Terrestrial Flora L4-12

What is a rainforest?

Anything that is a closed forest (>70% canopy cover, dense, medium-tall trees)

Where are rainforests located? Why?

• Globally restricted to certain latitudes

  • tropical rainforests near equator

  • temperate rainforests located on coasts in northern and southern hem

• Drivers: temperature and precipitation

Characteristics of lowland tropical rainforests (23°N to 23°S)

• Climate is uniformly warm wet - isothermal environment

• High rainfall, low elevation

• Regional differences in composition

• Rapid water and nutrient cycling = rapid growth

• PP globally is greatest in tropical rainforests

  • ⬆ precipitation, constant warm temp

  • PP: the rate at which energy is converted into organic substances (biomass) by producers

Factors influencing tropical rainforests

• High rainfall

  • High humidity

  • Saturated soils

• High temperatures

  • Optimal growth for fauna

• Rapid growth

  • Dense canopy cover (90%)

  • Intense competition

Whether its (+) or (-) influence is contextual

4 types of Australian rainforests

1. Monsoonal

• Hot temp

• Seasonal rainfall

2. Tropical

• Hot temp

• High, relatively consistent rainfall

3. Sub-tropical & warm temperate

• Warm to mild temp

• Relatively high rainfall

4. Cool temperate

• Cool temp

• High rainfall

Compare rainforest soils with sclerophyll soils

• Rainforest soils have high nutrient availability but poor retention in soils because of mobilisation and leaching (during high precipitation)

• Rainforest soils are often acidic due to organic matter decomposition and the loss of basic nutrients through leaching

Rainforest soils	Sclerophyll soils
Rapid nutrient cycling	Slower nutrient cycling
Relatively high nutrient turnover	Often low available nutrients
High phosphorous availability (more readily mobilised)	Low phosphorous availability (strongly bound to soil minerals)

*Nutrient cycling: nutrients are quickly released from decomposing leaf litter and reused by plants

Importance of Australian rainforests

• Surviving remnants of Gondwanan flora & fauna

  • There's global cooling but the continent itself is drifting towards the equator (relative difference is it's not really cooling) — environments remain relatively stable = organisms don’t change very much

  • 13 of 27 of the most primitive flowering plant families found in rainforests

    • Austrobaileya - pollen similar to oldest angiosperm fossils (120 my old) — the only one in its genus & family

    • Castanospermum australis (Black bean tree) - antiviral, antitumor + assisted migration by humans

  • Animals with primitive features from Gondwanan times

    • E.g. Hypsiprymnodontidae family (musky rat-kangaroos): simple rounded teeth, simple gut, fruit-eater, scaly tail

• High conservation value — NE Queensland Wet tropics World Heritage Area

  • Has a tremendous amt of early plant diversity: Ferns —> cycads —> angiosperms

  • “cradle of life” new life evolving, diversifying more frequently than other latitudes OR “museum” things persist, not changing, no selection pressures

  • High diversity and high amounts of endemism

• Species rich

Tropical vs Temperate rainforests of Austraila

Tropical	Temperate
Lowland — species rich	Fewer species (including vines)
Highly dense & diverse (100–200 tree sp per hectare)	Fewer layers, simpler vegetation structure
Many vines (lianas), ferns, and palms	Single species often dominant: E.g. Myrtle beech (Nothofagus cunninghamii)
Trees with large leaves	Smaller leaves

In SEA, what separates 2 faunal regions and what are those regions called?

Wallace’s line. The Indo-Malaysian region in the North and the Austro-Malaysian region in the South.

The line aligns with plate tectonics, but climate intolerance also prevented migration into Australia.

Leaf adaptations plants have to persist in rainforests

Morphological:

• Large leaves = SA to capture light

• Efficient shape e.g. drip tips = remove excess precipitation

• High wax content = beading of water to remove excess precipitation

• Hydathodes specialised pore for process of guttation = remove excess precipitation

Physiological:

• Guttation

• Adapted to understory

  • within a plant: sun leaves & shade leaves

  • b/w plants: canopy & understory

• Adapted to light gaps (sunflecks - high light in short intervals)

Leaf variation and complexity

Simple leaf: one leaflet

Compound leaves: divided into leaflets (can be pinnate or bipinnate)

• Large SA

• Captures light, but allow penetration to lower branches

• “Cheaper” to produce than branches

• The individual leaflets or blades can change their angle relative to wind or growth — can intercept light at different angles, is more efficient

New shoots (branches or inflorescences) arise from leaf axils

Root adaptations plants have to persist in rainforests

• Shallow roots

  • To take up readily available nutrients in the first 0.5-1 m of soil

  • Roots spread widely = stability relative to wind blow

• Buttress roots

  • Swollen towards the base, spreads out = Greater access to nutrients

  • Structural support

  • Stabilises soil = Erosion control — prevents soil from being washed away by high rainfall

  • Improves competitive ability

    • Access to light (height), nutrients

    • Increases cross sectional area of the tree

    • Girth displaces individuals from getting close

• Prop roots

  • Structural support

  • Tree branches move out horizontally = Displace competitors + access to additional nutrients

  • Stabilizes soil = Erosion control

  • Lateral expansion = Improves competitive ability

All are more common in tropical, but also found in temperate

Shoot/stem adaptations plants have to persist in rainforests

• Climbing habit (lianas) = reach canopy for light

  • abundant in tropics

  • some have thorns/spines/hooks to attach to host tree

• Thorns / spines (connected to vascular system) = deter herbivores, shred others and prevent competition when leaves blow

  • E.g. Calamus muelleri “Wait a while vine”

• Prickles (not connected to vascular system, epidermal structures)

  • E.g. Roses, raspberries

• Modified trichomes (epidermal structures)

  • Some are fluid filled, silica enriched

  • Some are needle shaped, resemble felt hairs

  • E.g. Sundew: Exude sticky resins to capture other organisms

  • E.g. Gympie gympie: Stinging nettles of the genus Dendrocnide produce potent neurotoxins (effects can last weeks - years)

