Plant Taxonomy

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Honorifics:

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Created to honor individuals who have made a contribution to botany

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Sources of generic names

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We often use generic names for plants without even realizing it. Ex. Iris, Gladiolus, Asparagus.

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Plant Nomenclature

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Systematists do not apply names at random, but must follow a specific set of guidelines.
• Guidelines referred to as the International code of Botanical Nomenclature (the code)
• Same code followed by all guide lines.
• Six basics principles underlie the code

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Principles of the code

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Botanical nomenclature is independent of the zoological nomenclature.
The application of names to plant groups is determined by the use of type specimens (each species name must be associated with a particular herbarium specimen, the type specimen)
The nomenclature of a group is based upon priority of publication (the first published name is the one that must be used)

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Naming a New Plant Species

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• Discover a new species and collect a type specimen
• Select and appropriate name for the plant
• Prepare a Latin diagnosis - which is a short description on how your new species differ from species similar to it.
• Publish the name and diagnosis in a scientific journal

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FAMILY NAMES

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• Plant families are named for a significant genus within the family.
• Family names are produced by adding the suffix –aceae to the root of the generic name. Ex. Magnoliaceae (named for the magnolia), Rosaceae (named for Rosa)
• Family names can usually be recognized by the characteristic suffix –aceae with some exceptions.
• The rules that govern the naming of plants allow an alternative name to be used for eight important plant families.

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Tautonyms

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scientific name in which the genus name and specific epithet are the same. Ex. American Bison – Bison bison, Blue star – Amsonia amsonia.

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Sources of Specific Epithets:

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•End with suffix “I” or”II” if male and “ae” or “iae” if female Ex. Juniperus ashei, Abronia ameliae.
•May indicate a geographic locality (in which case the epithet usually ends with the suffix “ensis” or “ense” Ex. Lupinus texensis
•Most specific epithets are simply adjectives that describe some aspect of the plant
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Principles of the code

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Each taxonomic group can have only one correct scientific name (with exceptions for eight plant families)
Scientific names are treated as Latin regardless of their origin
The rules of nomenclature are retroactive to the year 1753 (the year Linnaeus published his principle botanical work, Species Plantarum)

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Sources of specific epithet 2

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In these cases, the epithet must agree with the generic name in number and gender. Ex. Quercus Stellate – there isn’t an agreement between the ending of the generic name and the ending of the specific epithet. Also EX. Vinca rosea
•Tautonyms are not permitted in botanical nomenclature (acceptable in zoology)
•Tautonyms – a scientific name in which the genus name and specific epithet are the same. Ex. American Bison – Bison bison, Blue star – Amsonia amsonia

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Systematics

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scientific study of the diversity of organisms of any all relationships among them. It’s a broad field of study that cuts across many sub disciplines of biology

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Classification

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the ordering of organisms into groups on the basis of their relationships

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Taxonomy

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study of classification includes its principles, procedures, and rules

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Need for systematics

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1.Identification – naming etc
2.Relationships

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Goals of modern plant sytematics

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•To produce useful and convenient methods of plant identification.
•To inventory the plant life of the world
•To provide a classification system that can express the natural relationships of plants
•To detect evolution at work, discovering its processes and interpreting its results

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Plant identification

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an integral part of work in the field of plant systematics.

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Identification

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determining the correct group in which an individual organism belongs

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Difference between classification and identification

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Classification deals with groups of organisms, while identification deals with individuals. Identification requires that some system of classification already exists.

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Prerequisite for making accurate identifications

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•Knowledge of taxonomic terms, methods and characters.
•Be familiar with manuals and other resources for identification
•Experience in the process of identification

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Methods of plant identification

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Expert determination
Comparison method
Taxonomic keys

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Expert determination

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Ask someone who knows.

Advantages – Best method in terms of accuracy and reliability

Disadvantages – Requires access and time of an expert

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Comparison method –

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Compare an unknown plant with photos, illustrations, descriptions, or previously identified plant specimens.

