Taxonomy of Flowering Plants - LECTURE NOTES - Fall, 1998
Hugh D. Wilson - rm. 306, Butler Hall
31 August 1998

1.  Introductions
2.  A quick look at the path to be followed:  Lecture schedule and lab schedule
  
3.  Introductory notions:

    Botany 201 is an extension from introductions to plant science provided by introductory biology and botany classes.  As is the case with most advanced courses, the focus is narrowed to provide a more detailed set of information.  In this case, we are only concerned with single element of the plant kingdom, the flowering plants or angiosperms, and a single scientific view of this group, that of plant taxonomy or systematics.  Angiosperms dominate the world's biota.  As primary 'translators' of radiant energy to a form usable by animals, including Homo sapiens, the flowering plants are - from an 'animal' point of view - the most important element of the biosphere.  Thus, the educational foundation for those working at a professional level in the life sciences must include a technical familiarity with the angiosperms.

    The flowering plants are a large, complex group of organisms.  Familiarity with any complex array is signaled by an ability to identify,  recognize, and generally discern its elements via knowledge of the foundation 'structure' of the group.  Someone with a passing knowledge of automobiles can, for instance, distinguish between a 'sports car' and a 'utility vehicle'.  The ability to distinguish more detail, such as country of production, engine type, specific make/model/year, reflects advanced familiarity, knowledge, and - as a result - competence.

    Taxonomy, a fundamental life science discipline, deals with biological complexity and diversity to define elements, create order, provide linking symbols (scientific names), and identification aids (taxonomic keys).  This produces hierarchical systems of classification (taxonomy is also known as 'systematics') that serve as a structural foundation, used by the scientific community and the general public, that provides an infrastructure for all information relating to the group of organism in question.  It is important to keep in mind that hierarchical classification systems are made up of nested sets (taxa) that relate to one another by structural features that mark genetic/genomic relationship.  Thus, the classification system carries, in its internal structure, information about a given element (taxon) as it is positioned with the matrix of affinities or differences represented by the classification system.  It should be noted that the structure of modern flowering plant classification systems is based phylogenetic patterns, i.e., taxa represent lineages that share a common evolutionary history.  Thus, the foundation of this course - and essentially all life science courses -  is based in modern evolutionary theory.  Notions advanced by "creation science" are not relevant to the material presented in Botany 201.

    Flowering plant lineages or taxa are defined by shared structural features or key characteristics.  Since plants express many structural characteristics, it is important to be able to recognize the sub-set of features that define, or circumscribe (to draw a line around) taxa at various levels or ranks in the hierarchy of a classification system.  We will spend much time during the course of this semester developing a recognition 'eye' for flowering plant family identification, i.e., a focus on relevant variables or key characters that circumscribe major angiosperm families.  We will spend some time with ranks above the Family level (Classes, subclasses, Orders) and taxa that occur within the Family (Genera, Species), but the Family will be a central focus, especially about 40 'target' Families.

    As indicated above, the angiosperms (rank = Phylum or Division, technical name = Magnoliophyta) are a large, complex group of organisms.  The group includes over 200, 000 species with over 20, 000 present in the North American flora, over 5,000 in the Texas flora, and over 1, 000 in the local (Brazos and adjacent counties) flora.  Our local Spring flora is especially diverse and, to those with no experience,  training, or 'eye' for the flowering plants, the Spring flora presents a complex, chaotic assemblage of many different 'kinds' of plants.  This is represented by the image below which was taken from a native prairie site (Old Baylor) in Washington County near Independence, Texas.  The primary mission of Botany 201 is to provide a foundation for the student to develop an 'eye' for the flowering plants, i.e., a perspective - based on key characters - that allows resolution of patterns that connect 'kinds' (Species) to genera and Genera to Families.