• Cauliflory (flowering on woody stems where pollinators can easily reach flowers & fruits)

  • E.g. Figs: Cauliflory in figs aid seed dispersal by birds

    • Symbiosis: dispersal mutualism (both benefit)

Types of epiphytes

1. Elkhorn and staghorn ferns

2. Basket ferns

Epiphytes: Elkhorn and staghorn ferns

• Platycerium spp

• 2 leaf/frond types:

  • Fertile long leaves

    • Spreads out away from host, enables light capture

    • Photosynthesises

  • Sterile nest leaves

    • Collect litter (defecation, dead animals, fruit) for nutrients

Epiphytes: Basket ferns

• Drynasia spp

• 2 leaf/frond types:

  • Fertile foliage fronds

    • Senesce

    • Photosynthesise

    • Reproduce

  • Sterile nest fronds

    • Don’t senesce

    • Often brown - don’t photosynthesise

      • Traps nutrients and stabilises plants attachment to host

Hemiepiphyte: Strangling fig

• Starts life in the upper canopy as an epiphyte, then crushes host

• Seeds dispersed by birds

• Commensalism becomes parasitism

Parasitic plants in the rainforest

Hemiparasite: Taps into host and steals compounds but can still photosynthesise

Holoparasite: Can’t photosynthesise (no chlorophyll), depends fully on host

• Overcome need to access light by tapping into photosynthate

• Often lack roots, leaves or stems

E.g. Mistletoe has sticky seed which sticks to cloaca of mistletoe bird —> it wiped on other plants

E.g. Balanosophora spp - Holoparasite: Has roots, no leaves or stem —> Roots tap into nearby trees and plants and take up resources

Carnivorous plants in the rainforest

• 6 orders across angiosperms, 11 families

• Australia ~200 species

• Convergent evolution

• Evolved because of low nutrient environments

• E.g. Nepenthes “Pitcher plants”

  • Lineage found only in tropics

  • 85 species in SEA and Australia

  • Trap insects in modified leaf

  • Takes advantage of animal faeces when used as a habitat (larger = more interactions with fauna)

What is frugivory?

Animals feeding on fruits as a means of dispersal (they don’t eat the seeds)

What is the purpose of dispersal?

Extend range, avoid inbreeding, move progeny away from adults, and increase genetic diversity

Dispersal in rainforest

• 50-80% of tropical rainforest fruits are fleshy, often brightly coloured

  • There is energy available for growth and photosynthate production —> create large storage organs for sugar and photosynthate —> entice and interact with fauna in understory

• Few large fruits

  • “Small” birds disperse 97% of fleshy-fruited species (seeds <2 cm), mammals and cassowaries disperse other 3% (larger)

  • Australian rainforests do not have primates

  • Megafauna declining / disappearing

  • More susceptible to disease, herbivores, other biotic stress events e.g. falling over

Diversity of fruits and flowers in the rainforest

Fruit colour increases apparancy; flower colour associates with pollinators

• Fruit colour: 1. Red 2. Black 3. Blue

  • Birds can see better as they contrast the green background

• Flower colour: Mostly white

  • Understory can be dimly lit —> white reflects more light = more apparent to different animals

  • Pigments can be expensive —> if plant opens flowers at night, they use chemicals to attract insects that are active at night —> no advantage to invest in colour so they retain ancient traits of being white

Frugivores are common dispersers of rainforest fruits

What are the (+) and (-) of large seeds?

(+)

• Resistance to predation

• Energy reserves for seedling establishment

• Evolved in resource poor environments (e.g. high shade) with ample water

(-)

• Reduced mobility

• Increased apparency (seeds will be eaten)

• Large energy resource (for consumers / to produce)

Rainforest case study: Cassowary has unique role in gene flow of Javan ash

• Largest vertebrate in Australian rainforests, the only animal capable of long distance seed dispersal

• Javan ash has toxic seeds that struggles to germinate

  • Flowers smell like rotten flesh & food —> pollinated by cockroaches

  • Suffering range contraction and reduced recruitment

• Cassowaries are not poisoned after eating cyanogenic Ryparosa fruit because the ripe flesh contains little or no cyanogenic compounds and the seed is undigested during gut passage

• Exocarp changes colour —> increases apparency

• Seed doesn’t change toxicity but pericarp has low toxicity when ripe (more tasty — Cassowaries eat)

  • If it's defecated and has the right hospitable conditions, it will germinate and grow quickly

  • If left too long, germination success decreases as there are invertebrates that consume the scat and cause damage to the seeds —> susceptible to detritivory

• Cassowaries have a varied diet and are not eating Javan Ash as much = less recruitment

Phytochemistry — plants use chemical compounds to defend themselves against animals, while also attracting animals to disperse their seeds once fruits are ripe

• Secondary metabolites (compounds that aren’t primary to photosynthesis) diversifies / intensified with high selection pressure

• Ripe fruits have fewer toxins and are attractive

  • HCN, alkaloids: (black bean tree), phenolics, terpenoids

• Animals avoid toxins

  • Defecation ~3-4 hr

  • Coevolution (different enzymes and products)

• The plant re-mobilizes / reduces those defensive compounds to allow vertebrates to eat them, but it maintains high amounts when not ripe so nothing eats it

Mutualisms in rainforests + provide an example of defense mutualism

• Pollination

• Dispersal

• Defense

  • E.g. Myrmecophytes: Ant-feeding plants

    • Epiphytes (commensalism with host plant)

    • Plant base has bulbous, hollow chambers that house ants

      • Debris and excretia provide plant with nutrients

      • Ants forage for herbivores

    • Australia is uniquely diverse in Myrmecophytes

Arrange non-flowering fossils from oldest to most recent

1. Bryophytes >400mya

2. Ferns 350mya

3. Conifers >300mya

4. Cycads 290-251mya

Angiosperm (flowering plants) lineage only existed after 250mya

What did bryophytes evolve when they colonised land and adapted to climate change?

