Lecture 18: Wildflower Pollination, Floral Deceit & Seed-Dispersal Strategies
Course Context & Orientation
Nearing the end of the Natural History course; lecturer jokingly suggests they are “ahead of track” and might need “filler.”
Current unit: Plant reproduction → pollination → seed dispersal.
Previously covered animal reproduction; now finishing plant side before final unit on parental care/seed dispersal.
Pollination Fundamentals
Flowers exploit insects & other animals as “sexual surrogates.”
Colour & Form Cues
Bees/bumblebees: prefer blue.
Many flies prefer yellow.
Hummingbirds (in temperate zone): see red; the only pollinator of cardinal flower.
Tropical insects often see red—geographic difference stressed.
Nectar Guides & Landing Platforms
Bird’s-eye primula: concentric “Cheerio” bull’s-eye.
Butcher-and-Eggs: coloured landing strip.
Hidden UV patterns common in flowers & some animals—humans can’t see them.
Bribes & Manipulation
Food reward (nectar, pollen) lures the visitor; plant places pollen on strategic body parts (e.g. jewelweed coats hummingbird forehead).
Avoiding Self-Pollination
Genetic advantage of out-crossing highlighted.
Heterostyly (different style lengths)
If 3 lengths present → tristyly.
Example: Purple loosestrife (also Pickerelweed).
Each plant carries one floral form only: long-, medium-, or short-style.
The style is what determines the form of each flower
Each flower has two sets of stamens; only pollen from a stamen of matching length (on a different plant) can fertilise.
Colour differences even within same plant’s stamens.
Prevents self-pollinating; demands pollen transfer between forms.
Floral Deceit Mechanisms
Pink Lady’s-slipper (Cypripedium)
Slit entrance + blocking staminoid.
Exit tunnels partly blocked by sticky pollen masses → bee deposits old pollen on stigmatic surface, exits with new pollen glued to back.
Rose Pogonia
Showy “pollen” is pseudopollen; insects deceived, brush real sexual organs at rear; optimized for bumblebees.
Pseudonectaries
Look glossy (glisten) like sugar droplets but dry hairs
Grass-of-Parnassus
Milkweed – “Saddlebag” Pollination Trap
Individual flowers have shallow nectar cups separated by a slit.
In slit = pair of pollen sacs joined by a strap (pollinia).
Insect leg slips in → sacs (saddlebags) snap on; removed & delivered to next flower.
Costs for weak visitors
Some insects can’t pull free → lose legs or die; dead bodies often seen on umbels.
Narrative includes observation of crab spiders ambushing pollinators.
Slam-Dunk Orchid (Grass-pink / Calopogon)
Normally orchid lip is a lower landing petal; here flower twists so lip is uppermost.
Lip bears showy fake stamens with pseudopollen; has a hinged base.
Bumblebee lands → petal slams down, slam-dunks bee into trough (“coffin”); bee escapes past stigma (deposit) then anthers (pickup).
Dynamic & Explosive Flowers
Laurels (Sheep & Bog Laurel) ― “Bashing stamens”
Filament tips held in petal pockets; visitor weight releases spring tension → anthers whip up & dust insect.
After release, pollen on insect may contact protruding stigma of other flowers.
Bunchberry (Cornus canadensis) ― Catapult stamens
White “petals” are actually bracts; true flowers are central greenish knobs.
Each flower = hair-trigger; touched → stamens unfold & fling pollen straight up.
Explode like land mines and catapults the pollen for the insect to carry
Recorded speed 0.5ms – fastest known above-water plant movement (tied with bladderwort trapdoors).
Helleborine Orchid – Wound-Hormone Deception
Non-native Epipactis helleborine, nick-named “Helleboring.”
releases leaf-damage volatiles (wound hormones) without being eaten.
Attracts wasps that normally follow these cues to find caterpillars.
Wasps probe flower for nectar, acquire/transfer sticky pollen masses on head.
Sexual Deceit (Bee & Fly Orchids)
Not Canadian; illustrate pheromone + shape mimicry.
Flower mimics receptive female insect.
Males attempt copulation → pollinia attach.
Exceptions to Cross-Pollination
Cleistogamy (cleistogamous) (closed selfing flowers)
Spring ephemerals (e.g. Polygala/gay-wings) produce underground, never-opening, self-fertile flowers as Plan B if showy aerial blossoms fail (snow, cold).
they have another set of flowers next to the warm ground they have flower that self-pollinate and produce seeds
they never open and have both sexual parts and pollination occurs
Obligate Selfers / Colonisers
Dandelion; some Ladies’-tresses.
self-pollinates
Advantage in rapidly occupying transient open habitats.
