1. Chapter 28 - Sadava Plants without Seeds: from Water to Land

2. Before we start Plants, a review….
Domain Archaea
Prokaryotic, include extremophile bacteria
Domain Bacteria
Prokaryotic, includes what we knew as Kingdom Monera
Domain Eukarya
Eukaryotic
Includes:
Kingdom Fungi
What we knew as Kingdom Protista (green algae are related to plants)
Kingdom Plantae
Kingdom Animalia

3. Land plants are monophyletic
all descend from a single common ancestor
One shared derived character
a synapomorphy
development from an embryo protected by tissues of the parent plant
Why is this important on land?
Also called embryophytes

4. Land plants retain derived features they share with green algae (which are protists):
Chlorophyll a and b.
Starch as a storage product.
Cellulose in cell walls.
Photo Green algae of phylum Chlorophyta are most likely ancestors of plants.

5. “Plants” can be defined in several ways
Streptophytes include land plants and a paraphyletic group of green algae —all retain egg within parent’s body
Green plants: streptophytes plus all other green algae. All have chlorophyll b
This textbook: “plants” refers only to land plants
What we think of in Kingdom Plantae

6. Vascular plants, or tracheophytes
10 clades of land plants
Vascular plants, or tracheophytes
7 clades
all have conducting cells called tracheids
The seven groups of vascular plants constitute a clade themselves
Nonvascular plants
3 clades

8. Plants first appeared on land between 400–500 million years ago
Adaptations were needed to survive in dry environments
Large plants must transport water to all parts of plant
Needed support in air
Needed methods to disperse gametes

9. Characteristics of land plants:
The cuticle (waxy lipids)
Stomata – openings in stems and leaves; regulate gas exchange (except liverworts)
Gametangia enclosing gametes
Embryos in a protective structure
Pigments that protect against UV radiation
Spore walls containing sporopollenin
Mutualistic relationships with fungi to promote nutrient uptake from soil

10. Alternation of generations
All land plants have a life cycle with alternation of generations
multicellular haploid (gametophyte)
multicellular diploid (sporophyte) individuals

11. Alternation of generations
Sporophyte
Produces spores, all cells are diploid
Cells in sporangia (in sporophyte) undergo meiosis to produce haploid, unicellular spores
Spores are released
Spore develops into multicellular haploid structure, the gametophyte
Gametophyte
Produces gametes, all cells are haploid
Produce gametes by mitosis
Fusion of egg and sperm results in diploid zygote
Zygote develops into sporophyte

12. In plants that appeared later, this is reversed
Reduction of the gametophyte generation is a major theme in plant evolution
In nonvascular plants: gametophyte is larger, longer-lived, and more self-sufficient than the sporophyte
Gametophyte is photosynthetic
In plants that appeared later, this is reversed
In seed vascular plants (gymnosperms and angiosperms), sporophyte generation is dominate
Sporophyte is photosynthetic
Gametophyte might only be a few cells it is so small

13. Nonvascular plants Do not have vascular tissue
liverworts, hornworts, and mosses
These groups do not form a clade – why?

14. In nonvascular plants, the gametophyte generation is photosynthetic
Sporophytes may or may not be photosynthetic,…
but are always nutritionally dependent on gametophyte, and is permanently attached
Sporophytes arising from gametophytes
Gametophytes

15. Haploid gametophyte produces gametes in specialized sex organs (gametangia)
Female: archegonium  produces one egg
Male: antheridium  produces many sperm with two flagella each
Archegonium
Antheridium
Flagellated moss sperm

17. Nonvascular plants
Sperm must swim to archegonium, or be splashed by raindrops
Egg or archegonium releases chemical attractants for sperm
Water is required for all these events

18. Vascular Plants
Vascular plants include the club mosses, ferns, conifers, and angiosperms (flowering plants).
True roots and leaves

19. What Features Distinguish the Vascular Plants?
The vascular system consists of tissue specialized for transport of materials
Xylem
conducts water and minerals from soil up to aerial parts of plant.
Some cells have lignin — provides support
Phloem
conducts products of photosynthesis through plant.

