Plant Identification

by Anna Lawrence

  For instance, the first issue in Whitmore’s (1962c) key to bark types includes the option as follows: ‘Expansion tissue uniform, continuous at surface in wedges and/or fingers confluent externally into a pseudocortex’. A few subsequent authors have tried to develop this approach to more than Malaysian dipterocarps (for example, Yunus and Yunus, 1990; Trockenbrodt, 1990). However, because of the complexity, most actual field guide writers concentrate instead on simply describing or illustrating the more obvious visible slash patterns (for example, Hawthorne and Jongkind, 2006).

  144 Plant Identification

  Source: Hawthorne (1990)

  Figure 6.5 Standardizing use of terms for a tree field guide One of the commonest side effects of the dead outer bark not growing with the tree below is for it to break up into vertical fissures or cracks, especially where the bark is very fibrous – that is, largely composed of vertical fibres. There is no agreement about how such rough barks should be categorized; but Junikka (1994), adopting earlier recommendations by Wyatt-Smith (1954) and others, recommends various descriptive phrases. This is not all suitable from a field guide writer’s perspective either, and you will

  Plant characters suitable for field guides 145

  BOX 6.10 BARK FLAKES OR SCALES?

  As another example of where there is no agreement on a widely used term, both scale and flake have been used to describe (thin) patches of outer bark that become detached.

  Rosayro (1953) used flakes for large rectangular pieces and scales for smaller ones; but he did not specify, and there is no general agreement about the cut-off point. Corner (1988) and Letouzey (1986) use them interchangeably, a definition that Junikka (1994) recommends; but we suggest that a distinction is made in your own glossary – for example, specify that flakes are flexible or papery, often curved at the edges, and scales are barely flexible and especially used for large plate-sized ones. Flakes that are thin and flexible like paper can be called papery flakes, or the bark as a whole may be ‘flaking off in papery sheets’, or exfoliating. This can be called ‘paper-scrolled bark’ when the scrolls are more than 1cm in diameter. Papery scrolls are typical of several Bursera species and various Myrtaceae, for instance, and familiar to residents of temperate climates in the papery scrolled species of birch ( Betula) and cherry ( Prunus).

  still need to choose your own definitions, probably starting with Junikka’s (1994) summary (see Box 6.10).

  Slash characteristics

  Bark is made up of various layers and patches of different texture and colour visible in the slash. Every tropical forester knows that the tree slash is one of the best diagnostic tools for identifying large trees, but converting what can be learned from a ‘recognition’

  point of view to a diagnostic key of some sort is hard (Beard, 1944; Symington, 1943; Rollet, 1980–1982; Tailfer 1989). It is often possible to distinguish various layers in a slash, above the generally harder sapwood. Some authors, for example Wyatt-Smith (1954) and Wood (1952), show how to describe the slash in terms of various layers; but few field guides have made good use of such jargon. We recommend describing the patterns as below, without using special terms.

  Living tissues in the inner bark (mostly secondary phloem) can contain resin ducts or laticifers that exude liquids when cut (Serier, 1986). Similar exudates can also be produced from the sapwood of some trees:

  •

  The first consideration to make for a slashed bark is whether there is any ‘significant’ exudate, like latex or other coloured thick liquids. Many barks exude colourless sap or other watery substances when cut; this is widespread, fickle and not counted here as significant. It is useful to note the colours of any latex and other slash parts in the first 10 to 20 seconds of exposure. This is the about the time taken to cut the bark a few times to make a neat slash, put down the bush knife, take out your hand lens, open your notebook and look closely. In many cases, the colour will change, usually to a darker colour over a period of minutes or days, a fact that should also be recorded where possible.

  •

  The slash pattern and colour is usually hard to describe in the field without technical language and great patience, and is best done with photographs. However, it is also useful to refer to the texture of its components with words such as gritty, granular and fibrous. The overall texture might also be brittle, fibrous or corky, in their

  146 Plant Identification

  common English sense. In a bid to specify the bark colours accurately, Hawthorne (1990) tried calibrating slash colours with Royal Horticultural Society (RHS) Standard Colour swatches. Apart from colours that darkened rapidly, this did support the notion that at least a distinction between reddish (‘greyed red’) and orange-yellow barks (RHS definitions) were reasonably constant for a species, as proposed by Dawkins (see Box 5.8, page 104). Even with these terms and tools, a user-friendly key for tree barks is made difficult by the mixtures of subtle textures and gradients and changes of colour.

  •

  A detailed photograph is by far the best approach to bark description in a field guide, paying attention to record the true colours, particularly the ‘difficult’ shades between yellow and white. For this reason digital photography is highly recommended (see Plate 5, centre pages).

