How Plants Are Identified

Transcription

1 3 How Plants Are Identified T he easiest method, and the one probably used the most often for learning the names of the plants of a particular location or region, or just the name of a particular plant, is to ask someone who already knows. Perhaps the way used to learn plant names most often is to compare the unknown plant with the photograph or sketch of a similar one in a book. Many picture books have examples of the more common plants, but most species cannot be identified in this fashion. The third way is to identify the plants for oneself. To have the skill to identify an unknown plant is a most valuable asset and an important part of the study of systematics. Identification of unknown specimens is usually made by using a key that is, a device in which successive choices between contrasting statements are followed until the correct name is found by the process of elimination. Keys play an integral part in a flora, allowing for proper identification of families, species, and infraspecific taxa. 14 Most modern keys are constructed of paired choices. Each half of the paired choice makes a statement or several statements that are either true or false. The two forked, couplet, or paired choice keys are called dichotomous (meaning forking) keys. The first of this type was developed by Jean-Baptiste de Lamarck, the famous French botanist. In 1788, as a shortcut method to reading down the long lists and descriptions of plants found in the botanical literature of the day, he provided an artificial key as a means to identify the plants of France (Flore Française). Using a dichotomous key is like following directions to a distant destination. As one travels down a road or highway, decisions are made at junctions as to which way to turn. If the roads are properly marked, and if the directions are followed carefully, the destination should be reached. There are two main types of botanical keys: the indented key and the bracketed key. Figures 3.1 and 3.2 illustrate how both of these types of keys function for seven objects. In both keys, the objects

2 How Plants Are Identified Object with curved sides a sphere 2. Sphere solid white in the middle 2. Sphere black or partially black 3. Sphere all black 3. Sphere one-half white and one-half black 1. Object with straight sides 4. Object with four equal sides a square 5. Square white 5. Square one-half black and one-half white 4. Object with three equal sides a triangle 6. Triangle with spines at the points 6. Triangle lacking spines Figure 3.1 An example of an indented key. are divided into subgroups; by the process of elimination, the unknown can be identified. All objects must be accounted for, with none left out. In an indented key, the paired-couplet choices are identified in the same way and given the same number. This is important because, in large keys to many species, the halves of the couplet may be separated by some distance from one another and may even be on different pages. Some authors use letters (i.e., a, b, c, or aa, bb, cc, etc.) or symbols (i.e., 1, 1, 2, 2, etc.) in place of numbers to keep from confusing couplets. The bracketed key follows the same basic principles of contrasting choices and choices given the same number, letter, or symbol as an indented key. The choices, however, are always placed on adjacent lines, thus requiring less room on a page, and the couplets are kept together. Relationships between taxa are not as easily observed in bracket keys; and when mistakes in keying are made, backtracking is more difficult. Bracketed keys are commonly used in beginning, student-type keys. 1. Object with curved sides; a sphere 2 1. Object with straight sides 4 2. Sphere solid white in the middle 2. Sphere with black 3 3. Sphere all black 3. Sphere one-half white and one-half black 4. Object with four equal sides; square 5 4. Object with three equal sides; triangle 6 5. Object white 5. Object one-half white and one-half black 6. Triangle with spines at the points 6. Triangle lacking spines Figure 3.2 An example of a bracketed key. Some Basic Rules for Constructing and Using Dichotomous Keys Some basic rules common to all types of keys should be followed when constructing and using dichotomous keys: 1. Construct all parts of the key in a dichotomous fashion. In certain disciplines of biology or in older botanical manuals one will sometimes encounter keys with many branches. This can be very confusing and time-consuming and can cause one to make incorrect choices. 2. Always use a contrasting alternative condition of a plant character in the other half of the couplet. This means that if the character is a leaf character, the alternating leaf character must also deal with the same leaf feature. For example: 1. Leaves attached alternate 2. Leaves attached opposite Using the alternating choice leaves heartshaped would not be a correct contrasting choice, even though it is a choice dealing with leaves. 3. Construct the leads parallel within each couplet. This means that the beginning word of each alternating choice should be the same. For example, if the word of the first lead is petals, then the first word of the contrasting couplet should also be petals. 4. Describe the characters of the plant in a positive manner. The person using the key should be able to get a visual image of the condition of each character used. 5. Avoid using vague, unclear, overlapping measurements and general, broad terms (e.g., large vs. small, dark vs. light colored, mm [ in.] vs mm [ in.] long). 6. Keep the season of the year during which the key is to be used the same; that is, if the key is to winter twig features, they should not be mixed with the characters of leaves. An easy way to accomplish this and to make the key more seasonably usable is to include flower, fruit, and vegetative characters together in the couplets of the key. 7. Avoid using taxonomic names as key characters. The key may, however, be designed to key out

