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
Early Ordovician (Retallack 2019)- present
Above: Life cycle of a liverwort
Above: the Hepaticae from Ernst Haeckel
Additional Resources
"Ghostworts": Parasitic liverworts (In Defense of Plants, Jan 2018)
Time-lapse of liverwort growth (YouTube Sep 2017)
The Fascinating World of Liverworts (In Defense of Plants, May 2016)
Proto-Carnivorous liverworts? (In Defense of Plants, Jan. 2016)