Liverworts

Phylum Marchantiophyta

Liverworts are non-vascular and spore-bearing plants like other bryophytes. Some liverworts are thalloid, appearing flat and green, with a superficial appearance to kelp-like algae. This group also independently evolved leaves, which are called leafy liverworts. The name "liverwort" derives from the old Anglo-Saxon word "lifer", meaning liver and "wyrt", the Anglo-Saxon word for plant. The Doctrine of Signatures, a popular concept at the time, proclaimed that each plant had a mark or sign that pointed to its medicinal value, The liver-shaped lobes were believed to be useful for the treatment of liver ailments... they are not.

Gametophyte (=gamete-forming phase)

Vegetative features

  • Dominant, free-living generation, and photosynthetic phase

    • Chloroplasts are small and many (like mosses, unlike hornworts)

Stems

  • Thalloid liverworts have a "stem" that is flattened and algae-like

  • Leafy liverworts have a more cylindrical stem with leaves attached in two rows

Leaves

  • Leafy and thalloid forms exist (leafy more common than thalloid)

    • Thalloid liverworts look very algae-like (=thalloid), and there is no distinction between leaf and stem

    • Leafy liverworts have a two rows of small leaves on the ventral surface

  • No stomata in liverworts, but the complex thalloid liverworts have open pores (lack guard cells)

"Roots"

  • No true roots, but they have root-like rhizoids

  • Do not possess vascular tissue

  • Anchor plant, and may absorb small amts of water

  • Unicellular and clear in appearance (compare to the multicellular and brown rhizoids of mosses)

Above: a thalloid liverwort

Above: a leafy liverwort, Scapania

Reproductive Features

Asexual reproduction

  • Some have the ability to asexually reproduce

    • Possess gemmae, which are pieces of tissue in a cup-like structure

Sexual reproduction

  • Antheridia and archegonia emergent / visible from the body (like mosses, unlike hornworts)

  • Thalloid liverworts sometimes bear antheridia and archegonia on raised branches (e.g., Marchantia).

    • The egg-producing archegonia are formed in between finger-like projections on a long stalk, called archegoniophores (see image below)

    • The sperm-producing antheridia are formed on the underside of umbrella-like structures called antheridiophores (see image below)

Above: Gemmae cups on a liverwort

Above: Archegoniophores of a thalloid female liverwort

Above: Antheridiophores of a thalloid male liverwort

Sporophyte (=spore-forming phase)

  • Epiphytic and dependent on the gametophyte for nutrition

  • The sporophyte is basically a sporangium on a stalk

  • Sporophyte has determinate growth

  • Seta (stalk) is very short and clear; elongated prior to spore release

  • Special cells called elaters are present in the sporangium to help with spore dispersal

Diversity

Phylum Marchantiophyta or Hepatophyta or Jungermanniophyta

  • 3 classes, 15 orders, 85 families, 9,000 species

Haplomitriopsida

  • Leafy liverworts, consider basal in the Marchantiophyta clade

  • 2 orders, 2 families, 3 extant genera (Haplomitrium, Treubia, and Apotreubia)

Marchantiopsida

  • Thalloid liverworts

  • 5 orders, 20 extant families

Jungermanniopsida

  • Leafy liverworts

  • 8 orders, 65 families

Geologic Age

Above: Life cycle of a liverwort

Above: the Hepaticae from Ernst Haeckel

Additional Resources