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LECTURE 2

Land Plant Diversity

Liverworts

Systematics -A science that includes and

encompasses traditional taxonomy, the description,

identification, nomenclature, and classification of

organisms, and that has as its primary goal the

reconstruction of phylogeny, or evolutionary history of

life. (M. G. Simpson 2006)

Taxonomy - The theory and practice encompassing

description, identification, nomenclature and

classification of groups of organisms (species, genera,

etc.)

-Does not necessarily include phylogeny

Monophyletic taxon: A group composed of a collection of

organisms, including the most recent common ancestor of

all those organisms and all the descendants of that most

recent common ancestor. A monophyletic taxon is also

called a clade.

O X X X X X X XO X Y X X X G X

O Y X X Y X G G

GREEN PLANT - PHYLOGENY

(Simpson 2006; pg. 52)

GREEN PLANT SYNAPOMORPHIES

1) Chlorophyll b

2) Thylakoids Stacked

Into Grana

3) True Starch Storage

Chemical structure Chloroplasts in cells of

Elodea

Chloroplast

GREEN PLANTS - PHYLOGENY

LIFE CYCLE - ALTERNATION OF GENERATIONS

LIFE CYCLE – (NOT) ALTERNATION OF GENERATIONS

animals

ISOGAMY and ANISOGAMY

OOGAMY

GREEN PLANTS - PHYLOGENY

PLASMODESMATA- Canals interconnecting cells allowing for

transportation of molecules.

Coleochaete

Chara

GREEN ALGAE -

Most closely

related to the land

plants.

Both DNA and

morphological data

agree.

THE MOVE TO LAND

Landplant Adaptations:

1) Physically survive out of water: Avoid desiccation? Water

transport as plants get larger?

2) Sexual reproduction: Algae have free swimming sperm,

how does sperm get to egg on land?

LAND PLANT PHYLOGENY

(from Simpson 2006)

Landplant Synapomorphies:

1) Retention of Embryo on Gametophyte: Embryo is formed

on gametophyte of Charophytes and Coleochaete but

released.

2) Sporangium: A multicellular structure that protects and

produces spores through meiosis

3) Cuticle: A protective layer secreted by epidermal plant

cells for protection against desiccation. A transparent

layer of cutin, a polymer of fatty acids.

4) Antheridium (“male” gametangium): A multicellular

structure that produces and protects the sperm

5) Archegonium (“female” gametangium): A multicellular

structure that produces and protects the egg



Sphagnum Moss

(1N)




released.













Cuticle

Epiderma

l leaf

cells




released.











structure that produces and protects the sperm (male

gametes)


structure that produces and protects the egg (female

gamete)

A

B

antheridium archegonium

EXAMPLE FROM MOSS

Egg

kneck

cells

moss

gametophyte

Bryophytes

BRYOPHYTES - Paraphyletic

(From Simpson 2006)

BRYOPHYTES - Characteristics unique from other land

plants

1) Gametophyte Dominant- The predominant vegetative

form is the gametophyte phase of the life cycle; the

sporophyte is retained on the gametophyte and

dependent throughout out its life-cycle for survival

2) Lack Vasculature - Attribute of all other land plants in

the sporophyte phase that transports nutrients and

water and aids in rigidity

BRYOPHYTES - Representative Moss Life Cycle

Zygote

sporophyte

gametophyte


spores

BRYOPHYTES - Characteristics unique from other land

plants

1) Gametophyte Dominant- The predominant vegetative

form is the gametophyte phase of the life cycle; the

sporophyte is retained on the gametophyte and

dependent throughout out its life-cycle for survival

2) Lack True Vasculature - Attribute of all other land

plants in the sporophyte phase that transports

nutrients and water and aids in rigidity

LIVERWORTS (Marchantiophyta)

LAND PLANT PHYLOGENY

-Liverworts

(From Simpson 2006)

LIVERWORTS

Elater: functions in spore dispersal; elongate, spiral-

walled haploid cells that are hygroscopic (change

shape and move in response to moisture content)

Elater

Spores

Capsule

(sporangium)Elaters

LIVERWORTS

Oil Bodies: membrane bound organelles containing oil

found in the cells of most liverworts, function is not

known.

Figure 1. Diagram of relationships of major clades as resolved from

parsimony and Bayesian analyses of 5 loci (including chloroplast, nuclear, and

mitochondrial DNA). Numbers above the branches are Maximum Parsimony

bootstrap values/homogeneous Bayesian posterior probabilities (PPs)/5-

partition Bayesian PPs/14-partition Bayesian PPs. The Bryologist (Forrest et

al., 2006)

LIVERWORTS

Phylogenetic hypothesis - Based on molecular data

Leafy

Thalloid

LIVERWORTS5,500 - 9,000 species

-Gametophyte dominant

The vegetative body is thalloid, consisting of a thallus,

a flattened mass of tissue

- only a few cell layers thick, water uptake through

osmosis

-ventral (lower surface) has rhizoids, unicellular

elongate filaments that aid in anchorage and

absorption for external moisture retention and

multicellular scales

-the upper surface has air pores for gas exchange

or leafy, having two rows of lateral leaves and

frequently a third ventral row of reduced size along

a stem. Leaves are very thin (generally 1 cell layer)

and absorbent. Also have rhizoids.

Gametophyte: Thalloid

Form

Rhizoids

Thallus

Thallus

LIVERWORTS





osmosis





-the upper surface has air pores for gas exchange.





Thallus upper surface: air pores for gas exchange

Air pore

LIVERWORTS





osmosis





-the upper surface has air pores for gas exchange.





Gametophyte: Leafy Form

-Not homologous with leaves of mosses, evolved

independently

Homology- Similarity that is due to common ancestryLateral leaves

Ventral leaf

LIVERWORTS

Special Features

1) Vegetative reproduction - gemmae and gemmae

cups

2) Gametangium- antheridium and archaegonium

(sometime retained on antheridiophores and

archegoniophores)

GAMETOPHYTE MITOTIC

(VEGETATIVE)

REPRODUCTION

Example: Gemmae Cups and

Gemmae from Thalloid

Liverworts

Gemmae

Gemmae

Gemmae cup

Gemmae cup

Gametophyte - Archegonium holds egg; Antheridium holds

sperm.

-Sperm attracted to egg via excreted proteins

-Some Liverworts have specialized structures that retain

archegonia (Archegoniophore) and antheridia

(Antheridiophore).

antheridiophore

antheridiophore

antheridium

archegoniophore

archegonium

Marchantia

archegoniophore

Gametophyte - archegonium holds egg; antheridium holds

sperm. Example: Leafy liverwort (Porella).


LIVERWORTS

-Sporophyte - retained on gametophyte

• Sporangium - matures before seta (1N stalk)

• Spores - dispersed simultaneously from explosive

capsule with elaters.

• Homosporous: All spores identical in size.

Capsule 2N

Seta

Gametophyte

Sporophyte Phase: Capsule contains the sporangium

Immature

sporophyt

e

surrounde

d by

calyptra

elaters

Capsule with

apical sutures

Capsule wall

Sporophyte Phase: Capsule contains the sporangium

which produce spores through meiosis. Spores are

dispersed when capsule splits and spiraled elaters dry.

Review:

Liverwort Life Cycle

√

2N 2N

2N

Liverwort - life cycle

HORNWORTS (ANTHOCEROTOPHYTA)

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