Plant Kingdom: Embryophytes

Unique Features of Plant Kingdom (Embryophytes)

• Plants exhibit multi-cellularity
• Plants have alternation of generations, featuring both gametophyte and sporophyte stages as multicellular entities
• Plant embryos are retained within the archegonium and nourished by the gametophyte
• Spores are walled with sporopollenin for desiccation resistance
• Plants have multicellular gametangia: antheridia for sperm and archegonia for eggs
• Apical meristems are regions of active cell division
• A cuticle is present as a waxy layer to reduce water loss
• Stomata, except in some liverworts, are pores for gas exchange

Primitive vs. Advanced Characteristics in Plants

• Primitive plants feature a gametophyte-dominant lifecycle, lack vascular tissue, depend on water for reproduction, and have thalloid or leafy structures without true roots, stems, or leaves
• Advanced plants have a sporophyte-dominant lifecycle, developed vascular tissue like xylem and phloem, and true roots, stems, and leaves (seen in SVPs)

Bryophytes Overview

• Bryophytes are non-vascular, gametophyte-dominant plants
• Bryophytes thrive in moist terrestrial habitats
• Water is essential for fertilization in bryophytes
• Rhizoids in bryophytes provide anchorage but not absorption

Bryophyte Phyla

• Anthocerotophyta includes hornworts
• Marchantiophyta includes liverworts
• Bryophyta includes mosses

Common Traits of Bryophytes

• Bryophytes have thalloid or leafy gametophytes
• Sporophytes are dependent on gametophytes
• Spore dispersal happens from sporangia

Key Bryophyte Terms

• Antheridia are male gametangia that produce sperm
• Antheridiophore is a structure bearing antheridia, especially in liverworts
• Archegonia are female gametangia that produce eggs
• Archegoniophore is a liverwort structure bearing archegonia
• Bryophytes is a collective term for mosses, liverworts, and hornworts
• Calyptra is a cap-like archegonium remnant covering a moss capsule
• Capsule is the spore-producing part of the sporophyte
• Elaters are hygroscopic cells that help spore dispersal in liverworts
• Embryo is a young sporophyte retained in the gametophyte
• Gametangia refers to structures that produce gametes, such as antheridia or archegonia
• Gemmae are asexual reproductive propagules
• Hornworts are thalloid gametophytes with horn-like sporophytes
• Hydroid/Leptoid are conducting cells in mosses that transport water/sugar
• Liverworts showcase thalloid or leafy gametophytes without stomata
• Mosses have leafy gametophytes, often with stomata and an operculum
• Operculum is the lid of a moss capsule
• Paraphyses are sterile hairs among sex organs
• Peristome refers to teeth-like structures that aid moss spore dispersal
• Protonema is the first filamentous stage of a moss gametophyte
• Rhizoid refers to anchoring filaments of a gametophyte
• Seta is the stalk of a sporophyte
• Sporocyte is a diploid cell undergoing meiosis to form spores
• Sporophyte is the diploid spore-producing generation
• Thalli refers to the plant body in thalloid bryophytes
• Thalloid describes a flat, undifferentiated plant body
• Venter is the basal part of an archegonium enclosing an egg

Alternation of Generations in Bryophytes

• A spore (n) germinates and grows into a gametophyte (n)
• Antheridia and archegonia form; sperm swims to the egg, leading to fertilization
• The zygote (2n) is retained in the archegonium and becomes an embryo, then a sporophyte (2n)
• The sporophyte grows from the gametophyte and produces spores through meiosis
• Spores are dispersed, leading to new gametophytes

Ecological & Human Importance of Bryophytes

• Sphagnum (peat moss) helps with water retention and soil amendment, and serves as fuel.
• Sphagnum acidifies the environment and preserves organic material
• Bryophytes are pioneer species in primary succession
• Bryophytes serve as bioindicators of air quality
• Bryophytes have cultural uses, such as packing material and wound dressing

Liverworts Details

• Liverworts are either leafy or thalloid
• Gemmae cups present for asexual reproduction
• Liverworts have no stomata, only pores
• The seta elongates after the capsule matures
• Elaters inside the capsule aid spore dispersal

Mosses Details

• Mosses are always leafy
• The moss capsule features an operculum and peristome
• Rhizoids are multicellular in the mosses
• Some moss species possess hydroids and leptoids
• The protonema stage is unique to mosses

Hornworts Details

• Hornworts are always thalloid
• There is a single large chloroplast per cell
• A columella is in the capsule
• Stomata are on the sporophyte
• The sporophyte is photosynthetic and can grow independently