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Nonvascular Plants: Mosses, Liverworts, and Hornwarts (Characters of…
Nonvascular Plants: Mosses, Liverworts, and Hornwarts
Characters of nonvascular plants
Mostly well know
mosses
leafy stems look remarkably like flowering plants
liverworts
relatively unfamiliar
hornworts
nonvascular plants are not
spanish moss (flowering)
pineapple
club mosses
lycophytes
slimy, bright green mosses of ponds
several types of lichens
embryophytes: multicellular sporangia and gametangia
reproductive cells always surrounded by layer(s) of sterile cells
bodies are true parenchyma cells
have a lifecycle with an alternation of heteromorphic generations
sporophyte and gametophyte differ structurally
sporophytes large plants with leaves and roots
smaller, more temporary inconspicuous generation
absorb minerals
gametophytes are tiny and occur inside pollen grains and ovules
larger, more prominent generation
sporophytes
cannot grow to be large
tiny bodies permit them to thrive in microhabitats
microhabitats
little water or for the larger, more complex
Classification of nonvascular plants
not known how closely related mosses, liverworts, and hornwarts are
all groups called nonvascular plants
Often treated as three distinct divisions
Division bryophyta: mosses
The gametophyte generation
mosses are ubiquitous, occurring in all parts of the world
Perennial and thrive in many places within cities
Morphology
leafy stems, known as gametophores
grow close together
form dense mounds
grow from an apical meristem
cool wet areas
more open and loose
all moss stems
have leaves
these leaves not homologous to vascular leaves
leaf have cuticles
Water transport
hydroids
innermost cortex cells
elongates cells
leptoids
resemble sieve cells
elongate
prominent interactions
Rhizoids
small, multicellular trichome-like
anchor the stem
Development
spore germinates
sends out a long, slender chlorophyllous cell
protonema
branched system of similar cells
Reproduction
antherridia
short stalk
outermost layer or sterile cells
produce sperms
mature sperm cells break open antheridium
sperm goes down the tube to the eggs
archegonia
shaped like a vase with long neck
produce eggs
neck hollow at maturity
the Sporophyte generation
megagamete and zygote retained by gametophyte
megagametophytes of vascular plants are small
zygote undergoes transverse division
basal cell develops into foot
upper cell grows into a capsule
into a simple apical sporangium
between foot and sporangium is the seta
seta is a narrow stalk
metabolism and ecology
vascular plants tend to be large
bulk protects them from short term fluctuations
Large plants
trees and succulents
withstand dry conditions for long times
moss gametophores
thin incomplete cuticle
plant drys out after a few minutes
Division hepatophyta: Liverworts
Gametophyte generation
leafy liverworts
gametophyte phase starts when spores germinate
gametophore leaves resembles a moss leaves
thin leaves on a slender stem
thallose liverworts
show less resemblence to mosses
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flat and ribbon like
body is sometimes referred to as thallus
antheridiophore
umbrella shaped outgrowth
has a stalk several mm tall
dozens of antheridia
Sporophyte generation
little variability
morphology much like mosses
two groups distinct in structure
sporophyte has foot, seta, and calyptra-covered sporangium
sporangium
outer layer of sterile cells is much thinner
often one one cell thick
some cells differentiate into elaters
