Nomenclature, Classifying and identifying

 

The work of a botanist consists in three different tasks: Nomenclature or how to name plants, Classifying or the study of the relationships between the taxa, identifying and producing flora and revisions to help naming of plants.

Artificial classifications

Classifications appeared well before Linnaeus but they were all artificial including Linnaeus 'sexual system' (1754). Theophrastus (370-285 B.C.) did classify plant according to their gross morphology: tree, herbs, shrubs......

Artificial: Non predictive classification. Classes are created to help identifying and group plants into smaller manageable groups. The groups are usually define by a single character.

THE LINNAEAN ORDERS AND THEIR MEANINGS

Flowers perfect, each with stamens and pistils.
Cl.1. Monandria: stamen 1
Cl. 2. Diandra: stamen 2
Cl.3. Triandra: stamen 3
Cl.4. Tetrandia: stamen 4
Cl.5. Pentandria: stamen 5
Cl.6. Hexandria: Stamen 6
Cl. 7. Heptandria: Stamen 7
Cl.8. Octandria: Stamen 8
Cl.9. Enneandria: Stamen 9
Cl.10. Decandria: Stamen 10
Cl.11. Dodecandria: Stamen 12-19
Cl.12. Icosandria: Stamen 20 or more, inserted on the calyx
Cl.13. Polyandra: Stamen 20 or more, inserted on the receptacle.
Cl.14. Didynimia: stamen 4; 2 long and 2 short
Cl.15. Tetradynamia: Stamen 6; 4 long and 2 short. Fl. cruciform
Cl.16. Monadelphia: Filaments united below in 1 set.
Cl.17. Diadelphia: Filaments united in 2 sets. Fl. papilionaceous.
Cl.18. Polyadelphia: Filaments united in 3 or more sets.
Cl.19. Syngenesia: Stamen 5, anthers united. Fl. compound.
Cl.20. Gynandria: Stamens and pistils combined

Stamens and pistils in different flowers.
Cl.21. Monoecia: stamen and pistils on the same individual
Cl.22. Dioecia: stamen and pistils on different individuals.
Cl.23. Polygamia: Fl. perfect and unisexual on the same or on different individuals.

Fructification concealed.

Cl.24. Cryptogamia

Linnaeus 'sexual system' copied from the 10th edition of Systema Natura (1759).

Question: In which class, following Linnaeus sexual system, would Digitalis purpurea or Foxglove be placed ?

Natural classifications

Natural classifications are predictive and delimit natural groups. They show the relationships between groups and respect the evolution theory. The groups are based on several combined characters.

Adanson, M. (1727-1806), Jussieu, A.L. (1748-1836) and Lamarck, J. (1744-1829) and other 18th century botanists created natural systems and their family definition and names are still in use nowadays.

It was only much later than the Darwin theory of evolution (1859) and genetic advances (Mendel 1900) enabled the first phylogenetic classifications to appear.

Question: In which family is Digitalis purpurea most commonly placed according to the latest natural classification ?

Circular representation of the phylogenetic classification of the dicotyledones redrawn from Sporne 'The morphology of Angiosperms' 1974

Cladogram of the orders of Angiosperms representated as the transection of an imaginary phylogenetic tree, adapted from Dahlgren.

Cladogram of the orders of angiosperms taken from the 1966 version of Takhtajan's scheme of classification

 

Some definitions

Classification is the production of a logical system of categories, each containing any numbers of organisms, which allows easier reference to its components (kind of organisms).

Convergence: the possession of similar characteristics in two or more groups without an intermediate common ancestor.

Divergence: The possession of different characteristics.

monophyeletic: a group composed of an ancestor and all its descendants: diagnosed by synapomorphies (shared derived characters)

Parallelism: the possession of similar characteristics by two or more taxa which do have a common ancestor.

paraphyletic: a group containing a common ancestor and some but not all descendants: diagnosed by symplesiomorphies.

many botanists wish to know something of the evolutionary history and relationships of a group of taxa; in other words they will want the classification to reflect the phylogeny (phylogenetic or evolutionary pathways) of the plants.

A taxon (pl. taxa) is any taxonomic grouping, such as a phyllum; a family or a species. It is a useful general term.

