Field Guides to incomplete sets of species
A guide to an incomplete set of species is one for which one can not be sure from the title or definition of contents whether an unknown plant is actually included. 'Ornamental trees of the tropics', for instance will be an incomplete guide, firstly because one cannot always tell whether a particular unidentified tree is an ornamental and, even if it is obviously so, the book is hardly likely to include all trees that have ever been cultivated in the tropics for their ornamental value.
In other words, either the set is defined by some feature which is not obvious by looking at a plant in the field, or some eligible species are simply missing from the guide. Either way, some plants that might reasonably be considered for identification are not found in the guide.
It is not always straightforward to decide how incomplete a set is, as one may have to consider who are the users, not just the plants and guide contents. For example, Medicinal plants of Java would probably be an incomplete set because in the field it is not generally possible simply to observe whether a particular plant is medicinal. On the other hand, Medicinal might in some circumstances be an observable feature, e.g. if all the plants, and only the plants that are used medicinally in Java, are included in the guide, and also the users are only interested in identification of plants collected by local experts for herbal remedies. In this case, medicinal plants defines a complete set. These users can be sure that any plant in question will be in their field guide.
Field guides for the following sets of species are usually for incomplete sets, even if all such species are included:
- Edible, poisonous (unless the plant has poisoned a user!), medicinal or forage plants
- Rare, common, endemic, indigenous, exotic, pretty or (maybe) weedy plants
- Interesting or useful plants
A complete set is based on a complete check-list (for a given form of plant), for a defined area. Typical examples cover all species of:
- A defined habit and size: (e.g. Large Trees, Lianes, but be careful to define terms carefully)
- Woody Plants, Flowering plants.
- Ferns, Palms, Orchids, grasses, Rubiaceae etc. (assuming your users can recognise such distinctive groups). Narrow groups like this would lead to a type of guide we call a field monograph .
- Aromatic Plants (assuming the audience can smell and agrees with what aromatic means).
A given complete set might be reduced, and still be reasonably complete, by including only plants of well-recognised habitats in the area, e.g. savanna, forest, lakes or mangroves, ('generalist' species found in other habitats as well should also be included). When defining complete sets of forest species, it is important to be clear about whether plants found along roadsides in the forest or in clearings of various sizes are to be included. Many plants occur within forest boundaries but are not found in undisturbed parts of the forest mosaic.
Timber trees may define a complete set if all straight tree
species above a certain size are used for timber. It may be clearer
to state explicitly the guide is perhaps to large, non-fluted trees
rather than "timber trees" to make it clear which trees are
likely to be in the guide on the basis of appearance alone.
The problem with field guides to incomplete sets
Incomplete sets are hard to make reliable and accurate, because one of the major causes of error, as we found in our field trials of guide formats, is a strong tendency for users to match a plant in the field to the best available match in the guide, even if they know certain species are missing.
When incomplete set field guides might still be fit for purpose
There are Field Guides purposes for which accuracy does not matter, for instance if the main aim is to sell the book to tourists and day-trippers as a source of income for the vendors.
There are also techniques for making incomplete guides more accurate, by making it clear which species are missing.
Try to define a complete set, by carefully specifying geographical coverage and plant habit, unless:
- It is not really an aim to make an accurate identification guide, but merely a book with notes on species which, it is assumed, you can identify already, or where identification is not strictly important.
- Or, if accurate identification is important, information in your guide makes it clear that similar species (e.g. non-medicinal plants) are missing, especially if those mssiing species look like or key to the species in your guide. If you do not feel it is appropriate to include all the similar, missing species, try to highlight the special features, the spot characters, of the species you have included, with a more extensive description than might otherwise be felt necessary.
- Hopefully your images will be so clear, with all the crucial characteristics clearly marked, that there will be little scope for confusion with plants missing from the book.
- Local names may well be widely known and standardised, so the key to the identification could be through an index of reliable local names (Access methods). If verification of names is important to users, rather than identification from the plant form alone, then obviously the local name indexing will have to be researched and implemented fully.
It is often preferable simply to avoid defining your guide around incomplete sets, in all cases where accuracy is important. Make a book to larger trees rather than timber trees, or to herbs and shrubs rather than medicinal plants.
Modular Guides might be considered a special type of incomplete set guide. This is because not all plants of a given type are always included in a Modular Guide, due to user selection of species to include, and probably incomplete availability of species pages.
The distinction between Modular and Incomplete set Guides is made because a Modular guide will often be, and will certainly work best if, defined like a complete set (e.g. Trees>70cm diameter). It should always be possible to tell in the field whether a plant is eligible for inclusion in a modular guide, but even this may not be clear for an incomplete guide. In a modular guide, a virtue can be made of the fact that browsing of pictures of fingerprint characters can be made to work adequately, even if many species are missing.