Seed Plants 2

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Ginkgophyta

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>Only 1 species survives : Ginkgo biloba.
> Native to China, it has remained almost unchanged for almost 300 million years.
>It is dioecious and has triangular leaves are deciduous.
>Sperm are released from the end of the pollen tube (as in cycads).
>Ginkgo is resistant to air pollution, so is planted in many cities. The seeds smell very bad (like
rotting meat), so typically only the male trees are planted.
>Ginkgo is claimed to be useful in treating Alzheimer's disease, although more testing is needed.

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Coniferophyta

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>Over 700 species still exist.
>Usually evergreen, drought tolerant: they have needle shaped leaves, thick cuticle, stomata sunk in pits.
>Conifers are often the dominant trees in cold climates eg Canada. The stem is strengthened with
lignin so they can grow very tall. The stem gets wider ( secondary growth ) due to the cambium
which produces xylem on the inside of the stem and phloem the outside.
>Wind pollinated ; pollen tube grows all the way to the egg. Usually bisexual ( or monoecious ):
each tree produces small male cones and large, long lived female cones.

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uses of conifers

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Conifers are important commercially for wood, paper etc. Slash pine In Florida almost half the
state is forested, and in northeast Florida the paper and lumber industries have over $7 billion a
year in output. Example : genus Pinus.

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Dendrochonology

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>Dendrochronology involves dating past events by studying tree ring growth. Trees typically grow
fast in spring, and growth stops in the fall, producing annual rings in the xylem. A sample ("core")of the wood is removed using a stem borer.
>Conifers are often used, eg Pinus longaeva (Bristle cone pine). The oldest living bristle cone was
5,000 years old. Current records (using trees that died centuries ago) in Europe and US go back
over 9,000 years.
Dendrochronology is used in:
a) dating archaeological sites.
b) studying past climatic changes. A study in 2011 used dendrochronology to show that the Aztec
empire in Mexico collapsed due to many years of drought.
c) showing fire and insect damage in the past.

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Anthophyta (Flowering Plants)

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This is the only phylum of seed plants that is not included in gymnosperms.
Anthophyta evolved recently ( 150 million years ago)
There are roughly 350,000 species (much more than all the gymnosperms).
Anthophyta have efficient vessels in the xylem to carry water (gymnosperms have tracheids
instead of vessels).
Flowering plants are typically insect pollinated.

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Flower parts

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sepals ( protect the flower bud )
petals ( attract pollinators ).
stamens ( anther, filament ) produce pollen.
carpels or pistils ( stigma, style, ovary ) produce the egg.

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Flowering plant reproduction

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Anthophyta have double fertilization : one male gamete fertilizes the egg ( making an embryo )
and the other male gamete fuses with 2 polar nuclei (making a triploid endosperm ).
The seed is released surrounded by the ovary, as a fruit.

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Plants have several defenses against herbivores:

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a) many plants produce toxic chemicals.
b) plants may have mutualistic relationships with animals such as ants, which keep herbivores
away.
c) plants may release chemicals to attract predators that feed on herbivores.
Most wild plants are flowering plants. Anthophyta are vital as crops, including GM (genetically modified) plants.

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Monocotyledons

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One cotyledon (seed leaf)
Parallel leaf veins
Scattered vascular bundles
No cambium
Flower parts in multiples of 3
Fibrous roots
eg wheat, grasses, palms

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Dicotyledons

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Two cotyledons
Net-like veins in the leaf
Vascular bundles in a ring
May have cambium
Flower parts in 2, 4 or 5
Tap roots
eg rose, oak, tomato

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yellow or blue

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Insects eg bees
vanilla

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white (opens at night)

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Bats
Mussa (banana)

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white (opens in day)

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Beetles
Magnolia

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Red

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Bird
Hibiscus

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Green

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Wind
Zea (corn)

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Seed Dispersal

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Wind - light seeds with hairs or wings eg Acer.
- tumbleweeds : the whole plant blows around eg Salsola.
Water - floating seeds eg Cocos ( coconut ).
Animals - hooks or barbs catch on fur eg Bidens.
- ants collect seeds that have an elaiosome Fig 35-14 eg Acacia.
- larger fruits have hard seeds that can survive through the animals digestive system eg Malus (
apple ).
Hot pepper seeds are spread by birds, not mammals

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other forms of reproduction

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Some cultivated plants, like bananas, produce fruit without seeds, so reproduce asexually.
Seedless tomatoes and grapes are often sprayed with plant hormones to artificially produce parthenocarpy (fruits without seeds).
Finally seedless watermelons are produced by crossing two varieties that have different numbers of chromsomes, so the offspring are sterile (just like a mule, produced by crossing a horse and donkey, is always sterile).