NONVASCULAR
AND
SEEDLESS
VASCULAR
PLANTS
The earliest plants grew in
areas like the coastal mud
flats of the Devonian (410
million years ago):
The non-vascular :
Moss (1)
alongside vascular :
Cooksonia (2), Rhynia (3),
Zosterophyllum (4),
Drepanophycus (5).
The beginning of the
Carboniferous had a
more uniform, tropical,
and humid climate
throughout the year than
exists today. Seasons, if
any, were indistinct. The
number of plants during
the Carboniferous
became more numerous.
Vascular plants began to
dominate the landscape
and gymnosperm-like
plants began to appear.
Angiosperms would
appear much later.
Early Vascular Plants
a. Evolved from Charophytes, a group of green algae
b. Cooksonia oldest vascular plant fossil ; Rhynia
c. Late Silurian (414 - 408 million years BP)
d. No roots or leaves
e. Vascular plants dominated by the Devonian (408 - 362
million BP)
Plant Adaptations
a. Development of a 1) vascular system: xylem and phloem,
2) ground tissues: comprise the main plant body, and 3)
dermal tissue: provide protective covering to plants
b. Developed a waxy cuticle
c. Upright growth habit; lignin (for structure and conduction)
and cellulose
d. Stomata for gas exchange (O2, CO2, H2O)
e. Sex organs are multicellular gametangia
f. Fertilization of egg develops into an embryo
g. Roots evolved from underground stems
Four Major Groups of Plants and Their Respective Phyla
Bryophytes- nonvascular; reproduce via spores, seedless plants; includes the mosses, liverworts, and hornworts
Phylum Bryophyta (Mosses)
Phylum Hepaticophyta (Liverworts)
Phylum Anthocerophyta (Hornworts)
Seedless Vascular Plants- vascular plants which are seedless, use spores in reproduction; includes the
ferns and fern allies
Phylum Psilophyta (Whisk ferns)
Phylum Lycopodophyta (Club Mosses)
Phylum Sphenophyta (Horsetails)
Phylum Pterophyta (Ferns)
Gymnosperms- vascular, naked seed producing plants; includes conifers, cypress, cedars, cycads, etc.
Phylum Cycadophyta (Cycads)
Phylum Ginkgophyta (Ginkgo)
Phylum Coniferophyta (Conifers)
Phylum Gnetophyta (Welwitschia)
Angiosperms- vascular plants, producing protected seed; includes all flowering plants
Phylum Anthophyta (Flowering plants)
Class Dicotyledones
Class Monocotyledones
Class Magnoliids
Bryophytes- nonvascular; reproduce via spores, seedless
plants; includes the mosses, liverworts, and hornworts
Phylum Anthocerophyta (Hornworts)
Phylum Hepaticophyta (Liverworts)
Phylum Bryophyta (Mosses)
It is now widely accepted (from morphological and molecular work)
that a group of green algae called the charophytes represent the sister
group to land plants.
Homosporousone spore type
produced and
released)
Hetrosporoustwo spore types
produced one
developing into a
male gametophyte,
the other into a
female
gametophyte
Sporophyte
Gametophyte
All plants have alternation
of generations. There is an
evolutionary trend from a
dominant autotrophic (selffeeding) gametophyte and a
nutritionally dependent
sporophyte to a dependent
gametophyte and a dominant
autotrophic sporophyte. This
is exemplified by exploring
the life cycles of a moss, a
fern, and an angiosperm.
