LABORATORY 2:  Flowers

INTRODUCTION
 
 The goal of this laboratory exercise is to familiarize you with flowers, their structure, variation, and importance to the flowering plant.  By the end of today’s laboratory exercise you should be able to recognize and identify the parts of a flower, and to briefly describe their importance to the life of a flowering plant.  Through the study of flower morphology, you will also become accustomed to the correct use of a dissecting microscope.

ACTIVITY

 Carefully EXAMINE all floral material provided using the following exercise and questions as a guideline.  To gain an ultimate familiarity with floral morphology, compare the material against descriptions and definitions in your lecture hand-outs.

1.  Flowers are arranged in structures called inflorescences.  Inflorescences can be arranged in a variety of ways.  DRAW simple diagrams of the following inflorescences:  solitary, spike, raceme, panicle, umbel, catkin, and head.

2.  DRAW a longitudinal section of a typical flower labeling the following parts:  receptacle, calyx, sepals, corolla, petals, perianth, pedicel, ovary, ovule, style, stigma, pistil, gynoecium, anther, filament, stamen, and androecium.

3.  EXAMINE by dissection the floral material provided making longitudinal and transverse (cross) sections of the flower and its parts.  On a separate sheet of paper, SKETCH the flowers and label the parts.  Then, FOR EACH FLOWER, answer the following questions:

 A.  Is the flower actinomorphic (regular) or zygomorphic (irregular)?

 B.  How many sepals are present?  Petals?  Stamens?  Carpels?  To count carpels, count the style branches and/or count the zones of placentation by cross- sectioning the ovary.
 
 C.  Is the ovary inferior or superior?

 D.  Is the flower from a monocotyledonous or dicotyledonous plant?

1. Portulaca grandiflora (Portulacaceae) - Purslane, Rose-Moss (images)

 Floral structure: Calyx: 2 sepals Corolla: 5 petals Androecium: numerous stamens Gynoecium: 5 carpels (determined from stigma lobes) fused

 A typical Dicot

 2. Tulbaghia violacea (Liliaceae) - Society Garlic - (images of related genus Allium (onions))

Floral structure: Calyx: 3 sepals Corolla: 3 petals (sepals 'petaloid' - 6 'tepals' with calyx evident by relative position only) Androecium: 6 stamens Gynoecium: 3 carpels (ovary septa) fused

 A typical Monocot

 
3. Helianthus annuus - wild type (Asteraceae) - Sunflower (Helianthus images)

Cluster of small flowers to form a 'flower-like' inflorescence (capitulum) that marks this largest of dicot families.  Capitula take several forms, although all types found in the family are usually subtended by a cluster of bracts known as phyllaries.  This type - the radiate inflorescence - features fertile flowers ('disc' florets) with actinomorphic (radially symmetrical) corollas at the center and flowers ('ray' florets) that are non-functional reproductively around the margin.  A close look into the corolla tube of a ray floret shows no androecium or style and a reduced ovary that will not set fruit.  The disc florets (these from the domesticated type), on the other hand, are fully equipped (note fused anthers that form a tube [just above the corolla lobes] through which the style emerges [two yellow, coiled structures above the brown anther tube].

Floral structure - disc floret:  The calyx is represented by two 'awns' placed on top of the ovary near the point of ovary attachment of the corolla tube.  Highly specialized and variable in this family, and often absent, the term 'calyx' is replaced by the term 'pappus' for this family.  The tubular corolla is terminated by 5 lobes (5 petals involved), 5 stamens are attached to the corolla (epipetalous) and, while there is only a single locule and seed in the ovary, the two stigma lobes indicate a syncarpous gynoecium made up of two carpels.

Floral structure - ray floret: The corolla here is also sympetalous (5 petals fused), but the product of this fusion is a straplike or 'ligulate' structure that, within the context of the entire infloresence, serves an 'attraction' function.  It is a zygomorphic corolla (not radially symmetrical).

4. Croton capitatus (Euphorbiaceae) - Dove Weed (images)

Representing a large and economically important dicot family, dove weed produces unisexual flowers ('imperfect') with staminate and pistillate flowers present on an individual plant (= a monoecious species - species with individual plants producing only either staminate or pistillage flowers are dioecious)

Floral structure:  Calyx reduced and variable, no corolla, stamens variables (7 - 12) for staminate flowers, pistillate flowers with a tricarpellate (1 seed per locule), syncarpous gynoecium.
 

