Bryophyta and Marchantiophyta: Non-Vascular Plants

• This learning guide focuses on non-vascular plant diversity, specifically Bryophyta and Marchantiophyta.
• After completing this lesson, you should be able to categorize plant taxa based on morphological and physiological differences.
• Another objective is to assess the validity of basing plant phylogeny on available molecular and morphological data.

Hook

• The story of Miguel and his grandmother Coco, who suffers from long-term memory loss and possibly Alzheimer's disease, is used as an analogy.
• Though there are interventions to slow the effects of Alzheimer's, there has never been a cure.
• Secondary metabolites unique to non-vascular plants have shown potential in treating Alzheimer's disease.

Ignite

• This lesson discusses the evolutionary relationship and diversification of embryophytes.
• Plants can be categorized into non-vascular plants (bryophytes), vascular cryptogams (seedless vascular plants), and spermatophytes (seed plants).
• Bryophytes were the first to evolve, with more terrestrial members giving rise to vascular embryophytes.
• Bryophytes are tiny, leafy land plants with a thallus (body lacking differentiation) predominantly attached to moist substrates, making them appear flat.
• They can inhabit diverse environments, from the Arctic circle to dry deserts.
• Bryophytes lack vascular tissues and their bodies are composed of parenchyma cells, usually from the apical meristem.
• Lacking seeds, they rely on spores for propagation.
• A spore is a haploid cell that undergoes mitotic division to become a mature individual.

Life Cycle

• Germinating spores produce a protonema with a large surface area for efficient water and mineral absorption, resulting in buds and tissue-producing meristems.
• Buds then generate gametophytes, which are anchored by rhizoids.
• Mature gametophytes have gametangia protected by a sterile jacket layer where male and female gametes are produced.
• Sperm cells swim from the antheridium to the archegonium guided by sucrose secretion.
• Fertilization occurs when sperm fuses with the egg in the venter
• The zygote remains in the archegonium and is nourished.
• Mitotic divisions generate a multicellular embryo, developing into a mature sporophyte.
• Nutrient transport between the sporophyte and gametophyte is facilitated by a placenta.
• The sporophyte of bryophytes is never independent and relatively smaller than the gametophyte.
• Different sporophyte structures mature into the calyptra, capsule (sporangium), and stalk (seta).
• Meiosis in the capsule produces genetically diverse haploid spores.
• A single sporangium can generate 50 million spores.
• The operculum breaks off to expose the peristome teeth once the air is dry to allow for wind dispersal of the spores.
• Sporopollenin walls enable spore survival during air dispersal.
• Once a spore settles on a suitable substrate, the heteromorphic cycle happens again.
• In addition to sexual reproduction, bryophytes undergo asexual reproduction through fragmentation.
• Marchantiophyta members commonly reproduce via gemmae formation.
• Bryophyte growth and function rely on the atmosphere and their immediate environment.
• Bryophytes are ideal model organisms for studying air pollution and climate change, and even eradicating major illnesses due to features adapted to aquatic habitats and early proliferation.

Three different lineages

• Mosses (Bryophyta)
• Liverworts (Marchantiophyta)
• Hornworts (Anthocerophyta)

Phylum Bryophyta

• Members are collectively known as mosses with 13,000 known species found worldwide, but largely in tropical regions.
• Conspicuous leafy stems of mosses (gametophores) are tightly pressed together to form a mound, though some are loosely packed, especially in wet habitats.
• Moss leaves are not homologous to vascular plant leaves, evolving from a common structure and are gametophyte parts, not sporophyte parts.
• Several mosses and hornworts have stomata in their sporangia to regulate gas exchange and water uptake.
• Elongate, aerial sporophyte axis of mosses and hornworts may have preceded vascular plant sporophytic stems.
• Most moss leaves have cuticles only on their upper surface, allowing direct water absorption through the underside, but increasing desiccation when dry.
• Mosses have autapomorphies including conductive cells called hydroids (for water conduction) and leptoids (for sugar conduction), a thick spore outer layer (perine layer) for protection and desiccation prevention, and leaves with a central midrib costa resembling a vein.
• In 2000, Buck and Goffinet identified 6 moss classes: Takakiopsida, Sphagnopsida, Andreaeopsida, Andreaeobryopsida, Polytrichopsida, and Bryopsida.
• The most common mosses are peat mosses (Sphagnopsida), granite mosses (Andreaeopsida), and true mosses (Bryopsida).
• Sphagnum or peat moss has a distinct sporophyte with a red to blackish brown, almost spherical capsule, and is a known epiphyte in wetlands.
• It has high water-holding capacity and cell walls contain decay-resistant phenolic compounds and antiseptic properties.
• Granite mosses of Andreaeopsida are brittle, short, blackish, or reddish, growing on granite rocks in cool climates, and disperse spores through slits.
• True mosses compose the largest and most diverse Bryophyta class and have an operculum containing peristome teeth in the sporophyte capsule.
• In the Philippines, medicinal mosses are utilized for healing burns and wounds, treating colds and cardiovascular problems, as diuretics, and as a poultice to heal broken bones.

Phylum Marchantiophyta

• By tradition, it was named Hepaticae but more recently referred to as Hepatophyta.
• Major classes under this phylum: Marchantiopsida and Jungermanniopsida (Glime, 2017).
• There are roughly 5,200 species found around all the continents.
• They tolerate repeated dry and wet seasons, allowing them to exploit epiphytic substrates.
• Differs from other two Bryophyte lineages because:
  • They have a flattened appearance
  • They have thin-walled unicellular rhizoids
  • Their leafy and thalloid forms develop associations with fungi
  • The sporophyte is enclosed within gametophytic tissues
  • Their inoperculate capsules lack stomata and cuticles common in the other two.
• Liverworts have other apomorphies like distinctive oil bodies and elaters inside their capsules.
• Elaters are non-sporogenous cells with spiral wall thickenings that are hygroscopic and aid spore dispersal.
• Lack of elaters in some thalloid members.
• The liverwort life cycle includes a protonema that produces a bud which eventually develops into either a thallose or a leafy gametophyte.
• Thallose liverworts have thick thalli with pores.
• They also have pronounced gametophores that contain their gametes: the archegoniophore is the female sex organ and the antheridiophore as the male sex organ (Glime, 2017).
• They have gemma cups with propagules/gemmae.
• Leafy liverworts resemble moss, and typically lack the thick thallus and pores.
• Pores are not stomata since these lack guard cells.
• Marchantia is used as a medicinal plant in the Philippines to heal boils and abscesses.