Sept. 7, 2001
Getting started

I.  General terminology

Classification:  orderly arrangement of organisms into hierarchical systems
a) artificial:  based on convenient or obvious characteristics (e.g., height)
b) natural:  based on large, morphological characteristics
c) phylogenetic:  infer lineage and relationships
Taxonomy:  study of classification
Systematics:  study of classification and relationships among organisms
Keying:  process used to identify unknown plants, usually using couplets
(contrasting dichotomous choices)

II.  Categories of taxonomy

Kingdom
   Division (Phylum)
      Subdivision (subphylum)
         Class
  Subclass
    Order
        Family
  Genus
         Species (specific epithet)

III.  Why study systematics?

1) inventory of world’s flora
2) understand plant evolution
3) understand botanical diversity
4) communicate and archive information
 

IV.  Naming plants

1) Common names:
Advantages---simple, easy to remember

Problems---different common names for the same plant;
same names for different plants

2) Latin names:
Advantages---one universal name for a particular plant; named based on a common set of rules (International Code of Botanical Nomenclature)

Problems---long, difficult to pronounce, may be updated
Binomial nomenclature:  2 names; 1st, the genus, which is capitalized, then the 2nd (specific epithet) which is not capitalized.  These are italicized, but in older literature, they may be underlined.  The authority (person who named the plant) should be included as an initial after the specific epithet.

e.g.  Lilium longiflorum L.  cv. Ace
(Easter lily, cultivar Ace)

Kingdom Plantae

Several groups of plants called Divisions (similar to Phyla in classification of other organisms)

1) Bryophytaà mosses, liverworts, and hornworts
2) PsilophytaàPsilotum
3) EquisetophytaàEquisetum (horsetails)
4) LycopodiophytaàLycopodium
5) Pinophytaà gymnosperms (pines, firs, etc.)
6) Magnoliophyta (Anthophyta) à flowering plants  (235,000 species)
 2 classesà monocots
    à dicots
 

Characteristics of flowering plants

· Flowers
· Enclosed seeds
· Double fertilization

Characteristics of flowering plant classes

1)  Monocots (Class Liliopsida)

· Parallel venation
· Flower parts in 3’s
· Scattered vascular bundles
· Usually herbaceous
· 1 seed leaf

2)  Dicots (Class Magnoliopsida)

· Netted venation
· Flower parts in 4’s or 5’s
· Vascular bundles in a ring
· May be herbaceous or woody
· 2 seed leaves

Terminology of flowering plants

A) Vegetative organs:  roots, stems, leaves
B) Node:  point of attachment for leaves and buds
C) Internode:  regions between nodes
D) life cycles:  annual (1 year), biennial (vegetative the first year, blooms the second), or perennial (lives an indefinite amount of time)
E) Modified stems
i) Bulb—thickened stem with scale-like leaves (e.g., lilies)
ii) Corm—tall, thickened underground stem (e.g. gladiolas)
iii) Rhizomes—horizontally underground stems (e.g. irises)
iv) Runner—slender aboveground stems (e.g. strawberry)
v) Stolon—trailing aboveground stem, rooting at the nodes
vi) Tuber—thickened tip of a subterranean rhizome (e.g. potato)
 

Flower structure and terminology

1) Sepals—outermost set of modified floral ‘leaves’ (collectively called the calyx)
2) Petals—second set of modified floral ‘leaves’ (collectively called the corolla)
3) Stamens—male portion of the flower, consisting of the anther (containing pollen) and the filament (stalk); collectively called the androecium
4) Pistil—female portion of the flower, consisting of stigma, style and ovary; collectively called the gynoecium; may have one or more ‘units’ called carpels.  The ovary contains one or more ovules, which eventually become ripened seeds.  The ovary wall matures into the fruit.

· Pedicel = the stalk that holds individual flowers
· Peduncle = stalk containing many flowers in an inflorescence (group or cluster)
· Receptacle = upper portion of pedicel that bears floral parts
· Rachis = central axis of the inflorescence

· Perfect flowers have both male and female parts.
· Iimperfect flowers are lacking either the male or female part.
· Dioecious plants have separate male and female plants.
· Monoecious plants have both male and female flowers on the same plant.
· Complete flowers have all 4 floral parts.
· Incomplete flowers lack one or more of the parts.
· Determinate inflorescences have a set number of flowers, where the terminal flower blooms first (e.g. Verbena).
· Indeterminate inflorescences grow up the stalk (progressively inward and upward). *most common type

· Floral symmetry (orientation) is important in keying plants
i. regular flowers = radial symmetry = actinomorphic
ii. irregular flowers = bilateral symmetry = zygomorphic

Flower types  (see handout for diagrams)

1) ament (catkin)—unisexual, apetalous flower (e.g. willow)
2) spike—inderminate flowers with no pedicels (sessile)
3) corymb—indeterminate; flat-topped, pedicels on the outside are longer than those inside
4) cyme—determinate (similar to corymb)
5) umbel—indeterminate, flat topped inflorescence; pedicels are the same length
6) raceme—rachis with 1 pedicel and flower alternating up the rachis
7) panicle—complex raceme with 2 or more flowers on each pedicel
8) solitary—single large flower on pedicel or peduncle
9) head—indeterminate dense cluster of flowers (e.g. gallardia)
10) verticil—flowers in whorls up the rachis
11) spadix—thick spike-like inflorescence; often with imperfect flowers; surrounded by a large bract (modified leaf) called a spathe
 

Ovary position is a key factor in identifying plants!

· Superior ovary = hypogynous flower = other flower parts are below the ovary
· Inferior ovary = epigynous flower = other flower parts above the ovary
· Perigynous = calyx and corolla are fused to form a floral ‘cup’--> hypanthium
 

Fusion of floral parts is common.  And of course there is specific terminology to describe it!

Connation = fusion of like parts
Adnation = fusion of unlike parts
Distinct = not fused

The prefix apo means that the floral parts are not fused, while syn or sym or gamo means that they are fused.  For example, gamopetalous refers to a flower where the petals are fused.
 

Floral formulas are also used to identify plants.  A floral formula is a written way to describe the symmetry and number of floral parts, as well as whether or not certain parts are fused.

Floral formulas consist of 5 symbols.

Example:   *, 5, 5, 10, 3

* indicates radial symmetry; 5 indicates # of sepals; 5 indicates # of petals; 10 indicates # of stamens; 3 indicates # of carpels.

X is used to identify bilateral symmetry; $ is used to identify asymmetry.

Floral formulas can also identify fusion of parts.  For example, if the sepals were fused in the above plant, the first 5 would be circled.  If the petals and sepals were fused together, a line connecting the two 5’s would be included.  Also, a line above the number of carpels indicates an inferior ovary, while a line under the number of carpels indicates a superior ovary.