1. Seedless Vascular plants
Lecture #5
Plant Diversity I:
Non-vascular plants
&
Seedless Vascular plants

2. 1.2 billion years ago (BYA) – appearance of cyanobacteria on land
500 million years ago (MYA) – appearance of plants, fungi and animals
more than 290,000 known plant species today
plants inhabit all but the harshest environments
such as some mountaintops, deserts areas and polar regions
many plants have returned to their aquatic “roots”
e.g. some species of sea grasses
most present-day plants are terrestrial
presence of plants has enabled other life forms to survive on land
through their production of O2

3. Plants and Algae evolution of plants proposed from algae
(Opisthokonta)
(Viridiplantae)
Rhodophyta
Plants
Chlorophytes
Charophyceans
Red algae
Metazoans
Fungi
Choanoflagellates
Archaeplastida
Animalia
Chlorophyta
Plantae
Charophyta
Unikonta
Ancestral eukaryote
evolution of plants proposed from algae
closest relatives are located with the clade Charaophycea
these share a common ancestor with the clade Chlorophyta – include the green algae
similarities with algae:
multicellular
photosynthetic autotrophs
cell walls with cellulose
chlorophylls a and b

4. 4 key traits of plants Rosettes
four key traits of plants (and charophyceans)
provided by not only morphologic evidence but genetic evidence
1. rose-shaped complexes for cellulose synthesis – both charophyceans and land plants have rosette cellulose-synthesizing complexes
protein arrays found in the plasma membrane that synthesize cellulose microfibrils of the cell wall
plants and charophyceans have a higher percentage of cellulose in their cell walls than the chlorophytans
2. peroxisome enzymes – peroxisomes have enzymes that help minimize the loss of organic production as a result of photorespiration
3. flagellated sperm structure – similar to the charophyceans
4. formation of a phragmoplast – group of microtubules that forms between the daughter nuclei of the dividing plant cell during mitosis
synthesis of a new cell plate occures - divides the two daughter cells
Rosettes

5. Adaptations by Land plants
advantages of terrestrial life:
stronger exposure to sunlight for photosynthesis
atmosphere offered more CO2 for photosynthesis
soil rich in nutrients
initially relatively few herbivores
movement onto land would require protection of the zygote from drying out
development of layer of durable polymer called sporopellenin – prevents exposed zygote from dessication
movement onto land resulted in the development of adaptations– facilitated survival and reproduction on land
e.g. development of a structural system to withstand the forces of gravity
e.g. changes adapting to the relative scarcity of water
these adaptations have defined the plant kingdom
but what adaptations are unique to plants?
depends on how you draw the boundary separating plants from algae
some traits related to terrestrial life
for the earliest land plants – mycorrhizal associations with fungi for nutrient absorption
epidermis with a waxy covering called a cuticle
production of secondary compounds that are products of secondary metabolic pathways
primary metabolic paths produce lipids, carbohydrates, amino acids – not unique to plants
secondary paths produce compounds such as tannins, terpenes and alkaloids (defense against herbivores and parasites), plus phenolics (flavonoids – absorb UV radiation, deter attacks by pathogenic microbes)

6. ** plants can be divided into 2 major categories non-vascular
Kingdom Plantae contains the plants called embryophytes – plants with embryos
however, current debate advises some changes – 2 options:
Kingdom Streptophytae – Embryophytes (land plates) + Charophyceans OR
Kingdom Viridiplantae – Embryophytes + Charophyceans + Chlorophytes
botanists do not use the term phyla when classifying the plant kingdom – use divisions
currently accepted organization: development of two lineages or divisions: non-vascular and vascular (390 MYA) – called the Bryophyta and Tracheophyta
vascular lineage developed into the seedless vascular and seed vascular plants (360 MYA)
seed vascular plants developed into the gymnosperms and angiosperms (130 MYA)
Viridiplantae
Streptophyta
Plantae
Red algae
Chlorophytes
Charophyceans
Embryophytes
Ancestral alga
** plants can be divided into 2
major categories
non-vascular
vascular – subdivided into 2
more categories:
seedless
seed

7. Land plants: characteristics
4 key derived traits found in plants:
1. alternation of generations & multicellular, dependent embryos
2. walled spores produced in sporangia
3. multicellular gametangia
4. apical meristems

