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Chapter 20: Nonvascular Plants (Characteristics of Nonvascular Plants…
Chapter 20: Nonvascular Plants
Characteristics of Nonvascular Plants
technically embryophytes that does not have vascular tissue
have multicellular sporangia & gametangia
3 types
moss
liverworts
hornworts
reproductive cells always surrounded by one/several layers of sterile cells
bodies comprised of true parenchyma from 3D growth
almost exclusively terrestrial
Classification of Nonvascular Plants
not known how closely related the 3 types of nonvascular plants are
many features in common, however;
they also differ in significant ways
Division Bryophyta:
Mosses
Gametophyte Generation
Morphology:
gametophytes:
leafy stems of moss plants
all moss stems have leaves, but not homologous with vasc. plant leaves
grow from apical meristem w/ prominent apical cell
leaves of almost all only one cell thick, except midrib/along margin
cuticle occurs only on upper surface of most moss leaves
underside uncutinized & capable of absorbing water directly
stems always slender w/ little tissue differentiation
surface layer only slightly different from underlying layers
not called epidermis
stem tissue maybe be uniform in all parts
(called cortex)
outer cells may be slightly narrower w/ thicker walls
inner cells larger, more parenchyma, chlorophyllous
in some types they grow close together & form mounds
in cool/wet areas plants are more open & loose
Water Transport:
hydroids:
innermost cortex in some mosses
conduct water & dissolved minerals
elongated cells that lose cytoplasm when mature
end walls partially digested
leptoids:
cells that resemble sieve cells
elongated, prominent interconnections w/ adjacent cells
lack nuclei at maturity, retain cytoplasm
majority of mosses lack hydroids & leptoids
water conducted along exterior of stems by capillary action
leaves & stems so small they form spaces narrow enough to be capillary channels
rhizoids:
small multicellular trichome-like structures at base of stem
only anchor stem, do not absorb water or minerals
lack chloroplasts
Development
growth of gametophyte begins when spore germinates/sends out long, slender chlorophyllous cell
cell undergoes mitosis & produces branched system of similar cells
entire network is a
protonema
superficially resembles filamentous green alga
perennial & can grow extensively
Reproduction
gametophore at some point produced gametangia
all mosses
oogamous
every species has small biflagellate sperm cells & large nonmotile egg cells
sperm cells produced in micorgametangia called
antheridia
consist of short stalk, outermost layer of sterile cell, inner mass of cells
when sperm cells mature, antheridium breaks open liberating sperm
either by contracting the outer cells or accumulating liquid below sperm & pushing them out
1 more item...
eggs occur in megagametangia called
archegonia
egg shaped like vase w/ long neck
neck hollow at maturity, single egg located at base
antheridia & archegonia occur in same gametophore in bisexual species
others have both male & female gametophores
Sporophyte Generation
zygote undergoes transverse division
basal cell located at bottom of archegonium develops into small bulbous tissue
(called the
foot
)
interface w/ gametophore
absorbs sugars, minerals, and water
cells are transfer cells in many species
upper cell grows by cell division & expansion into simple apical sporangium
(called the
capsule
)
consists of outer layer of sterile cells & inner column of sterile cells
called columella
ring of these cells undergoes meiosis & produces haploid spores
between food & sporangium is narrow stalk
(called the
seta
)
all moss sporophytes have this simple structures
none ever branched, nor has leave/bracts/buds
has true epidermis w/ stomata on base (at least) of sporangium
apex of sporangium differentiates into lid,
operculum
separates from rest of sporangium as cells are torn apart
develops 2 rows of
peristome teeth
teeth respond to humidity
bend outward to open when air dry
bend inward to trap spores when air humid
spores released when light, dry, nonsticky, & easily carried by air
apex also often covered by
calyptra
layer of cells derived from neck of archegonium
Division Hepatoohyta:
Liverworts
#liverwort zygote divides same as moss
Gametophyte Generation
2 basic groups
leafy liverworts
gametophore greatly resembles moss’s
leaves differ w/ two rounded lobe leaves
no midrib
no conducting tissue
may bear gametangia either mixed w/ regular leaves or positioned on side branches
thallose liverworts
less resemblance to moss
not leafy, flat/ribbon like/or heart shaped
body referred to as
”thallus”
antheridia & archegonia may be grouped & surrounded by tube of chlorophyllous cells
both groups gametophyte phase initiated when spores germinate
establish small temporary protonematal phase
protonemata never as extensive/ratified/long lived as mosses
gametophores may be either bisexual or unisexual
Sporophyte Generation
little variability
basic morphology like that of mosses
sporoganium lacks a columella
some cells differentiate into
elaters
single, elongate cells w/ spring-shaped walls
elaters uncoil when sporangium opens & pushes spores out
Division Anthocerotophyta:
Hornworts
#superficially resemble thalloid liverwort
approximately 100-150 named species
Gametophyte Generation
always thin, especially along edges
center becomes 4-5 cells thick
upper surface in many smooth, some thin
gametophyte is parenchymatous
does not tolerate drying
internally have numerous chambers
young plants mucilage chambers formed as cells break down & contents altered into mucilage
become invaded by cyanobacteria
antheridia initials not surface cells
special mucilage chamber forms near upper surface
cells lining chamber grow into it becoming antheridia
archegonia formed from superficial cells, do not completely surround egg
egg lies below short neck & canal surrounded by vegetative thallus cells
zygote divides longitudinally, not transversely
Sporophyte Generation
not similar to mosses or liverworts
have foot embedded in gametophyte tissue, no seta/discrete sporangium
above foot meristem continuously produces new sporangium tissue
sporangium long, horn-like cylinder
have columella
#have comulla like moss
