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Nonvascular Plants: Mosses, Liverworts, and Hornworts (Division Bryophyta:…
Nonvascular Plants: Mosses, Liverworts, and Hornworts
Characteristics and Classification of Non-vascular Plants
Characteristics
Technical: Embryophytes that do not have vascular tissue
Multicellular sporangia and gametangia
Bodies composed of true parenchyma, derived by 3D growth
Almost exclusively terrestrial, cuticle covering most of their body, and many stomata
Gametophyte is the larger, moreprominent generation. Sporophyte is smaller, more temporary.
Never grow to be really large, being small and simple provides great selective advantage
Classification
3 different divisions
Hepatophyta: Liverworts
Bryophyta: Mosses
Anthocerotophyta: Hornworts
Sometimes all three classes are referred to informally as bryophytes, but this is not technically correct.
Division Bryophyta: Mosses
Ubiquitous and Perennial
Gametophyte Generation
Morphology
Gametophores grow from an apical meristem that contains a prominent apical cell.
Leaves are aligned in three rows at least while young, and most have a midrib (costa)
Leaves are only one cell thick except at midrib and along margins
Cuticle occurs only on the upper surface of most moss leaves
No stomata occur on the leaves, because they would be useless
Moss stems are always slender and have little tissue differentiation
Leafy stems (gametophores) grow close together and form dense mounds. Some are looser than others, and some even grow in ribbons
Water Transport
Hydroids
Cells in the innermost cortex
Conduct water and dissolved minerals
Elongated cells, lose cytoplasm after maturation
Each hyroid is lined up one on top of the other
Leptoids
Resemble sieve cells
Elongated, interconnected with adjacent cells
Lack nuclei upon maturation with retention of cytoplasm
Majority of mosses lack hydroids and leptoids
Water is conducted along exterior of stems by capillary action
Sugar is moved simply between parenchyma cells by slow transport
Rhizoids
Small, multicellular trichome-like structures
Located at the base of the stem
Support, no absorption
Development
Growth of gametophore occurs via the creation of a protonema
Protoenmata are perennial and can grow extensively
Reproduction
All mosses are oogamous
Sperms are produced by antheridia
Eggs occur in archegonia
Gametaphore produce gametangia
The Sporophyte Generation
In all embryophytes, the megagamete are retained by the gametohpyte
https://www.khanacademy.org/science/biology/crash-course-bio-ecology/crash-course-biology-science/v/crash-course-biology-135
Key terms
Foot= interface with gametophore; absorption
Capsule= simple apical sporangium
Set: a narrow stalk in between the foot and sporangium
Operculum: apex of sporangium differentiates into a caplike lid, the operculum
Perisome teeth: rows of bueatiful, complex teeth created from the operculum
Calyptra: Apex of the sporangium in many species
Virtually all mosses are homosporous
Metabolism and Ecology
Small size and lack of conducting tissues are 2 critical factors in the metabolism and ecology of mosses
Compensatory mechanisms exist for the inability of mosses to retain water
Mosses exist in moist habitats or microhabitats
Mosses may grow on hard impervious surfaces
Mosses are important in the later establishment of other species
Division Hepatophyta: Liverworts
The Gametophyte Generation
2 Basic Groups: Leafy liverworts and Thallose liverworts
Gametophyte phase is initiated when spores germinate and establish a small, temporary protonematal phase
Gametophore of leafy liverworsts greatly resembles that of a moss