Plant Identification

by Anna Lawrence

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  One of the fieldworker’s advantages over the herbarium botanist which you should exploit is that there is greater scope to explore in the field the limits of variable characters, comparing leaves on shade shoots, old branches and so on that rarely find their way into the herbarium.

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  When discarding jargon, do not ‘throw out the baby with the bathwater’. Egg-shaped is not the same as the more precise ovate (in the proper usage of ovate), and ovate is a shorter word, so is potentially better for use in a field guide for both reasons. An illustration may show one example of an ovate leaf, but the word allows for a range of shapes. You can define such words in a short glossary inside your front cover; this will make the whole guide more concise and accurate for almost all users, even if the text appears slightly less friendly to some.

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  Do not exclude jargon, fine details or other technicalities just because a focus group says that they do not like or understand it the first time they see it. People are initially ‘shy’ of new concepts and small details – the sort only visible with a good hand lens; but field botanists rely on them. Most amateurs soon discover a universe of interest in the fine print of plant life, and it is this factor above all – attention to small detail – that separates good from unreliable field botanists. However, do exclude small details and disliked words when you are sure that they are not needed for reliable identification.

  Plant characters suitable for field guides 125

  CASE STUDY 6.1 JARGON LEVELS IN THREE FIELD GUIDES

  Consider three field guides produced recently showing how one author and colleagues have attempted to resolve the need for conciseness with user ability: 1

  Photoguide to the Larger Trees of Ghana’s Forest (Hawthorne and Gyakari, 2005): an identification guide targeted at farmers and others from rural backgrounds, possibly seeking employment as tree-spotters or eco-tourist guides. The book was designed around photographs of bark and other whole tree features. The basic key to bark groups includes words such as ‘latex’ and ‘gritty’; but it was envisaged that those unable to read the English could, in any case, be taught by non-governmental organizations (NGOs) or forestry staff to recognize the groups and browse the pictures.

  Twenty minutes of explanation on our trials proved sufficient for many to reach 80 per cent accuracy.

  2

  Caribbean Spice Island Plants (Hawthorne et al, 2006): a guide to Grenadian plants, designed for secondary or higher education, eco-tourists (as a commodity to be sold by tour guides and also for identification), and English-literate but non-botanical Grenadian tour guides, foresters, conservationists, etc. The book is heavily picture based, so it can be used to some degree regardless of jargon. Most of the text is dominated by usage, folklore and historical information with little botanical jargon, but with some chemical or medical terms. Brief descriptions for the keener readers (in a small font) use words such as inflorescence and corolla, but leaf stalk and flower stalk instead of petiole and pedicel. Venation patterns are described by photographs. Slash details are not covered, and descriptions are limited to latex because this can be found in cut twigs. Keys use more jargon, explained in a glossary, but should be limited enough to intrigue the curious, while not putting off the casual browser.

  3

  The Woody Plants of Western African Forests: A Guide to the Forest Trees, Shrubs and Lianes from Senegal to Ghana (Hawthorne and Jongkind, 2005): for technical users to identify any of 2140 species of tree, shrub and climber in West African forests, and others needing a reference of African plant names or pictures. Many technical users might have limited prior knowledge of botany, but should be able to use the book as the basis for learning, in herbaria or on field trips, but probably not often while walking in the forest. More than 5000 illustrations (drawings and photographs) are provided to help interpretation of jargon; but keys use many technical words for conciseness. For leaf arrangement and form, words such as petiole, petiolule, rachis, mucronate and scalariform were indispensable. Bark and bole characters are explained in detail, and include gritty, latex, resin and concave/convex buttresses. For distinguishing closely related species or in family descriptions, words such as disc, corona, cystolith and androgynophore are explained and used within certain groups. Words such as megaphanerophyte and campylodromous are avoided completely.

  The level of jargon should therefore be tailored to the skills of your proposed users, possibly making the content slightly more jargon rich than they feel comfortable with at first sight (see Case study 6.1).

  An interactive and more comprehensive glossary on the Virtual Field Herbarium (see Box 1.1, page 6) uses the definitions provided in Table 6.1.

  126 Plant Identification

  Table 6.1 Jargon level: How unnecessary is that word or phrase?

  Undesirability,

  Examples

  The desirability of using these words

  in terms of

  in your field guide

  cost/benefit

  0 Generally

  Ovate; acute; bark;

  There is almost no scope to ignore these words in

  desirable

  buttress; leaf blade;

  any field guide unless you are explaining everything

  leaf stalk; petal; corolla; with pictures, or you want to substitute these merely fruit; buttress; lateral

  unusual, but concise, words for mealy-mouthed

  nerve; kidney-shaped;

  imprecise sentences.

  sand-papery

  1 Often

  Petiole; petiolule;

  Any field guide user with some technical or school

  reasonable in a

  lenticel; bole; 3°

  background can make good use of these words with

  user-friendly

  venation; rhizome;

  little ambiguity; but you may still be able to do

  guide

  scabrid; saprophyte;

  without them in some field guides.

  small serrations;

  mucronate

  2 Technical,

  Reniform; secund;

  Unless your field guide is for boffins – for example, a concise

  serrulate; Corner’s

  ‘pragmatic’ Flora used only by other scientists – or

  model; mucronulate

  needs to be short on illustrations for weight or

  expense reasons, you should rephrase these words,

  and there is generally a good substitute.