Illustrations and descriptions of comparison methods – favored by those with little training in the process of identification
Advantage – Easy, does not require technical knowledge.
Disadvantages – most field guides are not comprehensive

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Comparison with herbarium specimens

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Useful if you have access to a herbarium
Advantages – comprehensive, unknown plants are compared with actual plant specimens.
Disadvantages – access to herbarium, can be time consuming if you don’t know where to begin,

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Herbarium

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A collection of pressed and dried plants that have been identified and mounted on paper.

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Taxonomic keys

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Most widely used method when used properly, they allow quick and accurate identification.
Advantages – available for most areas and its comprehensive.
Disadvantages – Require practice and experience to use efficiently

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Key

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A sequence of choices between pairs of contrasting statements that identified plants by the process of elimination

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Classification

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Based on the similarities and differences among organisms

Should provide a meaning for referring to different groups of organisms

Should express the relationships among those groups

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Species

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the basic unit of classification

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Morphological species concept

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Organisms that look alike belong to the same species

Morphological similarity is the species criterion

Has the disadvantage of being subjective

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Nomenclature changes

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•As information about a group of plants become available, it sometimes becomes necessary to change plant names
•The code of Nomenclature specifies how nomenclatural changes are to be made

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Nomenclature changes 2

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• When a species is described in one genus and later transferred to another genus, the original specific epithet must be retained. Ex: Echinocactus intertextus Engel. Then 100ys later a cactus specialist reexamined the cactus and realized that it belonged to Neolloydia intertextus (Engel.) Benson: Name in parentheses indicated that a nomenclature change has been done

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Nomenclature changes 3

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•If two or more previously distinct species are combined to form a single species, the earliest legitimate specific epithet must be used. Ex: Amsonia amsonia (1809) then 20yrs later (1828) someone discovered Amsonia tabernaemontana and the in 1928 Amsonia Glaberrima and then in 1956 Amsonia repens was discovered in texas. In 1980s a plant systematist concluded that they are all the same plant just a little different, such as one had hair and one had different growth patter, but could all interbreed, so the name is Amsonia tabernaemontana

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Principles of classification 1

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•Systematics do not construct classifications randomly, but instead follow a widely agreed upon basic principles
1.As many characteristics as possible should be used in assessing relationships
•Classification should be based on correlations of characters- use multiple characteristics that occur at the same time
•Systematists try to avoid “one character classification”
•Character correlations give classification a predictive value, knowing one thing will let you know their things about it

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Principles of classification 2

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2.Only genetically controlled variation should be used for classification
•Characteristics that can be easily modified by the environment are not useful for classification
•Characteristics that have a strong genetic component are preferred

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Principles of classification 2 Ex 1

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• Ex. Flower color in hydrangeas (subject to environmental modification and not useful for classification) you would think that color would be good for separating species of hydrangeas but it the color has to do with the environment not genetics Blue flowers- When grown in acidic soil, pink flowers – alkaline soil…if you put a blue plant in alkaline soil it will grow pink

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Principles of classification 2 Ex 2

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• Ex: Fruit color in sumacs (under genetic control and constant for any particular species), correlated species…fruit color in a sumac is due to genetic control and correlated with other features…Red fruits – Found in all species of Rhus subgenus Rhus (sap is non toxic)…Greenish white fruits found in all species of Rhus subgenus Toxicodendron (sap is toxic).

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Principles of classification 3

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3. All taxa should be monophyletic
•Monophyly – the derivation if a taxon from a single ancestral taxon
•Polyphyly – The derivation of a taxon from more than one ancestral taxon
•Monophyly Requirement – 2 systematists are trying to work out the evolutionary relationships among 5 related species of organisms

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Principles of classification 4

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Parallel evolution must be distinguished from convergent evolution

•There are 2 different evolutionary processes that can cause groups of organisms to have similar characteristics, parallelism and convergence.

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Parallelism

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Resemblance due to a similar genetic background resulting from common ancestry
•Ex: Mint family and Verbena family share a large number of characteristics in common,
Common characteristics between the two families: opposite leaves, square stems, bilaterally symmetrical flowers, fused petals, 4-lobed ovary. Differences: Mints have a bifid stigma and a style attached to the bottom of the ovary. Verbenas have an entire stigma and a style attached at the top of the ovary

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Convergence

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Resemblance between evolutionary lines resulting from adaptation to similar environments.

