Seedless vascular plants

trends in reproduction

alternation of generations

sporophyte is dominant

all are oogamous

oogamous

large eggs and small sperm

egg stays in place, sperm moves

homosporous

1 type of spore by meiosis

most non-vascular and lower vascular plants

bisexual gametophyte

bisexual gametophyte

bear both sperm producing antheridia and egg producing antheridia

heterosporous

2 types of spores in 2 different kinds of sporangia

all seed plants and a few others

microspores in microsporangia

megaspores in megasporangia

unisexual or gametophyte

life cycle of SVPs

sporophyte is dominant

gametophyte is significantly reduced in physical size

both sporophyte and gametophyte are independent at maturity

most are homosporous, some are hetersporous

gametophytes can be male, female, or bisexual

rely on water for fertilization

Have archegonia (egg) and antheridia (sperm)

SVPs

evolution is uncertain, fossil record is incomplete

postulated that vascular tissue, waxy epidermis and others evolved over millions of years in freshwater algae

Dominated landscape around 350 mya, for ~100 million years

today only ~5% of living plant species

living phyla of SVPs

Phylum Lycopodiophyta and Monilophyta

hypothesis of the origins of SVPs

2 extinct phyla appear in the fossil record 450 mya: Rhyniophytes, Zonterophylls, and Trimerophytes

All had branching photosynthetic stems without roots or leaves

Phylum lycopdiophyta families

Lycopodiacease, Selaginellaceae, and Isoetaceae

microphylls

leaves with a single vascular trace or leaf vein

In all lycophytes

two hypothesis for origination enation theory and telome theory

enation theory

holds that microphylls developed when a vascular trace gradually extended into an enation, a non-vascular flap of tissue

telome theory

holds that microphylls evolved as a result of existing telomes

Lycopodiaceae

club mosses

15 genra, 400 species

8 species in WV

mostly tropical

epiphytes

evergreen

Lycopodiaceae physical structure

rhizome

vegetative propagation

sessile microphylls

branching: dichotomous and pseudo-monopodial

homosporous, spores produced in sporangium which group into stobilus

bisexual gametophyte

Selaginellaceae

spike mosses

1 genus, 700 species

2 species in WV

scattered around the world

wet areas

highly diverse in form

Selaginellaceae physical structure

have a ligule

heterospory -> 2 types of spores -> unisexual gametophyte

can produce microspores in microsporangium or megaspores in megasporangium

Isoetaceae

Quillworts

1 genus, 150 species

2 species in WV

Aquatic, seasonal pools

Corm

Long narrow sporophylls

have peculiarity

Isoetaceae reproduction

Heterosporous with micro and megasporangium

Phylum monilophyta

Mostly what people will look at and call a fern

12000 species, 75% in tropics

1000 in costa rica, ~61 in WV

Characteristics used to identify ferms

megaphylls

sporangium- eusporangium and leptosporangium

Sorus and indusium traits

homosporous vs heterosporous

megaphylls

leaves with more than 1 vascular trace

Eusporangiate sporangia

large, thick sporangium wall

produce large numbers of spores (100-1000)

Leptosporangia sporangia

Smaller, thin capsule wall

produce fewer spores (16, 32, 64, 128, etc)

Sorus and indusium traits

Sporangia usually borne in clusters called sori

Located on the under side of the blade or borne on fertile leaflets

Some sori have a protective covering (indusium)

homosporous ferns

produce only one type of spore which produce bisexual gametophytes

Heterosporous ferns

produce both megaspores and microspores; unisexual gametophytes (separate male and female gametophytes)

