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Liverwort characters
Thalloid plant body
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The character categories and their possible forms are:

Liverwort phylogeny

Below is an outline phylogenetic tree for the liverworts based on Crandall-Stotler, Stotler & Long. (2009). Below each order, only example genera and their families are listed.

Class: Marchantiopsida

Subclass: Blasiidae

Order: Blasiales
Blasia (Blasiaceae)

Subclass: Marchantiidae

Order: Lunulariales
Lunularia (Lunulariaceae)

Order: Marchantiales
Conocephalum (Conocephalaceae)
Marchantia (Marchantiaceae)
Preissia (Marchantiaceae)

Class: Jungermanniopsida

Subclass: Pelliidae

Order: Pelliales
Pellia (Pelliaceae)

Order: Pallaviciniales
Pallavicinia (Pallaviciniaceae)

Subclass: Metzgeriidae

Order: Metzgeriales
Apometzgeria (Metzgeriaceae)
Aneura (Aneuraceae)
Metzgeria (Metzgeriaceae)
Riccardia (Aneuraceae)

Subclass: Jungermanniidae

Order: Porellales
Suborder: Porellineae
Porella (Porellaceae)

Suborder: Radulineae
Radula (Radulaceae)

Suborder: Jubulineae
Frullania (Frullaniaceae)
Lejeunea (Lejeuneaceae)

Order: Ptilidiales
Ptilidium (Ptilidiaceae)

Order: Jungermanniales
Suborder: Cephaloziineae
Anastrophyllum (Scapaniaceae)
Barbilophozia (Scapaniaceae)
Bazzania (Lepidoziaceae)
Cephalozia (Cephaloziaceae)
Diplophyllum (Scapaniaceae)
Gymnocolea (Scapaniaceae)
Lepidozia (Lepidoziaceae)
Lophozia (Scapaniaceae)
Scapania (Scapaniaceae)
Nowellia (Cephaloziaceae)
Odontoschisma (Cephaloziaceae)
Trichocolea (Trichocoleaceae)
Tritomaria (Scapaniaceae)

Suborder: Jungermanniineae
Calypogeia (Calypogeiaceae)
Jungermannia (Jungermanniaceae)
Leiocolea (Jungermanniaceae)
Lophocolea (Lophocoleaceae)
Marsupella (Gymnomitriaceae)
Mylia (Myliaceae)
Nardia (Solenostomataceae)
Plagiochila (Plagiochilaceae)
Leafy liverwort
leafyliverwort

Dripping water from snowmelt saturates this large community of a crimson-coloured leafy liverwort. Growing on a metamorphic rock exposed in a cutting on the old railway line at Glen Ogle, between Lochearnhead and Killin, Stirlingshire.

Simple, thin thallus
  • Blasia pusilla*
  • Pellia endiviifolia
  • Preissia quadrata*
  • Pallavicinia lyellii
  • Metzgeria fruticulosa
  • Metzgeria furcata
Blasia pusilla Blasia pusilla (Blasiaceae)
Blasia pusilla

Simple, thin thallus

The thallus of Blasia pusilla is somewhat lobed, and the plant can be found in low-density colonies on fairly bare moist soil.

The thalloid liverworts can be split on morphological grounds according to whether the thallus comprises a simple, thin sheet (Metzgeriidae) or having a thicker, more complex layered structure (Marchantiopsida). However, the simple thalloids are not monophyletic, but are the ancestral group from which the complex thalloids and the leafy liverworts (Jungermanniidae) arose.

The plant body of the simple thalloid liverworts is thought to resemble some of the earlier plant colonisers of the land. Clearly, a flat layer of photosynthetic cells provides a high surface area for intercepting sunlight and also ensures close contact with the substrate for moisture and nutrients.



Complex, thick thallus
  • Conocephalum conicum*
  • Conocephalum salebrosum*
  • Lunularia cruciata
  • Marchantia polymorpha
  • Marchantia ruderale
Conocephalum conicum Conocephalum conicum (Conocephalaceae)
Conocephalum conicum

Complex, thick thallus

The thallus of Conocephalum conicum is thick, quite opaque and fairly leathery, often forming extensive communities. Like many liverworts, it grows in dimly-lit moist muddy banks.

Some of the thalloid liverworts have developed a complex layered structure with particular cells arranged in tissues and performing specialial roles. This division of labour represents an advance on the simple thalloid liverwort plant body.