  Smells and tastes are very important for characterizing barks as they are for some other field characters (see the earlier section on ‘Smells, taste and bark: The gourmet field botanist’).

  Ecology and distribution

  Your field guide will have been planned in the context of a specific region; but not all plants are found throughout. Although it is usually appropriate to mention species range and global rarity – for example, for conservation planning – this is only likely to be relevant as a field character if your guide covers thousands of square kilometres. If your guide does have a broad geographical range, and if you have very good herbarium or other survey data, you may well be able to make use of the distributional information to identify plants.

  Local endemics are species found only in a particular, limited place, such as an island, mountain range or river valley. Use this fact in your field guide if you are reasonably confident it is a true pattern and not due to under-collection. Conveniently, ‘sister species’ that are otherwise generally the hardest to distinguish purely on how the plants look often have distinct ranges.

  When distribution is determined by obvious environmental factors – rainfall pattern is one of the most important, so check rainfall maps – the constraint is ‘ecological’. Try to understand which part of the landscape (swamp, riverbank, hill top, etc.) each species prefers. Beware that the ecology of a species in one part of its range is often different from that seen elsewhere, perhaps under a different climate. Many species that are only found along rivers in savanna are frequently found away from them – for instance, on rocky slopes under wetter climates. Other species are truly swamp specific, or are restricted to particular altitudes or limestone soils or very exposed, disturbed areas. All such ecological characteristics can help your users to identify their plants and can be used like physical field characters.

  Herbarium specimen databases can be very useful for helping you to determine whether species are always, often or are merely randomly found along rivers. In many areas, such as Amazonia and the Congo Basin, historical collections have led to most specimens over large areas being recorded from riverbanks on herbarium notes or when the collection locations are mapped, but only because most of the collectors moved around on boats, so you have to see beyond this sampling bias. See

  Plant characters suitable for field guides 147

  http://herbaria.plants.ox.ac.uk/bol/home for free herbarium database software and what can be done with it.

  It may be useful to calculate from your database the proportion of specimens for each species that have been collected along rivers (or in a swamp, etc.) and divide this by the proportion for all species combined. This habitat preference index will give you some idea of the true prefer
ence of various species – a score of, say, 5 would be a species five times more common along rivers than the sampling bias would produce by chance.

  You will need to exclude specimens of collectors who make poor ecological and location notes, a common trait of specimens more than 100 years old.

  Some species are characteristically found in stands with few other species – that is, they are gregarious and locally dominant or at least locally very common, such as Gilbertiodendron trees and Rinorea shrubs, contrasting with the majority of species that are less so. Furthermore, adults of these and other tree species may characteristically have abundant seedlings around them. In extreme cases, the local dominance should be mentioned as a confirmatory character, but is rarely useful as a key character because other species may, on occasion, become gregarious. In species that form dominant patches due to due to local vegetative spread (such as bamboos and creeping herbs), the local abundance of stems is really a feature of the habit or life form, and is more likely to be worth emphasizing.

  CONCLUSIONS

  We have barely scratched the surface of the ranges of characters useful in field guides; but it is clear from even this sample that there is a vast range of relevant literature, though it has to be used very critically. Out of all the above types of field characters for flowering plants, distinction between all species in any one area (‘local resolution’) can, in general, be obtained by leaf and shoot details alone. For larger trees and lianes, slash characters of the bark can provide almost as much accuracy; but you will need to use colour photographs and pay attention to detail when taking your photographs. For shrubs, and especially herbs, which may be in flower or fruit for more of the time, you may be in a position to use some classical characters, possibly in simple terms (‘petals 5mm long, white’).

  Whether or not you are planning a detailed type of publication, your research will benefit if you scan, first, through all species in the herbarium for field notes and details from the specimens. Of course, for many of the most important characters, there is no substitute for seeing the plant in the field where the guide is to be used. Even for these cases, though, you will benefit by first noting what others have learned before you, and by making yourself aware of ways of checking the identity of your plant and of issues that need resolving through fieldwork.

  Some whole-plant field characters are not seen in the herbarium, and others do not survive the drying process, limiting the potential of the herbarium reference collection.

  On the other hand some useful characters for distinguishing sterile specimens – for example, colour and wrinkling on drying – are seen only on dried specimens (see Table 6.3).

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  Table 6.3 Where to look for and use various classes of character Type of field character

  Usability

  Herbarium/field

  Microscopic details

  Only generally feasible with lab/herbarium

  H

  (i.e. sub-hand lens)

  equipment.

  and chemistry

  Leaf type/outline/shape

  Identical for herbarium and fieldwork.

