Flowers

Pollination syndromesamong the phloxes

Butterfly and Moth Pollination• Butterfly and moth flowers similar to bee flowers because

moths and butterflies also guided to flowers by combination of sight and smell

• Some butterflies can see red, so often have red or orange color for flower

• Nectary is often at bottom of long, slender corolla tube or a nectar spur - only accessible to long sucking probocis of moths and butterflies

• Nectar is copious, but not so concentrated - often 25% sugar• Moths are nocturnal so many of their flowers emit heavy

fragrance at night, often pale or white in color - scent is sweet and penetrating

Erysimum – butterfly pollinated

Episcia – moth pollinated

Bird Pollination• Bird pollinated flowers produce copious, thin nectar - often

about 25% sugar, often very high in sucrose - may actually drip with nectar

• Usually have little odor because birds have poor sense of smell• Birds see red and bird pollinated flowers often very colorful

with reds and yellows - red columbine, fuchsia, passion flower, hibicus, poinsettia, many cactus and orchids

• The flowers are usually large or part of large inflorescence• Nectar usually held in long tubes that other animals can’t reach

Hummingbird pollination

Ipomopsis aggregata – hummingbird pollinated

Greater double-collared sunbird

Proteus – pollinated by perching birds

Bat Pollination• About 250 species of bat (25% of all bats) include some pollen,

nectar or fruit in their diet - many pollinate flowers as part of their feeding

• Bat flowers are similar to bird flowers - large, strong flower which produces copious nectar - Often dull colored because open at night - may only open at night

• Often have very strong fermenting or fruitlike odors, may be musky odors too

• Bat flowers often hang down below foliage to enable bats to easily get to the flower

• Banana, mango, sisal and kapok flowers pollinated by bats

Bat pollination

Wind Pollination• Usually have dull colors, relatively odorless, do not produce nectar, petals

small or absent, sexes often separated• Wind pollinated flowers are most common in temperate areas where large

stands of single species of plant occur• With trees, wind pollination occurs in spring before leaves have emerged -

usually have well exposed stamens to shed pollen to wind and stigma also exposed - often with feathery outgrowths to catch pollen

• Often the plants have various mechanisms to promote out-crossing - separate sexes - dioecious - willows, poplars

• unisexual flowers on same tree - monoecious - oaks, birches• Self-incompatible - grasses• Flowers are typically small, have single ovule per flower - however have

many flowers borne in inflorescences and multiple inflorescences

Box elder – wind pollinated – female left, male right

Wild Oats – Avena fatua

Wild oat flower – close up

Cottonwood CatkinsMale Female

Why Pollination?

Why Pollination?• Plants engage in pollination in order to ensure

successful sexual reproduction• Then – Why Sex?• The benefits of sexual reproduction are that it enables

the introduction of novel genetic combinations of DNA• This creates potential for plants to develop new genetic

combinations which may allow increased survival, reproduction and thus fitness – producing more offspring

Sexual reproduction introduces variation via three steps:

1. meiosis forms haploid cells with different combinations of chromosomes

2. genetic recombination occurs during meiosis via crossing over

3. fusion of gametes (eggs and sperm) from haploid cells to form new zygote

Pollination in Plant Breeding

Double Fertilization

• At double fertilization, several processes are initiated:

• the primary endosperm nucleus divides forming the endosperm;

• the zygote develops into the embryo; • the integuments develop into the seed coat; • the ovary and related structures develop into

the fruit

Embryo Development

• Early embryo development is similar in dicots and monocots - at first the embryo is a spherical body - however, differences appear when the cotyledons develop - the dicot has two cotyledons and the monocot has one cotyledon

Endosperm and Cotyledons• The primary endosperm nucleus divides mitotically

to form the endosperm - the endosperm tissue will provide food to the developing embryo and in many cases, to the young seedling too

• In many dicots and some monocots, the endosperm tissues are absorbed by the developing embryo before the seed becomes dormant - then the nutrition is stored in the cotyledons - peas, beans

Gymnosperm Seeds

• In gymnosperms like this pine, the food for the seed comes from maternal tissue (the gametophyte)

Ovary and Ovule Development

• As the ovule develops into the seed, the ovary develops into the fruit

• As this happens the ovary wall thickens to form a pericarp - the pericarp often has distinct layers - exocarp, mesocarp and endocarp or just exocarp and endocarp - the layers are easiest to see on fleshy fruits

Fruit Layers

1. Endocarp 2. Seed3. Mesocarp 4. Exocarp

1, 3, and 4 together makeup the pericarp.

Fruits• A fruit may be defined as a matured ovary. In

some plants the fruit may include other flower parts that are fused to the ovary. True fruits develop from a single pistil. A flower with one or more simple pistils produces a corresponding number of fruits. A compound pistil develops into one fruit but may split at maturity into a number of pieces that often corresponds to the number of carpels in the pistil (like a blackberry or pineapple).

Note: D should be Samara; E should be Achene

Note – missingPepo and hesperidium

Apples and Pears

Strawberry – flower and fruit

Seed Dispersal

Seed Dispersal Distances

Animal Seed Dispersal Shimba Hills, Kenya

Seed Dispersal by Wind

Seed Dispersal by Water - Coconut

Seed Dispersal by Self

Poppy – shaking in breeze Explosive

Hitch-hiking

Human Seed Dispersal

Limiting Seed Dispersal

• In violets there are two kinds of flowers:• chasmogamous flowers that open in the

normal way and are insect pollinated - these seeds disperse far away

• closed cleistogamous flowers that never open and reproduce by selfing - these seeds never disperse very far - the cleistogamous flowers form later in the summer

Violetflowertypes

More limits to Dispersal

• Peanuts limit their dispersal even further because their cleistogamous seeds are produced by underground flowers - these are called amphicarpic flowers and seeds - these seeds clearly don’t disperse

Peanut – Amphicarpic Seeds

Dispersal by Clonal Growth – Black Locust