LEARNING ABOUT BIODIVERSITY
The Green Kingdom
DEC 2015, VELD & FLORA
The Green Kingdom
All living organisms, from bacteria to baobabs, share certain features. They all replicate using DNA, and can convert the information stored in DNA into products for building cellular machinery using fats, proteins and carbohydrates. Scientists work out the relationship between all living things by comparing outward appearances, and more importantly, microscopic cellular composition, and grouping evolutionarily close organisms together on an evolutionary or phylogenetic tree. At the base of the tree is the ‘Last Universal Common Ancestor’ and at the very tips are the twigs which represent all species – living and extinct. The Veld & Flora Factsheet in the September 2012 issue of Veld & Flora, vol. 98(3) outlines the basics of classification of biodiversity in which all life forms are grouped into three Domains – Archaea, Bacteria and Eukarya, the latter containing five Kingdoms – Protozoa, Chromista, Plantae, Fungi and Animalia. Be aware that classification schemes are constantly changing and shifting as new discoveries are made, especially in the ‘nano-world’. In this factsheet we zoom in on plants and show how they are grouped within the Kingdom Plantae and placed on the phylogenetic tree according to shared characteristics that reflect evolutionary relationships.
The Kingdom Plantae
The most important feature of plants is their green colour, which is the result of a group of pigments called chlorophyll. Plants use chlorophyll to capture light energy, which fuels the manufacture of food in the form of carbohydrates.
Plant life cycles all include an alternation of generations (a haploid-diploid life cycle). Most plants are terrestrial.
The first plants seem to have evolved from the green algae which have enough physiological features of photosynthesis in common with modern plants to indicate this. One group of green algae, the charophytes (which includes Spirogyra), is more closely related to plants than to the other green algae
The fact that all plants have stomata except the Hepaticophyta (liverworts) suggests that liverworts were the earliest group to diverge. Other features used to distinguish different groups within the plant kingdom and work out their evolutionary relationships are reproductive strategies (spores, seeds, cones, fruits or flowers, sexual or asexual reproduction), and the presence or absence of features such as vascular tissue (specialized tissue for transporting water and nutrients – xylem and phloem) and leaves and roots.
Download the Factsheet on The Classification of Plants (above) here.
Download the Factsheet on The Classification of Life here.
Download these articles that are relevant to the study of plant classification:
The cycad amphitheatre at Kirstenbosch by Alice Notten, Veld & Flora 99(4), 178-179.
From crags to riches: Why is the flora of the Drakensberg alpine centre so diverse by Clinton Carbutt.
The art of plant identification by Wendy Hitchcock, Veld & Flora 100(2), 60-61.
Surviving at the edge of life: The tiny plants that eke out an existence on the frozen continent, by Martin Cocks, Veld & Flora 82(2), 46-48.
The all-blue agaric: a new record for South Africa by Clinton Carbutt and Marieka Gryzenhout, Veld & Flora 97(2), 84-85.
Of sea lettuces and green sea intestines: Common intertidal green seaweeds of the Cape Peninsula, Veld & Flora 86(3), 124-125.
Welwitschia mirabilis by Ernst van Jaarsveld, Veld & Flora 86(4), 176-179.
A very useful phylogenetic tree of life from the excellent book The story of life and the environment: An African perspective by Jo van As, Johan du Preez, Leslie Brown and Nico Smit, published by Struik Nature.
Green Algae: The nexus of plant ancestry from ScienceDaily, 12 October 2007.
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