•Ex: Some members of the cactus, spurge, and milkweed families are very similar in vegetative morphology: cactus has water filled stems with spines and so does the spurge and milkweed

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Convergence Ex

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•Ex: Some members of the cactus, spurge, and milkweed families are very similar in vegetative morphology: cactus has water filled stems with spines and so does the spurge and milkweed.

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Convergence Vs Parallelism

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* In parallelism, there will be more overall similarities than differences
* In convergence there will be more overall differences than similarities

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Basis of Classification

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•Classification = ordering organisms into groups on the basis of their relationships
•“Relationships” are obviously important to classification, but the term has different meanings to different Systematists.
•One way to understand is to look at how it has been used

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3 types of classification that have been used

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•Artificial systems – earliest system used, very simple
•Phylogenetic systems – evolutionary classification, related groups
•Natural systems-

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Biological species concept

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•Species are groups of actually or potentially interbreeding organisms.
•The ability to interbreed and produce viable, fertile offspring is the species criterion
•Offers more objective and testable definition

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Evolutionary species concept (phylogenetic species concept

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•Species should be recognized based on their evolutionary relationships
•Separate evolutionary lines should be recognized as a separate species
*Biological or evolutionary are favored

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Genus – a group of related species
Family – a group of related genera
Order – a group of related family

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Genus – a group of related species
Family – a group of related genera
Order – a group of related family

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Hierarchy –

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framework for classification composed of a sequence of graphs at different levels, arranged such that each group, except the lowest contains more subordinate groups

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Linnaean Hierarchy

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Kingdom, phylum, class, order, family, genus, species

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Taxon

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a group of real organisms that is recognized at any level of a taxonomic hierarchy.

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Category

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the levels in a hierarchy to which a taxa are assigned

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Taxonomic Rank

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relative position of either a taxon or a category in a taxonomic hierarchy

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Supraspecific Category

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Everything above the rank of the species

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Phylum

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largest unit in classification

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Intraspecific categories

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everything below the rank of the species

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The number of categories in a classification scheme is determined by:

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•Size of the group of plants being studied
•Diversity of the group
•How intensively the group has been studied

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Most common classifications in flowering plants

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•Family, genus, species, subspecies, variety

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Classification

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ordering organisms into groups on the basis of their relationships

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Nomenclature

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the application of distinctive names to the groups

•An integral part of plant systematics
•Refer to the groups recognized by the process of classification

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Scientific name vs. common name

Reason for not using common name:

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•Common names are only applicable in a single language
•Often applied indiscriminately to plants of different ranks
•Single species of a plant can have more than one common name

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Advantages of scientific name

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•Each taxon has only one correct scientific name
•Scientific names are universal, the same names are used by scientist throughout the world

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Basis of scientific names

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•No system before 1700
•Often named by descriptions

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Polynomial

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scientific name composed of three or more words

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Binomial nomenclature

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use of two latin of Latinized words to name each species

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Complete species

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consist of binomial plus authority

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The rules to follow when naming

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•Names of species and genera are italicized in print and underlined when handwritten
•Initial letter of generic name is capitalized, all other letters are lowercase

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Scientific names

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•Generic names always is a latin noun or a word treated as a latin noun
•Once written out in print, a generic name can be abbreviated by its initial capital letter
•Ex. Juniperus ashei – first usage, J.ashei – second or third usage

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Sources of generic names

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•Original latin or green names
•Honorifics
•Descriptive terms of the plants

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Principle of classifications 1 Ex.1

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•Ex: Characteristics of the oak genus – Acorns, small, green, wind pollinated flowers, buds clustered at ends of twigs, and pith of twigs is 5-angled

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Convergence Ex 2

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Similar characteristics:
•Leaves are absent
•Stems thick, fleshy, and succulent
•Spines are present
Different characteristics
•Floral morphology – all the features of the flowers are different in all 3
•Fruit type: Berries in cacti, capsules in spurges , follicles in milkweeds
•These 3 families are not closely related genetically and the similarities are a result of adaptation to similar environment. (hot, dry deserts)