  HF

  Leaf margin/midrib

  Midrib prominence or channelling usually

  HF

  prominence

  stays the same, but a smooth (channelled, flat

  or prominent) midrib of fleshier leaves will often

  become more wrinkled and grooved on drying.

  Leaf venation and

  The venation pattern does not change with

  HF

  surface

  drying, but prominence of minor veins will often

  increase with drying as the softer leaf tissues

  collapse. Patterns visible with transmitted light on

  fresh leaves are often more obvious in the herbarium.

  Leaf indumentum,

  These are generally well conserved on dried

  HF

  glands, translucent

  specimens, and you will usually need to allocate

  spots, domatia

  yourself a lot of time with a bench and a good

  (see Hamilton, 1897;

  lens and light to discover them. In the field, study

  Schnell et al, 1963;

  the behaviour of ants (Uphof, 1942) on your plants:

  Jacobs, 1966;

  are they showing an inordinate interest in one part?

  Belin-Depoux, 1989)

  If so, expect to see some form of glands or shelter

  there. In the field, you may also find it useful to

  inspect the leaf by holding it up to the light.

  Stipules, lenticels,

  Generally identical in herbarium and field,

  HF

  buds

  although dried stipules are sometimes slightly

  more inclined to fall off than fresh ones.

  Leaf, twig and hair

  These vary greatly and are often diagnostic,

  H or F, but often

  colours

  especially for herbarium use on dried leaves.

  not both with the

  Dried leaves on the forest floor correspond in

  same information

  relatively few cases to the herbarium version,

  usually because the leaf will have died and turned

  brownish before falling. Hair colours do often stay

  the same (white or silvery ones on dried leaves

  will usually be the same on fresh plants), but

  some do not (e.g. some hairs only become really

  red-brown after drying).

  Leaf scent (and taste)

  Stronger scents are retained for years in a

  F

  herbarium, but decades-old material almost never

  smells anything like living plants. Recently dried

  Annonaceae, etc. leaves are frequently very similar

  to the fresh plant. Dialium leaves retain their acid taste when crushed; but do not even think about tasting

  herbarium specimens since they are often sprayed

  with poison, and curators do not appreciate visitors

  eating their specimens.

  Plant characters suitable for field guides 149

  Table 6.3 continued

  Type of field character

  Usability

  Herbarium/field

  Exudates

  Although some exudates can be noted from dried

  F

  specimens (e.g. black stains on cut Anacardiaceae

  petioles; gum on Gardenia and Coffea buds), most exudates should be checked for in the field: look in

  the slash and on cut petioles and twigs.

  Bark/periderm of

  Lenticels and other bark patterns, such as small

  F(H)

  young twigs

  scales and even colours, are usually well conserved

  in herbarium specimens when they relate to the

  rhytidome (dead parts – e.g. corky patches). However, green young stems will often become black or other

  colours when dried, although in certain families such as Olacaceae they are more stable.

  Bark details for

  Almost impossible to do anything useful except in

  F

  larger stems

  the field. Photography is a good solution for comparing these sorts of characters, as field notes rarely capture all subtleties. An anatomist can make some use of

  dried bark specimens, however, and anyone can use

  them to distinguish – for example, lenticels and

  extremes of texture.

  Bole, base, crown

  Likewise, field only; but start building your herbarium F

  photo library now.

  7

  Information: Finding it

  and presenting it

  Anna Lawrence

  INTRODUCTION

  The access systems and botanical information outlined in
Chapters 4 to 6 form the basis of any field guide, together with illustrations, described in Chapter 8. However, a field guide usually contains a considerable amount of additional information other than simply botanical description. In Chapter 3, we described ways in which to decide how much information is appropriate to the purpose and user group of the guide. This might include background information about the area and the plants to be included, in an introduction; details about the uses or ecology of each species; and sources of further information, such as conservation organizations that the user might like to contact. But where does this information come from, how do we know that it is accurate, and what is the best way of organizing and presenting it? This chapter provides guidance on methods for collecting, checking and organizing information. It considers various sources of information and methods for gathering material from these sources; questions of accuracy, validity and comprehensibility; and sorting your results in a manageable way and preparing them for inclusion in the guide. As well as checking the accuracy of the information, we emphasize the need to check that typical users can understand and access the information once it has been written up and formatted on the page.

  KINDS OF INFORMATION

  Begin by listing the different types of information that you need. This comprises the information needed for each species, which should be systematic and consistent. It is confusing and appears careless to provide detailed information on, for example, the medicinal uses of one plant and nothing on the uses of another. Therefore, in order to ensure that you collect the information in a systematic way, and do not have to repeat your research or publish an incomplete guide, plan your information needs at the