  3 Undesirably

  Suberous (use corky);

  Avoid these words: although they are sometimes

  technical

  fistulose (hollow or

  used by botanists, they are ambiguous and/or

  pipe-like); complanate

  synonymous with a simpler word or short phrase.

  (flattened); trichome

  There is a better way of saying or showing the same

  (be specific)

  thing in your field guide.

  Source: William Hawthorne

  CHARACTERS OF YOUNGER STEMS AND LEAVES

  The young plant shoots – that is, young stems (sometimes called branchlets or twigs) –

  and the fresh leaves, stipules and bud scales that they support are most important for identifying virtually any type of plant: large or small, young or old, woody or not. Such details almost always deserve a prominent place in your field guide, even if only as descriptive text; many examples are on http://herbaria.plants.ox.ac.uk/VFH, but some important examples follow.

  Describing hairiness on leaves or other (generally young) parts There are very many terms for hairs, both for individual hairs and the covering (‘indumentum’) they constitute (Payne, 1978; Theobald et al, 1979), and their general importance for distinguishing related species, even when flowers are available, can hardly be overemphasized.

  Trichome is a general term including hairs, scales, colleters, superficial prickles and other h
air-like outgrowths of the epidermis, without vascular tissue (Hewson, 1988).

  Trichome and colleter can usually be avoided in non-technical field guides (use hair(s) or

  Plant characters suitable for field guides 127

  Table 6.2 Definition by various authors of some hair-related terms Hirsute

  Hispid

  Villous

  Pubescent

  Payne (1978) Long, rather stiff

  Long, very stiff

  Long, soft, curly,

  With trichomes;

  not matted

  or hairy, with soft

  hairs

  Hewson

  Coarse, long hairs

  Long, erect, rigid

  Long, soft, weak

  Somewhat

  (1988)

  hairs or bristles,

  hairs, the covering

  dense cover of

  harsh to touch

  somewhat dense

  short, weak,

  soft hairs

  McCusker

  Coarse, rough

  Stiff bristly

  Shaggy, long, weak Short, soft, erect

  (1999) relatively

  long

  Harris and

  Coarse, stiff

  Rough, firm, stiff

  Long, shaggy but

  Covered with

  Harris (1994)

  unmatted

  short soft hairs;

  or any hairs

  General

  Both terms imply rough hairy, with

  Not matted; some

  Some use it for

  longer hairs than ‘scabrid’, but

  say straight, some

  any sort of

  hirsute–hispid distinction varies

  curly, some allow

  hairiness

  appressed hairs

  scales, etc., as appropriate). Even the word ‘hairy’ can be ambiguous, as some people use it to mean a surface with even a single hair on it, or a fine coating of microscopic hairs; but others use it only for surfaces that are obviously hairy all over, to touch. The terms villous, pubescent and tomentose among many others have also been used ambiguously, so such terms must always be defined in a glossary in your field guide if you want them to be useful. It seems that most botanists have fairly precise definitions of such terms in their own minds; but these do not necessarily align very closely with the concepts of other botanists.

  Two of the most used reference works, Harris and Harris (1994), a simpler one, and Hewson (1988) differ in some of the details. Hewson’s short handbook is more thorough, but also complex, and goes into much detail – for example, about how the individual cells are arranged – that is of little use in a field guide.

  Hairs can be produced on all living surfaces, and the indumentum on different parts of one plant is often similar and diagnostic. However, they generally disappear, becoming bald (glabrous) with age; so try to specify the indumentum for recently formed parts.

  Your users may be expected to have access to fresh, young foliage, whereas taxonomists may consider the indumentum on leaves excessively variable because in the herbarium there is less chance of specifying age or relative position of leaves. In many cases, where a taxonomist might refer to the indumentum of the calyx or pedicel in a Flora, you may be able to substitute the indumentum of youngest shoots, apical bud or petioles in your field guide.

  In a technical field guide to many species it is useful to be as precise as possible about the form, length, density, colour and pattern of location of hairs or scales, even more so than in the Floras and monographs. Indumentum tends to change with altitude and habitat, so monographers will often see no merit in describing details very precisely for wide-ranging and variable species. But you may be in a position to be more specific.

  128 Plant Identification

  Glands and similar details

  The word gland covers a multitude of details in a plant, secreting water, nectar, oils and other substances. These are among the most useful of fine details to examine in certain families, and almost no value in others. A full review for West African plants is given by Hawthorne and Jongkind (2006).

  There is a natural tendency when collecting specimens, taking photographs or making field notes of fresh shoots to sweep away and disregard ants and their associated debris, as well as other insects. Think again – maybe your plant always has these features and you could count them among its field characteristics? In any case, they may well indicate the presence of glands (extra-floral nectaries).

