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The Field identification of eucalypts

by NORMAN HALL, Division of Forest Resources and Timber Production, and R. D. JOHNSTON, Division of Research, both of the Forestry and Timber Bureau, Canberra, Australia

Use of a Card Sorting System

THE conventional aid to the identification of species of plants is a dichotomous key. Such keys are typically designed for use within a restricted geographical area. Keys for genera and families are commonly of use in a wider area and may be of general application. The design of keys to separate a limited number of species within one genus does not usually present serious problems. Greater difficulty may occur, however, when trying to separate a large number of species within one genus, especially if the genus does not fall into clearcut sections. The genus Eucalyptus presents major difficulties in this respect as it is not possible to divide this large genus satisfactorily other than by using an antherial classification.

The only key which covers all eucalypts is that of Blakely (2). This depends upon an antherial classification and, while of value to the systematist, fails to serve the purpose of the non-specialist. There are many dichotomous keys which deal with the eucalypts of a restricted area, e.g. state or portion of a state. However, even these keys, when dealing with a large number of species, frequently use anthers as a criterion for separation of species groups. Some of these keys, when not dependent upon antherial classification, are of considerable local value and admirably fulfil the purpose for which they were designed. The need for a different type of key for the genus as an entity has been in evidence for a number of years. Kessell and Gardner (9) in 1924 developed a numerical coding system for use in Western Australia, and Hall (7) adapted the method in 1934 for eucalypts in New Zealand. Like the dichotomous keys the numerical coding system was of use in restricted areas but was too cumbersome for general application. Jacobs (8) in 1935 adopted the principle of illustrating fruits and leaves to aid in identification.

The possibilities of a card sorting system for the identification of plants have engaged the attention of foresters and forest botanists for some time. Dunkley (6) wrote in 1939 "The perforated card key system described by S. H. Clarke (3) has proved so successful for the identification of timbers that it was thought worthwhile to test this system for botanical determinations." A key was prepared for Uganda and another for British Honduras. Walker (11) in 1948 proposed a key for Malaya to cover 81 characters, including territory, habitat, form, bark appearance and gross leaf characters.

Use of the system

The use of card sorting systems in the field of timber identification is by no means new. Pioneer work in this connection, done by S. H. Clarke in England, was followed up in Australia by the Forest Products Division of CSIRO, and goes back to 1936 (5). During World War II, over 60,000 cards for timber identification were prepared for use in New Guinea and the islands to the north.

The first application, so far as the authors are aware, of card sorting as a method of botanical identification of species within a single genus, was that of R. H. Anderson, Government Botanist of New South Wales, who, about 1940, designed a card system for use in the identification of herbarium specimens of Eucalyptus.

The advantages of developing a card sorting key for the field identification of eucalypts have been recognized by the authors for some time, and, in 1949, a prototype card was designed. After various trials the design of the card was amended and they are now in a position to present a system which appears to be of practical value for forest workers.

A card sorting system has several distinct advantages, as well as some disadvantages, compared with a dichotomous key. Amongst the advantages are:

1. complete botanical material is not necessary. Dichotomous keys frequently break down on this point. There is little need to stress the fact that it is the exception rather than the rule to be able to gather flowers, buds and fruits at the same time;

2. it is possible to sort in any order. Most eucalypts have one or two distinctive features and full advantage can be taken of this in a card sorting system;

3. it is suitable for the use of the non-botanist;

4. additional species can be added without involving any basic change in the key.

Amongst the disadvantages are:

1. the key is relatively expensive to produce;

2. it is bulky.

The object of a card sorting system such as this is not to provide unequivocal identification of a specimen, but rather to enable the user to reduce the possibility of an unknown being one of a hundred or more species to one of a few. It then becomes practicable to check details against botanical descriptions.

The degree of sorting will depend on the species treated. Distinctive species such as E. globulus may be sorted out to a single card, whereas in certain cases the limits of sorting will produce a group of closely related species which even specialists in eucalypts cannot readily separate. Some of the species in Blakely's "white stringybark" group provide an excellent example of the latter condition.

