Plant Biology 260: Systematics of Flowering Plants

Lectures 6 and 7: Floral Morphology and Formulas

Announcements:

Your first take-home lecture assignment, worth up to 2% of your final grade, is due in class today (Monday, January 28th). This assignment is found on pages 35-36 of your Class Notes. Your answers can be submitted (neatly, please, for full point consideration) on a separate sheet of paper. Include your name and laboratory section (A,B,C or D). Remember to italicize or underline Latin names. Penalties will be assessed for assignments handed in late (i.e., after class); assignments more than 24 hours late will not be graded. Answers will be posted (on the web) immediately after lecture today. Graded assignments will be returned in lab.

Text and Other Resources:

Guide to Flowering Plant Families by Wendy B. Zomlefer

• Pages 357-390, Illustrated Glossary [An excellent resource!]

Plant Systematics, A Phylogenetic Approach by Walter S. Judd et al.

• Chapter 4, pages 53-58 (we use different floral formulas!): Taxonomic Evidence - Floral Morphology

Digital Flowers. Once in the program, access Morphology: Flowers and Morphology: Floral Formulas.

Other Web Resources:

Please note: The links provided in this syllabus lead to supplementary information offered by other on-line systematic courses at other universities or sources. Please use with caution, as some of the information presented may be different from what we cover in PB260.

• Texas A & M
• Texas A & M Lecture Notes
• Structural Parts and Types (from Radford et al.,) - Be sure to click on figures

General objectives:

After studying this material you should be able to:

1. Have a basic and working knowledge of flowering plant floral terminology. As in our lectures on vegetative morphology, there is a bewildering large number of terms but in this course we will stress only some of the more commonly-used ones.

2. Be able to explain, draw, compare, and contrast each of the terms listed below.

3. Know the relationship between each of the terms listed and the major category to which they belong.

4. Given a photograph of a flower or a description of it, you should be able to construct a complete floral formula for that flower (and, likewise, you should be able to interpret a flower given its floral formula).

Flower terminology

Parts
Receptacle-the more or less enlarged or elongated stem axis on which the floral parts are attached
Peduncle-the stalk of a solitary flower (or the stalk of a flower cluster)
Sepals (calyx)-First series; the outermost whorl or spiral of a typical flower (asexual/sterile)
Petals (corolla)-Second series; the second whorl or spiral of a typical flower (asexual/sterile); petals alternate with sepals
Perianth-collective term for calyx + corolla
Stamen(s) (androecium)-Third series; the third whorl or spiral; the male reproductive unit; stamens alternate with petals and are opposite sepals

Filament-stalk of a stamen
Anther-pollen producing portion of a stamen
Pollen-the male gametophytes
Connective-the sterile tissue connecting the two locules of an anther

Stigma-the pollen receptive portion of the gynoecium
Style-the elongated portion between stigma and ovary
Ovary-the basal portion that contains the ovules

Completeness (refers to flower)
Complete-all 4 floral series present (Ca, Co, A & G)
Incomplete-1 or more floral series absent
Perfect-flower with both functional androecium and functional gynoecium

IMPERFECT-flower lacking either a functional androecium or a functional gynoecium:

Staminate-a male flower; one that has a functional androecium but lacks a functional gynoecium
Carpellate-a female flower; one that has a functional gynoecium but lacks a functional androecium

Plant condition (refers to ENTIRE individual plant)
Synoecious-a sexual condition in which the flowers on a plant are all perfect
Monoecious-both staminate and carpellate flowers occur on the same plant
Dioecious-staminate and carpellate flowers occur on different plants

Fusion
Distinct-similar parts (of same embryonic origin) not fused
Connate-similar parts fused
Adnate-parts of different origin that are fused
Free-unlike parts that are not fused

Perianth
Biseriate-in two whorls or series (e.g., calyx and corolla)
Uniseriate-in one whorl or series (e.g., calyx only)
Apetalous-lacking petals
Caducous (sepals)-sepals falling off very early
Sympetalous-having the petals united (connate) at least at the base