Transition to Seed Dispersal
After pollination → protect developing seeds (armor + chemicals) until ripe.
Examples: cones, acorn shells, blueberry bitterness from terpenoids, milkweed pods rich in toxic cardenolides.
Seed Dispersal Strategies & Terminology
Wind – Anemochory (cf. anemophily for pollen)
Lightweight, small seeds, silk parachutes or wings.
Milkweed, thistles, fireweed
(70-100,000 seeds/plant), dandelion
Problem of landing in the right spot
mass seed production
Ghost Pipe (Monotropa/“ghost pipe”): post-pollination stalk turns upright;
capsule splits up gradually so wind can pick up minute seeds in fall when forest floor windy.
External Animal Transport – Epizoochory
Hooked/barbs cling to fur/feathers/clothes.
Beggarticks/sticktight (Bidens), burdock burs (inspiration for Velcro), Queen Anne’s Lace seeds.
Queen Anne’s Lace umbel (arms that hold flowers up)
closes in damp/cloudy weather by hygroscopic cell swelling → protects seeds from rain; reopens in sun
arms in umbel have cells that acts like an umbrella because of the moisture in the air
Internal Animal Transport – Endozoochory
Fleshy fruits: blueberries, buckthorn, etc.
Consumers (black bears, foxes, waxwings, sandhill cranes, pileated woodpeckers)
digest pulp;
hard seeds pass unharmed in droppings → deposited with fertiliser.
Seeds must resist mastication & gastric acids.
Ant Dispersal – Myrmecochory (term mentioned implicitly)
Spring ephemerals (Trilliums, Violets).
Seeds bear protein-rich elaiosome.
Ants carry seeds underground, eat elaiosome,
discard seed in storage chamber → safe germination.
Violets add ballistic ejection: drying 3-part capsules squeeze seeds metres away before ants collect.
Ballistic/Mechanical Ejection
Violets (above) and touch-me-nots (not detailed today).
Rain Splash – Ombrochory / Hydrochory Variant
Miterwort (Mitella) – cup-shaped “splash cups.”
Raindrop impact ejects seeds.
Foamflower (Tiarella) – hinged “springboard” lever
raindrop depresses board, seed rolls out & is flung with drop.
Water – Hydrochory
Aquatic/shoreline plants (Iris, Water-lily) package seeds with air-filled coats; float then waterlog & sink.
Special Forest Timing
Dense summer canopy limits wind; forest herbs time wind-dispersal to autumn (leaf-off), or rely on ants.
Trees use winged samaras (maples), paired wings (basswood single sail; birch tiny wings).
Wind-landed seed on rotting log can form “perch tree” with elevated, stilted roots.
Key Vocabulary Checklist
anemophily: wind pollination of pollen.
anemochory: wind dispersal of seeds.
zoochory: general animal seed dispersal.
epizoochory: outside of animals.
endozoochory: inside of animals.
myrmecochory: ant dispersal (elaiosome bearing).
hydrochory: water dispersal (inc. splash-cup variant).
Heterostyly / Tristyly: differing style lengths (3 forms).
Cleistogamy: closed, self-pollinating flowers.
Elaiosome: lipid/protein appendage on seeds that attracts ants.
Pollinium / Saddlebags: paired pollen sacs of milkweed.
Staminoid: sterile stamen-like structure (lady-slipper).
Pseudonectary / Pseudopollen: fake reward structures.
Splash-cup / Springboard / Ballistic ejection: rain or tension-driven seed launch mechanisms.
Numerical Highlights
Fireweed: seeds per plant.
Bunchberry stamen opening speed: 0.5s (half of 1/1000 s).
Concept Connections & Significance
Demonstrates plants overcoming immobility through diverse, often highly specialised partnerships or deceptions.
Cross-pollination mechanisms parallel animal out-breeding benefits → genetic diversity.
Backup selfing (cleistogamy) mirrors animal parental care insurance strategies (coming next).
Seed dispersal methods anticipate ecological succession (e.g.
selfing pioneers in transient openings).Numerous human technological inspirations: Velcro from burdock; catapult mechanics; hygroscopic actuators (Queen Anne’s Lace).
Looking Ahead
Final theme of course: Offspring success after reproduction.
• Plants → full exploration of seed dispersal (continued).
• Animals → parental care strategies (visual, behaviourally rich finale).