FIG. 1 Both sides of a typical card used in the system advocated by the writers of this article.

FIG. 2 Both sides of a typical card used in the system advocated by the writers of this article.

Notes on a card sorting system for the field investigation of eucalypts


1. This is not a eucalypt classification system. It is an aid to the determination of species by workers who are unfamiliar with the species of a given area.

2. The system is intended for the use of workers with some knowledge of botany but who are not experts on eucalypts.

3. The nomenclature is based on Blakely (1954). Species which have been published since then are also included. Where present day botanists differ from Blakely their views, on nomenclature, where known, have been added.

Basis of coding

It is emphasized that the coding, which has been based on original descriptions and extensive examination of herbarium material, has been made as inclusive as possible so that all normal variations will be included.

Users of the key should make themselves familiar with the definitions upon which the coping has been based.

Physical sorting of the cards

When a group of cards are to be sorted they should be placed together, taking care that all are correctly orientated. This is aided by the top right hand corner being clipped. The most suitable tool for sorting is a stout knitting needle. To sort for any feature insert the needle through the holes for that number and raise the cards off the table. Shake gently and the cards which have been clipped for that feature will drop. Cheek the cards that remain on the needle to ensure that all clipped cards have dropped. Continue sorting with the cards which have dropped.

The sorting of a species

The beginner should note down the features which characterize an unknown species, separating distinctive features which should be used first in sorting from those which are of less value and mainly of use in confirmation. Sort in order of the distinctiveness of the features present and not necessarily in numerical order. The user should not try to sort down to the last card, unless there are strong features which enable this to be done, e.g. as with E. globulus in Vict. or Tas. It is usually wiser to sort to a few cards and then examine these by hand, noting the illustrations and any comments on the species. Confirmation of the species should then be sought from Blakely or from any state reference book which may be available.

Selection of features for use in sorting

The following is a summary of notes on the group of features used in sorting. Illustrations of features 24-28, 37-39 and 47-75 are given on pages 2-4.

Geographical distribution, 1-12. Cheek that species is native to a state and not introduced. Species commonly met include E. ficifolis, cladocalyx and citriodora.

Habit, 13-15. Species normally found as trees may be stunted in habit on very unfavorable sites.

Bark, 16-21. It there is any doubt as to bark type omit from the sorting. Do not sort mallees on bark.

Mature leaves, 22-40. Only use typical leaves from crown. Features which are of high selective value in sorting include 22-,24, 27, 30, 33, 37 and 39. Other numbers are of little value in initial sorting but are of value in confirmation.

Inflorescence, 41-46. Cheek that solitary or few, fruited umbels are not due to non-development of the buds. Look at number of buds. F. 41-42 are of most value.

Operculum, 47-49. Cheek that operculi are mature. F. 49 is highly selective, F. 48 less so.

Markings on buds and/or fruits, 50-51. Only sort on good examples Cheek that markings are not due to insects.

Fruit, pedicels, 52-54. F. 51 is selective as also is 54; only use the latter in well developed examples.

Fruit, size, 55-58. Base on representative capsules. F. 58 is very selective, to a less extent 55 and 57.

Fruit, valves, 59-61. Typical examples of F. 59 and 61 are always of value in sorting but marginal cases, especially 60/61 should be omitted from initial sorting.

Fruit, shape, 62-69. Most species show a range in shape so that it is the exception for any one species to be coded on one shape only. Some species do not fit exactly into any of the eight shape. groups given but must be sorted on closest shapes. In most cases do not sort on shape until the final stages, unless the shape is quite distinctive, e.g., F. 64 for E. urnigers. etc.

Fruit, disc, 70-75. In most cases the disc is readily determined and is generally of considerable value in sorting. Only in the case of F. 73, narrow discs, is special care needed, since these discs - as seen in many mallees and boxes - may show F. 70, 71 or 72 in the same species. Well developed examples of 70 or 72 with 74 or 75 are a ways strong features upon which to sort.




It is desired to emphasize that the card sorting system does not in any way take the place of a flora. It is intended to act as an auxiliary to Blakely or any regional flora.