5.  Passiflora incarnata (Passifloraceae) - Granadilla, Passion Flower (images)
 
Floral structure:  An unusual flower that shows a deviation from the CA/CO/A/G sequence via 'insertion' of the 'fringed' whorle known as a 'corona'.  See the family description for more detail.

6. Capsicum annuum (Solanaceae) - Chile Pepper

Floral structure:  Calyx of 5 sepals (symsepalous), corolla of 5 fused petals, stamens 5 and EPIPETALOUS, gynoecium syncarpous (two carpels).  See fruit sections showing basic bicarpellate condition (bananna pepper) and derived septum (bell pepper).

7. Bauhinia forficata (Fabaceae - Leguminosae s.l.) - Orchid-tree(images)

Floral structure:  The interpretation offered for this flower (reduced synsepalous calyx with doubled corolla) is was incorrect.  The perianth is 10-parted with the lower 5 (falling easily) petaloid (yellow) representing the calyx and the 5 just above these representing the corolla.  The androecium has 10 stamens with differing anther sizes, this evidently relating to function of the pollen (food for vectors vs. reproduction).  The gynoecium, a marker for this large and important family, is unicarpellate.  Senna relatives are often treated as a distinct family.

8. Catharanthus roseus (Apocynaceae) - Periwinkle (images)

Floral structure:  calyx of 5, awn-like sepals, corolla of 5 petals fused to form a tubular base (side view) and a 5-lobed 'limb'.  Androecium of 5, epipetalous stamens that tend to clasp the stigma (see this in a relative, Vinca).  Gynoecium of two carpels that are fused to form a common style/stigma but separate at the base.  Thus, at maturity, each flower tends to produce two unicarpellate fruits.

9. Dendrobium sp. (Orchidaceae) - Dendrobium (images)

Floral structure:  3 sepals and 3 petals with one of the 3 petals modified in various ways to form a 'lip' or labellum thereby producing a zygomorphic flower.  Unusual feature that marks this largest monocot family:  reproductive whorles fused to form a single structure - the column or gynandrium and the pollen 'packaged' (pollinia) for vector transport.  See family description for more detail. 

10. Hibiscus sp. (Malvaceae)

Floral structure:  A family of local economic importance in that Cotton is a member.  Perianth, often subtended by a calyx-like whorle of bracts (epicalyx), of 5 sepals and petals and an androecium of numerious stamens that are fused to form a 'filament tube' around the style.  Carpel number ranges from 5 to numerous but always syncarpous and, in Hibiscus, 5 carpels as indicated by 5 'capitate' stigmas.

1.  What purposes do flowers serve?

2.  What is the difference between a monoecious and a dioecious plant in terms of their  flowers?

3.  What is a fruit?  What is a mature ovary?

4.  What is a seed?  What is a mature ovule?

5.  What is the difference between an ovule and a seed?

6.  What are two ways to count the number of carpels present in a pistil?  What is a carpel?

7.  What is the difference between a perfect and a imperfect flower?

8.  What is a gynoecium?  What is an androecium?

9.  What is a pollinium?  We saw pollinia in two different flowers, those of the Asclepiadaceae and Orchidaceae families.  What is the purpose of the pollinium in the life histories of these plants?

10.  A sunflower may look like a single flower, but it is definitely not.  Exactly what is a sunflower?

11.  What is a zygomorphic (irregular) flower?  What is an actinomorphic (regular) flower?

12.  A Gladiolus  flower is quite large and showy.  A grass flower is small, inconspicuous, and non-showy.  Based on this information, what can you say about the pollination of each of these?

13.  Be able to name and count flower parts if given a fresh flower.

14.  What is a complete flower?  What is an incomplete flower?

15.  Where are pollen grains produced and from where are they released?

16.  Name the parts of a flower which make up the pistil.

17.  What is a compound pistil?  What is a simple pistil?

18.  Why do you think a sunflower inflorescence so strongly resembles a flower?  What purpose, in terms of the evolution of such a structure, might this type of inflorescence serve?

19.  Name the parts which make up a stamen.

20.  Know the difference between a longitudinal section and a transverse (cross) section;  for example, of an ovary.

21.  Know how to properly adjust a dissecting microscope.

22.  We have now covered the vegetative and floral parts of the typical flowering plant.  Make a table which contrasts the vegetative and floral characters of monocots and dicots.
(i.e., How can you differentiate between monocots and dicots using vegetative and floral characters?)