  Strong scent in the Annonaceae, Myrtaceae, Rutaceae and other families is generally indicated visually by the presence of oil-producing ‘glandular hairs’ or dot-like oil pockets in the leaf tissue.

  Glands and other small structures on leaves and young shoots represent an area where, by exploration with a good lens, even in a herbarium, you are likely to discover previously undocumented field characters.

  Leaf types and arrangement:

  The primary questions in most field guides

  The most useful characters when first trying to identify a higher plant in the field are, as a rule, the leaf type and arrangement. These divide plants into useful groups of families and are usually available. There are, of course, exceptions – opposite-leaved species in alternate-leaved families; or simple leaves in plants from predominantly compound-leaved families, such as the mango amongst the golden apples and other Anacardiaceae; even old leaves or leaf scars may be hard to find in leafless deciduous trees or high in the canopy. Nevertheless, leaf type and arrangement are the most common choice for the first subdivision of the species list in keys in field guides (see Chapter 5) to tropical plants, wherever many families of plants are involved. But the difference between simple and compound leaves involves more than one line of definition. It is therefore a crucial judgement to make when planning the access method or arrangement in your guide if it is to be used by complete amateurs (see Box 6.4).

  You are not fully informing your readers if they do not end up understanding fundamental differences between types of plants, such as whether they have simple or compound leaves. If your field guide is appealing enough otherwise, a small learning period should be acceptable to most users.

  Non-technical guides might avoid the problem of defining different types of leaf by showing pictures of each category, and not describing technical differences in words.

  Compound leaves present other dilemmas in a field guide because the jargon can be confusing, and fieldworkers may only be able to retrieve a single leaflet from the canopy:

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  The numbers of leaflets, or leaflet pairs or pinnae, on a compound leaf is useful in a field guide; but herbarium specimens of fertile branches will rarely show the shade or sapling leaves of a tree, which almost always have a different number of leaflets than sun leaves (see Box 6.5). In Meliaceae, Rutaceae and Sapindaceae, pinnate-leaved species often produce simple or trifoliolate seedlings, rising to a maximum leaflet number in shaded ‘adolescent’ saplings, then declining again on exposed adults.

  Plant characters suitable for field guides 129

  BOX 6.4 ISSUES WITH SIMPLE AND COMPOUND LEAVES

  For simple, non-technical guides, one may question whether it is worth labouring the casual reader with the detailed differences between compound and simple leaves. If you have decided to base your guide on a few species of flowers, for instance, then you may not need to discuss finer details of leaf arrangement – just illustrate them. However, whenever a large number of plant families are to be included in your guide, leaves are likely to be obtainable or visible for many of them: you need an exceptional reason not to emphasize the leaf arrangement.

  In field tests in Grenada (see Case study 8.1, page 184) we found that non-botanists could usually match pictures of whole compound or simple leaves to real plants, without any textual assistance at all. At the other extreme, even experienced botanists make mistakes with exceptional cases – the apparently compound leaves of som
e Phyllanthus and Panda, for example, and the confusion caused by a compound leaf having an apical growing tip (suggesting a stem with simple leaves) as in Guarea and Dysoxylum species –

  these are the difficult exceptions, not the easily graspable rule. Take precautions to catch such easily made errors. Read through any keys you have made; but put yourself in the shoes of a beginner and imagine you have erred. Then place notes in the appropriate part of the wrong side of the key. Work out where the user would end up in the key if the Phyllanthus branch was perceived as a compound leaf and place a note there.

  Also, beware of the common confusion between similar terms. The axis of a compound leaf is divided into two parts: the rachis is the part beyond the first leaflet; the petiole is the part below it. There is usually no other visible distinction or cut-off line between the petiole and rachis, and the separate terms therefore often cause confusion, particularly as many users are also prone to confuse the word petiole with petiolule, the stalk of each individual leaflet. It may be useful to clarify this in keys wherever the question is critical – for example, ‘Petiole (stalk of the whole compound leaf) < 2cm long.’

  BOX 6.5 SEEDLING GUIDES

  Seedlings, short unbranched stems with only cotyledons and no adult leaves, present particular challenges (Duke, 1969). Their presence in a particular area of forest is often ephemeral. To make a good seedling guide, it is normally necessary to collect seeds from adults that are identified and vouchered in the normal way, and to germinate these in a nursery. Hence, purely seedling guides are seldom available and often not called for, except for problem weeds of agricultural land, where early recognition is vital. In many guides, seedling characters are included alongside adult details (for example, Taylor, 1960; Hyland et al, 2002). Seedlings can be photographed as a whole, or scanned or pressed, dried and laminated on card easily (see Chapter 8). Published seedling guides for agricultural weeds (many can be found on the internet; search with key words ‘weed seedling identification’) are mostly based on single, detailed photographs for each species, with perhaps some notes on key points to look for.

  Even if you do not include all seedlings in your field guide, it is useful to illustrate seedlings for species (usually shade-bearing ones) that characteristically have profuse regeneration in their vicinity. The seedlings in these cases are like field characters of the adjacent adult plant, and will help to confirm or refute initial diagnoses.