In the design of the card consideration was given to the following: :

1. the unit should be of convenient size and easy to manipulate in the field. The card size selected by the authors is 4½ x 6 in. (11 x 15 cm.);

2. the possible combination of features provided should be sufficient to cover the number of species in the genus;

3. the features selected should be such that a sufficient number would be readily available in the field at any one time;

4. all features used should be readily recognizable without optical aids;

5. features used should be relatively constant at a specific level;

6. sufficient alternatives should be provided in feature groups to ensure that:

(a) specific differences can be distinguished;

(b) normal variability can be covered;

(c) intermediate forms between two extremes can be sorted direct. (Several card sorting keys show one less feature than the number of possible alternatives; the features omitted being sorted "by default." Where, as in eucalypts, two alternatives out of three may be found in one species, then this system breaks down).

The features which were finally selected for coding are tasted below:

A. Geographical distribution


1. Western Australia

2. South Australia

3. Victoria

4. New South Wales

5. Queensland

6. Tasmania

7. Northern Territory

8. Extra-Australia






(These are intended for geographical divisions within any one State and are hence not of application for a general set of cards. An example of geographical subdivision is that of western plains, western slopes, tablelands and coast for New South Wales).

B. Habit

13. Trees

14. Small trees or shrubs

15. Mallees

C. Bark

16. Decorticating

17. Half barked

18. Stringybarks

19. Peppermints and boxes

20. Ironbarks

21. Other types

D. Mature leaves


22. Opposite

23. Sessile


24. Narrow lanceolate

25. Lanceolate

26. Ovate

27. Orbicular, cordate, including peltate, etc.

28. Falcate

Texture and color:

29. Coriaceous

30. Glaucous

31. Even shade both sides

32. Slightly darker upper surface

33. Much darker upper surface

Venation: Visibility of general network

34. Faint

35. Intermediate

36. Conspicuous


37. < 25°

38. 25 - 60°

39. > 60°

Intramarginal vein:

40. Visible and separate from margin of leaf

E. Inflorescence

41. Solitary

42. Umbels - Buds in 3's

43. Umbels - Buds mainly 4 - 7's.

44. Umbels - Buds over 7's usually numerous

45. Panicle or corymb.


46. Peduncle distinctly flattened


47. Hemispherical or depressed hemispherical L = D or < D.

48. Conic to conic-acute L > D to = 2D

49. Elongated. L > 2D

Markings on bud and/or fruits:

50. Striated or angular

51. Warty or rugose


52. Absent or very short

53. Short, i.e. < 1/4 in. (0.6 cm.)

54. Long, i.e. > 1/4 in.

F. Fruit


55. Small, D < 1/4 in.

56. Medium, D = 1/4 to 3/e in. (0.6 to 0.9 cm.)

57. Large, D = 1/2 to 3/e in. (1.3 to 0.9 cm.)

58. Very large, D = 3/4 in. and over


59. Sunk

60. More or less rim level

61. Exserted


62. Globular or globular-truncate

63. Ovoid

64. Urceolate

65. Pyriform or clavate

66. Hemispherical or flattened

67. Cylindrical or oblong

68. Campanulate

69. Cone-shaped or conic turbinate

Disc: position

70. Raised

71. More or less flat (level)

72. Depressed


73. Narrow

74. Intermediate

75. Wide.

(Numbers unallocated on the cards are 76-84).

The use of juvenile foliage as a feature for identification has been championed by some workers, and it is felt that an explanation of its absence from the coding features is called for. This feature was used in the prototype card, but it was found that it could not be used as a sorting feature for species of eucalypts since satisfactory descriptions did not exist for a large number of species. In addition, it should be pointed out that juvenile foliage does not commonly occur on mature trees. When juvenile foliage is only on young plants and cannot be positively associated with buds and fruits of mature trees, it is of restricted value in identification. In some localities of Australia one may find the cards for E. dalrympleana, rubida and viminalis sort out together. Notes on the front of the cards will readily separate E. viminalis from the other two species on the difference in juvenile foliage. The separation of the remaining two species is more difficult, especially for the novice.