Taxonomy: study and description of the variation of organisms, the investigation of the causes and consequences of this variation, and the manipulation of the data obtained to produce a system of classification. Such a definition is wider than that sometimes given, and has intentionally been drawn up to coincide with the meaning of the term systematics. In fact the two terms are nowadays commonly used synonymously.

APG Angiosperm Phylogeny Group

The Angiosperm Phylogeny Group, or APG, refers to two international groups of systematic botanists who came together to try to establish a consensus view of the taxonomy of flowering plants that would reflect new knowledge in angiosperm relationships molecular systematics. (The Angiosperm Phylogeny Group. 1998 An Ordinal Classification for the Families of Flowering Plants. Annals of the Missouri Botanical Garden. )

Molecular systematics, is the use of the structure of molecules to gain information on an organism's evolutionary relationships. Previous classification being only based on morphological and anatomical characters.

The major difference of this new classification are:

  • Not to use formal, scientific names above the level of order, but rather to have named clades, such as eudicots, monocots and rosids.
  • To place a substantial number of taxa whose classification has traditionally been uncertain.
  • To offer alternative classifications for some groups, in which for example a number of families can either be regarded as separate or can be merged into a single larger family. APG II refers to such groups as "bracketed" taxa.

As a result the Eudicots (true dicots) or tricolpates (refering to the tricolpate pollen grains) are created and previously Dicotyledones orders are placed into Basal Angiosperms and Magnoliids.

Phylogenetic tree of the Angiosperms according to the Angiosperms Phylogeny Group (http://www.mobot.org/MOBOT/research/APweb/ - April 2008)

Question: In which order, following the APG system, would Digitalis purpurea or Foxglove be placed ?

The hierarchy of taxonomic ranks

Division Magnoli-ophyta
Class Lili-opsida = Dicots, Monocots
Subclass Ros-idae
Order Ros-ales
Family Ros-aceae
Subfamily Ros-oideae
Tribe Ros-eae
Subtribe Ros-inae
Genus Rosa etc.
Subgenus Rosa subgen. Rosa etc.
Section Rosa sect. Rosa, Cassiorhodon etc. (sing. nouns) ; Rosa sect. Synstylae, Caninae etc. (plur. adject.)
Subsection Rosa subsect. Pimpinellifoliae etc. (plur. adject.)
Series Rosa ser. Stylosae etc.
Species Rosa stylosa
Subspecies Rosa stylosa subsp. gallica
Variety Rosa stylosa var. glabra
Subvariety Rosa stylosa subvar. alba
Forma Rosa stylosa forma variegata

Be aware that the APG classification deliberately do not use formal, scientific names above the level of order, but rather has named clades, such as 'eudicots', 'monocots' and 'rosids'.

Advanced, Primitive and Evolved

One method of inferring phylogeny is to pinpoint primitive (i.e. ancient or least specialized) as opposed to advanced (i.e. recent or derived from the primitive) characters and to assign primitiveness to taxa which possess high proportions of the former.

Evolved can also be used to refer as a taxon with advanced characters.

Bessey Hutchinson
Chlorophyll/ no Chlorophyll Chlorophyll/ no Chlorophyll
  Terrestrial/ aquatic
Woody/Herbaceous Woody/Herbaceous
  Trees/ climbers
Stem simple/branched  
Bundles collateral/ scattered Bundles collateral/ scattered
Leaves simple/compound Leaves simple/compound
leaves evergreen/ deciduous  
Leaves opposite/ spiral Leaves spiral/ opposite
Venation reticulate/ parallel  
  Flowers solitary/clustered
  Floral parts spiral/whorled
Flowers polymerous/ oligomerous Flowers polymerous/ oligomerous
Flowers bisexual/ unisexual Flowers bisexual/ unisexual
Flowers monoecious/ dioecious Flowers monoecious/ dioecious
Flowers petalous/ apetalous Flowers petalous/ apetalous
Flowers actinomorphic/ zygomorphic Flowers actinomorphic/ zygomorphic
Flowers polypetalous/ gamopetalous Flowers polypetalous/ gamopetalous
Stamens many/ few Stamens many/ few
Stamens separate/ fused Stamens separate/ fused
Pollen powdery/ massed  
Flowers hypogynous/ epihynous Flowers hypogynous/ epihynous
Gynoecium polycarpous/ oligocarpous Gynoecium polycarpous/ oligocarpous
Gynoecium apocarpous/ syncarpous Gynoecium apocarpous/ syncarpous
  Fruits single/ aggregate
  Fruits capsule/ drupe or berry
Seeds with/ without endosperm Seeds with/ without endosperm

Comparison of characters alleged to be primitive/ adavanced by Bessey 'The phylogenetic taxonomy of angiosperms' Ann.Mo.bot.Gdn 2, 109-164. 1915 and Hutchinson 'The families of Flowering Plants' Macmilan 1926.