Bryophytes- (9000 Mosses), (6000 Liverworts)
and (100 Hornworts)
a. Have no conductive tissues, thus no way to efficiently assimilate
photosynthates or minerals; since they are reliant on diffusion, they are
typically very small
b. Three distinctive phyla
c. Absorptive structures called rhizoids; “leaflike” blades/leaves
d. Typically separate male and female gametophytic plants; sperm
must swim through a thin film of water to fertilize the egg; a diploid
zygote forms and grows into a mature moss sporophyte; spores will
be released from the sporophyte and will germinate to form a
protonema which further develops into the gametophyte
e. The gametophytic generation is the dominant form of the life
cycle
f. Liverworts may exhibit a leafy morphology or a thalloid (thallus) body
form; some reproduce asexually using gemmae cups containing gemma
Life cycle of a moss. The
sporophyte generation is
dependent on the photosynthetic
gametophyte for nutrition. Cells
within the micro- and
megasporangia undergo meiosis to
produce male and female spores,
respectively. These spores divide
mitotically to produce multicellular
male and female gametophytes.
Differentiation of the growing tip of
the gametophyte produces
antheridia in males and archegonia
in females. The sperm and egg are
produced in the antheridia and
archegonia, respectively. Sperm are
carried to the archegonia in water
droplets. After fertilization, the
sporophyte generation develops in
the archegonium and remains
attached.
Seedless Vascular Plants (11,000 Ferns),
(Club Mosses 1,000), (Horsetails 15) and
(Whisk Ferns 12)
Seedless Vascular Plants- plants which have
distinct tissues for conducting water and nutrients
throughout the plant; use spores for reproduction
instead of seeds; there are four phyla of SVP
1. Phylum Psilophyta (Whisk ferns)
2. Phylum Lycopodophyta (Club Mosses)
3. Phylum Sphenophyta (Horsetails)
4. Phylum Pterophyta (Ferns)
Whisk Ferns
A. Exhibits a dichotomous branching pattern
B. Stems are the main photosynthetic organ
C. Most are extinct; very primitive vascular plant
Club Mosses
A. Once dominant plants in the landscape, 300my ago
B. Strobilus are present to bear spores
C. Some are homosporous, some are heterosporous; If
heterosporous, male microspores (n) will be produced along
with female megaspores (n); once shed, these spores will
develop into male and female gametophytes which will produce
sperm and egg respectively; when the egg is fertilized a
sporophyte (2n) will form; within the strobilus spores form and
the process repeats
Horsetails
A. Once dominant plants in the landscape,
300my ago
B. True roots, stems and small leaves
(reduced megaphylls); hollow jointed
stems impregnated with silica; green stem
main photosynthesizing part
C. Reproductive branches bear a terminal
cone-like strobilus
D. Life cycle is similar to fern life cycle;
also requires water
Ferns
a. Conductive tissues present; xylem and phloem!! Thus may be larger,
and allowed for true leaf evolution!
b. Two Basic Leaf Types: 1) Microphyll- possess a single vascular
strand and are typically small and 2) Megaphyll- possess more than one
vascular strand and are typically larger than microphylls; webbing effect
seen
c. Sporophyte is the dominant generation! Consists of roots,
rhizomes and fronds; fiddleheads are young fronds; sori appear on the
fronds and house spores
d. Spores (n) germinate into a prothallus (n) which will produce eggs (n)
in the archegonium and sperm (n) in the antheridium; they combine to
form a zygote (2n); the zygote grows into a young sporophyte (2n); the
mauture sporophyte of most ferns produce only one type of spore
(homosporous- one spore type produced and released); some are
hetrosporous, that is they produce two spore types, one developing
into a male gametophyte, the other into a female gametophyte
Water is required for the sperm to use as a medium to swim to the egg
Life cycle of a fern. The
sporophyte generation is
photosynthetic and is
independent of the
gametophyte. Meiosis of the
tissue within the sporangia
yields a haploid spore that
divides to produce a heartshaped gametophyte that
differentiates both
archegonia and antheridia
on one individual. The
gametophyte is
photosynthetic and
independent, although it is
reduced in size relative to the
sporophyte. Fertilization
takes place when water is
available for sperm to swim
to the archegonia and
fertilize the eggs.
The Sporophyte
continues to
grow while the
Gametophyte
dies.