Floral tube (cylindrical base), throat (gradually opening), and lobes

SYMMETRY:

Actinomorphic (radial, regular)-divisible into equal halves by two or more planes
Zygomorphic (bilateral, irregular)-divisible into equal halves in one plane only

Androecium
Staminodes-sterile stamens (they do not produce pollen); variable in form and size, may be petaloid or secrete nectar
Epipetalous-stamens adnate to corolla

Alternating with petals or corolla lobes
Opposite petals or corolla lobes

Gynoecium
Carpels 1 per flower (monocarpous gynoecium)

Carpels more than 1 per flower:

carpels distinct (apocarpous gynoecium)
carpels connate (syncarpous gynoecium)

NOTE: In PB260 we will NOT use the terms pistil, simple pistil or compound pistil!
Pistil-equivalent to gynoecium; formed from one or more carpels
Simple pistil-a gynoecium with one carpel
Compound pistil-a gyneocium with two to many separate or fused carpels (it combines both apocarpous and syncarpous gynoecia)

Placentation-the arrangement of ovules within the ovary
Ovule-the structure containing the female gametophyte; it differentiates into the seed after fertilization
Locule-the chamber within the ovary; there may be one or more locules
Placentae-the region or line along which the ovules are attached
Septum (septa)-an interior wall which separates the locules in those instances where two or more chambers occur (walls=septa)

PLACENTATION TYPES:
Marginal-only found in a monocarpous or an apocarpous gynoecium; the ovules are attached to the folded margins of the carpel.
Axile-only found in a syncarpous gynoecium; the placental area of the ovary is attached to an axis derived from the connate margins of the component carpels-such an ovary is divided into two or more locules by septa. The ovules are borne along the central axis.
Parietal-only found in a syncarpous gynoecium; the placental areas are attached to the side walls of the ovary (or extrusions of the wall)-such an ovary usually has one locule (therefore no septa). NOTE: Your textbook considers marginal placentation a type of parietal placentation; we won't in this course.
Apical-attachment of ovules to the top of the ovary (one locule, no septa)
Basal-attachment of ovules to the botton of the ovary (one locule, no septa)
Free-central-attachment of ovules to a free-standing central column in a syncarpous unilocular ovary (one locule, no septa)

Insertion (the method of attachment of one structure to another)

SUPERIOR OVARY-ovary situated ABOVE the point of attachment of the perianth and androecium and wholly free from them (stamens may be adnate to corolla)

Hypogynous flower-a flower with perianth and androecium arising from below the ovary (gynoecium).
Perigynous flower (if hypanthium not adnate to ovary)-a flower with perianth and androecium arising from a floral cup that is NOT adnate to the ovary. Remember - the ovary is still superior!

INFERIOR OVARY-ovary is BELOW the point of attachment of the outer flower parts (perianth and androecium). In other words, the outer floral whorls are adnate to the ovary. A hypanthium (floral cup) may or may not be present.

Epigynous flower (if hypanthium adnate to ovary)-a flower with perianth and androecium apparently arising upon the ovary (rather than the receptacle).

What is a flower?
An axis bearing one or more carpels or one or more stamens or both and usually one or two series of perianth parts.

Evolutionary Development of the Carpel
See page 46 in your Class Notes

What is a carpel?

• Basic unit of gynoecium
• The foliar, ovule-bearing unit of a flower that forms either all (apocarpous or monocarpous) or part (syncarpous) of the gynoecium.
• Leaflike megasporophyll with infolded or inrolled connate margins bearing one or more ovules on the inside.

How can the number of carpels comprising a gynoecium be determined?

• Count the stigmas
• Count the styles
• Count the lobes of the ovary
• Count the locules in the ovary
• Count rows of placentae

Floral Formulas

Access Digital Flowers. Note that the name Lamium amplexicaule replaces the name Glechoma hederacea; both flowers have identical floral formulas.

When examining a flower, ask yourself:

What parts are present?
How many of each part?
What is the shape of each part?
Are any parts connate? If so, which?
Are any parts adnate? If so, what to what?
What are the relationships of parts to each other?

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