The ferns

enter the stage during the late Devonian,

and they have been a very successful plant group ever since.

Ferns are vascular plants and reproduce with spores, just as the club mosses but

they made revolution in that they developed large lobed leaves that were more and

more efficient to capture the sunlight, and

at the same time generated new strategies for understorey ecosystems.

Ferns soon diversified into a large variety of forms with

small plants up to these tree fern types with trunks.

Here we have a staghorn fern that has an epiphytic growth habit,

meaning that it grows on other plants, often on tree trunks.

The spores are generally hidden underneath the leaves.

The ferns had their peak during the Mesozoic, but they have remained very

successful, and even today, they represent the second-most diverse group of plants

specializing in damp understorey and epiphytic niches.

Another major revolution in life on land was the appearance of

seed bearing plants during the late Devonian.

The seed was a structure where by the egg cell, and

indeed the whole gametophyte stage of the plant life cycle,

was enclosed in the protective tissue of the parent plant.

This was a tremendous advantage because it meant that the egg cell received both

physical protection and a steady supply of nutrients from the robust parent plant.

Although not strictly identical,

a seed is somewhat comparable to an egg in the animal world.

Both the egg and the seed are advanced life support systems for

the new generation.

Here we are going to focus on the so-called living fossils, plants that

are common during the Mesozoic, but they barely managed to survive a series of

mass extinction events and competition from more successful groups

to persist in small numbers into the modern age.

One characteristic of these living fossils,

is that they typically have a very limited diversity, and

are restricted to very narrow geographical ranges.

One peculiar plant group,

that today is completely extinct, are those with fern-like leaves

but, they reproduced with seeds instead of spores.

These plants got a confusing title "seed ferns".

They are afterall not ferns at all.

When found in the fossil record it can sometimes be rather difficult to

distinguish between the leaves of true ferns and the seed ferns.

One must find the distinctive reproductive structures to securely tell them apart.

Cycads are seed plants with a woody, usually barrel-shaped trunk, and

with a crown of large, stiff, evergreen leaves.

They can grow to the size of quite large trees but

most are rather small shrub-sized forms.

They typically grow very slowly and live for a very long time.

A few examples are known that have reached the incredible age of thousand years.

Cycads were very common and

diverse during the Jurassic, and today they are still three families surviving.

They have actually changed remarkably little since the Jurassic, but

they occupy much less ecospace than in former times, probably because they have

been largely out-competed by the more, opportunistic flowering plants.

Here you can see the male cones that produce pollen grains and

if we instead look at this female tree, there is a female cone which is

more robust and contains ovules instead of pollen.

If you look closer at the leaves, you can see that some of them have nasty spines.

This is the plant's way to defend itself against herbivores and

during the Jurassic this might have been a defense against herbivorous dinosaurs.

The Ginkgo tree, as the ones that you see behind me,

is another example of living fossils.

During the Jurassic, they had a broad geographical distribution spanning all

continents and they were represented by many species.

But today they survive in the natural state only in

a small part of Southwestern China,

although they are planted in parks and botanical gardens worldwide just as you

can see here as it's a nice ornamental tree.

Ginkos are large trees, normally reaching a height of

about 35 meters and the leaves are very characteristic.

They have a fan-like shape and numerous parallel veins without cross connections.

Just as with the cycads, ginkgo trees have separate sexes,

some trees are males and other females.

Male plants produce small pollen cones, whereas the female plants,

have ovules that develop into seeds if they become fertilized.

Ginkgos are deciduous which means that they shed their leaves in the autumn.

And Ginkgos are also long-lived with some species claimed to

be as much as 2,500 years old.

Interestingly, they are very resistant to diseases as they contain poisonous agents.

7.2 Origin and early development of plants: Ferns - Vivi Vajda

起源：宇宙、太阳系、地球和生命的形成

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