Desiccation tolerance: the ability to tolerate drying out completely, going from this really turgid or full volume plant body to a crusty, still alive but dry moss

• Nucleation enables moss to draw in water from the atmosphere

• Desiccation and rehydration of mosses greatly increases resource fluxes that alter soil carbon and nitrogen cycling (when rehydrated, they release substances provide resources for soil microorganisms, such as bacteria and fungi)

Describe bryophyte species richness in Australia

• Highest in wet forests

• But also found in arid areas

  • Important components of soil crust — contribute to water & nutrient cycling, and buffer that region from extremes in aridity

  • Seals everything in as it dries out during the dry season in b/w rain events, preventing evaporation from the soil

  • Fungi, bacteria, invertebrates live in and under this in a protected place, so the diversity is maintained

  • Footsteps would damage that protective area and lead to potentially erosion and death

Bryophytes: 3 lineages of non-vascular plants

1. Liverworts

   • Often small

   • Often look like leaves that move across the landscape

2. Hornworts

   • Fuzzy

   • Very common

3. Mosses

   • Dawsonia superba

     • How it grows so tall: passive movement through different through diffusion, lives where there's a lot of moisture

• Arose before vascular tissues evolved, transport by osmotic gradients

• All are non-vascular plants — no vascular systems and no true leaves

Where is fern species richness highest in Australia? Are ferns vascular or non-vascular?

Wet forests. Vascular.

Diversity & endemism of Australian ferns and bryophytes

• Ferns: ~450 species; 35% endemic

• Mosses: ~980 species; 26% endemic

• Liverworts & hornworts: ~870 species; 23-28% endemic

How were early plant life cycles were adapted to common conditions?

Water is important (ferns and moss can't sexually reproduce without it)

• Can be small - raindrops, puddles

• Fertilisation occurs when the sperm joins with the egg.

• Gametes can only swim from male to female reproductive structures in an aquatic environment

• They can vegetatively reproduce without water, but that reduces genetic diversity overtime

Describe the spores of bryophytes and ferns

• Produced in large numbers (>10 mill/m^2)

• 1n (half the chr of the parent)

• Dust-like, mostly 5-70 um

• Tolerant to desiccation, high UV, temperature extremes

• Persistent - can travel long distances across vast oceans, etc

How do ferns and bryophytes survive in drier habitats?

• Use sheltered micro-sites

• Infrequent sexual reproduction

  • Not always in water (mostly asexual reproduction / vegetation propagules)

• Persistent spores (can remain viable for >15 years / until rain event that facilitates replication comes)

• Desiccation tolerance

Describe conifers diversity and distribution

• Largest biome in the world is the Northern Hemisphere is coniferous forest

• 44 sp — 39 endemic (89% endemic)

  • 5 species not endemic are distributed in New Guinea or associated parts of Asia (not unique to Australia because they arose so long ago)

• Australian conifers have ancient Gondwanan origins

  • As climate became drier and fire became more common, conifers declined in many areas and survived mainly in moist, sheltered habitats where fires are less frequent or intense.

• Fossil record suggests substantial contraction / extinction in most lineages

What are the 3 families of conifers that make up the dominant gymnosperms found in Australia?

1. Araucariaceae (most recent)

• arose when Aus and SA were still connected

• have a fossil record in southern Australia, in areas where they no longer occur

• Bunya pine

  • Found on the coast of Australia, exists in very tropical regions (ample moisture), but also found in the cool temperate regions (more arid)

  • Have cones with large seeds ~10 kg

    • Edible — humans are developing an industry for consumption more commercially

• Wollemi pine

  • Fossil lineage with a record >120 mya

    • Fossils similar to current ones (not a lot of morphological change over time)

  • Living specimens are isolated in deep canyons

2. Podocarpaceae

• arose earlier when still connected to Africa

• Plum pines

  • Reduced cones

  • Seeds have fleshy attachments (bird dispersal) — different from other gymnosperms (conifers and cycads)

• Huon pine

  • Oldest individuals dates at ~3500 yrs old

  • One ancient male plant in Mt Read (Tas) has survived for >10k yrs by continually producing clones (clone stand)

  • These can be very old lived individual trees because the environment has been static for so long (has not changed much or has changed within survivability zone)

3. Cupressaceae (oldest)

• widely distributed, arose a much longer time ago that when the land masses were more unified

• Native cypress-pines

  • The only conifers in semi-arid/arid Australia (filled the niche by adapting to aridity)

  • Tight cones formed along stems

• White cypress pine

  • Also found in arid regions (central Australia)

  • Light-coloured foliage, white reflectance = reflects light/heat

  • Small leaves; stems round = reduces SA for water loss

  • Woody female cone protects seed from fire and desiccation

3 genera of cycads in australia

• 7 living families, 11 genera, c. 100 spp.

• Australia: 4 genera, 69 species, All endemic !! 100%

• Old lineage (Gondwanan)

• Seeds in cones or on loose clusters of female branches

• Dioecious: separate male and female plants

• Macrozamia

  • Found in isolated regions because they can persist in gorges or microclimates that have ample moisture

• Bowenia

  • Was once more widespread but now survives naturally in tropical rainforests of northern Queensland (fossils are found elsewhere)

  • Very old

• Cycas

  • The only one with NO AUSTRALIAN FOSSIL RECORD

  • Because it recently colonised from Sunda (Indonesia) to Sahul (Australia)

• Fossils of other Australian genera indicate substantial range contraction

• Very ancient lineages ~290-300 mya (living fossils)

• But massive diversification in the last 10 my

  • It’s possible that all those fossils went extinct and they were highly diverse in the past, but we'd have no way of knowing

Categorise Bryophytes, Ferns, Conifers, and Cycads into whether they 1. need water to reproduce 2. have vascular tissue 3. disperse by spores 4. disperse by seeds

When did flowering plants originate?

Early cretaceous, 125-130mya.

