Plant Taxonomy

Definitions Taxonomy (systematics) - the 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 Classification (as process) - the production of a logical system of categories, each containing any number of organisms, which allows easier reference to its components, the kinds of organisms Classification (as object) - is that logical system itself

Definitions cont’d Identification - naming of an organism by reference to an already existing classification system Taxon - any taxonomic grouping - phylum, class, family, genus, etc. Description - statement of the characteristics of a taxon Characters that contribute to a taxonomic description are known as taxonomic or systematic characters

Definitions cont’d flora (lower case) - plant life of a given area Flora (upper case) is a book or other work describing the flora of a given area

Need for Classification need for some system of classification is absolute, because it is only by first naming organisms and then grouping them in recognizable categories that we can begin to sort out and understand the vast array of diversity which exists Our current estimate is that there are about 280,000 total plant species; with 263,000 species of higher vascular plants that have been described and named - ferns, gymnosperms, flowering plants - about 2,000 new species of flowering plant are described every year

Southern magnolia – Magnolia grandifolia

Rank Ending Example Kingdom Plantae Division (Phylum) - phyta Magnoliophyta Or Anthophyta Class - opsida Magnoliopsida Order - ales Magnolioales Family - aceae Magnolioaceae Genus Magnolia Species grandifolia

Hierarchies of plant taxonomy – from Stace

Taxonomic Systems Predictivity - Ideally our systems of classification should allow us to place similar species of plants together in the same category

Two Types of Classification Schemes Artificial classification schemes - these systems allow one to quickly categorize a particular organism, usually so that it can be quickly found in a book or a herbarium Natural classification scheme - organize together related groups of plants and have a high degree of predictive power

Artificial Classification Scheme

Artificial Classification Scheme Red Trillium White Trillium

Natural Classification Scheme – For Seed Plants

Ancient Classifications

Oaks - Fagaceae

Maples - Aceraceae

Pennisetum – a grass - Poaceae

Carex – sedge meadow - Cyperaceae

Juncus – rushes - Juncacaea

Vegetables from Brassica oleracea Brassicaceae

Theophrastus 370-285 BCE

Dioscorides – 1st Century AD

Page from 15th century Arabic edition of Dioscorides herbal

Leonhart Fuchs - 1542

Fuchs’s History of Plants - 1542

Gerard’s Herbal 1597

Gaspar Bauhin - 1623

1623 – first use of binomial names

Carolus Linneaus

Systema Naturae – first published 1735

Classification After Darwin

Evolutionary Classification Schemes Botanists have tried to develop classification systems that are natural and also show evolutionary relationships - this has been surprisingly hard to do In developing classification systems, we attempt to group plants which share advanced or derived characteristics - presumably these characters have only arisen once or at most a few times - it is not always easy to tell what is an advanced character though

Natural Classification Scheme – For Seed Plants

Basics of Characters A taxonomic character is any expressed attribute of an organism that can be evaluated and that has two or more discontinuous states or conditions - for example the number of petals on a flower - can be in 3's, 4's or 5's - thus distinct states and they are discontinuous The taxonomic value of a characteristic is increased if the biological significance of the characteristic has been determined

Goat Dandelion - Asteraceae

Buttercup - Ranunculaceae

Morphology Plants are highly plastic in their growth forms - how tall they grow, their shape will vary depending upon environment and growing conditions However reproductive structures tend not to differ in form from plant to plant of the same species - they may differ in number, but form is conservative - flowers, cones tend to be similar within all members of a species - thus much plant classification and identification is based upon reproductive structures

Umbel – flower head in Apiaceae

Brassicaceae – The mustards

Oak acorns - Fagaceae

Birch catkin Betulaceae

Other important characteristics Internal anatomy – mostly important for studies of evolutionary relationships – not often used in identification guides  Physiology – mostly for classifying parasites and saprobes (plants that decompose dead matter)  Chemistry – can be important because some groups have distinct chemical compounds – the mints are aromatic with distinct odor DNA –there is interest in developing easy methods to differentiate species based on short sequences of DNA – much work done with the DNA for RuBisCO – an important enzyme in photosynthesis Ecology and geography can also be important – some plant species or families are restricted to particular environments or geographic areas

Mint

Cactus