Marchantia berteroana | Plantz Africa about:reader?url=http://pza.sanbi.org/marchantia-berteroana

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Marchantia berteroana | Plantz Africa

What is a liverwort? A liverwort is a small leafless, flowerless, spore-producing plant. Liverworts were the first of the early green land plants to evolve (after algae and before the ferns), about 500 million years ago, making them the oldest living land plants! Liverworts are grouped into three main groups according to their structure: the simple thalloid, complex thalloid and leafy liverworts.

Marchantia belongs to the complex thalloid group. The Marchantia thallus (plant body) is a flattened strap-like structure, 325 -925 µm thick, divided into three layers: the upper layer with pores (under a lens it can be seen to be dotted with closely crowded, whitish pores) with smooth, somewhat glossy surface, the middle layer with air pockets and chloroplast-containing cells, and the lower layer that stores carbohydrates. The thallus of Marchantia berteroana is yellow-green to green or reddish-brown, 600-900 µm thick, with branches up to 20 mm long and about 12 mm wide, with wavy margins. The thallus has scales on the lower surface (ventral scales) that extend nearly to the margins, and rhizoids (hair-like structures that act as roots) with which it attaches to its substrate.

The life cycle is divided into two phases alternating with each other:

the dominant haploid gametophyte phase (with a single set of unpaired chromosomes); actually the flat green plant that you see and which is responsible for all the plant's metabolic functions — photosynthesis, gas exchange and water absorption.

the dependent diploid sporophyte phase (with paired chromosomes and therefore with twice the haploid number) during which sexual reproduction takes place.

M. berteroana is dioicous, which means that the male and female gametangia (sex organs) are formed on separate plants. The male and female plants can easily be distinguished from each other by their gametangia, which are very distinct structurally and which are produced from the apex of the terminal segment of the main or short lateral branch.

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The male gametangia, called antheridia, are stalked, disk-like structures that produce sperms. The antheridiophore (the stalk of antheridium) is about 30 mm long and arises in August. The antheridial disk, on top of the stalk, is up to 10 mm wide and shallowly segmented into 8 or 9 symmetrical lobes which have brownish or colourless margins.

The female gametangia, called archegonia, are stalked umbrella-like structures that produce eggs. The archegoniophore (stalk of archegonium) is about 80 mm long and it appears in September. The archegonial umbrella, on top of the stalk, is called the carpocephalum and is up to 10 mm wide, dorsally (above) with small round median projections, and deeply divided into 9 linear rays. This sporophytic phase begins in the spring and continues through the summer months.

M. berteroana can reproduce sexually or asexually.

In sexual reproduction water is required for fertilization to take place. The sperm cell has multiple flagella (long whip-like outgrowths) that propel it forward to reach the archegonium. When it reaches the archegonium it swims through the neck and fertilizes the egg at the base of the archegonium, and a diploid zygote forms, the first cell of the diploid sporophyte.

This sporophyte phase, totally dependent for its survival on the mother gametophyte, is attached to it by a foot through which nutrients are passed between the two phases. The sporophyte also has a stalk, called a seta, that connects the foot to the sporangium (capsule). Inside the sporangium the spores are produced and among them are yellow-brown, bispiral (in a double spiral) structures, called elaters, whose function is

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to help in the release of the spores. The stalk is fragile and remains short until the sporangium has fully matured and the spores are ready for release.

Once the sporangium has matured, the stalk elongates by absorbing water, stretching its cells, growing taller so that it reaches high above the mother gametophyte. The sporangium then breaks open exposing the spores and the elaters. The elaters wiggle, stretch and bend according to the humidity in the surrounding air, thus aiding spore dispersa, after which the fragile stalk disintegrates. This is a very short process. A magnifying glass might come handy if you are lucky enough to see this fascinating process happening right before your eyes.

For asexual reproduction to take place the plant produces special fun-to-look-at cup-like structures, called gemmae cups, located on the upper surface of the gametophyte, 4 mm wide and 3 mm high.

Minute, multicellular, disc-shaped structures called gemmae are produced on the floor of the gemma cups, each attached by a minute stalk and showing two lateral growing-points. When mature, the gemmae break away from their stalks. When water or rain droplets hit inside the gemmae cups, they splash out the gemmae which, when landed in favourable substrate (e.g. damp soil), develop directly into a new plant.

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