Plant Classification and Nomenclature Spring 2012
Elements of UnderstandingBiological Diversity Description:requires observation and measurement of characters and their states and synthesis of this information Classification:requires hierarchical organization of taxa based on evolutionary relationships Naming (nomenclature):requires following nomenclatural conventions and enables communication Identification:requires tools such as keys that are based on previous description, classification, and naming of taxa
Naming of Diversity Elements of UnderstandingBiological Diversity Description of Diversity Observation & Organization Classification of Diversity Convention & Communication Naming of Diversity
Description • Provides some basic identifiable set of characteristics to associate with the organism; also basis for characters and character states for phylogenetic analysis. • Can be as general or as detailed as practicality dictates. • Needs to contain enough data to provide adequate discrimination between similar organisms. • Needs terminology. • Descriptions are linked with a name when there is consistency in the set of observed characters for a given organism.
Classification • A systematic arrangement in groups or categories according to established criteria; biological classification involves the delimitation, ordering and ranking of taxa. • Classification provides ORDER to the group of entities. • Relies on observations, many definable and comparable characters, and an ability to discern them. • Completely effective classifications can be artificial, that is, not necessarily reflecting evolutionary relationships: i.e., trees vs. shrubs vs. herbs. • But modern classifications are based on evolutionary history (phylogeny) because this provides predictive power and synthesis of many types of data is possible. • Biological classifications are hierarchical (= information storage system).
Classification in Your Life… • Do you classify things? • Do you do it deliberately? Unconsciously?
Let’s go home...* • In your room or apartment, think about what groups of items you automatically classify… • What characteristics and criteria do you use to do this? • Is the classification a continuous, ongoing thing, does it happen occasionally, or at very distinct times? • WHY do you do this? *Mentally, that is – so just sit down and think…
Some examples: • Kitchen: - Silverware [knives, forks, spoons], plates, bowls, pots, pans, cooking utensils, trays, etc. - Refrigerator – meats, vegetables, fruits, eggs, bottles, cans, salad dressings, frozen foods. • Bedroom: - Closet & dresser [shoes, boots, shirts, slacks, etc.] - Jewelry • Living room: - CDs, Video tapes/DVDs, books, magazines • Study: - Textbooks, pens & pencils, paper, etc.
A basic fact of life: “Everyone is a Taxonomist”
Artificial taxonomy • These classifications are based on use or similarity of shape. • Generally based on one or few “characters”. • Single character taxonomy may work in these situations, but…
What makes a good classification? - Groups recognized according to overall similarity within groups (as seen by multiple characters) and discontinuities between groups and relatedness (evolutionary history). - The classification has predictive value – Characteristics of other related organisms can be predicted by the classification because of the evolutionary perspective. - The classification is practical and useful.
Why is biological classification possible? Because variation exists in nature. Four species of the bamboo genus Chusquea
Discontinuity of Biological Diversity • Must be able to identify discrete “packages” • of biological diversity: species. • Discontinuity is caused by: • 1. evolution and speciation, or • 2. extinction, or • 3. a combination of 1. and 2.
Assessing Biological Discontinuity • To establish a classification, one must be able to use discontinuities to delimit groups at various hierarchical levels, e.g.: • - How different are populations to warrant • calling them distinct species? • - How distinct are two groups to be able to • recognize them as separate genera? • Establishing ranks can be very subjective – the more objectivity we can impose on the process, the more reliable the classification.
Evolutionary Time Speciation Phylogeny
Effects of Extinction Speciation Phylogeny
Speciation Apparent Phylogeny
Hierarchical (nested) categories and phylogeny GENUS FAMILY TIME ORDER CLASS PHYLUM
Principles of Biological Classification • Should be based on a well established hypothesis of relationships (a phylogeny) whenever possible • Ideally only recognizable (morphologically diagnosable) clades are formally named • Ranks should represent more or less equivalent branching points (but this is often ignored)
Phylogenetics and Classification Branching order can be inferred from the written classification. Fig. 2.19A-C
In terms of nomenclature, so far… • We have been using names of plants to discuss their “position” in the plant kingdom, reflecting some level of evolutionary understanding. • The names for plant species or genera have been used as a “given” – that is, we did not talk about how those names came into being or how they are correctly used. • We need to understand how the accepted system of nomenclature works – how the giving of names to plants follows a specific set of guidelines and rules.
Naming and Nomenclature • Plants did not evolve with a name! • However, weneednames to communicate about the plant • Organized system of names enables fitting the plant into an accepted scheme • Following formal naming rules = nomenclature • The system must allow for changes as new information (and other species) are discovered • It is helpful if names are descriptive
What about common names? • Positives: - easily recognizable - easier to pronounce and spell (!) • Negatives: - Name varies by language or region - Not specific (ironwood, bigleaf, ivy, etc.) - Conveys no evolutionary information - Does not include classificatory information • Botanists rely on the ‘botanical’ or scientific name for accurate communication about the plant in question
Common name? Whitlow grass ‘Real’ name: Drabaverna (Brassicaceae)
The International Code of Botanical Nomenclature (ICBN) is the “legal” code for naming of plants. A new version is produced following each international botanical congress (ca. every six years).