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Artificial classification

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•Only one or a few characters of the organisms are used for classification
•Earliest mentioned, introduced by the ancient Greeks ins 300 b.c.
•Simple system that is easy to use
•Usually doesn’t accurately reflect evolutionary relationships
•Despite this, it was used for 2000yrs

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Theophrastus

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•Lived from 370 to 256 bc
•Student of Aristotle
•Considered the father of botany
•Classified plants based on the growth form and divided plant kingdom into four major groups –trees, shrubs, subshrubs and herbs
•Each group subdivided into cultivated and uncultivated plants

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Carlos Linnaeus

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•Father of plant taxonomy
•Did not invent binomial nomenclature, just the first to use it consistently
•He introduced the “sexual system

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Sexual system

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•Based on the number of reproductive parts in a plant
•Plants divided into 24 classes based on the number of stamens
•Each class was subdivided into orders based on the number of styles in each flower
•Mostly used because of its simplicity
•Allowed for classification of the large numbers of plants being discovered by European explorers
•Eventually fell out of favor because it was still artificial

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Post Linnaeus systems

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•Years 1750-1850, were the transitional period when classification fell out of favor
•Scientists began to realize that there were “natural relationships” between plant groups and wanted a system to express this

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Charles Darwin

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•Published “origins of species” in 1859
•Not a plant Systematists
•Ideas had profound influence on the thinking of Systematists

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Basic ideas with respect to classification

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•Species can change over time
•All species have evolved from pre existing species
•Systematists were presented with a new foundation for classification and should reflect evolutionary species

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Phylogenetic classification

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•Ordering organisms into groups based on their evolutionary relationships
•Evolutionary classification
•Assumes that evolutionary primitive characteristics can be identified and the features of an organism
•Many plant groups have poor fossil records, making it difficult to understand there phylogeny
•Methods are available to infer phylogeny but with many plants we cannot know it with certainty.
•Phylogenetic classification is theoretically desirable, but difficult to achieve in practice

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Natural classification

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•Simple in principle but difficult for many biologists to accept philosophically.
•Classification is based on resemblance and evolutionary relationships are ignored
•Uses as many characteristics as possible for classification with each being given an equal weight
•Goal is to remove subjectivity from the process

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Taxonomic characters

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•Any feature of an organism that can be counted, measured, described, or otherwise assessed
•Classifications are constructed using the characteristics of organisms to divide them into groups

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Morphology

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•provides most of the characters that are used for identification and many of those characters are used for classification, and there are 2 types

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Vegetative characters

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•Often are more plastic/variable than reproductive characteristics
Ex Measurements are variable from plant to plant (height of stem, etc.)
•Commonly use to delimit species and sub specific taxa

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Reproductive characters

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•Features of the inflorescence, flower, fruit, and seed.
•These are the most important characters of plant classification
•Tend to be less variable and more numerous than vegetative characters

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Morphological characters are important but many other sources of taxonomic characters exist

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•Anatomy, cytology, phytochemistry, embryology, palynology, molecule biology

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Anatomical characters

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•Study of internal structures, can provide useful info
•Used more for understanding plant phylogeny than for identification

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Embryological characters

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•Involves studying the development of pollen grains and ovules
•Often more important for phylogenetic characters than identification

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Cytological characters

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•Usually involves chromosomes
•Chromosome numbers and structure are often characteristics of different plant species

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Palynology

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•Study of pollen grains in seeds and spores
•External form varies tremendously and is useful for classification/identification

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Phyochemistry

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•Technically includes the study of all chemical constituents of plants
•Usually studies secondary compounds, pigments attractants etc.
•Examples include alkaloids, flavanoids

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Molecule biology

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•Involves sequencing portions of genes
•Has proven to be a powerful tool for understanding phylogenetic relationships at higher taxonomic levels

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Good vs. bad characters
Good

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•Genetically determined
•Largely affected by the environment
•Relatively constant throughout a population of individuals
Characters not listed here are considered bad characters.