METHODS OF PLANT IDENTIFICATION 

Identification is associating an unknown entity with a known entity (or recognizing that the unknown entity does not have a known counterpart). In other words, identification is a judgment that some perceived object is similar enough to a known entity that it falls within the criteria of belonging to the same class as the known entity.

METHODS OF PLANT IDENTIFICATION

As mentioned earlier, identification first necessitates describing the plant in question. This can involve anything from a glance at a flower to a complete morphological characterization of vegetative and reproductive features. The second criterion of plant identification is having a list of the possibilities.

Cultivated plants can be particularly difficult to identify. This is partly true because the number of plants taken into cultivation is quite large and continues to expand yearly. There are several methods of identifying plants. These are described below.

TAXONOMIC KEYS

Perhaps the most useful method of identification is a taxonomic key. A key is an identification device that consists of sequentially choosing among a list of possibilities until the possibilities are narrowed down to one.

Most keys are practical, narrowing down the identity of a taxon in the most efficient and effective means. The key may or may not split a larger group into smaller, natural (monophyletic) subgroups.

The most common type of key, particularly in floras and monographic treatments, is dichotomous. This consists of a sequence of two contrasting statements, each known as a lead; the two leads together comprise a couplet.

The leads of a couplet may be indented and numbered. Identification proceeds by choosing between the contrasting leads of a couplet. The lead that best fits the organism to be identified is selected.

All couplets hierarchically beneath that lead (either by indentation or numbering) are sequentially checked until identification is obtained. A well-written dichotomous key may have several types of evidence presented, with every character of the first lead matched, respectively, in the second lead.

Most keys are artificial or practical, meaning that the sequential groupings of the key do not intentionally reflect natural groups; their goal is to most easily and efficiently identify a given taxon, with no concern about classification into other groups.

Rarely, a key may be natural or phylogenetic, in which diagnostic (or even apomorphic) features are used to delimit natural groups, usually formal taxa. An example of a natural key might be one of the tribes of the Asteraceae.

More technical but less obvious characters are used in natural keys, so they are generally less useful in practical identification but may denote the features used to separate taxonomic groups.

Some precautions should be taken in using a dichotomous key. Most important is to read all parts of both leads before deciding which fits the plant best. Never read just the first lead; although it might seem to fit, the second lead may fit even better.

If, after reading both leads of a couplet, you are not certain which is correct, both should be considered. The two (or more) possibilities attained can then be checked against descriptions, illustrations, or specimen comparisons.

Haemodoraceae   BLOODWORT FAMILY
1. Fertile stamens 3 or 1 (Subfamily Haemodoroideae)
2. Ovary superior
3. Fertile stamen 1 Pyrrorhiza
3 Fertile stamens 3
4. Corolla actinomorphic
5. Inflorescence a simple raceme; functional carpel 1; ovule 1; style subterminal Barberetta
5 Inflorescence an elongated thyrse with lateral monochasial cymes; functional carpels 3;
ovules 20-30 per carpel; style terminal Xiphidium
4 Corolla zygomorphic
6. Stamens unequal, the 2 latero-posterior anthers reduced; ovules 3-4 per carpel Schiekia
6 Stamens equal; ovule 1 per carpel Wachendor a
2 Ovary inferior
7. Ovule 1 per carpel Dilatris
7 Ovules 2 or more per carpel
8. Ovules 2 per carpel; perianth glabrous  Haemodorum       8 Ovules 5-7 per carpel; perianth abaxially tomentose Lachnanthes 1 Fertile stamens 6 (Subfamily Conostylidoideae)
9. Flowers actinomorphic; perianth not splitting along mid-anterior line
10. Perianth glabrous to glabrate Phlebocarya
10 Perianth lanate to tomentose
11. Perianth lanate; trichomes simple to sparsely branched, white-whitish; anthers with broad, apical connective appendage Tribonanthes
11 Perianth tomentose, trichomes dendritic, yellow, whitish, reddish, pink, orange, or purplish; anthers without broad, apical connective appendage.
12. Flowers pendulous; perianth reddish to pink-orange Blancoa
12 Flowers generally ascending; perianth usually yellow or whitish, rarely orange to                  purplish Conostylis 9 Flowers zygomorphic; perianth tube splitting along mid-anterior line
13. Ovule 1 per carpel; perianth trichomes black Macropidia
13 Ovules >1 per carpel; perianth trichomes red, yellow, orange or green. Anigozanthos

1 Woody plants (excl. suffrutices)
2 Herbaceous plants (incl. suffrutices)
3 Aquatic plants, leaves oating or submerged
4 Chlorophyll absent (parasites or saprophytes)
5 Bulb present (monocots only)
6 Milky Juice present
7 Spiny stems or leaves
8 Tendrils present
9 Cladodes or phyllodes (modi ed branches or petioles)
10 Hairs glandular
11 Hairs stellate (also 2-armed, branched and tufted)
12 Hairs stellate (not 2-armed, branched and tufted)
13 Hairs, 2-armed or t-shaped, non-glandular
14 Hairs branched
15 Hairs tufted, non-glandular
16 Hairs peltate or scalelike
17 Hairs vesicular or bladderlike