20. First plant fossils are from Silurian (408-440 mya)
Tracheids are main water-conducting element in xylem
Evolution of tracheids in plants set stage for invasion of land
First plant fossils are from Silurian ( mya)
Made land more hospitable for animals
Amphibians and insects arrived soon after plants

21. Vascular plants also have a large, branching, independent sporophyte
Mature sporophyte is nutritionally independent from gametophyte
Fern prothallus
Small independent gametophyte (left) and branched sporopythe (right) of ferns

22. Vascular plants
Euphyllophytes
“true leaf plants”
Includes:
Monilophytes – seedless vascular plants that have megaphylls
seed plants (gymnosperms and flowering plants)
Synapomorphies include overtopping growth — new branches grow beyond the others —an advantage in the competition for light

23. True leaves evolved
flattened photosynthetic structures arising from a stem or branch
has true vascular tissue
two types
Microphylls – small, one vascular strand
Club mosses have these
Megaphylls

24. Heterosporous vascular plants produce two types of spores:
Megaspores develop into female gametophytes — megagametophyte
Megaspores are produced in small numbers in megasporangia
Microspores develop into male gametophytes — microgametophyte
Microspores are produced in large numbers in microsporangia

26. Nonvascular seedless land plants: three clades:
liverworts
mosses
hornworts

27. Embryophytes Nonvascular Seedless plants Hepatophyta
Liverworts: Hepatophyta
Sporophytes very short
Remember that gametophyte generation is dominant in nonvascular plants
Can reproduce asexually
Do so by dispersing gemmae which are in gemmae cups

28. Embryophytes Nonvascular Seedless plants Bryophyta
The mosses: Bryophyta
Mosses (plus hornworts and vascular plants) have stomata important in water & gas exchange

29. Embryophytes Nonvascular Seedless plants Anthocerophyta
Hornworts: Anthocerophyta
Gametophytes are flat plates of cells
Have stomata, which do not close

30. Seedless Vascular Plants
Seedless VASCULAR plants – three monophyletic clades:
club mosses
horsetails
whisk ferns
plus ferns and allies (not monophyletic, though 97% are)

31. Seedless Vascular Plants
Small, short-lived gametophyte is independent of the large sporophyte
Single-celled spore is resting stage
Can grow larger because of vascular tissue but must have water for part of life cycle — for the flagellated, swimming sperm

32. Embryophytes Seedless Vascular Plants Lycophytes
Lycophytes: club mosses, spike mosses, and quillworts
Roots and stems have dichotomous branching
Leaves are microphylls
Strobilli – clusters of sporangia
Lycopodium annotinum

33. Embryophytes Seedless Vascular Euphyllophytes Monilophytes
Monilophytes (a.k.a. Pteridophytes) — horsetails, whisk ferns, and ferns & allies, form a clade
Horsetails and whisk ferns are both monophyletic, but ferns are not
But 97% of ferns form a clade — the leptosporangiate ferns

34. Embryophytes Seedless Vascular Euphyllophytes Monilophytes
Horsetails
15 species in one genus — Equisetum
Silica in cell walls — “scouring rushes”… used for cleaning
Equisetum hymale

35. Embryophytes Seedless Vascular Euphyllophytes Monilophytes
Whisk ferns
15 species in two genera
No roots but well-developed vascular system
Psilotum nudum

36. Embryophytes Seedless Vascular Euphyllophytes Monilophytes
Sporangia occur on undersides of leaves in clusters called sori

38. Monilophytes (Pteridophytes) – Ferns
Fern gametophytes produce antheridia and archegonia, not always at same time or on same gametophyte

39. Embryophytes Seedless Vascular Euphyllophytes Monilophytes
Most ferns found in shaded, moist environments
Tree ferns can reach heights of 20 m
Dixie Woods fern, Dryopteris australis
Tree ferns