8. Land plants: 4 characteristics
1. alternation of generations: alternation between multicellular haploid and diploid stages in a life cycle
seen also in some chlorophytans – but not in the charophyceans
must be multicellular!!
alternates between the gametophyte (haploid) and sporophyte (diploid)
diploid sporophyte (mature plant) produces haploid spores via meiosis
mitotic division of the haploid spore produces a multicellular gametophyte (reproductive organ) which is still haploid!!
the gametophyte produces haploid gametes by mitosis
gametes fuse via syngamy to produce the zygote
zygote grows via mitosis to develop a new sporophyte
in ferns (non-vascular plants) – the sporophyte and gametophyte have distinct phenotypic appearances – but they are forms of the same species
in vascular plants – the gametophyte is microscopic
Mitosis
Spores
Zygote
Gametes
Haploid multicellular
organism (gametophyte)
Diploid multicellular
organism (sporophyte)
MEIOSIS
FERTILIZATION
-sporophytes – multicellular, diploid, produce spores via meiosis
-gametophytes – multicellular, haploid, produce gametes via mitosis

9. maternal tissue provides nutrients embryos are called embryophytes
1. Alternation of generations and multicellular dependent embryos cont….
in a life cycle with alternation of generations – the multicellular embryos develop from zygotes retained within the female gametophyte
maternal tissue provides nutrients
embryos are called embryophytes
embryo receives nutrition during development from placental transfer cells
development of elaborate ingrowths of the plasma membrane and cell wall of the embryo
lined with transfer cells
enhance the transfer of nutrients from parent to embryo
analogous to the placental relationship to the mather in eutherian animals
Multicellular,
Dependent Embryos
Maternal
tissue
Embryo
2 µm
10 µm
Wall
ingrowths
Placental
transfer
cell (blue line)

10. Land plants: 4 characteristics
3. walled spores in sporangia
developing within the diploid sporophyte are multicellular organs called sporangia (singular = sporangium) – production of haploid spores via meiosis
within a sporangium are diploid cells called sporocytes or spore mother cells – undergo meiosis to generate the haploid spores of the sporangium
the spores are protected by sporoporellin – key adaptation to terrestrial life
4. multicellular gametogangia
the haploid gametophyte undergoes production of gametes within multicellular gametogania (singular = gametoganium)
the production of gametes is through mitotic division
female gametogania = archegonium - produces a single egg
male gametogania = antheridium – produces many flagellated sperm
Walled Spores
Produced in Sporangia
Multicellular
Gametangia
Longitudinal section of
Sphagnum sporangium (LM)
Spores
Sporangium
Sporophyte
Gametophyte
Sporophyte and sporangium
of Sphagnum (a moss)
Archegonia and antheridia
of Marchantia (a liverwort)
Male gametophyte
Antheridium
with sperm
Female gametophyte
Archegonium
with egg

11. Land plants: characteristics
4. apical meristems
light and CO2 are available above ground, water and minerals are found mainly in the soil
must be a way of collecting these components
plants do this by growing in length – through the production of stems and roots
apical meristem – localized regions of cell division located at the tips of shoots and roots
e.g. shoot apical meristem – cells divide by mitosis and cytokinesis to produce progenitor cells for the rest of the stem
progenitor cells are the source for the tissues of the stem and root:
protoderm (epidermis, cork),
provascular tissue (xylem and phloem, vascular cambium)
ground meristem (pith and cortex)
Apical
Meristem
of shoot
Developing
leaves
Shoot
Root

12. Plant Diversification
plant fossils dating back to 475 MYA
one major way to distinguish groups of plants is to classify them as: vascular & non-vascular
vascular tissue – extensive system formed by cells joined into tubes
conduct water and nutrients
those without these tubes – non-vascular plants
bryophytes: term used to refer to all non-vascular plants
do not form a monophyletic group or clade
known popularly as the mosses, liverworts and hornworts
debate as to how they are related to each other
don’t possess the advanced adaptations of vascular plants (e.g. roots & leaves)
they do share many characteristic with vascular plants – see the slide on plant characteristics
vascular plants: clade that includes 93% of all surviving plant species
categorized into smaller clades:
1. lycophytes – club mosses
2. pteryophytes – ferns
3. gymnosperms
4. angiosperms