 

 
 
 
    A similar complex pattern is evident in any complex array of 'kinds', such as that found in the 'bolts' section of a hardware store.  The first level of complexity is represented by individuals.  This is also true of our local flora.  It is composed of millions of individual plants, but these represent only about 1, 000 'kinds' or Species of flowering plant.  Thus, to simplify and thereby better resolve a complex array, we need to be able to 'see' key characters that circumscribe the basic unit.
 

 

    Application of this notion of 'basic units' or 'kinds' is pretty much a matter of matching 'like with like' for bolts, and this process (left) functions to bring order to a complex (above) array.  This operation also applies to plant species, but the 'trained eye' must also be able to deal with non-relevant (non-genetic or environmentally induced = phenotypic plasticity) variation between plants of the same Species.  Bolts, like flowering plants, have evolved from primitive or archaic 'kinds' to advanced or derived types and also diversified into different 'kinds' that do a similar job.  Thus, kinds of bolts are historically and structurally connected and these connections or 'lineage' relationships present the observer with an information-rich pattern or structure.

    Bolts, like plants, show variation in many attributes - size, color, shape.  Which of these variable 'characters' are relevant with regard to bolt 'lineages'?  An answer to this question requires detailed analysis and this, in turn, forces a close examination of variation with efficient communication among those determining 'key characters' (taxonomists) and those using the results of their work.  Individual bolts show two conspicuous structural features, an expanded upper portion, and an elongate, threaded extension from this.  To simply communication, a simple terminology can be developed for these features using terms applied to mushrooms - pileus (=expanded upper portion), and stipe (=elongate, threaded extension).  This conversion of phrases to single terms results in an efficient, standard 'vocabulary' that is essential for those dealing with complex patterns of variation, both developers and users of classification systems.  Most of our effort during the next two weeks will be dedicated to building a botanical vocabulary or suite of terms that is linked to structural variation in flowering plants.

    Taxonomic research is accomplished by individuals and, in some cases, different results or interpretations of biological relationships and 'key characters' can emerge.  Classification systems can also change through time as more data become available for flowering plants from new sources.  Thus, application of the scientific method for the development of classification systems (for any taxonomic rank) forces the user of this information to be flexible.  However, bolt evolution can be tracked from the historical record and this tells us that the outline of the pileus is a significant key character for the taxon ('Genus') that includes kinds ('Species') of bolts.

    The 'hex' Genus, circumscribed by the presence of an hexagonal pileus, includes five kinds of bolt or 'Species' that share this key character and, as indicated (left) these can be each circumscribed and identified by 'Species-level' key characters that might include size, extend of stipe threading, or color.  Further taxonomic analysis, an exercise that you will be pursuing in lab next week, involves the assignment of names to circumscribed taxa (nomenclature) and, via the application of key characters, development of an identification system (key) that allows someone to place an unknown 'kind' within the set of taxa that you have established within your personal system of bolt classification.

Finally, with regard to fundamental structure and content of the flowering plant classification system that we will follow this semester (the Cronquist System used in your text), the flowering plants are treated as a Division or Phylum of the Plant Kingdom, one of 15-20 taxa at this rank, depending on the Kingdom-level classification system.  The Phylum Magnoliophyta (-ophyta = rank-related ending), includes two Classes, the Magnoliopsida (dicots - opsida = rank-related ending) and Liliopsida (monocots).
 
 

Class
Magnoliopsida
Liliopsida
Subclass
Magnolidae (1 of 6)
Alismatidae (1 of 5)
Order
Magnoliales (1 of about 63)
Cyperales (1 of about 18)
Family
Magnoliaceae (1 of 315)
Liliaceae (1 of 65)
Genus (plural = Genera)
Magnolia (1 of about 7, 000)
Lilium (1 of about 2, 000)
Species name or epithet
grandifolia (1 of about 165, 000)
parvum (1 of about 54, 000)
Author (person responsible)
L. (= Linnaeus)
Kellogg
As is the case with 'Subclass', all ranks in the hierarchy can include a 'Sub' rank and some other formal ranks are available.

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