What are Australia’s 3 largest angiosperm families, and what is the level of endemism?

1. Proteaceae

2. Fabaceae

3. Myrtaceae

• Relative to the global species, Australia represents a very small percentage of all the plant species found on Earth

• But highly endemic — 90% of flowering plants in Australia are endemic

Describe flower parts

Flower organs are established in concentric layers (whorls)

• The outermost floral organs are sterile (non-repro)

  • Whorl 1: Sepals (vegetative)

    • Outermost whorl, encloses the others

    • Deters herbivores, bacteria, and fungi (if tightly sealed)

    • Maintains humidity

    • Often photosynthetic, but sometimes pigmented like petals

  • Whorl 2: Petals (vegetative)

    • Contain coloured or UV pigments

    • Thin and delicate

    • Patterned to attract pollinators

  • Whorl 3: Stamens (male repro parts)

    • 2 parts: filament + anther

  • Whorl 4: Carpels (female repro parts)

    • 3 parts: stigma + style + ovaries

How can flower structure vary?

• Flowers can be complete (all whorls) or incomplete (missing a whorl)

• Monoecious or dioecious

  • Monoecious “one house” — complete or incomplete

    • Male (staminate) and female (carpellate) flowers occur on the same plant

    • Often in wind pollinated plants

  • Dioecious “two houses” — incomplete

    • Male (staminate) and female (carpellate) flowers are found on different plants

    • Often in vector (non-abiotic) pollinated plants

• Shape can vary: can be typical or modified form

Proteaceae overview: Diversity, habitats, traits, fruits & roots

• 1500 species, > 1000 spp (2/3) in Australia

• Habitats:

  • Forests, woodlands, heathlands — have low nutrient soils E.g. Banksia, Grevillea

  • Rainforests E.g. Macadamia, Telopea

• Sclerophyll woody shrubs and trees with corky bark, often lignotubers

  • Sclerophylly is a key trait in proteaceae, associated with many lineages in the family

  • Lignotubes will store moisture

• 2 types of fruits:

  • Woody follicles (split open)

  • Fleshy drupes (don’t split open)

• Proteoid / clustered roots

  • Within days, many lateral roots will shoot out from the main root.

  • Root hairs can get so dense that they'll start to senesce on themselves because they're not able to access nutrients and water

Distribution of Proteaceae

• Wide range

• Diversity associates with low P

  • Nutrient limitation that has led to the adaptive strategy of creating branching root structures (lateral roots)

• But not all Proteaceae are sclerophyllous or live in low phosphorus environments

• Banksia, Grevilia and Hakea are most rich in the Southwest, Persoonia (fleshy) lineage is found more on the eastern side

  • Proteaceae arose b/w 80-120mya (around the time where the continents were starting to spread out a bit more)

  • Hypothesis: 2 entry points, one in southwestern Australia and one in southeastern Australia relative to how the continents were aligned to Antarctica

Age of Proteaceae and how its distribution across continents changed as Gondwana broke apart

• Old Gondwanan family with fossil pollen record 80 my old (Cretaceous)

  • demonstrate that these plants existed when Australia still had connections to Antarctica

• When Gondwana broke apart, populations became geographically isolated through vicariance

Typical floral structure of Proteaceae

• In Grevillea

  • 1 whorl of perianth consisting of 4 tepals - fusion of whorl 1 & 2 (4-lobed)

  • Only 4 stamens attached to tepals

  • Ovary has 1 or 2 compartments

  • 1. style is long and acts as pollen presenter (male phase) 2. style receives pollen from other plants (female phase)

  • As the anthers mature, pollen is released and deposited onto the stigma

    • After ~24–72 hours, the stigma becomes receptive to pollen from other flowers, and the style extends outwards to facilitate pollination.

• In Banksia

  • Flowers aggregate into dense inflorescence

  • Flowers density, structure and apparency attracts pollinators

  • Styles are extended as pollen presenters in older flowers

  • Have robust structures that serve as functional perches to support the weight of animals (coevolution for mutualism)

Proteaceae: Why birds as pollinators?

• Pollinators have sensitivities to different wavelengths

• Birds: tetrachromatic vision (Blue, green and red)

  • Much better at discerning sharp contrasts in colour on the landscape although they can't see UV

  • Coevolution of bird vision and flower colour

  • (Insects: trichromatic vision (UV, blue, green))

Proteaceae: Fruits, seeds, and fire

• Grevillea

  • leathery

  • tend to occur broadly, but also associate with moist conditions

  • Seeds have these little fans on them that allow them to float and disperse more

• Banksia

  • Only a few ovaries develop as fruits

  • Fruit is a woody follicle

    • Requires fire to open

    • Evolved in response to environment (aridity, fire, low P)

  • Do NOT have hard seed coat

  • 2 winged seeds per follicle

• Hakea

  • woody structures that pop open with fire

• Macadamia

  • Edible, oil-rich nuts

  • Woody follicle

  • 4 different species

    • 2 of them are commercialised crop

• Persoonia

  • Fleshy sweet drupes

  • Occur in clusters

What are 2 main genus in Fabaceae (Legumes) and their uses?

1. Peas

2. Wattles (Acacia)

• Seed pods (fruits) are called legumes

• Uses of legumes

  • Food plants - peas and beans

  • Native species contains toxins

    • Antivirals, medicinal properties

    • Antidigestives, reduced by cooking

Peas overview: forms, seeds, leaves, pollinators

• Can be trees, shrubs, herbs, creepers, climbers

• Seeds have hard resistant coats

  • Survive fire, aridity

  • Protect embryo — will germinate when conditions are right

• Leaves are often compound - 3 leaflets or more

• Sclerophyll forms: simple leaves, reduced to spines or scales, or sometimes absent

  • Adaptation to low P habitat

  • Photosynthesise by green stems

• Nitrogen fixing — often associates with bacteria in the soil (Rhizobia)

• Fabaceae colours and sizes associate with distinct pollinator groups

  • ~95% insect pollinated E.g. ‘Egg and bacon peas’

  • Birds pollinate less — only flowers in the red spectrum e.g. certain species of Gastrolobium

Describe pea flowers

Butterfly flowers

• 5 petals: 3 free, 2 united

  • Keel petals largely protect the reproductive whorls

  • Standard petal is big showy and helps signal colour

• 10 stamens

• Bilateral symmetry

How are ‘Egg and bacon peas’ pollinated?

