Liverworts

Liverworts are differentiated from mosses by several factors. The main ones are – the sporophyte (capsule) is fleshy and short-lived (a few days), but in mosses the sporophyte (capsule) is on a wiry stem (seta) that is long lasting.

Plate 1. Liverwort sporophyte. Note that it is ‘fleshy’ as opposed to wiry. Taken from www.hiddenforest.co.nz.

If there is no stem and ‘leaves’, and the thallus is made up of fleshy lobes, it is a liverwort.

Plate 2. Thalloid or lobed liverwort (Marchantia sp.) Copyright S McCurdy, University of Waikato, 2003

If there is a stem and ‘leaves’ then in a liverwort these are usually arranged in three rows (see diagram below). Mosses only have two rows.

Figure 2. Leafy liverwort showing the three rows of leaves. Copyright S McCurdy, University of Waikato, 2003.

When you look closely at the leaves (usually this means under a dissecting microscope) if there is a ‘nerve’ (like a mid-vein but made up of elongated cells) then this is a moss. Liverworts do not have ‘nerves’.

The rhizoids (like roots but not as structurally complex) are generally made up of one cell whereas in mosses they are multicellular and have divisions between the cells that are at an oblique angle.

The Hepaticopsida are divided into five orders: Calobryales, Jungermanniales, Metzerigales, Monocleales and Marchantiales.

We won’t go into detail on the characteristics of each of these orders, as there are very good descriptions in Allison and Child (1975).

But, we will give brief outlines of the most commonly found orders as these will be what you will identify at home and in the lab.

Monocleales – this is a thalloid type and is the largest species of liverwort in New Zealand. It is often found in the bush near waterfalls or seeps and has extremely large lobes (can be up to and exceed 25mm in width). The thallus does not have surface pores or gemma cups and there is only one species found in New Zealand, Monocleales forsteri.

Marchantiales – specimens belonging to this order are what you most commonly find in an urban area. These are also a thalloid type but when you inspect the surface closely you will see many small ‘holes’. These are in fact pores and are the openings to a small chamber in the thallus. They are called barrel pores and the chambers are thought to help in gas exchange in photosynthesis.

In the laboratory you can do a cross-section and examine the slide under a high power microscope. You will see that there is a grouping together of similar cell types. This is likely to be a very early example of the formation of ‘tissue’ – groups of cells with similar function are organised into tissues or organs.

If you are lucky and the weather has been on your side you may collect samples of Marchantiales when they are fertile. Their reproductive organs are not just soft stalks that last only a day or two – they are elegant, delicately shaped, erect umbrellas! The male ones are called antheridiophores and the female are called archegoniaphores. (Have a look at the life cycles again to get these two terms sorted out in your mind).

Plate3. Thalloid liverwort showing reproductive structures (antheridiophores). Copyright S McCurdy, University of Waikato, 2003

The book “The Forest Carpet” by Bill and Nancy Malcolm (1989) has some of the most superb photographs of liverworts and their structures that you will ever see. See if you can find a copy at your local library or the University library, and the book will be in the lab during the course.

If you look in your garden (or in someone else’s garden) or on the top of shade loving plants in the Garden Centre you will probably find a thalloid liverwort growing. You may find two different types, but both belong to Marchantiales. The first one we want to key out is called Lunularia.

Photo of Lunularia in pot or garden Plate 4

Using Allison and Child (1975) we will key this specimen out and you will have lots more to try in the laboratory work in the Flora course. If you look carefully at the key you will see that it is arranged somewhat differently from the lichen key we’ve already used. With this one you have to work by each number. These don’t run consecutively down the page, but step in toward the centre of the page. It’s just a matter of getting your ‘eye in’. Look first at number one; this will be divided as 1a and 1b. The next clue will be to go to 2 or 3. If you need to go to number two then it will give you choices, 2a or 2b. The next clue will be perhaps, 5a and 5b etc. See it’s easy!

With our sample of Lunularia, and our omnipresent handlens, examine the surface of the thallus. You will see small white pores in the surface. These are called ‘barrel pores’ and are characteristic of the Order Marchantiales.

The next thing you will notice is the presence of some half-moon shaped structures, and these will have tiny green fragments in them like miniature green eggs in a nest. These half-moon shaped structures are called gemma cups, and the green eggs are gemmae (singular: gemma). Gemma cups are not always half-moon shaped and the picture below shows circular ones.

Plate 5. Thalloid liverwort with circular gemma cups. Copyright S. McCurdy, University of Waikato, 2003.

These are reproductive units but are asexually produced so are genetically identical to their parent. Raindrops land in these cups and splash the gemmules out into the environment where they grow. So, let’s look at the key.

We know already by the presence of the barrel pores that this is in the Order Marchantiales so go to the Marchantiales key.

The next liverwort that may be easy to find is another thalloid type. The leafy varieties are generally found in low light, damp habitats in the bush so will be less easy to obtain for many of you. Search around and you will find another thalloid liverwort genus.

When you examine the surface you will find that this specimen also has barrel pores. When you were keying out the Lunularia you were asked if the shape of the gemma cups was crescentic or not. This should suggest to you that they are therefore, not all crescentic! Indeed, they are not. The liverwort you have collect has probably got fully circular gemma cups.

Plate 6. Thalloid liverwort species Marchantia. Copyright S. McCurdy, University of Waikato, 2003.

Referring to Allison and Child (1975) you will see that this also fits into the Order Marchantiales.

References

Alison, K.W. and Child, John. 1975 Liverworts of New Zealand. University of Otago Press, Dunedin.

Beever, Jessica, Alison, K.W. and Child, John. 1992 The Mosses of New Zealand, University of Otago Press, Dunedin.

Raven, Peter H., Evert, Ray F. and Eichorn, Susan E. 1999 Biology of Plants, Publishers, New York.

Terminology

Capsule – the structure that holds spores. This is the ‘sporophyte’ generation in mosses and liverworts and is diploid tissue.

Crescentic – half-moon shaped.

Gemma cups (gemmae pl.) – cup-shaped structures that contain gemmules

Gemmules – small ‘balls’ of tissue. These are genetically identical to the parent plant and are part of a vegetative reproductive cycle.

Nerve – a section of the moss leaflet that looks similar to the mid-vein in the leaf of a higher plant.

Rhizoid – Thin threads of cells that act as anchors for the moss plant. They are similar to roots but far less complex

Seta – the thin wiry stalk that hold up the capsule. In liverworts it is usually very fleshy and short-lived.