|Plant Taxonomy (BIOL308) - Stephen G. Saupe, Ph.D.; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321; firstname.lastname@example.org; http://www.employees.csbsju.edu/ssaupe/|
General Procedure: Obtain a sample of each fruit. Sketch, label, and identify the indicated parts. As you study each fruit, consider the following questions:
1. Legumes. Simple, dry, dehiscent along two sutures, monocarpellate
Study a green bean fruit (pod) or snow pea pod. Legumes are restricted to the Bean family (Fabaceae). From what part of the plant does it develop? Look for remnants of the floral organs (pedicel, sepals, stamens, stigma, style). With a dissecting needle, carefully open the fruit. Notice the seeds inside. From what did the seeds develop? Note each seed is attached by a short stalk (funiculus). The inner edge of the pod to which the funiculus is attached is the placenta. Locate the dorsal (region of carpellary folding) and ventral (region of capellary fusion) sutures.
Obtain a peanut. Can you identify the: pericarp, seed coat, embryo (cotyledons, epicotyl or plumule, hypocotyl). Which part(s) do you eat?
A loment is a specialized type of indehiscent legume with constrictions between the seeds. The fruit breaks into one seeded sections. It is common in Desmodium (tick trefoil). Study the loment provided.
2. Follicles. Simple, dry, dehiscent along one suture, apocarpous gynoecium. This is the most primitive fruit type. These fruits dehisce along the ventral suture and are common in Apocynaceae, Asclepiadaceae, Ranunculaceae, and Paeoniaceae.
Study a milkweed pod or other follicle (Aquilegia, Nigella). Look for the pericarp, dorsal and ventral sutures, and seeds. What other structures can you locate?
3. Capsule. Simple, dry, dehiscent, syncarpous gynoecium, that splits along
regular lines. A capsule wall splits into sections called valves.
Examine several types of capsules. Note whether each is septicidal (opens up along the septa - the ventral suture; the most primitive type; uncommon, occurs in Yucca, Digitalis), loculicidal (opens up along the locules or midrib or each carpel - dorsal suture; most common type), or poricidal (as in poppy, Papaver). A pyxis is a special type of capsule that splits open around a horizontal ring (termed circumscissile dehiscence). Plantain (Plantago), purslane (Portulaca oleracea), lambs quarters (Chenopodium album) and pigweed (Amaranthus) are a good examples of this type of capsule. The poricidal capsule is derived from a loculicidal capsule by restricting the length of the opening and is especially common in Papaveraceae and Campanulaceae.
4. Silique/silicle. Simple, dry, dehiscent, syncarpous gynoecium. Restricted to
the mustard family, Brassicaceae. Special capsules whose two valves become detached
leaving a partition still attached to the receptacle. A short broad silique is a silicle.
Obtain a pod from the money plant (Lunaria annua). These are commonly used in floral arrangements. Note the septum, placenta, funiculus, stigma/style. Where are the pericarp and seeds?
Obtain a mustard pod. Note the position of the stigma and style. Where is the ovary? Look for the receptacle. Use the dissecting microscope to note the scar left from the separation of the other floral structures. Carefully pry off the pericarp from one side. Observe the position of the seeds and funiculus. Locate the placenta. Remove the pericarp from the other half. Note the septum.
5. Achene. Simple, dry, indehiscent, syncarpous or apocarpous gynoecium
depending on species, one-seeded with a firm and close-fitting pericarp that is attached
to the seed in one location. Especially common in Ranunculaceae, Polygonaceae and
Asteraceae, although in the latter family the fruit is called a cypsela. Derived from a
follicle by a failure of dehiscence and reduction of seeds to one. There are several types
including: cypsella (achene with adherent calyx), samara (winged achene), and utricle
(bladdery achene in which the pericarp loosely fits around the seed). Buckwheat, dandelion
and sunflower are good examples of achenes.
Obtain a dandelion fruit. Note the pericarp and examine it with a dissecting microscope. Describe the texture. Note the white tufts called pappus (from which part of the flower do these come? From what type of inflorescence does this develop? What is the function of the pappus? Make similar observations with sunflower fruits (seeds). Carefully dissect one and observe at which point the seed is attached to the ovary wall (pericarp).
6. Grain (Caryopsis). Simple, dry, indehiscent, syncarpous gynoecium, pericarp
wall adherent to the seed. Restricted to the grass family (Poaceae).
Study a corn grain. Observe the pericarp. On the front side, look for the U-shaped depression indicating the position of the embryo. Just above the depression is a slight projection, the silk scar. What part of the plant is the silk? The sharp end of the grain is the peduncle, where it was attached to the ear. Cut through the grain to expose the embryo. Note the endosperm tissue. Note the single large cotyledon and the embryo.
