Taxonomy of Flowering Plants - LECTURE NOTES
Hugh D. Wilson

Flowering Plant Taxonomy - History

History celebrates the battlefields whereon we meet our death, but scorns to speak of the plowed fields whereby we thrive. It knows the names of the kings’ bastards but cannot tell us the origin of wheat. This is the way of human folly.

J. H. Fabre


Human interaction with the flowering plants is a fundamental biological activity in that we, and all other animals, rely on angiosperms for subsistence.  The average individual member of 'hunting-gathering' human groups operating around the World 20,000 years ago was probably much more familiar with the local flora, in terms of species recognition, than most people today.  This is because a local angiosperm flora offers a mosaic of valuable resources - food, medicine, and 'hardware' - and also a suite of potential hazards, especially toxins.  Thus, it has always been important to be able to discern patterns of flowering plant variation, recognize significant structural features (key characters), and identify 'kinds' (species).  Thus, the discipline of Plant Systematics has extremely deep cultural roots in all parts of the world.  While it is clear that African, Asian, and Native American cultural groups carried a wealth of botanical lore into modern times (see the Plant Trivia Timeline), current angiosperm classification systems have been derived from a European base that is briefly reviewed here.

THE ANCIENTS

One of the first documented efforts to systematize a local flora was that of Theophrastus (370 -285 B.C.), a Greek student of Plato and successor to Aristotle as director of the Lyceum and its botanical garden.  His written botanical products, including "Inquiry into Plants" and "The Causes of Plants" provided, among other things, a systematic treatment of over 500 species ordered according to 'habit' (trees, shrubs, herbs, etc.) and separated according to flowering and non-flowering.  A few generic names currently in use, such as Daucus (carrot), Asparagus, and Narcissus (daffodil), originated during this time.  A Roman military surgeon, Dioscorides (1st century A.D.) later added about 100 additional 'kinds' or species from the Mediterranean flora and some illustrations to produce a similar document, Materia Medica, that described the plants and their medicinal applications.  This included natural groupings of species that represent well-defined modern Families (Fabaceae, Apiaceae, Lamiaceae).

Intellectual stagnation of the middle ages resulted in minimal original work in plant systematics and much use of information developed by the early Greeks and Romans.  However, Albertus Magnus (German - 1200-1280 A.D.) produced a classification system that recognized - for the first time - monocots and dicots.

THE HERBALISTS

The Renaissance was an active period of learning and exploration and, with the invention and implementation of the printing press (1440) many large volumes about plants and their uses, known as herbals, were produced throughout Europe for use - mostly - by physicians.  Given the diversity of useful European plants, and the presence of new species from on-going exploration of the planet, the herbalists were forced to extend and enhance the initial efforts of the 'ancients' to structure and order flowering plant diversity.  Many 'natural' and well defined genera and families were established during this period and plants were, for the first time, depicted via woodcut or metal plate engravings with key characteristics a featured element.  Major herbalists include:

John Gerard - English (1542-1612) - The Herball, or, Generall Historie of Plantes (1597) - Described by some as Rembert Dodoens’ Herball rendered in English.  He plagiarized a manuscript by Dr. Robert Priest that was a translation of Dodoens’ Stirpium Historia Pemptades Sex, added 182 new plants, revised the arrangement, and appended his own observations. In a rush to publish, Gerard made a great number of errors in his first edition. Thomas Johnson, an apothecary, corrected many of these in a second edition published in 1633 and 1636.  Johnson’s edition (a copy at the A&M Cushing Library) also used Christopher Plantin’s woodblocks which were superior to the blocks in the 1597 edition.  However, Gerard's Herball became required reading by botany students for over two centuries
and formed part of the essential education of botanists well into the nineteenth century.  In addition, Gerard produced the first description of the potato - one of the most economically significant plants to come from the New World.

Leonhard Fuchs - German (1501-1566) - De historia stirpium  (1542) - (and, in 1543, as New Kreuterbuch) based mainly upon Dioscorides,  one of the first illustrated herbals that recognized the painter, the draftsman, and woodcutter for their contributions (portrait above was taken from the herbal).  The illustrations, respected for their clarity and style, influenced botanical illustration for many years.  A number of later herbals contain illustrations copied from Fuchs or were even printed from his actual blocks.  The  introductory chapter of  De historia stirpium, "An Explanation of Difficult Terms",  is the earliest known vocabulary of botanical terms.

