PLANTS AND PEOPLE- Botany 328- Laboratory

LABORATORY EXERCISE-- Eight major plant families   You can download the powerpoint for this lab here)
 
 

INTRODUCTION

The goal of this laboratory is to familiarize you with eight families of flowering plants that are important sources of food.  We'll take time to survey many of the important food crops and products from members of these families.

Today we will examine vegetative and floral morphology and survey various products. We will concentrate on the following seven major flowering plant families: Asteraceae, Apiaceae, Brassicaceae, Cucurbitaceae, Lamiaceae, Liliaceae, Rosaceae, and Solanaceae.

By the end of today's lab activity you should be able to recognize and identify the vegetative, floral, and fruit characteristics of each family, as presented through lecture, discussion, and examination of plant samples. You should be able to recognize which of the eight families are monocots and which are dicots. In addition, you will be expected to recognize by name (common, scientific, and family name) the highly important food crops on display. Many of these you have "met" in the vegetable or fruit labs or both, so you should already have them in one of the charts.  Be sure to write down the information for anything new (like tobacco) and note characteristics of the different varieties of each crop you see.  Since past laboratories have focused on food crops in general, some of this lab will serve as a review and synthesis of information previously presented. 

Click here for more information on the spices and herbs you will see today.
 
 

ACTIVITY--FAMILY STUDIES: For each family, examine the material provided, including material for dissection and the food products displayed.

1. ASTERACEAE-Sunflower family. (Compositae is an old name for the family)

Flowers in the Asteraceae are highly modified, very reduced, and are grouped into head inflorescences. A typical head, such as the sunflower, appears to be a single flower but is actually an entire inflorescence composed of tiny flowers, or florets, situated together on a common receptacle. Subtending the cluster of florets is a whorl of green bracts known as phyllaries or involucral bracts. Collectively, these bracts compose the involucre.

Like other flowers we have studied, florets are composed of a perianth, androecium, and gynoecium. The perianth consists of modified calyx, called pappus, and a sympetalous (fused) corolla. The pappus takes numerous forms (bristles, awns, scales) which often correspond to modes of seed dispersal (e.g., the delicate pappus of the common dandelion facilitates wind dispersal). The androecium consists of five stamens with the anthers united into a tube (synantherous) and the filament bases attached to the interior corolla wall. The gynoecium is bicarpellate (consisting of two carpels) with one inferior ovary and a two-branched style. Along the inner surface of each style branch is a stigmatic zone, or stigma.
 

Florets come in three models:

  1. Disk florets- actinomorphic (regular); usually bisexual; when associated with ray or ligulate florets, situated in the center of a head.
  2. Ray florets- zygomorphic (irregular); usually unisexual-pistillate; with a ligule; when associated with disk florets, typically situated on the margin of the inflorescence like the rays of the sun.
  3. Ligulate florets- zygomorphic (irregular); usually bisexual; with a ligule; typically not found in association with disk florets, situated throughout the head.
Depending on the composition of florets, a head inflorescence in the Asteraceae family comes in one of three models:
  1. Discoid head- disk florets only (e.g., Cirsium- thistle)
  2. Radiate head- disk florets in the center; ray florets around the margin (e.g., Helianthus- sunflower)
  3. Ligulate head- ligulate florets only (e.g., Pyrrhopappus- false dandelion)


EXAMINE the three samples provided (possibly different from the species listed below, depending on what we can get fresh) and sketch what you see.

     A. Helianthus- sunflower.  DIAGRAM ray and disk florets sitting in a head inflorescence and label the parts. Which is perfect? Which is imperfect? Which is zygomorphic? Which is actinomorphic? What is the head type?

    B. Pyrrhopappus- false dandelion.  EXAMINE, DRAW, and LABEL a ligulate floret. Note the pappus of capillary bristles. What is the head type?

     C. Cirsium- thistle.  EXAMINE an inflorescence. Note lack of ligulate and ray florets. What floret types do you see? SKETCH and LABEL a disk floret. What is the pappus type? What does plumose mean? Draw a plumose pappus bristle.  What is the head type?

     D. A "sunflower seed" is not actually just a seed! What is a "sunflower seed"? In other words, what is cracked open and what is eaten? Think about the fruit type-- achene.
 
 

2. APIACEAE- Carrot and parsley family. (Umbelliferae is an old name for the family)

This family is characterized by having dissected leaves, umbellate inflorescences, and fruits that are schizocarps.

EXAMINE the members of this family that are on display. Note the typical leaf morphology and inflorescences which are characteristic of this family. What are you eating when you eat celery? What are you eating when you eat a carrot? When a restaurant chef decorates your plate with parsley, what exactly is placed on your plate (a leaf, a bunch of leaves, a petiole, etc...)? The leaves of members of the Apiaceae tend to be aromatic.  Which of the herbs/spices displayed come from Apiaceous leaves?

