Plant Studies

PPLLAANNTT SSTTUUDDIIEESS IINNTTRROODDUUCCTTIIOONN TTOO TTRREEEESS AANNDD GGRRAASSSSEESS SSEECCTTIIOONN 22 IInnttrroodduuccttiioonn ttoo TTrreeeess –– PPaarrtt 11 All rights reserved. No part of this material may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and recording by any informational retrieval system, without the permission of the author. BUSHVELD TRAINING ADVENTURES © 2006/7/8 BUSHVELD TRAINING ADVENTURES INTRODUCTION TO TREES AND GRASSES 2 TABLE OF CONTENTS 1. OUTCOMES FOR THIS MODULE...................................................................................3 2. NOTES..........................................................................................................................3 3. INTRODUCTION TO TREES..........................................................................................4 4. WHAT IS A TREE ? .......................................................................................................4 5. TREE IDENTIFICATION ...............................................................................................4 6. LEAVES ........................................................................................................................5 6.1. Simple Leaves ............................................................................................................5 6.2. Compound Leaves ......................................................................................................5 6.2.1. Pinnately compound leaves ............................................................................5 6.2.2. Bi-pinnately compound leaves ........................................................................5 6.2.3. Compound leaf shapes...................................................................................6 7. HOW DID PINNATELY COMPOUND LEAVES EVOLVE ?................................................6 8. LEAF CHARACTERS ......................................................................................................7 8.1. Common Leaf Shapes .................................................................................................7 8.2. Leaf Apices ................................................................................................................8 8.3. Leaf Bases .................................................................................................................9 8.4. Leaf Margins ............................................................................................................ 10 9. BARK..........................................................................................................................11 10. THORNS AND SPINES................................................................................................11 11. FLOWERS AND FRUITS..............................................................................................11 12. INTRODUCTION TO TREES - PART 2.........................................................................11 13. BIBLIOGRAPHY .........................................................................................................12 2 BUSHVELD TRAINING ADVENTURES INTRODUCTION TO TREES AND GRASSES 2 1. OUTCOMES FOR THIS MODULE 2. NOTES On completion of this module, you will: The notes for this module were compiled by Marion Melville. • Have an understanding of the use of the following important characteristics to identify No part of these notes may be reproduced, copied trees: or utilised in any form or by any means, without the permission of the author or the management of o Shape and growth form Bushveld Training Adventures. o Leaves and bark o Thorns or spines o Flowers o Fruit • Have an understanding of the various leaf shapes and know them by name. • Recognise the most common leaf margin types • Know the shapes of the most common leaf bases • Know the shapes of the most common leaf apices • Identify the differences between the various leaf arrangements, including: o Opposite leaf arrangement o Sub-opposite leaf arrangement o Alternate leaf arrangement o Spiral leaf arrangement o Whorled leaf arrangement • Describe the differences between o Simple leaves o Pinnately Compound leaves o Bi-pinnately compound leaves • Understand the use of a Dichotomous Key as an aid to tree identification • This set of notes on the Introduction to Trees and Grasses consists of three sections, namely: o Introductions to Grasses o Introduction to Trees – Part 1 o Introduction to Trees – Part 2 Important icons which accentuate key notes: ³A definition tTake Note 3 BUSHVELD TRAINING ADVENTURES INTRODUCTION TO TREES AND GRASSES 2 3. INTRODUCTION TO TREES ³A SHRUB is a woody, perennial plant Fortunately, trees are to be found everywhere in with two or more stems arising from or near Africa, and if one has been lucky enough to have the ground. It differs from a tree in that it is explored this vast continent of ours, one is left in smaller and does not have a trunk or bole. awe of the large diversity, as well as the great beauty of trees. When one stands in the shade of an old giant many hundreds of years old, one can’t Trees vary greatly in shape and form. They may be help but imagine the array of wildlife that must have huge and dominate the skyline, for example, the rested under it, used it for shelter or simply passed Baobab – Adansonia digitata, or have no leaves at it by. all, as is the case with the Euphorbia family. Then there is also the Ploughbreaker – Erythrina zeyheri, A show of colour as the leaves turn red and yellow a tree which has a large underground stem and in the autumn, or a mass of flowers in the spring produces annual aerial flowering shoots which will raise many questions by interested nature resemble veld flowers! lovers, so the ability to identify and understand the different tree species is a must for any field guide or 5. TREE IDENTIFICATION nature enthusiast. Furthermore, trees have interesting medicinal and cultural uses, the The ability to identify trees is acquired over time, knowledge of which will greatly enhance your and is not an instant acquisition attained without learning experience, and eventually enlighten those putting in the necessary work and time. to whom you pass on this interest. Because botanists largely identify and classify trees One would think that because trees are firmly according to their floral structure (flowers) and rooted in the ground and are not prone to moving fruit, it is often difficult for the amateur botanist or away swiftly and disappearing behind a rise, that learner field guide to identify trees, when both they would be easily identified. flowers and fruit are absent. It is therefore important that other general characteristics are also Not always so! Two examples of a single species used in the identification process. These may vary greatly in size and shape, but with the use characteristics include: of information contained in this introduction, you will be well on your way to enjoying the skill of tree • Leaves – are they simple or compound, hairy or identification. smooth. What is the leaf margin like? • Bark – is it smooth, rough, peeling or blocky Remember that your identification skills will improve in leaps and bounds with practise, and also as you • Thorns – are they straight or hooked, white or become more familiar with a particular area or blue vegetation type. • Latex – is it present, and if so, is it milky or clear 4. WHAT IS A TREE ? • Growth form – do the branches grow upwards There are various definitions recorded of what many or do they droop, is the canopy rounded or flat authors consider to be a realistic description of a and is the foliage dense or sparse. tree. The accounts differ considerably, but suffice to In this publication, all the above characteristics will say, a tree grows above a certain height, has a be simply explained. Study them carefully and be perennial stem, a vascular system and a crown of sure to remember them. foliage. For the purpose of this course, a tree is described as follows: ³A TREE is a perennial woody plant, with a single (usually) main stem exceeding a height of 3m, a trunk diameter of 15cm or more and a distinctive upper crown. A tree is not to be confused with a shrub, which is described as follows: 4 BUSHVELD TRAINING ADVENTURES INTRODUCTION TO TREES AND GRASSES 2 6. LEAVES 6.2. Compound Leaves Leaves are divided into two different configurations; A compound leaf is composed of several similar parts (leaflets), attached oppositely, sub-oppositely o Simple leaves, and or alternately on either side of a central rachis. o Compound leaves ³The RACHIS is the central axis of a 6.1. Simple Leaves pinnately compound leaf, to which the leaflets are attached. Simple leaves have a single blade which is attached to a petiole (a stalk). This in turn is attached to a stem. Simple leaves may also be sessile and The leaflets resemble small simple leaves and can attached directly to the stem. Simple leaves are by be confused as such. far the most common type and are undivided. Compound leaves may also be bi-pinnately SIMPLE LEAF MORPHOLOGY compound, in other words, twice compound. These leaves are found on Acacia and Albizia Apex species, amongst others. Margin 6.2.1. Pinnately compound leaves PINNATELY COMPOUND LEAF Vein A pinnately compound leaf is once divided with Base many leaflets arranged alternately or oppositely Petiole along a common axis. Axillary bud This axis is called the Stipule rachis. ³A STIPULE is a leaf-like structure

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