Insect pollinated

• Standard petal

  • Large and showy with nectar guides

  • Yellow broadly attractive to different insect lineages

• Keel and wing form a landing platform for pollinator

Flower variation in Gastrolobium of Fabaceae

• Birds tend to pollinate a fewer number of the Fabaceae (pollinate in the red spectrum), whereas insects pollinate a large number of Fabaceae across different spectrums

• When they tend to be more red-coloured, or larger or more showier, they're gonna be largely associated with birds as opposed to all the other colours that are largely associated with insects.

Wattles (Acacia): age and habitat

• NOT of Gondwanan origin

  • known in Australia since the early Miocene (recently within cenozoic)

  • arised after Aus moved away from Antarctica

• Acacia is the largest genus of woody flowering plants in Australia with ~1073 species

• Genus can occupy different habitat types

  • Occur in rainforests and wet eucalpyt forest e.g. Acacia melanoxylon

  • Widespread, can be understory or tall wet sclerophyll forests

  • Dominant in semi-arid and arid regions e.g. mulga lands

Wattles (Acacia): keystone resource used by ecosystems and people

• Green Acacia seeds roasted and eaten

  • 18-25% protein content

• Acacia gum - contains carbohydrate rich sap

  • Sweet / sugary

  • Used as glue or as food resource

• Timber e.g. A melanoxylon

  • Hard wood can be used in many timber processes

• Keystone species

  • Has root nodules that fixes N

  • Helps with recovery in fire damaged regions

What are the 2 foliage types of Wattles (Acacia)?

1. Bipinnate leaves

   • Compound leaves

   • Leaf structure is bifrucated with leaflets pointing off each side

2. Phyllodes (dominant in Aus)

   • Simple leaves

   • Not true leaves — they are equivalent to a flattened and expanded petiole of a pinnate leaf that photosynthesise

   • Juvenile (young) leaves are bipinnate but as the plant matures, it develops phyllodinous leaves

Both have nectaries at the base of stem near axle

Wattles (Acacia) pollination biology

• Very small flowers, in clusters (globular head or spikes)

• Closed flower head

  • Sepals and petals are wrapped around all the other parts protecting it

  • Petals will curl back and expose male and female reproductive parts

• Maturation and how it becomes receptive for pollination is OPPOSITE from Proteaceae (grevillea)

  1. Female phase: The stigma becomes receptive and can receive pollen from other flowers.

  2. Male phase: The anthers mature and release pollen.

• Can differentiate Acacia based on pollen grains

• Showy inflorescence of many flower clusters

• Extra-floral nectaries on leaves or phyllodes

  • Honeyeaters and Honey possums feed off nectaries (Both have convergently evolved forked tongues)

  • Can also attract non-pollinators (e.g. ants)

    • (-) Takes nutrients that might be reserved for pollinators

    • (+) Can keep plant relatively free of fungal spores (insect cleans)

    • (+) Ward off herbivorous insects

Wattles (Acacia) fruits and seeds

• Fruit a legume (pod)

• Soil seed banks

• Hard seed coat

  • Requires scarification: cutting it open / breaking it (e.g. by heat of fire or sharp object) — Seed takes in water and germinates once cracked

• Often have an eliasome (funicle)

  • Structure that's highly enriched in lipids

  • Helps attach the seed to the pod, but it also attracts ants to disperse it when it falls to the ground

• Ants take seed underground to their burrow

  • Remove the eliasome, cast the seed out, and put it in underground in a protected place (their garbage pile)

    • Seed will now be protected from predation and being broken down by fungal pathogens etc.

    • Ants can help maintain the acacia seed bank

Myrtaceae (Eucalypts) overview: diversity, fruit, flowers, leaves

Bottlebrushes, tea trees, eucalpyts, etc.

• 3000 spp worldwide, 1/2 in Aus

• Largest genus is Eucalyptus

• Widespread across all habitat types

  • Dominate forests and woodlands

• Used for horticulture, timber, paper, oils, spices - cloves (Syzygium aromaticum flower buds)

  • Typically have secondary metabolites that have evolved into different oil components

• 2 fruit types - scrub cherries, guava, feijoa

• Floral variation exists across genera

  • Despite looking very different they are genetically and morphologically the same

  • Fuzzy, many stamens

• Most have leaves with aromatic oils in oil glands

2 common fruit types of Myrtaceae

1. Dry-fruited forms (most common) e.g. eucalypt capsule opens by valves

2. Fleshy-fruited forms (less common) e.g. rainforest lilly pilly, midgem berry

What are the shared features of Myrtaceae flowers?

Flower structure may vary but there are shared features

• 4-5 sepals, 4-5 petals

  • actinomorphic = radically symmetrical (equal halves on either side when bisected in many different ways)

• Many ( >10) stamen

• Inferior ovary (whorls are above ovary)

How are Myrtaceae pollinated?

Mostly insects, but some by birds.

Myrtaceae (Eucalypts) distribution

• Some Eucalypts also only occur in Alpine

• Typically don’t occur in central arid regions

• The eucalypts dominate most habitats because they can get very large

Myrtaceae (Eucalypts) include the tallest angiosperm in the world. What is it called, where is it found, and is it fire sensitive?

