Part III
Introduction to Botanical Diversity
In this part of our course, we will make a survey of the different
organisms studied by botanists. These include all the organisms once considered to
be plants. In the early nineteenth century, zoologists claimed for their study
everything that moved, and botanists everything that was "vegetative" (growing
without ingesting food). The two disciplines overlapped for organisms that both
moved and were vegetative. Example of organisms claimed by both zoologists and
botanists are plasmodial slime molds and some unicellular organisms, such as
Euglena. Euglena are motile but also have chloroplasts. Plasmodial slime molds
move and hunt and engulf bacteria, but also form sporangia like fungi, which were
considered vegetative. We now know that true plants and animals are only two of
many different evolutionary lineages, and all attempts to classify everything as either
a plant or as an animal are artificial. However, we are still left with the consequences
of this defunct system in the division of biology into Botany and Zoology. In this
class we will directly consider all major groups of living organisms except animals.
We will indirectly consider animals, however, in their role as herbivores, pollinators
and seed dispersers.
Populations of similar and closely related organisms are considered to
constitute a species. Species are the products of a process of descent with
modification (evolution), which can be hard to visualize. Metaphorically, species can
be thought to represent the tips of a massive tree. On this tree, closely related
species are represented as tips descended from the same branch system. This
concept of a tree of life, based on evolutionary descent, has come to be used as an
important organizing scheme for classifying living species into a series of nested
groups called taxa (singular = taxon). A taxon is a distinct branch of the tree (a
"clade"), and includes all the species that derive from that branch. Taxa (clades) can
be easily recognized, on inspection of the tree, because a single cut of their basal
branch will remove all the members of that group. Sometimes unrelated species
come to look very similar. Biologists can recognize these superficially similar species
as distinct and unrelated through careful study of their structure, of their
development, of their fossil record, and through the use of modern molecular
techniques. Then, by careful analysis of these data, they are able to determine
exactly where on the tree of life each species belongs.
The organizational scheme provided by the book, is classic and will be
followed in our lab exercises. By this system organisms are hierarchically arranged
in groups in the following order:
Domain/ Kingdom/ Phylum/ Class/ Order/ Family/ Genus/ Species
One big issue with this scheme is that all groups at a particular hierarchal level are
not all equally distant in an evolutionary sense. For example, plants, assigned to a
kingdom, Plantae, is actually a clade within the phylum Chlorophyta (the green
algae), itself, in a different kingdom, Protista. This organization, however, is useful
culturally, and, hence, we will teach it.
In lab we will take a tour of the tree of life visiting the larger branches that
include organisms traditionally considered plants. We will dwell, however, on the
branch representing the true plants, and particularly on the branch leading to the
flowering plants - the dominant plants of land and the most important organisms for
the survival and well being of humans.
Because there are so many different species, and this is an introductory
course, we will generally not ask you to identify organisms to the species level. For
lab exams, we will expect you to be able to assign organisms to some of the
important taxa within which they are classified.
We make explicit which taxonomic groups we wish you to know in the list below.
Domain: Bacteria
Kingdom: Cyanobacteria
Genus: Oscillatoria
Genus: Anabeana
Domain: Eukarya
Kingdom: Protista
Phylum: Euglenophyta
Genus: Euglena
Phylum: Rhodophyta
Phylum: Myxomycota
Phylum: Chlorophyta
Genus: Chlamydomonas
Genus: Pandorina
Genus: Volvox
Genus: Ulva
Class: Charaphyceae
Desmids
Genus: Spirogyra
Genus: Chara
Domain: Eukarya
Kingdom: Protista / Heterokonts
Phylum: Oomycota
Genus: Saprolegnia
Phylum: Bacillariophyta
Centric Diatoms
Pennate Diatoms
Phylum: Phaephyta
Genus: Sargassum
Genus: Fucus
Order: Laminariales (Kelps)
Domain: Eukarya
Kingdom: Fungi
Phylum: Zygomycota
Genus: Rhizopus
Phylum: Ascomycota
Yeasts
Powdery Mildews
Genus: Sordaria
Genus: Morchella
Phylum: Basidiomycota
Rusts & Smuts
Domain: Eukarya
Kingdom: Plantae
Phylum: Hepatophyta
Genus: Marchantia
Phylum: Anthocerophyta
Phylum: Bryophyta
Phylum: Lycopodiophyta
Genus: Selaginella
Genus: Lepidodendron (extinct)
Club Mosses
Phylum: Pteridophyta
Wisk Ferns:
Genus: Psilotum
Horsetails
Genus: Equisetum
Ferns
Phylum: Coniferophyta
Genus Pinus
Phylum: Cycadophyta
Phylum: Ginkgophyta
Genus: Gingko
Phylum: Gnetophyta
Phylum: Anthophyta