13. Seedless vascular plants Origin of vascular plants
Land plants
Vascular plants
Bryophytes
Seedless vascular plants
Seed plants
Gymno-
sperms
Angio-
sperms
Liverworts
Hornworts
Mosses
Lycophytes
Pterophytes
Charophyceans
Origin of seed plants
(about 360 mya)
Origin of vascular plants
(about 420 mya)
Origin of land plants
(about 475 mya)
Ancestral
green alga

14. Non-vascular plants commonly known as the bryophytes three phyla –
even though Bryophyta is one of the 3 phyla in this group
three phyla –
1. Phylum Hepatophyta: liverworts
gametophytes are flattened into a thalloid or a leafy shape
2. Phylum Anthocerophyta – hornworts
sporophyte can grow quite tall – sporangium along the length
3. Phylum Bryophyta – mosses
mosses are not to be confused with the vascular mosses – lycophytes
life cycle is dominated by the gametophyte stage
gamete forming stage
gametophyte is only a few cells thick
anchored to the ground by rhizoids – long tubular single cells
NOT roots – not composed of tissues (cells only), lack specialized conducting cells and are not responsible for water and mineral absorption
some mosses are NOT mosses at all – Irish moss (red seaweed), reindeer moss (lichen), club mosses (seedless vascular plant)
Plagiochila deltoidea = liverwort
Marchantia polymorpha = moss

15. General Life Cycle: The Gametophyte
dominant stage in these three phlya
when bryophyte spores land on favorable habitats – germinate and grow into gametophytes
the spore develops into a threadlike protonema – covers a large surface area for absorption or water and minerals
each protonema produces a bud with an apical meristem (stem-cell like tissue for growth)
the AM generates gamete-producing structures known as gametophores
gametophore bears the male or female gametangia
the protonema + gametophore = gametophyte
at the tip of the gametophore develops the reproductive structures = gametangia (singular = gametangium)
multiple gametangia develop on each plant
some bryophyte gametangia are bisexual – both antheridium and archegonium on the same gametophyte = monoecious
most mosses have separate antheridium and archegonium located on separate gametophytes - dioecious
“male and female” gametophytes
production of the gametes by mitosis since the gametophyte is haploid already
Gametophore of
female gametophyte
Marchantia polymorpha,
a “thalloid” liverwort
Foot
Seta
Sporangium
500 µm
Marchantia sporophyte (LM)
antheridium
archegonium

16. General Life Cycle: The Sporophyte
in the plant kingdom – the sporophyte is the mature plant
fertilization is followed by development of the embryo within the archegonium
the embryo grows into a small sporophyte (diploid) - remains attached to the archegonium via a foot – for absorption of nutrients
the sporophyte grows in length upward to produces a seta (stalk)
at the tip of this stalk forms a sporangium surrounded by a capsule
haploid spores develop in this sporangium via meiosis
in most mosses the upper part of the capsule forms a peristome – for gradual spore discharge
when the capsule matures – the peristome “pops” off and the spores are dispersed
from these spores comes new protonemata (singular = protonema)
hornwort and moss sporophytes tend to be large and more complicated
their sporophytes also have specialized pores = stomata
support photosynthesis by allowing the exchange of CO2 and O2
also allow for the evaporation of water
also found in vascular plants
sporophyte

17. Life Cycle of a Moss
Male
gametophyte
“Bud”
Spores develop into
threadlike protonemata.
Protonemata
The haploid protonemata produce “buds” that grow into gametophytes.
Raindrop
Sperm
Antheridia
Most mosses have separate male and female gametophytes, with antheridia and archegonia, respectively.
Egg
Haploid (n)
Diploid (2n)
Key
A sperm swims through a film of moisture to an archegonium and fertilizes the egg.
Archegonia
Rhizoid
Female
Gametophore
Spores
Sporangium
Peristome
MEIOSIS
Meiosis occurs and haploid spores develop in the sporangium of the sporophyte. When the sporangium lid pops off, the peristome “teeth” regulate gradual release of the spores.
The sporophyte grows a long stalk, or seta, that emerges from the archegonium.
FERTILIZATION
(within archegonium)
Archegonium
Zygote
Embryo
Calyptra
Young
sporophyte
Attached by its foot, the sporophyte remains nutritionally dependent on the gametophyte.
The diploid zygote develops into a sporophyte embryo within the archegonium.
Capsule
(sporangium)
Seta
Foot
Mature
sporophytes
Capsule with
peristome (SEM)
gametophytes

