Bryophytes - liverworts

Liverworts are, like true mosses, bryophytes, but their form and physiology are quite different, though they also exhibit alternation of generations.

See mosses for an introduction to bryophytes

Marchantia polymorpha

Marchantia on stone step

Above: Marchantia growing on a stone step. The archegoniophores almost totally conceal the green thalli
underneath. The upper part of the step's riser, where it is drier, has been colonised by lichens.

Marchantia gemma cup

A close-up view of the thallus of Marchantia. Note the pores and the gemma cup containing
several gemmae (asexual spores). The gemmae are loose and waiting for rain splash to scatter them.

Marchantia gemma cup

Marchantia pores

Above: a close-up view of the pores in the surface of the thallus which allow air containing carbon dioxide to enter the thallus for photosynthesis.

Marchantia archegoniophore

Above: a developing archegoniophore of Marchantia, in side view. Note the white frilly membranes hanging down from the underside: This is the involucre which covers and protects the flask-like egg-containing archegonia within.

Marchantia air chamber

Above: an air chamber filled with photosynthetic cells in the thallus of Marchantia.

Marchantia scale

Above: a multicellular scale in Marchantia.

Marchantia rhizoids

Marchantia rhizoids

Rhizoids of Marchantia in longitudinal section (above) and transverse section (left). Each rhizoid is an extension of a single epidermal cell. Some cyanobacteria associated with the rhizoids are visible in the photomicrograph at top left.

Marchantia thallus in section

Above: a section through the thallus of Marchantia sp. Note the curious shapes of the innermost parenchyma cells: is this due to mechanical stresses or an adaptation for transport of materials from cell to cell?

Pellia gametophyte

Pellia gametophyte section

Pellia gametophyte unlabeled section

Pellia epiphyta is another liverwort which grows on damp soil in streams and ditches. It is another non-leafy thallous liverwort anchored by unicellular rhizoids and differentiated into a photosynthetic epidermis and cortex and a starch-storing medulla. The thallous is parenchymatous (comprised of largely undifferentiated plant cells that non-fibrous)). The antheridia produce the male gametes (spermatozoa) and the involucre is a flap which shields the flask-shaped archegonia which contain the eggs. The sporophyte grows up from a fertilised archegonium, protruding from the flap as a stalk several cm long bearing a dark sphere containing the spores. Unlike Marchantia, Pellia has no stomata or air-chambers.

Diagrams based on information from Plant Types 2: Mosses, Ferns, Conifers and Flowering Plants - an excellent book by Ruth Miller (Pub. Hutchinson).

Pellia life-cycle

Above: the life-cycle of Pellia epiphylla. The spermatozoid-producing antheridia are spherical flasks, each inside a pit which opens to the outside via a pore. Each antheridium will give rise to many spermatozoids. The archegonia are flask-shaped structures situated beneath the involucre shield at the tips of the ripe thallus (in mosses the archegonia are usually on the shoot tips, protected by a sheath of leaves) and each contains one developing ovum (oosphere). After fertilisation the sporophyte grows out from beneath the involucre, but is diploid, but produces haploid spores by meiosis, which give rise to haploid gametophytes.

Unlike mosses, the spore capsule of liverworts does not possess a peristome to assist or regulate spore dispersal. Instead, the capsule contains elaters, which are elongated cells with spirally thickened cell walls which cause the elaters to twist and thrive as they drive, breaking up the spore mass and scattering the spores.

Spore capsule

Section through the spore capsule of the liverwort Pellia.

elaters up close

Close up of the elaters. Note the spiral thickenings which cause the elaters to twist as they dry.

elaters in spore capsule

Elaters extending from the lower wall of the spore capsule.

Elaters up close

Close up of the elaters. As the elaters dry and twist, they help scatter the spores.

Spores

Close up of the spores. Note the elaters entwined amongst them.

Spore capsule wall

Close up of the spore capsule wall.

Bryophytes, or bryophyte-like plants were possibly among the first plants to colonise the land on Earth some
400 million years ago. (It is possible that today's bryophytes evolved from larger and more complex plants by
miniaturisation, but they are certainly ancient, the oldest known moss fossil is some 360 million years old).
Giant myriapods - millipedes the size of human beings, bulldozed through these primordial forests. In later
times, the bryophytes may have become overshadowed by trees of one kind or another, but they continue to
thrive, covering soil, rocks and trees. Indeed, those that grow on trees are helped off the ground, toward the
light and the fresh air which brings in carbon dioxide for photosynthesis and dispersal spores. It is easy when
walking in a wood not to pay too much attention to these ancient and miniaturised plants, but closer inspection
reveals amazing diversity and beauty of form in the tiny, and often overlooked, forests that these plants often
form. It is remarkable how such small plants have made such diverse use of chemistry and physics in so many
ingenious ways in order to solve life's problems.

Liverworts

Liverworts growing on a post on a stream bank. Although it is hard to tell without a closer look, the larger thalloid liverwort is possibly Conocephalum (Snakeskin Liverwort) whilst the form with smaller lobes could be Lunularia.

More Pages


Mosses and Introduction to Bryophytes

Sphagnum moss

Leafy Liverworts

External Links

An excellent online book on bryophytes, detailed and with photographs: http://www.bryoecol.mtu.edu/

Article updated:
29 Oct 2016
10 Nov 2016
27 Nov 2016
18 Feb 2017

12 Aug 2018
19 Dec 2019
24 Dec 2019