Mosses Flashcards
Phyla of Bryophytes (refers to all non-vascular plants)
- Marchantiophyta (Liverworts)
- Anthocerophyta (Hornworts)
- Bryophyta (Mosses)
Monophyletic
Linear group of phyla
- The 3 bryophyte phyla divereged independently early in plant evolution before the origin of vascular plants
What is a cladogram?
A diagram that shows ancestral relations without a time frame between taxa
Which bryophyta phyla are the most reasonable models of early plants?
Liverworts and hornworts
Which bryophyte phyla are the most closely related to vascular plants?
Mosses
Charophytes
Division of green algae most closely related to byrophytes
- Aquatic algae
Bryophyte evolution
- Bryophytes were the first plants for 100 million years that terrestrial communities existed
- Then vegetation began to take on a taller profile for better access to light, therefore vascular tissue developed
What does a gametophyte consist of?
- Gamete producing structures, the gametophores
- Root-hair-like rhizodes
- Haploid
- Photosynthetic
Moss reproduction
- Gametes produced in Gametangia
- Dioecious with separate male and female gametophores
- Female produces a vase-shaped Archegonium with a single egg
- Male produces elongated antheridia with many flagellated sperm
- Sperm need at least a small amount of water to disperse and ‘swim’ to female
What is the dominant form in a moss?
Gametophyte, haploid is dominant over diploid sporophyte
Sporophyte
- Diploid, less dominant, moss structure that is only present part of the year
Homosporous
Bryophytes have spores that are all the same size
How do mosses grow?
Spores germinate in favourable habitat and grow by mitosis into masses of branched 1 cell thick filaments called protonemata
Mitosis
Produces more haploid
Meiosis
Produces spores
What is a protonemata?
Mass of green, branched, one-cell thick filaments that produce meristems when sufficient resources are available
What is a meristem?
Region of active cell division that generate gametophytes
How do sperm find the archegonia?
Chemotaxis
- they follow chemical attractants
What is the Zygote?
Young sporophyte that is retained and nourished by the parent gametophyte 9placental nutritive cells transport materials from parent to embryos)
Liverwort and Hornwort reproduction?
Simple sporophytes that consist of a short stalk (Seta) bearing round sporangia which contain the developing spores and have a nutritive foot embedded in the gametophyte tissues
- Seta is not elongated, protected inside
What are Rhizoids?
Multicellular filaments that anchor bryophytes
- Not composed of tissues
- Not photosynthetic
- No specialized conducting cells
- No primary role in water and mineral absorption
What 2 features make the sporophyte?
- Seta (Stalk)
- Sporangium (holds spores)
Why are moss leaves so thin?
Being one cell thick situates all cells close to water and dissolved minerals
How is water and nutrient transport accomplished in gametophores?
By external transport
- sometimes by costas
What is a Costa?
A nerve of specialized cells that runs lengthwise on a gametophyte leaf.
- One costa can be a midrib
- Can contain specialized cells that are not structural
- Primitive tissue to transport water (Hydroids)
- Analagous to a nerve, but do not call it a nerve!
What is a Hydroid?
Specialized cell that can conduct water within gametophyte
- not the same as tracheid of vascular plants
- non-structural
What are Leptoids?
Specialized cells that conduct organic compounds (minerals and Carbs from photosynthesis
- not the same as tracheid of vascular plants
- non-structural
What are Lamina?
Leaf blade cells that provide structure and are continuous on either side of the guide cells
What are guide cells?
Noticeably larger cells that are continuous with the cells that make up the rest of the leaf blade (lamina)
- May be part of costa
Seta?
Term for the stem of a sporophyte that bears the bishops cap (sporangium)
and
the stem of the moss gametophyte
- Do not call it a stem!
What do most stems consist of?
Concentric layers of:
- Central cylinder of water conducting hydroids and nutrient conducting leptoids
- Undifferentiated parenchyma cells
- Supportive cellulotic stereid cells
Parenchyma
Basic cell in a plant
- Early tissue appearing on 1st terrestrial plants
- Undifferentiated cells
Why are most bryophytes so small?
