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Chapter 20: Nonvascular Plants: Mosses, Liverworts, and Hornworts…
Chapter 20: Nonvascular Plants: Mosses, Liverworts, and Hornworts
Characters of Nonvascular Plants
Spanish moss of the southeastern United States is the flowering plant Tilandsia usneoides
Club mosses are lycophytes, not mosses, and the slimy, bright green "mosses" of ponds and slow-moving streams are green algae, usually Spirogyra
Hornworts
Is relatively unfamiliar, even to most botanists
All mosses and liverworts have leafy stems that look remarkably like small versions of flowering plants
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Nonvascular plants are almost exclusively terrestrial and have a cuticle over much of their bodies, and many have stomata
Most people are at least somewhat familiar with nonvascular plants because mosses are well known, and many people have heard of liverworts
Like all plants, nonvascular plants have a life cycle with an alteration of heteromorphic generations
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Nonvascular plants can never grow to be really large, but being small and simple provides great selective advantage in certain habitats
The tiny parenchymatous bodies of mosses and liverworts permit them to thrive in microhabitats such as
Fences
Bare Rock
Stone Walls
Classification of Nonvascular Plants
They are often treated as three distinct divisions
Division Bryophyta
Mosses
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Division Anthocerotophyta
Hornworts
Division Hepatophyta
Liverworts
In the past, all three were grouped together
In Division Brophyta
They have many features in common but also differ in many respects
It is not known how closely related mosses, liverworts and hornworts are
Division Bryophyta: Mosses
The Gametophyte Generation
Morphology
Moss stems are always slender and have little tissue differentiation
Water Transport
Leptoids
Cells that resemble sieve cells
Rhizoids
At the base of the stem are rhizoids, small multicellular trichome-like structures
They are elongated cells that lose their cytoplasm when mature
Development
Growth of the gametophytes begins when a spore germinates and sends out a long, slender chlorophyllous cell
In some mosses, primarily the family Polytrichaceae, the innermost cortex is composed of cells called
Hybroids
Reproduction
Gametophores
Of many mosses grow closely together
Tightly appressed and forming dense mounds
Grimmia, Pohlia
Leafy stems
Moss gametophores grow from an apical meristem that contains a prominent apical cell
Leaves of almost all mosses are only one cell thick except at the midrib and along the margin
Mosses
Are ubiquitous, occurring in all parts of the world and in almost every environment
They are perennial and thrive in many places within cities
Tortula on walls
Mnium on soil