Mountain ash, Eucalyptus regnans

• Occurs in wet sclerophyll forests

• Up to >100 m, >400 yrs old

  • Centurion in Tasmania was tallest one recorded 100.5 m

  • When tall it is subjected to wind events (might fall)

  • When old it becomes a keystone species: nest hollows are a resource for animals

• Adult is fire sensitive but seeds are stored in canopy and are released with fire

Myrtaceae (Eucalypts) flower and fruit development

1 is the Sepal operculum (top cap) - 5 sepals fused

2 is the Petal operculum (bottom cap) - 5 petals fused

1. Both operculum will pop off as the flower matures and expose many stamens

2. Male reproductive phase: pollen is released

   • The numerous stamens produce and release pollen

   • Nectar is produced to attract pollinators, such as insects, birds and mammals (produced by nectaries on the floral disc around the base of the style)

   • As pollinators feed on the nectar, pollen sticks to their bodies

3. Female reproductive phase: pollen is received

   • The stigma becomes receptive to pollen

   • When a pollinator visits another flower, it can transfer pollen from the first flower onto the receptive stigma (cross-pollination)

4. Fertilisation

   • Pollen reaches the ovules inside the ovary, allowing fertilisation to occur

   • The fertilised ovules develop into seeds

5. Fruit development

   • Once fertilised, ovaries will swell into large gum nut or capsule type structures

The male and female phases can overlap in eucalypts, and the timing of stigma receptivity varies between species. Not every eucalypt flower follows a strict male-then-female sequence.

Eucalypts are complete (4 whorls) but when flowers mature, sepals and petals pop off (2 whorls)

How to describe fruit shape of Myrtaceae (Eucalypts)

• Elongated, spherical, angular

• Disc level with rim, ascending, or descending from rim

• Valves flat, above, or below rim

• Pedicellate gumnuts: each fruit has a pedicel connected to a group stalk

• Sessile gumnuts: attached directly to the group stalk (peduncle)

Bark type of Myrtaceae (Eucalypts)

Thick fibrous bark promotes fire resistance

Leaf type of Myrtaceae (Eucalypts)

Eucalypts have distinctive foliage at various life stages (like Acacia)

• Juvenile leaves:

  • arranged in pairs

  • rounded shape

  • leaves often opposite one another

  • horizontal

  • sessile

  • dorsiventral (2 different tissue types on 2 sides) anatomy — palisade and spongy mesophyll

• Adult leaves:

  • long, droopy

  • arranged in spiral or alternate arrangement

  • petioles twist during development and leaf hangs vertically

  • isobilateral (one type of tissue on 2 sides) — palisade mesophyll only

    • when sun hits from any angle, more efficient in taking up energy

Some Eucalyptus species retain juvenile foliage: Neoteny - retaining juvenile features in adult form e.g. E. shirleyi

How do to identify Myrtaceae (Eucalypts) based on leaf and bud type?

Where in Australia is water limiting to plants?

Arid = < 250 mm per year

Semi-arid = 250-350 mm per year

• Half of Aus is arid / semi-arid

• Northern Aus has warmer temps (follows distance from equator)

• Even aquatic environments can be a dry habitat because if it is ephemeral

  • Water can accumulate on some of the very clayey, tightly poor soils

  • Water can evaporate and dry up

• Alpine habitats can be dry habitats too

  • When its most available its snow

  • Water can be locked away as ice or if it's rain it percolates through the system

• ⬆ precipitation = ⬆ biomass production

  • Vegetation is the densest and the tallest where there is the most precipitation

What drives water transport in plants?

• Plants take up water to replenish water loss through transpiration

Vapour pressure deficit = amt of moisture in the air relative to how much it should be able to hold if it was saturated

• If air is saturated (raining, high humidity) = value is less negative = water potential gradient wont be as strong = transpiration flux will be slower (often good for the plant unless they are in rainforests they may have too much water)

• If air is unsaturated (hot, windy) = gradient more extreme = ⬆ transpiration = water columns may break

Gas exchange requires ____ ____

open stomata

• Atmospheric CO₂ enters plant through stomata

• Stomatal aperture is controlled by turgor of guard cells

• Water loss depends on VPD

Plants differ in _____ use efficiency

Water.

WUE: relative to how much H2O is used per how much CO2 is fixed

• WUE is associated with the type of photosynthesis they perform

• CAM photosynthesis is most efficient (temporal separation)

  • C4 (spatial separation)

  • then C3

*C4 grasses open their stomata during the day but generally to a lesser degree than C3 plants

What are plant strategies for avoiding drought?

Xerophytes: adapted to survive under arid conditions

• avoidance

• escape

• tolerance

What are the 2 types of drought avoidance

1. Water spenders — rainforest & riparian (near water) plants

• Ample water available, near water source

• Deep rooted or high Root:shoot ratio (deep root systems, laterally extensive as well)

  • Ample access to water from groundwater

• Have continuous access + steady water supply, can transpire even in arid seasons

• Mycorrhizae (fungal organisms) help

  • Freely distributed and colonised with ~80% of plant species

  • Mycorrhizal fungi hyphae act as root hairs

    • ⬆ SA (⬆ nutrient and water uptake as it becomes limiting)

2. Water savers

• Leaf rolling: e.g. desert grasses -Triodia (spinifex)

  • Improve water efficiency by reducing water loss

  • Spines within the curled part interrupt boundary layer of the plant

  • Stomata stomatal crypts / grooves (invagination where the stomata at the bottom) also interrupt the boundary layer (surface of plant)

  • = slow down those water molecules from moving away from stomata = reduce the VPD = improved water efficiency by reducing water loss

• Have sclerophyll (type of cells that are highly lignified)

  • Have spines

  • Tough, rigid, unpalatable plants = deter herbivores living in an environment

What are anatomical features of water savers?

• Thick, waxy cuticle = reduce heat flux, light penetration, and water loss

• Sunken stomata = water not blown away easily

• Thick-walled cells (sclereids, fibres) - lignin in walls

• Leaf hairs (trichomes) = alter the boundary layer for heat = reduce heat transfer to leaf + reduce water loss

What are forms of drought escape?

