Marchantiales

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Marchantiales
Fountain liver moss (Marchantia polymorpha)

Fountain liver moss ( Marchantia polymorpha )

Systematics
without rank: Streptophyta
Empire : Plants (Plantae)
Department : Liverworts (Marchantiophyta)
Class : Marchantiopsida
Subclass : Marchantiidae
Order : Marchantiales
Scientific name
Marchantiales
Limpr.

The Marchantiales are an order of mosses within the liverworts with around 180 species.

features

Structure of the thallus

The Marchantiales are complex thallous , that is, flat-growing liverworts. The thallus has an upper side and a lower side. On the underside of the thallus there are unicellular, root-like structures, the rhizoids . The rhizoids attach the thallus to the ground and supply it with water, but are not related ( homologous ) to the roots of higher plants. Furthermore, there are multicellular abdominal or ventral scales on the underside. Both rhizoids and ventral scales have the function of absorbing water.

The thallus itself can be divided vertically into two layers. The underside contains so-called oil cells that store lipids , water storage cells and parenchymal cells that are poor in chlorophyll . In the upper half there are regularly arranged large intercellular spaces, into which "pins" made up of a few cells, so-called "assimilators", protrude and sometimes reach the upper epidermis. These are rich in chloroplasts and are primarily used for photosynthesis . This arrangement of the assimilators in the air-filled intercellular spaces (air chambers) serves for more efficient gas exchange. The intercellular parcels each have a breathing pore that is a simple thallus opening or a complex barrel-shaped structure. In the latter, the cells collapse when they dry out, thereby closing the breathing pore and preventing further water loss.

The thalli of the Marchantiopsida generally have only weakly pronounced central ribs. In the Marchantiales there are only three genera with vegetative propagation, including Marchantia . These form brood cups in which a large number of brood bodies are formed. These arise upright in the brood cups and therefore have no top or bottom. Only after it has spread does it develop into a dorsiventral thallus. It is spread by raindrops that hurl the brood bodies out of the incubator (splash cup mechanism).

Gametangia

Archegonia stand with 9 umbrella beams. On the underside, the spores with the elaters swell out as "whitish cotton wool" .

The gametangia (tissue for the formation of the gametes ) are located in the Marchantiales on typical umbrella-like stalked gametangia stands ( gametangiophore ), which are usually of separate sexes. So there are male and female gametangiophores. The male antheridiophores carry the antheridia on the upper side, where they sit sunk into the disk-shaped stand, which is often eight-fold slightly lobed. The archegonia are formed on the underside by umbrella-shaped archegoniophores and stand there in radial rows.

When the spermatozoids are ripe, the wall cells begin to slimy and swell when exposed to moisture, so that the spermatozoids are pressed out. When it rains, the spermatozoids are injected under the umbrella of the archegoniophores. Therefore, the antheridiophores are lower than the archegoniophores. There are also sessile gametangiophores , here the transport of the spermatozoids takes place via the rainwater on the thallus surface. Regarding the height of the gametangiophores, there are all intermediate levels between the seated and 10 centimeters high.

Sporophyte

The sporophyte is, as is generally typical of the Marchantiopsida, hidden in the archegonia shell for a long time. The embryo that develops a few days after fertilization grows into a small sporogon that is phytosynthetically active, but physiologically completely dependent on the mother plant. The sporogon is as good as sessile and very small compared to the gametophyte, compared to all other moss groups. It sits on the underside of the archegoniophore and opens with four to six longitudinal fissures. The spores are then spread by the wind. In some genera (e.g. Corsinia ) the sporogon remains embedded in the thallus, so that the spores are only released after the gametophyte has decayed.

  • Formation of the brood bodies

  • Antheridia stand

  • female gametophyte and sporophyte

  • Thallus in plan and cross-section

Occurrence

The species have occupied a wide range of ecological niches . There are representatives in alpine snow valleys ( Asterella lindenbergiana , Sauteria alpina ), species on stream banks ( Conocephalum conicum ) and in swamps ( Marchantia aquatica ), but also in arid and semi-desert locations ( Targionia hypophylla , Plagiochasma rupestre ). The species in dry locations roll up their thallus when they dry out. The ventral scales then turned upwards offer protection from radiation.

Systematics

The order contains four sub-orders with twelve families and a total of around 180 species:

The moon cup moss ( Lunularia cruciata ) has long been part of the Marchantiales, but has been considered a separate (monotypic) order since molecular studies.

literature

Individual evidence

  1. ↑ a b Wolfgang Frey, Eberhard Fischer, Michael Stech: Bryophytes and seedless Vascular Plants . In: Wolfgang Frey (Ed.): Syllabus of Plant Families - A. Engler's Syllabus of Plant Families . 13th edition. tape 3 . Borntraeger, Berlin / Stuttgart 2009, ISBN 978-3-443-01063-8 , pp. 29-33 .

Web links

Commons : Marchantiales  - collection of images, videos and audio files