Plant Evolution 4

It is an important and surprising fact that modern day vascular plants have retained the same system of operation as the prehistoric plants from which they have evolved!

excerpt 4 from Science for the Gardener  Book 

Mosses and Liverworts

These came a little bit later after the algae and look like dense green mats.

You get mosses everywhere where it is damp.  They grow on the surfaces of soil, rocks, plant containers and paths and are associated with damp, shady and compacted conditions.  Moss can be an attractive plant to cover bricks, stones and other hard surfaces that you might want to cover up, but it is an unwelcome sign of bad drainage in lawns and on soils in flower beds.

Liverworts, also non-vascular, growing on the soil of a plant you are about to buy, is a sign that the plant was potted quite some time ago.

In the Carboniferous period around 360-290 million years ago Britain was covered in vast swamps out of which rose dense forests of the first true leaf bearing plants.  Club mosses, ferns and equisetites the first vascular plants, sucking up the nutrients required to allow them to grow to huge proportions in a relatively short space of time.  When these enormous plants died they fell back into the swamp eventually becoming the coal we know and use today.

Climate change is nothing new.  Can you image back then our climate was that of a tropical rain forest, hot, wet and very humid and, not for the squeamish, there were some extremely large bugs and flying insects beginning to emerge.

Club Mosses

Giant club mosses tall upright plants with a forked trunk out of the top of which sprouted long grass-like leaves grew in the swamps reaching up to 150 feet high.

Ferns

Ferns are some of the oldest surviving plants.  They reproduce by spreading spores which are found on the backs of the leaves but some modern day ferns (such as bracken) can be very  invasive as the plants have adapted to reproduce not only by spores blowing in the wind but also by growing rhizomes, a mass of creeping invasive underground roots.  And boy are they successful, but also rather wonderful with their fronds (leaves) emerging from a large underground clump and gradually uncurling.  Their roots are good for holding soil together in some of the more tricky planting positions such as stream banks.  Ferns live in many different habitats and come in varying shapes and sizes.  I have several different species in my garden and they are very welcome.

Horsetails

There is another very important prehistoric plant group, the equisetites, commonly known as horsetails, which also produce spores as well as underground rhizomes similarly to some species of ferns.

Equisetites were originally in prehistoric times over 100 feet tall, but have evolved to become the much smaller modern day plant, the equisetum.  They can be very attractive – they look great in a tall glass vase – but unfortunately again can be very invasive so be careful if and where you plant them.  They have an uncanny habit of not waiting to be planted but just turning up uninvited as unwelcome weeds all around the world.

Cycads

 Cycads are an interesting group of sub-tropical plants which lived over 200 million years ago, even before the dinosaurs, so we are led to understand.  Cycads have very wide woody trunks with an impressive crown of evergreen pinnate leaves and can be several metres tall, or just a few centimetres.   They are very attractive plants which are related to palm trees and tree ferns but are not suitable for growing outside in cooler temperate climates.

Unlike ferns, they bear both male, pollen producing, and female, seed bearing, cones, the size and shape of which are very impressive, particularly the male cones!  They have a pollinator which is a special species of beetle.  These plants grow very slowly and live a very long time – as much as 1,000 years.

So cycads evolved to produce seed and have adapted to live in many and varied conditions.  They can be found in swamp and boggy conditions, in a harsh dry desert or a wet rainforest climate, in full shade or full sun, although they are an endangered species and  today there are just 250 species compared to over 300,000 in prehistoric times.   I find them fascinating survivors that have adapted very well to their surroundings, having had plenty of time to do so!

Swamp cyprus-Bald cyprus Taxodium distichum Cyprus – Taxodiaceae family Pic by Editor from N Trust Stourhead uk

Conifers

Starting their life in the same time period as Cycads are the Conifers.  They are the largest group of living gymnosperms (which means they bear open, unprotected seeds).  They are non flowering plants and mostly evergreen.

Some conifers have broadleaves, a good example being the Gingko, but most have simple needle-like leaves like pines or scale leaves as with the cypress – cupressus family – and then there aresome with very soft scale leaves as with the swamp cypress family.

Conifers prefer a colder climate and they can often grow to huge sizes.  One well known example, a Californian Redwood (sequoia), is not only over 70 meters high, but is nearly 10 metres in circumference.  Wow!

NEXT CHAPTER   ANGIOSPERMS FLOWERING PLANTS