• Annuals

  • Annual (over a yr) / ephermeral (over a couple yrs) plants spend drier times in dormant state as seeds

  • Grow and reproduce quickly when moisture is available

  • E.g. Wildflowers in Western Australia (everlasting daisies), Sturt’s desert pea (legume)

• Plasticity

  • Depending on the time of year, plant is physiologically plastic

  • Winter: Stomata will open maximally, driven by hormonal and water gradients throughout the day to uptake CO₂ without exporting too much water

  • Summer: Tighter control of maximising carbon uptake in mornings and evenings resulting in slower growth rates relative to carbon taken up

What are examples of plants with drought tolerance?

• Have desiccation tolerant enzymes

• Osmotic adjustment of cells using solutes

Australian succulent plants

• ~400 spp that have higher degree of succulence (spongy, thicker layers)

• Coastal and inland saline areas

• Small number of succulents in arid Australia — lack the large stem succulents seen in other arid parts of the world

• most CAM plants are succulents (but not all succulents are CAM)

E.g. Boab tree Adansonia gregorii

• Long lived ~2000 yr and can grow up to 15 m diameter

• Up to 100 kL water stored in trunk = persist in arid times

• Drought deciduous (one of the few species in Aus that are) — when very arid, they will lose their leaves & when favourable conditions return, they will resprout leaves (phenotypic plasticity)

E.g. Chenopod shrublands /Chenopodiaceae (saltbushes) of deserts

• drought and salt tolerant

  • Can concentrate salts into specialised cells in the leaf tissue (e.g. vacuole)

  • Draws water in by maintaining higher levels of salt and using it as a gradient for water

• Surface colour reflects radiation (greyish blueish colour)

• Covered with bladder cells to excrete salt

  • Salts form on leaf surfaces as a protective layer = alters boundary layer = reduces high UV hitting the plant

Maximising water supply ≠ drought resistance in most plants. What is an example of a plant that maximises water supply?

E.g. Mulga (small Acacia, Acacia anuera)

• Acacia anuera can grow throughout the year

• Has plasticity and adaptations to enhance water uptake and water preservation = adapted to conditions, not really drought resistant

• Extensive root systems (up to 3m)

• “funnel” habit can eek out more water from dry environment

• NOT drought avoiders as they continue to grow (slowly) and metabolise through dry periods

What are sclerophylls and why did they first evolve?

They are hard-leaved plants

• Tough leaves, reduced SA, thick short stems (reduced internodes), high lignin

• Fossil evidence shows sclerophylly arose prior to acidification (rainforest still present) but soil weathering likely occuring

• Experimental evidence shoes P addition can reduce rigid leaves

• Contemporary biogeographic patterns link P to sclerophylly

What are the 2 hypotheses to how sclerophylly evolved

Evidence for Beadle comes from biogeography and experimentation:

• Many sclerophyll plants thrive in areas with abundant moisture (e.g. Eucalyptus, Acacia, Epacris)

• Sclerophyll plants were evident before the onset of aridity in Australia (e.g. first fossil of Banksia > 50 mya — alot of rainforests present)

• Sclerophyll plants when given additional P can become soft-leaved

• When starved of P, roots become proteoid / clustered

Why might sclerophylly be an adaptation to low nutrient soils?

• Lack of nutrients can limit plant cell growth and metabolism

  • Excess carbs are thus invested into lignin structures

• P deficiency can imbalance metabolism

  • P will be used for traits relative to survival through evolution

When did sclerophylly first evolve?

Beadle’s hypothesis: Sclerophylly first evolved on soils of low nutrient level - especially low P

• Under rainforest conditions —> high amt of weathering —> high mobility —> competition and adaptation to access P

• Current lineages that are highly sclerophyllous have low conditions of P

What are 3 examples of sclerophyllous plants?

E.g. Heaths

• Southern heaths; Epacris

• Bell-shaped flowers

• Distributed on heathlands that have low P soils

  • Because of extensive weathering and laterite soil (oxidation = low pH = mobilised P can be leached out by rain events)

• Small stature: small leaf size, short internodes

• Proportionally thick leaves

• Reduced SA:Vol of leaves

E.g. Acacia

• ~1000 species in Australia, dominant vegetation of deserts

• Tough “leaves” that are phyllodes (flattened leaf stalk)

  • Water loss from phyllodes is less than leaves (⬇SA:Vol)

• Long-lived, grow slower during drought

E.g. WaxflowerMyrtaceae

• Often small leaf size, short internodes

• Proportionally thick leaves

• Reduced SA:Vol ratio of leaves

  • Sometimes cylindrical or needle shaped

• Less SA for water loss through stomata

What does sclerophylly do?

• Reduces damage caused by wilting during drought

• Reduces damage caused by herbivores, as sclerophyllous tissue is not highly palatable or nutritious (high C:N ratio)

  • applying fertiliser to sclerphoylls (e.g. by cattle / sheep waste) can lead to their demise

    • Plant crown foliage may overdevelop

    • Plant may become palatable (ruminants will eat) and prone to disease (foliage may develop) e.g. eucalypt “dieback”

The current prevalence of sclerophyllous plants in Australia is related to…

• Low nutrient soils

• Increased aridity since Australia separated from Antarctica 

• Increased frequency of fires since Australia separated from Antarctica

What are the types of grasslands in Australia and where are they found?

Used to be 70% of Australia, now only 25%

• Arid tussock grasslands

  • Clumps of grass

  • Astrebla spp

• Arid hummock (widespread) grasslands

  • Grow into large mound shape = habitat for animals, alters precipitation, contributes to different crust formation

  • Triodia, spinifex

• Coastal grasslands

  • Xerochloa, northern coastline

• Subhumid grasslands

  • Can occur in Tropical (Themeda), Temperate (Themeda), Subalpine

Keystone species: Kangaroo grass (Themeda triandra)

An example of subhumid grasslands, occurring in both tropical and temperate regions.