What is a schizocarp?  The fruits in this family have tubes filled with aromatic oils.  Which of the spices here are Apiaceous fruits?
 
 

3. BRASSICACEAE- Mustard family.  (Cruciferae is an old name for the family)

 EXAMINE the flowers. How many sepals? Petals? Stamens? Note the arrangement of the stamens: four long, two short (tetradynamous). How many styles do you see? How many locules in the ovary?

EXAMINE the fruits of this family: silique and silicle. What is the difference between the two? What is the replum? Examine the replums of Lunaria. Note where the seeds were attached.  The seeds of Brassicaceae are often pungent because of mustard oils and various sulfur-containing compounds.  Which of the spices displayed is from the Brassicaceae?
 

4.  LAMIACEAE--Mint family. (Labiatae is an old name for the family)

EXAMINE the leaves and stems of the samples.  What is the leaf arrangement?  What shape is the stem in cross-section?  Most members of the family have aromatic foliage--many of our cooking herbs belong to this family:  mint, rosemary, thyme, marjoram, oregano, lavender (yes, you can cook with it!), sage, basil, etc.

EXAMINE the flowers of the samples.  What is the corolla symmetry and shape?  Members of this family have 2 or 4 stamens (if four, usually didynamous--two long and two short), and the fruit is a cluster of 4 tiny nutlets.

5. LILIACEAE- Onion family.

EXAMINE and SKETCH flowers. How many petals are present? Stamens? Pistils? How many carpels are present in the pistil? Is the pistil compound or simple? So, is this family dicotyledonous or monocotyledonous?

EXAMINE the food crops on display, such as garlic and onion. What are we eating when we eat onion rings? What is an onion composed of? An onion is a bulb. What purpose does this modified shoot serve for the plant? Which of the seasonings displayed is from a member of the Liliaceae?

  
6. ROSACEAE- Rose Family.

EXAMINE flowers paying particularly close attention to characters of the gynoecium and its position relative to the androperianth(androecium plus perianth). SKETCH AND LABEL what you see. These flowers represent three of the subfamilies of the Rosaceae:

    A.  Prunoideae- Ovary superior, of a single pistil. Fruit (mature ovary) a drupe. Examples: cherries, peaches, plums, nectarines, apricots, pluots, almonds.

    B.  Maloideae- Ovary inferior, of 2-5 carpels. Fruit is a pome with the fleshy, edible portion derived from the hypanthium and/or receptacle tissue and not from the ovary itself. Examples are apples, pears, quinces.

    C.  Rosoideae- Ovaries (gynoecium) are superior, of many free, simple pistils arranged within a hollow receptacle/hypanthium (rose hip) or on the outside of an elongated receptacle (blackberry or raspberry). What is an apocarpous gynoecium? The actual "fruits" (mature ovaries) are achenes or drupelets, which compose the compound fruit types we call aggregates, hips, and accessories (strawberry).

 EXAMINE the fruits of the family Rosaceae. Can you name the layers of the pericarp exposed in a cross-sectioned peach? What is the fruit type? What do you eat when you eat an apple? What is an almond? What do we eat when we eat a strawberry?
 
 

7. SOLANACEAE- Nightshade, tomato, and pepper family.

EXAMINE flowers of this family. Are they actinomorphic or zygomorphic? What is the ovary position? Are sepal and petal lobes fused? How many sepals and petal lobes are present? SKETCH a flower paying special attention to the connivent androecium and its arrangement relative to the gynoecium. The anthers have poricidal dehiscence. What does this mean?

EXAMINE fruit types. Typically the fruit is a berry. How many carpels do you see in the fruit cross-sections displayed? Note the wandering placenta.

EXAMINE the potatoes. A potato is a ___________ which is actually a _________ modified for ___________growth and storage of ___________. What is an eye of a potato?

EXAMINE the other products of the Solanaceae. Note the toxicity which is common to this family. What is tobacco?  Which seasonings are from members of the Solanaceae?  Are Capsicum peppers related to black pepper?
 
 

8. CUCURBITACEAE- Cucumber, melon, and squash family.

EXAMINE preserved flowers. What is the term for a plant with separate male and female flowers on the same plant? What is the ovary position? Are the petals free or fused? Note the nectary disk present in both staminate and pistillate flowers. What purpose do the nectary disks serve? Why do you think both sexes of flowers possess nectary disks?

Note the common cucurbitaceous fruit type, the pepo, and examine those which are displayed. How many locules are present? How many carpels? What type of placentation is characteristic of this family? Exactly what is a pickle?
 

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last updated 2-16-2006