Classes of phylum monilophyta

psilotopsida, marattiopsida, polypodiopsida, and equisetopsida

Orders of psilotopsida

Ophioglossales and psilotales

eusporangiate, homosporous ferns

Ophioglossales

eusporangiate

homosporous

1 leaf/rhizome per year

Psilotales

whisk ferns

2 living genra: Psilotum and Tmesipteris

homosporous

bisexual gametophytes

simple habit=derived condition

Psioltales physical characteristics

no leaves and no roots

hair-like rhizoids

underground rhizomes

photosynthetic stem

dichotomous branching

two kinds of appendages in psilotales

enations and synangium

enations

no vascular tissue

synangium

groups of 3 sporangia

on ends of short, lateral branches

psilotales gametophytes

subterranean

devoid of chlorophyll

symbiosis with mycorrhizal fungi

rhizoids

bisexual

Marattiopsida

euosporangiate, homosporous ferns

polypodiopsida

35 families, 320 genera, 10,500 species

leptosporangiate ferns

leptosporangiate ferns

order filicales (filicalian ferns)

orders marsileales and salviniales (water ferns)

filicalian ferns

homosporous

water ferns

salvinia and azolla

heterosporous ad aquatic

heterosporous sporocarps are modified sori

feathery pinnae

fronds

ferns leaves that are megaphylls

filicales

fiddleheads

a large diversity in the sporophyll

different morphologies of sporophylls

little or no difference in form between sterile and fertile fronds

large difference between the two stages

only distal pinnae are fertile

different morphologies of sori

with or without an indusium

bare

margins of the blade rolled back a false indusium

covered by kidney-shaped indusia

growth of the prothallus

generally one cell layer thick except at apical sinus

no vascular tissues

bisexual

sequential differentiation of sex organs

major steps in polypodium lifecycle

1. differentiation of sporangia

2. release and germination of spores

3. growth of prothallus

4. fertilization and formation of the zygote

5. development of the embryo

6. growth into a mature sporophyte

Marsilea

Water Clover

shallow ponds

compound leaves

stolon-like stem

leaves alternately arranged, in 2 rows

sporocarps

heterosporous sporocarp is a modified pinna

have a gelatinous ring

Asexually reproducing ferns

water ferns

in some species, the gametophyte stage persists indefinitely without ever producing sporophytes

reproduce by gemmae

sporophytes never induced

populations estimated to be over 1000 years old

extinction of sporophytes possibly result of glaciation cycles

Equisetopsida

horsetails or scouring rushes

only one living genus Equisetum

indistinguishable from fossils 300 million years old

whorled microphylls at nodes

historically used to clean pots

good at vegetative propagation

poisonous livestock because of enzyme thiaminase

Equisetopsida reproduction

homosporous

gametophyte is photosynthetic and bisexual or male

practically

sporophyte has a hollow, jointed stem

fertile and sterile stems

has a strobilus with spores and elaters

Equisetum gametophyte

free-living

photosynthetic

no vascular tissue

no stomata

bisexual or male

Challenges of land plants

1. harvesting light energy

2. staying wet when things get dry

3. dealing with gravity

4. divide or be conquered

5. leveraging resources

solution of SVPs to harvesting light energy

evolution of leaves

lycopodiophyta, psilotopsida, and equisetopsida have microphylls

ferns have megaphylls

solution of ferns to staying wet when things get dry

conductive tissues (vasculature)

solution of ferns to dealing with gravity

strengthens cell walls

lignin

principle building block of plant cell walls is cellulose

lignin strengthens cell walls by replacing water and coating or encrusting cellulose

no seen in bryophytes

lignin

substance in vascular plants that makes cell walls rigid

allows for increases in size and height

solution of ferns to divide or be conquered

homospory vs. heterospory

significance of heterospory is associated with:

Reduction of the gametophyte

Almost complete retention of the gametophyte in the spore wall

No need to develop large vegetative bodies

Reduced risk of damage and/or death

Rapid production of gametes because of precocious germination

Difference in spore size results because of the greater demands on the female gametophyte and therefore on the megaspore

evolutionary process resulting in increased efficiency

benefits of leaves

increased photosynthetic surfaces, increased food and energy

benefits of vascular tissue

increased ability to move water and increase in range

benefits of lignin

stronger cells, get to greater heights and out compete neighbors

benefits of heterospory

lead to an increase in reproductive efficiency