3 16 Contemporary Plant Systematics taxonomic categories above the rank of species, as well as species below the species level. 8. Choose characters for a key that have the most reliable, least variable features available but that are still easily observable. Generally, flower features are less variable than vegetative ones. 9. Omit highly technical and obscure features as key characters (e.g., chromosome morphology or number, detailed anatomical features, the presence or absence of compounds, and localities). The person using the key normally does not go to great lengths to get the information requested by a couplet. 10. Consider both sexes in species that are dioecious (reproductive structures on different plants), because the specimen to be identified may have flowers of only one sex. 11. Try to avoid difficult or irregular arrangements or identification words in the couplets. The purpose of the key is to provide an easy method to identify an unknown plant specimen. Therefore, the design of the keys should be for convenient and self-evident use. 12. Remember, keys are not absolutely reliable and without mistakes. The key is only as good as the material used in its construction. Plant specimens that exhibit extreme variation and have not been observed by the writer of the key may not key out properly. Also, interpretation of characters may vary, so the student should understand the author s use of a term. It should be remembered that the key is another person s way of interpreting how a group of plants should be identified. The clarity and ease of use of a key depends on many factors; therefore, it should be remembered that a key is not magic, and that to master a key may take some time before one can identify unknown plants without making errors. Keying specimens takes skill and considerable practice. One should not guess when keying, if at all possible. Guessing almost always brings a wrong determination. Correctly learning and applying terminology is the best way to identify and key plants. Other Identification Methods The keys we have been discussing provide the traditional tools that botanists use to identify plants. In recent years, however, other techniques have developed that do not follow the very structured, singlebeginning point of the dichotomous key. These are the polyclaves and computer methods. The polyclave, or synoptical, keys are multientry keys that use cards stacked in any arrangement on top of one another, with holes or edges punched in such a way as to allow cards with the desired taxa to be retained or eliminated until the card with the desired taxon listed on it is the only card remaining. The holes or punched edges correspond to characters chosen by the investigator. During the 1960s, computer technology methods and their associated programs developed greatly. Programs began to be developed that would provide for automated identification of specimens by the computer, computer-developed multi-entry keys, and computer-stored information. The past thirty years have seen the rapid development and use of the micro computer (MacLeod, 2007). These machines and the programs perfected for them have expanded the potential for their use especially for smaller, more specific groups. As the technology and programs are further perfected, future use of them will certainly increase. Accompanying this text is a multi-entry computer key to the 519 families, including those illustrated in the Photo Atlas DVD that also accompanies it. By looking at the readily available features of the live specimen in hand, following the instructions given by the CD, and clicking on the choice that best fits the features, the name of the family and photo images of species examples found in the family can be observed. This method will allow you, the student, to identify the world s most common vascular plant species to family using a personal computer. Selected references for this chapter appear in Appendix I.

4 Families of Flowering Plants (Angiosperms) 173 Family Monimiaceae (Monimia) Figure Hedycarya: (a) leafy branch with male flowers in axillary clusters; (b) female flower with individual pistils. Peumus: (c) front view of female flower; (d) pistil or gynoecium; (e) stamen with two basal staminodes; (f) front view of male flower. (b) (c) (a) (e) (f) (d) General Description: shrubs or woody vines; fragrant ethereal oil cells and needlelike calcium oxalate crystals usually present in the parenchyma tissues; aluminum accumulators. Leaves: simple, opposite (rarely alternate), serrate, punctuate dotted with special looped venation joined near the margin; no stipules. Flowers: small to medium size, regular, perfect or unisexual, hypogynous or perigynous with a cup-shaped hypanthium, commonly with nectar glands inside; inflorescence of a solitary flower or flowers in axillary cymes. Perianth: of 2 pairs of fleshy sepals. Petals: 7 many, sometimes indistinguishable from one another or lacking altogether. Stamens: many, filaments short, in 1 2 series, with or without paired nectar glands at the base; anthers opening by longitudinal slits or valves upward from the base. Pistil: simple, of 1 many individual carpels; locule 1; ovule 1 and born on an apical or basal placenta. Fruit: of individual drupes or nuts enclosed by the perianth. Seed: small- to medium-sized embryo and oily endosperm. Distribution: 22 genera and 200 species in subtropical and tropical regions mostly in the southern hemisphere. The largest genera are Kibara (45 species), Mollinedia (90 species), and Tambourissia (45 species) found in the tropics. Economic Value: little, except locally where aromatic oils from the bark and leaves are used in perfume and medicines (Peumus boldus). Classification: cup-shaped, concave floral axis and carpels sunken into the cup tissue make the family distinctive from other magnolia-type flowers. Chromosome Numbers: n = (18-) 19 (-22, 39, 43, 57, etc.). Fossil Record: some Eocene fossils and fossil pollen from Oligocene and more recent deposits.

5 Families of Flowering Plants (Angiosperms) Eudicots I (a) Core Eudicots (1), Order Caryophyllales, Family Caryophyl laceae, Lychnis chalcedonica Rosea ; face-view of corolla. (d) Core Eudicots (1), Order Caryo phyllales, Family Droseraceae, Dionaea muscipula; trap leaves show ing trigger hairs. (g) Core Eudicots (1), Order Caryo phyllales, Family Nepenthaceae, Nepenthes raja; large leaf pitcher. 299 (b) Core Eudicots (1), Order Caryo phyllales, Family Chenopodi aceae, Chenopodium album; flowers close-up and scurfy surface feature. (c) Core Eudicots (1), Order Caryo phyllales, Family Chenopodiaceae, Salicornia virginica; clone habit. (e) Core Eudicots (1), Order Caryo phyllales, Family Droseraceae Drosera sp., undetermined species; close-up of glandular hairs. (f) Core Eudicots (1), Order Caryo phyllales, Family Molluginaceae, Mollugo verticillata; fruits and whorled leaves. (h) Core Eudicots (1), Order Caryophyllales, Family Nyctaginaceae, Bougainvillea spectabilis, undetermined species; colored bracts around flowers. (i) Core Eudicots (1), Order Caryo phyllales, Family Phytolaccaceae, Phytolacca americana; flowers and young fruits. PLATE 11.5 Flowering Plants (Angiosperms), Eudicots (Tricolpates), and Some Core Eudicots