LABORATORY 6- Seven major plant families

INTRODUCTION

 The goal of this laboratory is to familiarize you with seven families of flowering plants that are important sources of food. Our last laboratory activity focused on the two most important food-plant families, the Poaceae and Fabaceae. We studied the basic vegetative and floral morphology which characterize these families. We also took time to survey many of the important food crops and products from members of these families.

Today we will continue our study of important flowering plant families by examining vegetative and floral morphology, and by surveying harvested products. We will concentrate on the following seven major flowering plant families: Asteraceae, Apiaceae, Brassicaceae, Cucurbitaceae, Liliaceae, Rosaceae, and Solanaceae.

By the end of today’s laboratory activity you should be able to recognize and identify the family-specific vegetative, floral, and fruit characteristics emphasized through lecture, discussion, and examination of plant samples. As a continuation of your past accumulation of botanical knowledge, you should be able to recognize which of the seven families are monocots and which are dicots. In addition, as we have done in the past laboratories, you will be expected to recognize by name (common, scientific, and family name) the highly important food crops on display. Since this exercise concentrates on major plant families and the important food crops in each family, you should be able to place given food crops in their correct families (i.e., cabbage in Brassicaceae; onions in Liliaceae). In this context, because past laboratories have focused on food crops in general, some of this laboratory may serve as a review and synthesis of information previously presented .

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

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 united 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); bisexual; when associated with ray or ligulate florets, situated in the center of a head.
2. Ray florets- zygomorphic (irregular); 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); bisexual; with a ligule; typically not found in association with disk florets, situated throughout the head.

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)

 1. 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?

 2. Pyrrhopappus- false dandelion

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

 3. 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?

 4. 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.

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...)? What is a schizocarp?

EXAMINE the preserved 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.

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?

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:

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

 

2. 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.

 

3. 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 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?

READ the toxic plant descriptions which are displayed on the side table.

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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