Most of the characters used to study evolution are in relation with the flower, because they are less subject to natural selection. For example a plant growing in shady condition with lots of competition might evolved in a tree to reach more light.

Nevertheless a widely accepted evolution trend in the Angiosperms or flowering plants is the simplification of the flower morphology and the specialization in pollination mechanisms. Often we refer the Magnoliids as 'primitive' with there many undifferentiated tepals arranged in a spiral, their many unfused carpels and anthers also organized in a spiral. In comparison with an orchid having a whorled perianth, a fused zygomorphic corolla with 6 tepals, an inferior ovary and a targeted pollination mechanism.

Species concept

A species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are often used, such as based on similarity of DNA or morphology. Presence of specific locally adapted traits may further subdivide species into subspecies.

This definition doesn' t always apply to plant where breeding between different species is common. This explains why species description and synonymies are so high in plants: there are 928 000 taxa entries in IPNI (International Plant Names Index) but there are thought to be only 13900 genera and 250 000 plant species on earth.

The concept of biological species is sometimes used. This concept is assessed on their morphological or structural distinctness (which is really subjective to the author).

You will often hear of a 'Lumper' or a 'Splitter'. A 'Lumper' will try to group taxa in quite heterogenous but robust group, the 'Splitter' will try to recognize and value any morphological difference observed.This can lead to great variations in the treatment of a same group.

IPNI (International Plant Names Index) has around 928 000 names and around 4000 are added every year. But the species number has dropped from 330 000 to around 240 000 in 20-30 years and is still diminishing. This fact shows well that the species concept is still misunderstood and problematic.

Chart showing the percentage fertility of hybrids between various taxa of Nigella from the Aegan region taken from Strid.

Speciation

Mutations in the DNA and natural selection could be the main drive of evolution.

But other forces drive evolution like:

  • Geographical isolation (Allopatric speciation) example with Platanus occidentalis from North America and Platanus orientalis form the Mediterranean region.
  • Hybrids, Polyploidy... (Sympatric speciation)
  • Apomictic species (produce seeds without fecondation) example with Rubus with 430species only in the UK or Taraxacum with 180 species in the UK..
  • Inbreeding species.

 

Nomenclature

Plants were first described by a common name which would vary in different languages or even areas. example: Foxglove.

They were then described using a latin descriptive sentence.

Linnaeus became famous by using the latin binomial name system. example: Digitalis purpurea L. Sp. Pl. 2: 621. 1753 [1 May 1753]

Where Digitalis represents the genus name and purpurea the species name, L. the abbreviation of the author of the description of the species, Sp. Pl. for Species Plantarum 2 page 621 published in 1753 the publication where this description can be found and the type specimen located

Nomenclature follows strict rules gathered under the International Botanical Code.

All those names can be found on IPNI or the International Plant Names Index

Identifying

Identifying consists in giving a name to a plant specimen using a Flora, a botanical revision or simply by comparing with a herbarium specimen or photographs.

If no names match a description of a new species could be made.

Nowadays there are several Flora online and many revisions are available on journals that are also online.

Flora of North America

Flora of Pakistan

Flora of China

Flora Brasiliensis

Flora Iberica

Flora of New Zealand

Flora of Australia

Flora of Chile

There are also Flora you ll find in libraries covering the rest of the world

Flora Europaea

Flora of the USSR

Flora of Tropical East Africa

Flora Capensis

Flora of British India.......

Bibliography

Judd, W.S.; Campbell, C.S.; Kellogg, E.A.; Stevens, P.F. 1999. 'Plants systematics, a phylogentic approach' Sinauer Associates Inc. Publ. , Sunderland, 464p.