18. Moss Life Cycle

19. The Economics of Moss Sphagnum moss
mosses have very lightweight spores
easy distribution has allowed for the establishment of mosses around the globe
very common and diverse in moist forests and wetlands
can help retain nitrogen in the soil
many species harbor cyanobacteria that increase the availability of nitrogen to the moss
many species can survive drought and rehydrate when moisture reappears
one wetland moss = Sphagnum or “peat moss”
peat moss = partially decayed remnants of Sphagnum
major component of partially decayed organic material called peat
regions with thick layers of peat = peatlands (3% of Earth’s surface)
peat contains 30% of world’s soil carbon
450 billion tons of carbon is stored as peat
Sphagnum does not decay easily – phenolic compounds in its cell walls
peat – fuel source in northern Europe rather than wood
overharvesting of Sphagnum – could alter CO2 levels globally
Sphagnum moss

20. Seedless Vascular Plants
bryophytes prominent during the first 100 million years of plant evolution
but they are not very tall
rarely over 20 cm in height
those plants that could achieve heights would have better access to sunlight, better spore dispersal
height would mean the need for a transport system for water and nutrients
would also need a structural support system
ferns are example of the evolution of plants that began to develop height and a vascular system
fossils of present day vascular plants date back 425 MYA

21. Seedless Vascular Plants
4 major characteristics of vascular plants:
1. dominant phase in the alternation of generations life cycle is the sporophyte
e.g. ferns – the leafy plant is the sporophyte
the sporophyte becomes the larger and more complex stage of the life cycle
dramatic reduction in gametophyte stage – may be under the soil
sporophyte no longer dependent on the gametophyte for nutrition
2. development of vascular tissues – xylem and phloem
xylem – conduction of water and minerals
included tracheids – dead, tube-shaped cells for the conduction of water and minerals up from the roots
so vascular plants are often referred to as tracheophytes
water conducting cells contain a phenolic polymer – lignin
cells are said to be lignified
this permits vascular plants to grow tall – lignin strengthens the walls
phloem – conduction of sugars and other nutrients
living cells
arranged into tubes for the distribution of sugars, amino acids and other organic products

22. Seedless Vascular Plants
4 major characteristics:
3. development of sporophylls: modified leaves that bear sporangia
vary in structure
two types: microphyll and megaphyll
e.g. in ferns – megaphylls with clusters of sporangia called sori
e.g. in lycophytes and gymnosperms – microphylls that form cone-like strobili
most seedless vascular plants are homosporous – one type of sporangium that produces one type of spore
this spore produces the two types of gametes = bisexual
heterosporous species has two types of sporangia that develop into two types of spores
megasporangium - megaspore = egg
microsporangium - microspore - sperm

23. Seedless Vascular Plants
4 major characteristics of vascular plants:
4. development of roots and leaves
rather than rhizoids – the sporophytes of vascular plants have evolved roots
roots – organs for the anchorage of the plant & absorption of water and nutrients
resembles the stem tissues of fossilized plants –evolved from them?
leaves – organs for the increase of vascular surface area to capture more solar energy
the sporophyte has two types: either megaphylls or microphylls
megaphylls are larger and have a highly branched vascular system (of veins) running through them
greater photosynthetic capacity
microphylls are spine-like
supplied by a single, unbranched vein
appeared to have evolved first

24. Evolution of Leaves
evolution of microphylls from clusters of sporangia
evolution of megaphylls from an accumulation of branches on a stem
one branch with overtopping growth
smaller branches flattened and fused to one another and to the overtop branch