7. Samara. Simple, dry, indehiscent, syncarpous gynoecium, winged achene.
Study a maple, ash or elm fruit. From what structure is the wing produced? Open the fruit and observe the seed and seed coat. What is the function of the wing?
8. Nut. Simple, dry, indehiscent, syncarpous gynoecium. A nut is essentially
an achene that has become enlarged and hardened. The seed is usually very large and wall
Study an acorn. The hardened ovary wall is the pericarp. The cup-like structure (cap) is the involucre, which is an accessory structure consisting of fused bracts. The involucre is common to most nuts, although it may be somewhat modified in different species.
9. Berry. Simple, fleshy, indehiscent, syncarpous or apocarpous gynoecium. The
entire pericarp becomes fleshy, with a pulpy interior, no stony layer, and usually several
to many seeds. May be derived from a superior or inferior ovary. In the latter case, the
berry is made up of the pericarp and associated floral cup tissues.
Study a tomato or pepper. Note the exocarp (outer skin), mesocarp (middle areas) and endocarp (inner edge). There is no distinct line separating these areas. Notice the vacant areas (pepper) or water filled spaces (tomato). These are locules. Note the arrangement of seeds and its method of attachment to the placenta, which is often lobed. Which placentation type does this represent?
10. Pepo. Simple, fleshy, indehiscent, syncarpous gynoecium. Formed from an
inferior ovary in the gourd family (Cucurbitaceae). They have a hard or leathery rind and
fleshy inner layer.
Study a cucumber, watermelon, pumpkin or other pepo.
11. Drupe. Like a berry with a hard endocarp. Most often one-seeded. Good
examples include peach, cherry, plum, olive, and avocado. Note that the pericarp is
divided into three distinct layers. The skin (exocarp), middle edible fleshy part
(mesocarp) and hard endocarp. The stone or pit is comprised of the endocarp that encloses
Study a cherry or avocado. Carefully open the pit and look for the seed with the seed coat.
12. Hesperidium. Berries with a leathery pericarp like oranges, lemons,
grapefruits and other citrus fruits (Rutaceae).
Study a hesperidium, such as an orange. Look for the exocarp, mesocarp and endocarp.
13. Pome. The ovary wall forms a papery core surrounded by an enlarged
receptacle and calyx tissue. Apples, pears, hawthorne and quinces are good examples. Most
of the edible portion is derived from the receptacle, so this is also a good example of an
Examine the longitudinal section of an apple. You can see the peduncle, and often other floral structures especially sepals and stamens. The "peel" is the original epidermis of the receptacle. Observe the very center of the fruit. Each seed is located within a cavity (locule). The papery core lining the wall of the locule is the endocarp. Each seed is attached to the central placenta, which may be somewhat split into sections and slightly separated. The other tissues of the ovary wall, mesocarp and exocarp, are fleshy and occupy a position external to the core. Usually about 1 cm from the endocarp you can locate what appears as a continuous greenish-brown ring around the core region. This ring consists of several vascular bundles and they may branch out into the fleshy tissue beyond. The fleshy area between the endocarp and this layer is the exocarp and endocarp. The area between the peel and vascular bundles is the receptacle and calyx tissue. Thus, you are really eating the flower stem.
14. Aggregate Fruits. Fleshy fruits derived from a single flower with an
apocarpous gynoecium. Blackberry, raspberry and strawberry are good examples. Note that
the individual components may consist of various types. For example, the tulip tree
produces an aggregate of samaras and a strawberry is an aggregate of achenes.
Obtain a strawberry. Locate the pedicel and remnants of the calyx, stamens and corolla (rarely present). The large fleshy swollen red region is the enlarged receptacle. Note the numerous "seeds" dotting the surface of the fruit. Each "seed" is actually an achene. Cut open the fruit. Observe the vascular bundles that lead to each achene.
15. Multiple Fruits. These are formed from ovaries in several flowers crowded
together onto a single unit on a common axis. Pineapple provides a good example. These
fruits are also common in the Fig family (Moraceae).
Study a pineapple. How many flowers, each with a separate ovary, formed this fruit? Note the prickle on each section, this is the bract. Now observe a longitudinal section. The core is the original stem (rachis) to which the flowers were attached. Look at a cross section of an individual flower. Look for petals, sepals, locule with ovules (aborted), stamens and style.
16. Schizocarp. Simple, dry, dehiscent fruit that breaks up into single-seeded
sections. Common in the Carrot family (Apiaceae), and also found in geranium and maple.
Study a Sweet cicely (Osmorhiza sp.) or other fruit.
09/18/2007 / © Copyright by SG