Heywood, V.H. 1985 'Flowering Plants of the World' Equinox publ., Oxford, 336p.

Jeffrey, C. 1982. 'An introduction to plant taxonomy', 2nd ed. Cambridge Univ. Press, Cambridge. 154p.

Spichiger, R.; Savolainen, V.; Perret, M.; Figeat, M. 'Systematic Botany of Flowering Plants: A New Phylogenetic Approach to Angiosperms of the Temperate and Tropical Regions Published by Science Publishers, 2004

Stace, C.A. 1989. 'Plant Taxonomy and Biosystematics', 2nd ed. Cambridge Univ. Press, Cambridge.

Internet resources:

Angiosperm Phylogeny Group http://www.mobot.org/MOBOT/research/APweb/

IPNI International Plant Names Index http://www.ipni.org/

Wilkipedia http://en.wikipedia.org/wiki/

 

Home Page

Artificial classifications

Natural classifications

some definitions

APG classification

the hierarchy of taxonomic ranks

Advanced, Primitive and Evolved

Species concept

Speciation

Nomenclature

Identifying

Bibliography

Practical

Exercise 1

Exercise 2
     

Exercise 1: Questions

With the images of the Herbarium specimen provided below (classified according to the Babington system), fill the table with the character state 0 or 1 for each species.

Find the shared character between species.

Translate the shared characters onto the tree and fill the boxes with the corresponding species name and the circles with the corresponding shared character.

Complete the dichotomous key with the same informations.

Characters state:

  1. Leaves:alternate (0)Opposite (1)
  2. Leaves:Compound (0) Simple (1)                               
  3. Stamens:Many (0) Few (1)
  4. Flowers: Symmetrical (0) Asymmetrical (1)
  5. Gynoecium: Apocarpous (0) Syncarpous (1)
  6. Petals: free or absent (0) Fused (1)

 

1  leaves alternate/opposite

2 leaves simple/ compound

3 Stamens Many/ few

4 corolla symmetrical / asymmetrical

5 Gynoecium apocarpous / syncarpous

6 Petals free / fused

Helleborus viridis L.

 

 

 

 

 

 

Papaver rhoeas L.

 

 

 

 

 

 

Cardamine pratensis L.

 

 

 

 

 

 

Silene vulgaris Garcke

 

 

 

 

 

 

Lamium album  L.

 

 

 

 

 

 

 

Dichotomous key

1 Gynoecium apocarpous…………………………………………........…….Helleborus viridis
1 Gynoecium syncarpous………………………………………….......…….go to 2

2 Stamen few……………………………………….…………….......……….go to 3
2 Stamen many………………………………………………...………..?________________

3 Leaves opposite and entire………………………………….........………..go to ?
3 Leaves alternate...……………………….…………………..………..?________________

4 ?                                                        ……………………..................Lamium album
4 Flowers symetrical and petals free...................………….............…________________

Division: Thalamiflorae

Class: Dicotyledones Order: Papaveraceae or Poppy-worts Genus: Papaver Species: rhoeas L.

Characters of the order: Flowers regular, Corolla of 4 petals, sepals 2 deciduous. Stamen indefinite. Fruit syncarpous with parietal placentas. Seeds many, albuminous. Style 1 or stigmas sessile. Leaves alternate, exstipulate. From Papa , pap the juice of the poppy formerly used in children's food.

Division: Thalamiflorae

Class: Dicotyledones Order: Caryophyllaceae Genus: Silene Species: vulgaris Garcke

Characters of the order: Flowers regular. Petals 5 or 4 clawed. Sepals 5 or 4. Stamen 8 or 10. Anthers opening longitudinally. Ovary one, often stalked. Stigmas 2-5 sessile, filiform. Capsules syncarpous, 1 celled, placenta free central. Seed many, small albuminous. Leaves opposite usually connate at base. Stipules small or 0 and scarious. From Karyon a nut and phyllon a leaf refering to the appearance of the flower buds.

Division: Corolliflorae

Class: Dicotyledones Order: Labiatae Genus: Lamium Species: album L.

Characters of the order: Corolla 2 lipped, upper lip entire or bifid, lower 3 fid or nearly regular, hypogynous. Calyx inferior, tubular or 2 lipped, persistent. Stamens 4, didynamous rarely 2 epipetalous. Ovary 4 lobed, 4 celled, ovules solitary in each cell. Style from between the lobes, stigmas bifid. From Latin Labia, a lip; in allusion to the shape of the corolla.