25. Seedless Vascular plants
two clades: Phylum Lycophyta and Phylum Pterophyta
have modified leaves called sporophylls that bear sporangia
two types of sporophylls: microphylls and megaphylls
most seedless vascular plants are homosporous – one type of sporophyll producing one type of spore that develops into a bisexual gametophyte
Phylum Pterophyta – ferns, horsetails and whisk ferns
the pterophytes are divided by some botanists into separate phyla:
phylum Sphenophyta – horsetails
phylum Psilophyta – whisk ferns and relatives
phylum Pterophyta – ferns
most recent information consider these groups now to be one clade
Phylum Lycophyta – club mosses, spike mosses and quillworts

26. Phylum Lycophyta club mosses, spike mosses and quillworts
Diphasiastrum tristachyum, a club moss
Strobili
(clusters of
sporangia)
club mosses, spike mosses and quillworts
1200 species today
NOT true mosses since they have vascular tissue
most ancient line of vascular plants
microphyll line of evolution
distinct line of evolution that came out of the first land plants
development of leaves from clusters of sporangia
earliest lycophytes formed primitive leaves = enations
enations were small (4 cm) and contained a single trace of vascular tissue – also very effective at photosynthesis
enations are now called microphylls
“micro” refers to the evolution from small enations not their size
evolution of true roots – increased the size of the sporophyte
sporangia became clustered into compact cones or strobili
many species evolved heterospory
modern lycophytes grow on tropical trees as epiphytes – BUT they are NOT parasites
epiphytic ferns

27. Phylum Pterophyta megaphyll line of evolution
development of leaves from a branching system of stems
seen in all seed plants, ferns and arthrophytes (horsetails)
telome theory: main stem with dichotomously branching lateral stems
the lateral branches developed subdivisions – all on one plant
the last lateral branches = telomes
during evolution - tissue grew in between (webbing)
the telomes also acquired spore-forming ability
positioning of the branches became very regular and controlled
development of phyllotaxy – arrangement of leaves on a stem
four basic patterns developed
some lateral branches became arranged in a spiral pattern = spiral phyllotaxy
some phyllotaxy developed an alternating or an opposite pattern
others became more complicated (e.g. whorled pattern)
opposite
alternate
whorled

28. Phylum Pterophyta ferns leaves are known as megaphylls
fern sporophyte is comprised of underground, horizontal stems called rhizomes
from these come vertical shoots that give rise to large leaves called fronds divided into leaflets
frond grows as the fiddlehead
leaf primordial cells as they grow curl inward
mature frond is called the megaphyll
megaphyll is a compound leaf with a center rachis and multiple leaflets
although some fern species – e.g. staghorn fern – have a simple leaf structure

29. Phylum Pterophyta
gametophyte is very small and shrivels and dies after the young sporophyte develops
the diploid sporophyte bears sporangia (singular = sporangium) clustered under the leaflets in structures called sori (singular = sorus)
a sporangium contains spore mother cells (2n)
the spore mother cells undergo meiosis to produce spores (n)
these spores are for development of a haploid gametophyte

30. Annulus and spore dispersal
the sporangium is stalked with spring-like devices that disperse the spores = annulus
annulus, a row of cells that bisects the sporangium like a sturdy spine.
annulus walls are permeable to water
as the sporangium dries, evaporating water is drawn out from the annulus, causing the cells to shrink – this pries the sporangium open
the presence of water within the sporangium propels the spores out like a catapult

31. Fern Life Cycle meiosis of spores within a sporangium
spore release from the sorus and germination
the spore develops into a young gametophyte – bisexual
bisexual gametophyte develops male and female gametogania
male antheridium
female archegonium
antheridium produces and releases sperm – swims to the egg within the archegonium – fertilization and development into a zygote
the zygote develops into the diploid sporophyte – emerges from the gametophyte
growth of the sporophyte produces fronds or megaphylls
young, developing frond is called the fiddlehead
gametophyte disappears
fronds contain sporangia for the production of spores (meiosis)
heterosporous species have megasporangium and microsporangium –production of distinct spores for male and female gametophyte
almost all fern species are homosporous
Spore
Sperm
Antheridium
Egg
Haploid (n)
Diploid (2n)
Key
Young
gametophyte
Sorus
Sporangium
MEIOSIS
FERTILIZATION
Archegonium
Zygote
New
sporophyte
Mature
Gametophyte
Fiddlehead
Fern Life Cycle

32. Fern Life Cycle