Integrative Biology 335 — Flower Terminology

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Text and Other Resources:

Plant Systematics, A Phylogenetic Approach by Judd et al., Third Edition, Chapter 4, Floral Morphology, pages 61 – 67. NOTE: We use a slightly different way to write floral formulas than those shown in the text.

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

Other Web Resources:
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 IB 335.

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 (i.e., character states) and the major category to which they belong (i.e., characters).

  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).

The Flower:

A characteristic feature of the angiosperms, the flowering plants, is the grouping of reproductive structures with sterile auxillary ones into a single unit known as the flower.

A flower is a highly modified shoot bearing specialized appendages that are referred to as modified leaves.

Why Do Plants Have Flowers?

Does Size Matter?

Floral 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, terminal flower (or the stalk of an inflorescence)

    A Flower Typically has Four Parts

    ---

  • 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

    A three year olds interpretation of alternating sepals and petals

  • Stamen(s) (androecium) – Third series; the third whorl or spiral; the male reproductive unit; stamens alternate with petals and are opposite the sepals

  • Filament – stalk of a stamen
  • Anther – pollen producing portion of a stamen (meiosis occurs within the pollen sacs)
  • Pollen – the male gametophytes
  • Connective – the sterile tissue connecting the two locules of an anther

  • Carpel(s) (gynoecium) – Fourth series; the terminal or centermost component; the female reproductive unit (the site of pollination and fertilization); 1 to many separate or fused carpels comprise a gynoecium

    Miscellaneous

    Various floral parts may be modified for the production of nectar or other pollinator attractants, such as oils or fragrances. Nectaries are often produced near the base of the androecium and gynoecium or in nectar spurs formed by floral parts.

    CORONA: An extra series of floral parts. Coronal structures are often showy and diverse, and are formed from outgrowths of the perianth parts, stamens, or receptacle.

    Completeness (refers to flower)

  • Complete – all four floral series present (Ca, Co, A & G)
  • Incomplete – one or more floral series absent

    The four series of a complete flower

  • Perfect – flower with both functional androecium and gynoecium
  • Imperfect – flower lacking either a functional androecium or a functional gynoecium:

    A quiz question! Can an incomplete flower be perfect?
    Longitudinal section of a flower of wild ginger, Asarum canadense. In this flower, the petals are missing.

    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

    Another quiz question! What plant condition is exemplified by this member of the birch family?
    Note that the male and female inflorescences are separate but on the same plant.

    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

    There are various other specialized terms that are used for various types of connation and adnation:
    apocarpous, epipetalous, sympetalous, syncarpous, monadelphous, diadelphous

    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

  • Sympetalous – having the petals united (connate) at least at the base
  • Floral tube (cylindrical base), throat (gradually opening), and lobes

  • 3-merous, 4-merous, etc. – indicates number of parts in a specific floral series (e.g., a 4-merous flower might have four sepals, four petals, eight stamens, and four carpels)

    Symmetry:

    Another quiz question! What is the symmetry of this flower? It can be divided into two equal halves by only one plane.

    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

  • Hypanthium (floral cup) – a structure derived by the adnation of the perianth bases and stamens. It is variously shaped.

    Perigynous insertion in black cherry, Prunus serotina

    Gynoecium

  • Carpels 1 per flower (monocarpous gynoecium)
    Note: In this class, we make a distinction between a monocarpous and an apocarpous gynoecium; your textbook does not.

  • Carpels more than 1 per flower:

    Another quiz question! Is the gynoecium of this Hepatica flower monocarpous, apocarpous, or syncarpous? Note the many distinct carpels in the center of the flower.

    NOTE: In this class we will NOT use the terms pistil, simple pistil or compound pistil!

    Placentation:

    PLACENTATION TYPES:

  • MARGINAL – only found in a monocarpous or an apocarpous gynoecium; the ovules are attached to the folded margins of the carpel.

    Monocarpous gynoecium with marginal placentation

    Apocarpous gynoecium with marginal placentation

  • 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 (i.e., lateral placentation); we won't in this course.

    Syncarpous Gynoecia

  • 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)

    Basal and apical placentation in syncarpous gynoecia

  • FREE-CENTRAL – attachment of ovules to a free-standing central column in a syncarpous unilocular ovary (one locule, no septa)

    Free-central placentation in a syncarpous gynoecium

    Placentation types from Walters and Keil, 1988, Vascular Plant Taxonomy, 3rd ed.

    Figure 4.22, Placentation Types, from your text

    Quiz questions!
    1. Placentation type?
    2. Placentation type?
    3. Placentation type?

    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)

  • 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.

    Figure 4.21, Insertion Types, from your text

    Quiz questions!
    4. Insertion type?
    5. Insertion type?
    6. Insertion type?

    So, what is a flower?

  • A highly modified shoot (or floral 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

    What is a carpel?

    Variation in fusion and closure of carpels from Walters and Keil, 1988, Vascular Plant Taxonomy, 3rd ed.

    Figure 4.20, Three carpels, variously connate, from your text

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

    NOTE: Not all are necessarily present or equally useful in a given flower. Extreme connation may cause difficulties.

    Quiz questions!
    7. Number of carpels?
    8. Number of carpels?
    9. Number of carpels?
    10. Number of carpels?

    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?

    Floral Formulas:

    See Morphology: Floral Formulas in Digital Flowers.
    NOTE: We use a slightly different way to write floral formulas than those shown in the text.

    A convenient short-hand method of recording floral symmetry, number of parts, connation and adnation, insertion, and ovary position.

    They may be useful tools for remembering characteristics of certain plant families.

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