• Only been in Aus for ~1.5 m yrs (recent immigrant)

• Tufted perennial

• Poor tolerance to high grazing

  • Environmental indicator

  • Overgrazed = reduced recruitment

• Native grain (flour)

• Origins trace back to SEA

  • Floral spikes have barbed seeds that attach to animals very well

• They are a keystone species

  • Regular biomass removal maintains diversity

  • Deep rooted, taller competitors win over time

  • Irregular (changing) land management can lead to local extinction

Fire regime of kangaroo grass (Themeda)

With regular biomass removal (fire comes every 3-5 years)

• Tussocks burn back to their core and then grow back profusely

• Creates high fire load of vegetation

  • ⬆ amt of vegetation that will dry out and burn within the season

• Grasslands grows fast — can burn quickly and release nutrients

• Forbs and wildflowers take advantage of inner tussock space — there is nutrients and now light (1.5 m tall plants are gone)

• Biomass that grasslands create contribute to their ability to catch the landscape on fire when there are dry conditions and lightning

With irregular biomass removal (no fire regime)

• Grasslands keep growing taller and putting on more biomass

• Eventually shade out other species, and that can lead to local extirpation of some of these species

When and why did grasslands evolve?

• Evolved during the Late Cretaceous period 94-110mya

• Ancestors to grasses were in rainforests / evolved in rainforest ecosystems

• Diversified and adapted to a changing global climate

  • Aridity (shift Northward)

  • Cooling temperatures

  • Changes in landscape

• Dispersed across continents

• Sunda-sahul interchange occurred during glacial maximum — cooler temp and connectivity increased range / speed

How did grasslands persist?

• Evolved drought avoidance mechanisms

  • Long fibrous deep roots

• Grasslands occur wherever clay is high

  • Slow water percolation and poor aeration occurs when wet & excessive moisture loss when dry

  • There is aerenchyma or special cell types that allow for oxygen flow in the plant

  • Plants have swollen or thickened root structure

• C4 photosynthesis

C4 photosynthesis

• Convergently arose x60 across different lineages)

• C4 arose ~60mya, grasses arose >100 mya

  • It was getting too warm and challenging for grasses to take carbon and not lose water

• Common in subtropical and tropical ecosystems

• Many grasses (including crop species) have C4 photosynthesis e.g. maize, sugarcane, millet

  • ~ 1/4 of global GPP is by C4 plants

• ⭐ Australia has the highest dominance of C4 vegetation of all continents

  • 14 families that have different C4 plants i.e. Chenopods (Chenopodaceae), Sedges (Cyperaceae), grasses (Poaceae)

• Neuranchne, mulga grass is now a model for photosynthesis evolution

  • Started off largely C3 but the incidence of C4 is occurring, and the reversion back to C3 is also occurring

Grasslands are home to what other species?

1. Orchids (Orchidaceae)

• CAM photosynthesis

• Epiphytes (in the tropics) and ground dwelling (in southern Australia)

• Occur in diverse range of habitats

• 28k spp globally, 1800 spp Australia

2. Lillies (Asparagales)

• C3 photosynthesis

• High endemism

• Thysanotus (fringed lily)

• Drymophila

  • Tropical

• Dianella

Orchidaeae - 2nd largest family of flowering plants. What mutualisms do they have and what kind of photosynthesis do they use?

2 mutualisms:

1. Mycorrhizae dependent seed germination

• Orchids seeds do not contain storage tissue (do not have an endosperm) —> they have no way to mobilize nutrients

• Mycorrhizae get resources eventually when orchid produces photosynthate, and they help this orchid germinate (hyphae grabs moisture and nutrients)

2. Pseudocopulation (deceptive) pollination

• Orchids mimic the smell of saw fly females (has a sex pheromone) and kind of looks like saw fly

• Mutualism: orchids maintain high degree of fedility

Earliest described Australian CAM plants were orchids

• CAM plants lacked succulence (compared to Crassulaceae)

• 2/3 of all orchids showed CAM physiology

CAM photosynthesis

• The most water efficient

• Convergently arose across plants x30

• A way to tolerate arid conditions, lack of moisture e.g. Epiphytes have no roots to tap into moisture

At night (cooler and moister):

• Stomata open

• CO₂ diffuses into storage at night

• Transported and fixed into acid — malic acid

• Stored in vacuole

During the day (hot and dry):

• Stomata closed (water loss reduced)

• Acid is broken down into carbohydrates through the Calvin cycle

• CO₂ released form storage

• CO₂ fixed in usual Calvin cycle reactions

• Light is available and can drive the Calvin cycle

What are other CAM plants that are not Orchids?

Isoetes quilworts

• Some submerged aquatic plants have CAM

• Ancient vascular plant lineages

• Reason for evolution of photosynthetic pathway

  • During the day, photosynthetic algae rapidly deplete CO₂ in the water

  • At night, CAM draws in CO₂ that is being released through respiration from other organisms, fixes that carbon the next day when the sun is up

Caustic vine

• Gondwanan origins

• Cynachum viminale

  • Subsp. Australe (Apocynaceae)

• Dogbanes / milkweeds

  • Type of endemic in Aus

What is an example of a facultive CAM plant?

Parakeelya spp

• Australia’s first identified succulent (desert CAM)

  • Calandrinia (parakeelya) polyandra (Montiaceae)

• Nocturnal acid accumulation relative to water status (trait has plasticity)

• Only CAM under certain conditions

  • Under well-watered conditions operate like C3, but when droughted they turn CAM on

  • Induced to perform different physiological states as a means to adapt to env

Why is too much sunlight a bad thing for plants?

Energy is gained through net radiation by leaves / plant (sun, environment, biochemical reactions) & is lost (reflectance, evaporation, environments)

• The bigger the difference in air and leaf temperatures, the greater the sensible heat flux

• The bigger the difference in the air and leaf water vapour concentrations (VPD), the greater the latent heat flux

• Plants need to maintain optimal physiological temps (heat denatures proteins)

Latent heat loss: Heat energy lost from plants through water vapour formation is called latent heat loss

Sensible heat loss: Heat energy loss through transfer to the air