By observing the many and various identifying tree features, or characters, listed below, you will be able to build a composite picture of and arrive at a name for the particular plant you are observing. Turn to the Glossary on pages 516-522 il you arc unsure of some of the technical terms (the numbers that appear in square brackets refer to the appropriate Glossary illustrations).
Apart from the book itself, your most valuable items of equipment arc a pair of sharp eyes, a retentive mind, and a small field notebook and pencil A I Ok handlens or a magnifying glass can also be a great help when studying a small object. Alternatively, reverse a pair of bim>culars and look though the 'wrong' end. Binoculars are also useful in identifying leaf details, flowers and fruit in the upper parts of trees (and for bird-spotiing!)+ A pair of small secateurs and a plastic bag can come in handy when collecting material for later study.
However, you should really accumulate as much information about the tree as you can while you are in the field. Certain characters can only be reliably observed in living specimens (for example, the presence or absence of latex). Positive identification of most trees requires physical handling of the plant material, so do not be afraid to touch and smell as well as look.
Tree size, form and foliage colour Nole the size and shape of the tree, as well as the colour of the crown, from a distance Basic tree shape is genetically determined; each species has a specific tree architecture, though one that can be modified, within limits, by environmental and physiological conditions. Shape and colour are the two most useful features for identifying trees, especially in savanna areas, from a distance.
Bark; Nole the bark of the tree. Every spccies has its own characteristic mature bark pattern. Mature trees with a flaky or rough and thick covering usually have thin smooth bark when young, Therefore you should examine only mature specimens when attempting to identify trees by their bark characters.
Hranches and twigs Note the surface texture and colour of branches and twigs. Young twigs are often marked with small, light-coloured pustules called Jem ice Is [451- Check whether twigs and older branches are round, flattened or more or less square in cross section. In deciduous species, thick twigs tend to indicate compound leaves. Record the presence of any spines or thorns, and note their arrangement.
Latex Test for the presence of latex ¡53. 54], Any abundant liquid exudate, whether watery (clear), cloudy, milky, or other* ise coloured* is here referred to as such. Pick a hcalthv green leaf, preferably one from an actively grow ing shoot; break il off ¿it lhe point where ihe stalk (petiole* is attached to the siem. and check immediately whcther any liquid oozes out at the broken end or from the scar on the stem. The exudate needs to be fairly copious preferably forming a drop that completely covers the wound. If no latex is detected, check a few other leaves from different parts of the tree to confirm the f;ictT
I .eaf samples: Always examine a variety of leaves, preferably from the canopy of the tree, to determine characters such as si/e, shape, colour, texture and degree of hairiness. A single leaf can be misleading Leaves on coppice shoots may differ substantially from those in the canopy.
Simple and compound leaves Determine at the outset whether the leaves are simple (undivided! (1,2) or compound iihat is, made up of separate leaflets> [3—81- if in doubt, look for the axillary bud to determine whether the leaf is realK compound or not, There is a small bud (which can develop into a leafy shoot, or a flower* in ihc a\il between the stem and the petiole, but not between the rachis and stalk of a leaflet. Moreover, in a compound leaf there ts no grow ing tip at the end of the rachis,
I^nf arrangement: Note how the leaves are arranged on the stem 1^-1^1 Are they alternate, opposite, or whorled? In compound leaves, these characteristics refer to the leaves themselves, not the individual leaflets Clustered leaves are nearly always alternate, unless the clusters themselves are arranged in opposite pairs.
l^eai texture and hairiness: Touch the leaves on bolh sides. Are they smooth or rough, thin or leathery, woolly. hairless, or sticky?
External glands: Cheek for the presence of external glands on the leal . These arc often located at the point where the petiole is attached to the blade in simple leaves, or on the petiole or rachis in the case of compound leaves (55, 56), l,eaf margins; Are the leaf edges smooth, toothed, scalloped, wavy, lobed or rolled under? [35-3S)
Venation; Note the venation pattern. Is there only a single midrib, or several veins from the base of lhe blade? Arc the veins prominently raised or obscure on one or both surfaces? Arc the lateral veins more or less parallel and terminating at the margin without forming an intra marginal vein? Check for the presence ofdomatia |57, 5KJ in the axils of the principal lateral veins.
Secretory cavities: Test for the presence of these cavities in the leaf blade . Hold the leaf up to lhe sun (Other light sources are invariably not bright enough) and look for translucent iJols These are extremely small (the size of pinpricks) and uniformly scattered all over the bbde (here, the use of a hand lens is recommended). Practise looking at a leaf known to contain them Hot instance, any citrus oreuculypt species),
Bacterial noduJes: These nodules |hfl] are also detected by holding the leaf up to the ^un. These structures should he sought only in plants with opposite leaves and intcrpctiolar stipules [50|. They are much larger than sccreiors cavities, dark-coloured, not translucent and are easily visible although often confined to a specific area of the blade, particularly towards the midrib.
Odour: Crush the teat and check its smell. Leaves wiih ¡secretory cavities arc usually strongly .irornatjc, hut not all aromatic leaves have secretory cavities.
Stipules: Check for the presence of stipules at the base of the petiole 11. 4fv-49|r This is best done with young leaves near the tips of actively growing shoots, These structures can be very small jnd* .igain, a handlens is recommended. Stipules air often deciduous or shrivelled in mature leaves and, if the stipules have been shed, a distinct stjr is usually left on the stem, In the ease of opposite leaves, Uxik out for the presence of imerpetiolar stipules ¡50, 51 ].
Flowers: Exx>k carefully for flowers which, on many trees, are small and inconspicuous. Although we have tried to limit the use of floral technicalities in this book, four easy-io-observe characters are particularly useful (especially for family recognition), namely; flowers regular or irregular (43, 44); petals free or united; stamens many (more than Hi) or ver> few (4 or lessi; ovary superior or inferior [4L 42|.
Fruit: Examine the tree carefully to establish whether the mature fruit is dry (pud. capsule, nut) or fleshy (berry, drupe), ll >oti tlon'i see any fruit, look on the ground directly beneath lhe tree; One can often find old pods, capsules* nuts and seeds (in this way. even the leaves of deciduous species can he studied). Make sure you understand the difference between a fruit and a seed; the two concepts are often confused.
Collecting material: It is always worthwhile collecting one or more twigs with a number of leaves attached (a single leal does noi show the leaf arrangement) together with any other fertile material that might be present, for more leisurely examination, These samples may he kept for several da>^ in a moist plastic hjg, provided that it is kept ct>ol and not exposed 1o direct sunlight. If your atiempts to identify the tree ,*re unsuccessful, the material can be pressed and dried as a specimen, which you could then submit to an individual expert or herbarium (sec next Section),
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