Apart from the 75 features which have been coded, provision has been made for individual users of the system to incorporate special features if they so desire, in that nine spaces on the cards are not allocated. It is intended that additional information should be shown on the face of the card, where provision has been made for Blakely's number, botanical and common names, related species, features distinctive to the species and natural distribution.

Definitions of the features used and notes on the technique of sorting have been prepared, as an aid to users of the key. As far as possible the conventional botanical meanings of terms have been used but in some cases it has been necessary to use a modified interpretation of a term, e.g. a narrow lanceolate leaf has been arbitrarily defined as one in which the ratio of length to breadth of a typical mature leaf exceeds 10:1. Some of the terms used, especially those relating to shape of the fruit, are not so readily adapted to definition in words and a plate has been prepared to illustrate features 24-28, 37-39 and 47-75.

In the same manner in which wood anatomists found that photographs illustrating wood structure were needed on the wood sorting cards, it was found that illustrations of the fruits and buds on these cards were extremely helpful. These have been based on specimens figured by Maiden (10) and produced in a form suitable for use on the cards.

Preliminary coding was done from the descriptions in Blakely and reference made to post-Blakely publications. This was amplified by a careful examination of many thousands of herbarium specimens in the leading herbaria of Australia, especially New South Wales. The basic idea in coding was to cover the normal botanical range of a species, but not allow for freak or doubtful specimens. When a species shows only a tendency to a given condition the feature is marked with a bar, e.g. "24". The bar is also applied to geographical distribution when the occurrence is limited or very rare, and to features which are found as an occasional alternative to the normal condition. In the case of valves the coding is sunk, more or less rim level, exserted. A species in which the valves are usually sunk but at times tend to be more or less rim level would be coded 59, 60.

Full acknowledgements are made to Mr. Anderson for his help in providing a sample card of his herbarium key and in allowing access to the extensive herbarium material under his control. Thanks are due to Mr. D.A.N. Cromer, Officer in Charge, Resources Division of the Forestry and Timber Bureau, for help in suggestions and in the loan of equipment in making the set of illustrations; and to the Government Botanists of Queensland, Victoria and Western Australia, and the botanists of Adelaide University and the University of Tasmania.


1. ANDERSON, R. H. - The Trees of New South Wales. 2nd. Ed. 1947. Government Printer of N.S.W., Sydney.

2. BLAKELY, W. F. - A Key to the Eucalypts. Published by the author. 1934.

3. CLARKE, S. H. - The Use of Perforated Cards for Multiple Entry Identification Keys and in the Study of the Interrelation of Variable Properties. Chronica Botanica IV, 6, pp. 517-518, 1938.

4. DADSWELL, H. E. et al. - The Extension of the Card-sorting Method to Wartime Problems in Timber Identification. Journal of the Council for Scientific and Industrial Research, Vol. 20 pp. 321-327, 1947.

5. DADSWELL, H. E. and ECKERSLEY, A. M. - Journal of the Council for Scientific and Industrial Research, Vol. 14, pp. 266-280, 1941.

6. DUNKLEY J. L. - A Multiple Entry Perforated Cardkey for the identification of Uganda Trees. Empire Forestry Journal, Vol. 18, pp. 83-90, 1939.

7. HALL, N. - A Key to the Species of Eucalypts growing in New Zealand. Journal of the N. Z. Institute of Horticulture, Vol. 4, No. 3, pp. 5-9, and No. 4, pp. 19-32, 1934-35.

8. JACOBS, M. R. - A Survey of the Genus Eucalyptus in the Northern Territory. Bulletin 17 of the Forestry and Timber Bureau, Canberra, 1935.

9. KESSEL, S. L. and GARDNER, C. A. - Key to the Eucalypts of Western Australia. Bulletin 34 of the Forest Department of Western Australia, 1924.

10. MAIDEN, J. H. - A Critical Revision of the Genus Eucalypts. Parts 1-75, Government Printer of N.S.W., Sydney, 1903-33.

11. WALKER, F. S. -- Field Identification of Trees by Multiple Entry in a Perforated Card System. Empire Forestry Journal, Vol. 27, pp. 130-133, 1948.

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