Distinctly bifurcating
  • Blasia pusilla*
  • Pellia endiviifolia
  • Preissia quadrata*
  • Metzgeria fruticulosa
  • Metzgeria furcata
  • Riccardia palmata (Q) Note:
    Both dichotomous and trichotomous-braching lobes can be found in Riccardia palmata.
Metzgeria furcata Metzgeria furcata (Metzgeriaceae)


Metzgeria furcata

Distinctly bifurcating

The individual Metzgeria furcata seen here formed a more or less circular patch on the smooth surface of a Beech tree. Note the conspicuous midrib on the otherwise thin translucent thallus lobes.

Metzgeria furcata has a very thin thallus that creeps over rock and tree surfaces, portions of the thallus lobes overlapping one another as they grow towards the leading edge of the plant on its substrate.

Similar "expanding disk" growth forms are found in fungal colonies and even some mineral crystal aggregates, all characterised by incremental growth at the ends of existing flat structures, with growth more or less equal in all radial directions.



Conspicuous midrib
  • Marchantia polymorpha
  • Metzgeria fruticulosa
  • Metzgeria furcata
Marchantia polymorpha Marchantia polymorpha (Marchantiaceae)
Marchantia polymorpha

Conspicuous midrib

The lobes of this Marchantia polymorpha possess a conspicuous dark band in the centre, surrounded by a pattern of green hexagonal air chambers.

A number of the complex thalloid liverworts have a zone of cells lying along the central axis of the lobes, which differs in appearance from the adjacent tissues. Often this difference is noticeable as a band of differential coloration, as seen in this photo of a thallus lobe of Marchantia polymorpha.

In the simple thalloid liverwort, Metzgeria furcata (see previous image), the midrib literally stands out, as it is a number of cells in thickness while the rest of the thallus is only one cell thick. Whether this midrib is homologous with that of the complex liverworts, I don't know.



Obvious air chambers
  • Conocephalum conicum*
  • Conocephalum salebrosum*
  • Lunularia cruciata*
Conocephalum conicum Conocephalum conicum (Conocephalaceae)
Conocephalum conicum

Obvious air chambers

The central pore in each hexagonal air chamber in Conocephalum conicum plays a role similar to stomata, although it has no mechanism for closing the aperture to prevent water loss.

The complex thalloid liverworts differ from the simple thalloids in the development of layers of cells in the thallus with different roles. Conocephalum conicum has a hexagonal pattern of air chambers which contain a loose aggregate of cells specialised for photosynthesis. A central pore facilitates gas exchange while the chambers help retain moisture.



Gemmae at ends of lobes or on projecting columns
  • Blasia pusilla*
  • Metzgeria fruticulosa
  • Metzgeria furcata
Blasia pusilla Blasia pusilla (Blasiaceae)
Blasia pusilla

Gemmae on lobes

When viewed under magnification, the masses of gemmae on Blasia pusilla, supported on projections of the thallus, look quite amazing.

In Blasia pusilla, rounded masses of yellow gemmae are clumped together in what appears to be a gelatinous slime, and borne on projections rising from the thallus.



Gemmae in receptacles on thallus surface
  • Conocephalum conicum*
  • Conocephalum salebrosum*
  • Lunularia cruciata*
Lunularia cruciata Lunularia cruciata (Lunulariaceae)
Lunularia cruciata

Gemmae in receptacles

A close look in a crescent-shaped gemma cup on the top surface of Lunularia cruciata reveals many flying saucer-shaped gemmae.

The sharp-edged disk shape of the gemmae in Lunularia cruciata is shared by the gemmae of another complex thalloid liverwort, Marchantia polymorpha.

As the photo shows, gemmae can be green: they are presumably photosynthetic, and this would no doubt give a "kick-start" to each new plant developing from a gemma after dispersal.


Large antheridiophores / archegoniophores
  • Marchantia polymorpha
Marchantia sp. Marchantia sp. (Marchantiaceae)
Marchantia sp.

Archegoniophores

This patch of Marchantia bears spoked wheel-shaped archegoniophores. Embedded in the lower surface of the "spokes" are the archegonia where eggs are fertilised to produce the diploid sporophyte generation.

The antheridiophores and archegoniophores on complex thalloid liverworts such as Marchantia polymorpha are quite intricate structures, showing a high degree of differentiation of parts. This is a reminder that although liverworts were represented on Earth long before the vascular plants, it's somewhat simplistic to refer to them as "lower" plants.

    Thalloid plant body character table       View these data from a taxonomic viewpoint with notes on substrate and habitat
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Arrangement of the leaves
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Details of the leaves
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Summary
    The liverwort line
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