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Nonvascular Plants: Mosses, Liverworts, and Hornworts (The Sporophyte…
Nonvascular Plants: Mosses, Liverworts, and Hornworts
Concepts
Plants are divided into either
Nonvascular plants
Have neither vascular tissue nor seeds
Arose first
Vascular cryptogams
Have vascular tissue but no seeds
Strengthening material known as xylem evolved
Good at conducting water
Phloem permitted roots to extend deep into the dark soil
Vascular tissue made feasible the evolution of truly heterotrophic tissues
Spermatophytes
Have both vascular tissue and seeds
Characteristics of Nonvascular plants
A well known vascular plant is moss
Have a life cycle with an alternation of heterotrophic generations
Sporophyte and gametophyte differ from each other structurally
Nonvascular plants can never grow to be really large
Are embryophytes that don't have vascular tissue
Have multicellular sporangia and gametangia
reproductive cells are always surrounded by one or several layers of sterile cells
Bodies are composed of true parenchyma derived by 3D growth
Usually from apical meristems
All mosses and many liverworts have leafy stems that look like small flowering plants
Classification
Often treated as three distinct divisions
Liverworts
Division Hepatophyta
Small plants that have an alternation of heteromorphic generations
Hepatic gametophytes are divided into two basic groups
Leafy liverworts
Thallose liverworts
Thallus
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Air pores
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Mosses
Division Bryophyta
Ubiquitous, occurring in all parts of the world
All moss stems have leaves
Are always slender and have little tissue differenation
Inner most cortex is composed of cells called hydroids
Conduct water and dissolve material
Species typically have leptoids as well
Resemble sieve cells
Rhizoids
Small, multicellular trichome-like structures that penetrate the surface of the substrate
Development
Protonema
Reproduction
All mosses are oogamous
Sperms are produced in microgametangia called antheridia
Consists of a short stalk, an outermost layer of sterile cells, and an inner mass of cells that differentiate into sperm cells
Eggs occur in megagametangia called archegonia
Each is shaped like a vase with a long neck
Hornworts
Division Anthocerotae
Inconspicuous thalloid plants that grow on moist soil, hidden by grasses and other herbs
Superficially resemble thalloid lverworts
The Sporophyte Generation
Foot
The foot is the interface with the gametophore
Absorbs sugar, minerals, and water
Capsule
Consisting of an outer layer of sterile cells and an inner column of sterile cells
Seta
Narrow stalk between the foot and the sporangium
Operculum
Separates from the rest of the sporangium as cells are torn apart
Peristome teeth
Cell breakage is elaborate and precise, resulting in one or two rows of beautiful, exquisitely complex teeth
Calyptra
A layer of cells derived from the neck of the archegonium