Principles of Nomenclature • Botanical and zoological classification systems are independent of one another • Applying names to taxonomic groups is based on a system of nomenclatural types • Names are based on the priority of publication – the earliest valid name is the one to use (later names for the same taxon are called synonyms); starting point for plants is Linnaeus’s Species Plantarum (1753) • Each taxon can have only one correct name • Scientific names are in Latin or are treated as Latinized words, regardless of origin • Rules of nomenclature (ICBN) are retroactive unless expressly limited
Plant Names An exception to the rule that there is only ONE legitimate name per taxon: Eight angiosperm families have two acceptable names: (Arecaceae = Palmae; Apiaceae = Umbelliferae; Asteraceae = Compositae; Brassicaceae = Cruciferae; Clusiaceae = Guttiferae; Fabaceae = Leguminosae; Poaceae = Gramineae)
Classification of Black Pepper Kingdom Viridiplantae (Chlorobionta) Division/Phylum Anthophyta (Embryophyta) Class Magnoliopsida Subclass Magnoliidae (often not used now) Order Piperales Family Piperaceae Genus Piper Species Piper nigrum Genus and species names are always italicized.
Species names are binomials! All binomials have three parts… Piper nigrumL.
Piper nigrum L. = Black Pepper Piper – Genus name or generic epithet – Member of the genus Piper nigrum – Species epithet – Latin for ‘black’ L. = Linnaeus – Author – Person who described plant Black Pepper – Common name
Naming a New Species • These steps must be followed in naming a new species, according to the ICBN: 1. The name (specific epithet) must be in Latin or Latinized (but Latin diagnoses or descriptions are no longer required) 2. The rank of the new name must be clearly indicated (in this case, species novum or new species) 3. A type specimen must be designated (including the herbarium where it is deposited) 4. All of this information and any additional material (e.g., illustrations) must be effectively published (presented in a publication that is widely available to other botanists) Following all of these steps results in valid publication of the name. The process of describing a new species can take a year or more, depending on what studies are needed to justify it as a new species, how long it takes to prepare illustrations and keys, and which journal or book it is published in.
The Type System • Each species name must be based on a type specimen, with which the name is permanently associated. • Types are preserved as reference specimens, often kept separately from the remaining collections in the herbarium. • The type specimen must fit within the concept of the species, but does not necessarily have to be representative of average variation (i.e., it may represent one of the extremes of variation in the species) • The species name used for the type specimen is considered the basionym, or original name as described, and follows that specimen in perpetuity • Names of higher ranks are based on typified names published validly and effectively
Types by Rank • The type is one physical specimen deposited in an herbarium to which the name is attached and upon which the species description is based (holotype); the holotype can be an illustration although this is unusual. • Every species has a type specimen. • Every genus has a type species. • Every family has a type genus (and so on): - Asteraceae -Aster; Poaceae – Poa; Lamiaceae - Lamium.
Type Specimen of SobraliakerryaeDressler (Orchidaceae) Holotype
Botanical Types • Holotype – The one specimen (or illustration) designated by the author that will serve as the nomenclatural type • Isotype – A duplicate of the holotype (part of the same gathering); always a specimen • Lectotype – The specimen designated as the nomenclatural type if no holotype is available or indicated by the author • Syntype - Any specimen that is cited in the original description when no holotype was designated by the author • Neotype – A ‘new’ type specimen designated when all material for the original type description is missing
Also common to explain derivation of name and to highlight distinguishing features as well as to summarize distribution and habitat.
Illustrations, maps, and dichotomous keys distinguishing the new species from related ones are usually included.
Publication • Names of new taxa must be published effectively and validly to have recognition in the systematics community under ICBN: - Effective Publication – The information must be published in a recognized botanical journal or book (…not a seed catalog or newspaper, internet, etc.); electronic publication is now also approved. - Valid Publication – All of the conditions laid out in the ICBN have been met, including effective publication. - The new name is considered to be a legitimate name if all of the correct publication conditions are met. Whether the name becomes accepted (or not) depends on how the botanical community agrees with the author.
Why (and how) do plant names change?
Plant names change when: • The classification system has changed - By far the more typical and frequent cause of name changes - New data often support revision of concepts of generic, familial, or other circumscriptions, necessitating name changes • Because of nomenclatural errors - Errors made in original descriptions or taxonomic revisions may need to be corrected by changing the names of plants due to improper format, invalid publication, etc.
Capsella bursa-pastoris(L.) Medik. • Original Description - Described by Linnaeus as Thlaspi bursa pastorisL., because the species fit in his concept of Thlaspi - Placed as one species in genus Thlaspi, but was not the first species described in the genus (that was T. arvense L.) • Subsequent Revision of Taxonomy - Friedrich KasimirMedikus (Dir. BotanischesGarten Mannheim) thought the species should be placed in a separate genus, which he named Capsellain 1792 -The specific epithet must be retained in such a transfer and the original name becomes a synonym • This is an example of a taxonomic transfer. The author names reflect the history of publication of the original species name (basionym) and the subsequent transfer to a new genus
Capsella bursa-pastoris (L). Medik. Syn.: Thlaspi bursa pastoris L. basionym The type specimen of the basionym (original name) stays the same and is the type of the currently accepted species name in Capsella. The concept of the species has not changed; only its generic placement has changed.
Synonyms - Priority • If two (or more) different names are determined to be the same entity, the earliest validly and effectively published name has priority. • Maluspumila Miller, 1768 (invalid) • MalusdomesticaBorkh., 1803 • MaluscommunisPoiret, 1804 (SYNONYM) • If the same name has been used for more than one taxon, these are considered HOMONYMS. • PlatoniaRaf. 1810 is a genus of Cistaceae (rock rose family) • PlatoniaKunth 1829 is a genus of Poaceae (bamboo); this name was changed to NeurolepisMeisn. in 1843
Chusquea – 138 species Neurolepis – 21 species