18 Hairs stinging
19 Cystoliths present (dicots only)
20 Leaves opposite or verticillate
21 Leaves alternate (excl. distichous monocots)
22 Leaves distichous (monocots only)
23 Leaves equitant (e.g., Iris)
24 Leaves not compound
25 Leaves compound
26 Leaves pinnately compound (4 or more leaves)
27 Leaves ternately compound (3 leaves)
28 Leaves palmately compound (4 or more leaves)
29 Venation pinnate or hardly visible in leaves or leaves (incl. no. 30)
30 Venation invisible or leaves 1-nerved (monocots only)
31 Venation longitudinal in leaves or lea ets (incl. 3-nerved leaves)
32 Venation palmate in leaves or leaves

Another type of identification device is the poly clave key. A poly clave key consists of a list of numerous character states, whereby the user selects all states that match the specimen. The advantage of poly clave keys over dichotomous ones is that they permit using a limited subset of information to narrow down the possibilities.

For example, if a dichotomous key lists only floral characters, its usefulness may be limited if your plant specimen lacks flowers. A poly clave key, however, will have a listing of floral characters and features of the roots, stems, leaves, fruits, and seeds.

Thus, the poly clave key will often enable the user to identify the plant, even if one or more data types are missing from the specimen. A second advantage of poly clave keys is that if the specimen cannot be identified, its identity may be narrowed down to a few alternatives, which can be checked by other means.

The only major disadvantage of poly clave keys is their availability; they are generally written only for a limited number of taxonomic groups.

WRITTEN DESCRIPTION

A second means of identification is to compare features of the unknown plant with written descriptions of the possible known taxa. This is a good method of determining with certainty whether the range of variation of the unknown plant corresponds to that listed in the description of a known plant.

However, because reading all of the written descriptions of flora is impractical, this method relies on narrowing down the possibilities first. In addition, gleaning the diagnostic characteristics from a long list of features may be difficult.

Thus, written descriptions are best used to verify an identity after one or a few possibilities are presented.

SPECIMEN COMPARISON

A third identification method is to compare the plant in question to a live or preserved plant collection, usually an identified herbarium specimen. This is an excellent method of identification, as many features of a plant (e.g., coloration and surface features) are often not adequately denoted in written descriptions or visible from photographs or illustrations.

As with the preceding methods, comparison to an herbarium specimen is practically limited to verifying an identity after a subset of possibilities is narrowed down. Synoptic collections, which generally house one specimen of each taxon for a given region (e.g., a county), are very useful.

If a taxon can be narrowed to a smaller group, such as a family or genus, a quick search through a synoptic collection for that region may often allow for site identification of the unknown.

However, one precaution about this method is that it depends on the fact that the herbarium specimens are correctly identified. Thus, a possible match should always be verified with a written description.

IMAGE COMPARISON

A fourth method by which an unknown plant may be identified is by visually comparing it to photographs or illustrations of known taxa. These are usually obtained from books, although Web page images have become useful.

A practical problem with this method is that photographs and illustrations are usually available only for a small subset of possible taxa. In addition, locating the matching photograph or illustration may be cumbersome, necessitating an examination of all those available.

However, visual comparison to an image can still be an excellent way to identify a plant, particularly if the possibilities can be narrowed down beforehand.

The major precaution about this method is that two or more taxa may look very similar to one another based on a photograph or illustration; the differences between them may reside in obscure, easily visible morphological features. Thus, a technical plant description should confirm any match of the unknown to a visual image.

EXPERT DETERMINATION

A fifth and final means of identification is asking someone else, preferably an expert in the group. This method may be time-consuming, as it usually requires sending a specimen away for identification (as well as knowing who the experts of a given group are).

However, expert identification is perhaps the best way to identify a specimen, as the expert will usually know the taxa of that group over a wide geographic range.

If the expert is familiar with all recent literature on the group, his or her determination is often more accurate and current than any flora. Expert determination is often essential for certain groups where species or infraspecific identification is difficult.

PRACTICAL IDENTIFICATION

The practical steps taken in identifying plant taxa often depend on the experience of the person making the determination. The more you know, the easier it is to identify a plant.

For example, most floras begin with a key to the plant families, which may be cumbersome because they must consider the variation within the total flora. Thus, knowing the general characteristics of several families beforehand helps, as you may proceed directly to the key of genera within that family.

Similarly, suppose you have an idea as to the general group within a family to which the taxon belongs (e.g., a suspected genus). In that case, you may wish to check the keys, illustrations, descriptions, or specimens within that group first. However, when in doubt, it is best to start from the beginning to be certain of eliminating the close but incorrect choices.

FAQs

1. What is identification?
2. Describe how identification is used in your everyday life.
3. What two procedures are necessary before an identification can be made?
4. Define diagnostic characterization (= diagnosis).
5. What are the difficulties with identifying cultivated plant taxa?
6. Name the five major ways to identify plant taxa, citing the advantages and disadvantages of each.
7. What is a dichotomous key?
8. What is a couplet? A lead?
9. What precautions should be taken in using a dichotomous key?

10. What is the difference between a natural and an artificial key?
11. What is a poly clave key?

13. Name ways, other than a taxonomic key, to identify a plant specimen.
12. What are the advantages and disadvantages of a poly clave key?
14. What is a synoptic collection, and what is its advantage in plant identification?
15. State the practical steps made in identifying a plant specimen.