Division: Thalamiflorae

Class: Dicotyledones Order: Cruciferae Genus: Cardamine Species: pratensis L.

Characters of the order: Flowers cruciform, Petals 4, Sepals 4, 2 lateral often larger. Stamen 6, tetradynamous, 2 shorter opposite the lateral sepals. Ovary free. Stigma 2, fruit a 2 celled capsule or pod, the valves opposite the shorter stamen. Seeds exalbuminate. From Crux, a cross, referring to the arrangement of the 4 petals.

Division: Thalamiflorae

Class: Dicotyledones Order: Ranunculaceae Genus: Helleborus Species: viridis L.

Characters of the order: Flowers regular. Stamens indefinite (polyandrous) anthers, adnate opening lenghtwise. Sepals 3-6 often petaloid. Petals 5 or more, rarely 0. Pistils usually many 1 seeded achenes or many seeded follicle (apocarpous). Seeds erect or pendulous albuminous. From Rana a frog, many species are found in places frequented by Frogs.

 

Practical

Exercise 1

Exercise 2

Exercise 2: Guided reading questions: Stace, C.A. 1989. 'Plant Taxonomy and Biosystematics, 2nd ed. Cambridge Univ. Press, Cambridge, 264 pp.

pages 4 to 64
  1. 1. Define Systematics
  2. 2. What are the uses of Systematics ?
  3. 3. Define Herbaria and describe some of their uses.
  4. 4. Arrange the following taxonomic ranks in order of their hierarchy (higher rank first): Caryopphyllid, Caryophyllales, Dicotyledonidea, Melocactus, Cactaceae, Cactoideae, Angiospermopsida.
  5. 5. What is the difference between identification and classification ?
  6. 6. How many species of seed plants are there in the world ?
  7. 7. What is the difference between alpha-taxonomy and omega-taxonomy
  8. 9. What wa Linnaeus main contribution to the world of Botany ?
  9. 10. Explain the two major problems encountered by practice of phylogenetic systems and their consequences.
  10. 11. What is parallelism, convergence, divergence ?
  11. 12. What do you understand as: plesiomorphous and apomorphous characters ?
  12. 13 What is the most important parameter to be identified when working out a cladistic or phylogenetic system ?

Discuss this cladogram and find synapomorphy, convergence, parallelism, plesiomorphous and apomorphous characters, monophyletic and polyphyletic groups.

Answers

  1. 1. Study and description of the variation of organism. Page 4.
  2. 2. Naming organisms and grouping then grouping them in recogizable categories Page 7
  3. 3. Place where plant collections are stored as pressed and dried plants, mounted to sheets. Uses: provide info with ,ocality, habitat so they can be further studied. Types.
  4. 4. Angiospermopsida; Dicotyledonidae; Caryophyllid; Caryophyllales; Cactaceae; Cactoideae; Cactaceae; Melocactus
  5. 5. Identification is the naming of an organism classification the production of a logical systeme of categories. Page 4
  6. 6. Approximately 240 000 species. Page 6
  7. 7. Natural classifications: Classifications which have high levels of predictivity, the groups they delimit are called natural groups. Artificial classifications: one could, for example, classify plants like inanimate objects- by size, shape, colour, texture etc.. or even alphabetically if they had a name, or in numerical sequence if they had numbers. Page 12
  8. 8. Alpha taxonomy: Classification based solely upon more or less obvious external morphological (exomorphic) characters. Omega taxonomy: Classification based upon all available characters. Page 19
  9. 9. Binomials and the sexual artificial classification. Page 27
  10. 10. It is rarely possible to reconstruct the past evolutionary pathways and hardly possible to devise a satisfactory method of designating a branching pattern by means of a single linear sequence. Page 36
  11. 11. Convergence: the possession of similar characteristics in 2 or more groups without an intermediate common ancestor. Parallelism: the possession of similar characteristics by 2 or more taxa which do have a common ancestor. Divergence: The possession of different characteristics Page 42
  12. 12. Pleisomorphous is the ancestral character, apomorphous the derived character. Page 48
  13. 13. the outgroup.