Lack supportive tissues
- Some family in NZ can grow really big though!
- Show extreme examples of very small to quite large even in the same evolutionary family
Why are bryophyte leaves and stems not considered true?
They lack lignin-coated vascular cells
- Lack the wax that is common protective feature on vascular plants
- Vascular plants have a stomata for gas exchange on vascular leaves
Why are moss leaves so thin?
- Lack a cuticle and are only one cell thick to enhance water and mineral absorption from moist environment
What are the 2 growth habits of mosses?
- Ascocarpus
- Pleurocarpus
Ascocarpus
Mosses with erect growth form and apical sporophytes
Pleurocarpus
Decumbent Mosses or feather-like with lateral sporophytes that are not produced on the meristomatic tip
Perichaetium?
Whirl of leaves around the archegonium which will eventually produce the sporophyte
Capsule
Sporangium
What is special about Hair-cap mosses?
They have more complex leaves with ridges (lamellae) to enhance absorption of sunlight and increase photosynthesis
- The ridges are coated with cuticle
What does a moss sporophyte consist of?
- Foot
- Seta (elongated stalk)
- Sporangium (capsule)
What does the Foot of the sporophyte do?
Gathers nutrients and water from the parent gametophyte via transfer cells
What does the Stalk of the sporophyte do?
Conducts materials gathered in the foot to the capsule
Why is the Seta elongate in most mosses?
So that the capsule can be elevated to enhance spore dispersal
Where does meiosis occur?
In the moss capsule (sporangium)
- Can generate over 50 million spores
Calyptra
Bishops Cap produced by all masses
- Protective cap of gametophyte tissue on immature capsule
- Haploid
- Lost when capsule is ready to release spores
Peristome?
Upper part of capsule that can be specialized for gradual spore release
- Under the calyptra and revealed when calyptra falls off
- May have peristome teeth
Embryo
Diploid structure
Sphagnum
Peat moss
- Abundant and widespread
- Peatlands: High-latitude boreal wetland
- Important carbon reservoir stabilizing atmospheric CO2 levels
- Absorbent, comfortable, and antimicrobial so Historically used as diapers and antiseptic wound dressings
- Harvested today as soil conditioner and packing material for plant roots (b/c they hold a lot of water in ‘dead’ cells)
- Burned as blocks of fuel
Peat
- Extensive deposits of undecayed organic material formed from sphagnum, a wetland moss
- Sphagnum is genus
- Peat is product
Peat Bog
Wet region dominated by sphagnum moss
Why does peat moss not decay?
Does not readily decay due to resistant phenolic compounds and acidic secretions that inhibit bacterial activity
What is the growth form of sphagnum?
Rosette form
Hyaline
Clear, see-through cells
- LargeDead cells of sphagnum surrounded by smaller living photosynthetic cells
Sphagnum hold lots of water, why?
- Hyaline dead cells fill up like a cistern (only sphagnum does this)
- These cells give the leaf a lot of structure
- Cells have pores
- Cross walls of dead cells give structure and hold it even when dry
Rithet’s Bog
- Sphagnum Bog
- Present water table can support sphagnum growth
- Must transplant peat sphagnum to raise water table and hold onto water, not forest sphagnum
- Need to remove shore pine (log to prevent further terrestrialization) and surface muck from shore pine needles an bark (produces non-wetland soil)
Restoration Study for Rithet’s Bog
Before-After-Control-Impact
- Split plots
- Paired control
Treatment: plots planted with sphagnum, with muck removal, and without
Control with no muck removal or planting
And all replicated
- 2 controls: spatial (paired), and temporal (before/after impact assessments, need 5 years of data at least to get temporal control)
- Other possible treatments include different depths of surface removal, or different combinations of peat moss species
Spatial Control
Paired plots beside each other, one treated, one without (control)
Temporal Control
- Time
- Before and after data collected
- Needs at least 5 years
Rithet’s Bog study comparisons
With Spatial and Temporal controls
- Pairwise btwn treated and untreated plots
- Pairwise before and after
- Track difference btwn pairs
- Get trend data, may fluctuate some before treatment
