liverworts typically have many smaller chloroplasts per cell. You'd need a microscope to see the chloroplasts.
Gametophyte growth habit may give you some clues. A leafy bryophyte growing on soil and showing a tufty or tussock-like growth habit is far more likely to be a moss, especially in a dry, exposed location. There are numerous mosses and leafy liverworts that have a creeping growth form. In the photo (right) you see leaves in two distinct rows either side of the stem. Such a leaf arrangement is far more common in leafy liverworts than in mosses, which tend to show a spiralled leaf arrangement. However, these features simply suggest which of moss or leafy liverwort is more likely. It is the features of the leaves themselves that carry a lot of information that will help you distinguish a moss from a leafy liverwort. Those features are explained in the LEAF page.