Rembert Dodoens - Flemish (1517-1585) - Cruydeboeck (1554) was illustrated by 715 woodcuts of plants, including many copies from those in the Fuch's herbal. Dodoens' used Fuchs as his model for the description of each plant. The method of arrangement is his own.  He indicates the localities and times of flowering in the Low Countries, information that could not have been derived from an earlier writer.

Original editions of the three herbals described above are available at the Texas A&M Cushing Library - see this overview - or visit the library to have a look.

ARTIFICIAL CLASSIFICATIONS

Botanical research on the European flora during the Renaissance and subsequent global exploration produced an 'overload' of biological diversity that required a simple, efficient system of organization.  This demand produced several purely 'artificial' systems of classification exemplified by Species plantarum (1753 - 23 volumes) of Carl Linnaeus.

Linnaeus - Sweden - (1707-1778) created a 'sexual' system that divided plants into 24 classes based in large part on the number, union, and length of stamens.  Secondary grouping with these classes (Order) was based on the gynoecium mostly the number of styles.  While the artificial approach allowed quick sorting and identification, its application produced 'unnatural' groupings.  The next step along the path of systematizing flowering plants involved an effort, which progressed through the 1700s and first half of the 19th century, to employ as many characters as needed to insure that natural patterns of variation were reflected by the classification system.

NATURAL CLASSIFICATIONS

George Bentham (1800-1884) and Sir Joseph Hooker (1817-1911) produced "Genera Plantarum" (1862-1883 - 3 volumes), collection of over 7,000 generic descriptions from 200 families taken from original observation of all major seed plants.  This was the last great work produced on the assumption that angiosperm taxa are fixed entities, unchanging through time and placed on earth by the Creator.  While the scientific rationale changed with Darwin, many taxonomic circumscriptions developed by Bentham and Hooker, remain valid today and many large herbaria remain structured according to the classification system expressed by Genera Plantarum.

PHYLOGENETIC CLASSIFICATIONS

Concepts of natural selection and lineage relationships present in Origin of Species, published in 1859  by Charles Darwin encouraged botanists to incorporate evolutionary concepts into classifications. The first move in this direction was expressed in a very complete, multi-volume work by german botanists Adolf Engler (1844-1930) and Karl Prantl (1849-1893) - "Die Naturlichen Pflanzenfamilien" (1887-1915) started with the most primitive plants and progressed to most structurally complex.  The Englerian System positioned conifer-like (anemophilous; reduced, unisexual flowers) angiosperms at the phylogenetic base (especially the Casuarinaceae) with taxa producing large, showy flowers, such as many Magnoliidae, as derived or specialized.  Thus, taxa now treated as the Hamamelidae (Engler's 'Amentiferae') represented the basal element and monocots are basal to dicots.  While this notion has been abandoned by most involved with flowering plant classification, the Englerian System remains as a significant cataloging device in that, due to the size, scope, and quality of Die Naturlichen Pflanzenfamilien, most non-british herbaria of the world, at least the larger collections, are arranged according to the Englerian sequence.

Many recent systems of flowering plant classification are influenced by phylogenetic 'dicta' first published by American (University of Nebraska) Charles Bessey (1845-1915) which were outlined in our discussion of the Magnoliidae.  A comparative overview of three such systems (Cronquist, Takhtajan, and Thorne)  is available at the Flowering Plant Gateway.  Fundamental alignments, by Order, are depicted by "Bessey's Cactus" (from your text, p. 473):

Future systems of flowering plant classification, exemplified by the 'Angiosperm Phylogeny Group' (see 'APG' system at the Flowering Plant Gateway) may seek to avoid phylogenetic assumptions or premises and approach the problem with a single assumption, i.e., that the most direct lineage path represents the actual evolutionary history of a given group.  This 'cladistic' approach, coupled with its analysis of gene sequence data, offers new and potentially interesting classification structures.

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