Plant Lab
Materials for lab
Bring a digital camera if you have one available
Teaching Objectives
Plant diversity: Applications and importance
Plant form and function: Plant survival and human use
Local and global examples of terrestrial plant types
Student Learning Objectives
(1) View the plant diversity on campus
(2) Know how to access information regarding plant identification
(3) Be aware of differences between mosses, ferns, and flowering plants
INTRODUCTION
Plants are the producers in a food web. Solar energy is stored in the chemical bonds of the sugars produced by plant photosynthesis, the biochemical process by which plants utilize light energy from the sun to produce sugar from carbon dioxide and water. Consumers in a food web derive their energy by breaking down these bonds during respiration, which releases the stored energy. Energy flowing within the food web therefore enters it by way of plant photosynthesis.
The importance of plants to the survival of humans and other animals cannot be over-emphasized. Our basic needs of oxygen, food, shelter, and clothing are provided, directly or indirectly, by plants.
Because plants absorb carbon dioxide and release oxygen in photosynthesis, they may be a significant factor in reducing the
"greenhouse effect", which is caused by human activities that increase the carbon dioxide in the atmosphere. Deforestation and the burning of fossil fuels (oil, coal, and gas) are two examples of such activities.
There are about 235,000 species of flowering plants in existence today. Approximately a third of these are native to temperate regions, and the remainder are found in the tropics. A vast number of tropical plants are in danger of extinction in the wild within the next hundred years because the human populations of most tropical countries continue to double every 20 to 25 years, and because the forests are rapidly being cleared for wood and cultivation. More than half of the world's tropical forests have already been cleared, and experts predict that most of what is left will be gone in less than 50 years. With them will vanish a quarter of all life-forms including, perhaps, a plant that could provide a cure for cancer or help end world hunger.
So little is known of the plants of the tropics that many have not even been given scientific names. Preserved samples of these plants may well be all that are passed on to our descendants in the 21Stcentury and beyond. The useful properties these plants possess can certainly be determined better today, when species are still in existence, than at any point in the future.
This week's lab is designed to introduce you to the incredible diversity within the plant kingdom, to note some of the purposes for which plants have been utilized by humans, and to help you appreciate the forms into which they have been modified and shaped by evolution.
We will look at examples of several types of terrestrial plants: ferns, conifers, and flowering plants. The emphasis will be on form and function, from the perspective of both plant survival and human utility.
PLANT DIVERSITY
Terrestrial (land-dwelling) plants can be separated into four major groups based on their anatomy, reproduction, and life cycle. These four groups are mosses, ferns, gymnosperms, and flowering plants.
Mosses are non-flowering terrestrial plants that reproduce by spores. Mosses don't have vascular tissue (analogous to human veins) to distribute water within their bodies. Instead, they absorb water through pores located on all parts of the plant body. Since mosses lack veins, they are small in size and close to the ground where moisture is readily available. Ferns are non-flowering plants that also reproduce by spores but that have vascular tissue to distribute nutrients and water to all portions of the plant body. Since ferns have veins, they can grow taller than mosses.
Gymnosperms are non-flowering plants that reproduce new plants with seeds. You probably remember from your previous work on seed germination that a seed contains the embryo of a young plant, in addition to nutritive tissue and a protective outer tissue called the seed coat. The largest group of gymnosperms, called conifers, produce their seeds in cones.
Flowering plants, more technically called angiosperms, are the most successful, diverse, and widespread of the land plant groups. Flowering plants range in size from tiny duckweed, a few millimeters in size, to Eucalyptus trees more than 100 meters (328 ft.) in height. There are even flowering plants that have invaded the oceans where they produce flowers underwater.
PLANT ORGANS
Just as your body has separate organs to carry out special functions (e.g., heart, lungs, stomach), so, too, are plant tissues organized into organs that carry out specific functions.
Leaves are the major photosynthetic organs in plants.
Stems support the photosynthetic organs and serve as a conduit for
water and nutrients between the roots and leaves. Some plants have
stems modified for storage of water or carbohydrates, or for asexual
propagation.
Roots are generally used to anchor the plant in the soil and to absorb
water and nutrients from the soil.
Flowers are the reproductive organs of angiosperms.
The ovary, or female reproductive organ of a flower, develops into a fruit after fertilization by the male pollen.
The seeds produced by the plant are enclosed in the fruits. Most people are familiar with large, colorful flowers such as hibiscus, plumeria, orchids, and lilies.
Many people would be surprised, however, to discover that familiar plants such as palm trees, sugarcane, and bamboo also produce flowers. Similarly, while we are all familiar with edible fruits such as bananas, mango, and pineapple, most of us would have difficulty recalling what the flowers from which they develop look like. Botanists study flowers intensively since they have proven to be very useful in the identification of different plant species.
CAMPUS FIELD TRIP
A WORD OF CAUTION: Plants contain a wide range of substances used by humans as food, medicines, dyes, etc., but leaves, fruits, seeds, and thorns may cause skin irritations, sneezing, external or internal discomfort, eye inflammation, or puncture wounds. A basic rule when observing plants is to never put any unfamiliar plant or plant part in your mouth, and use caution in touching any unfamiliar plant you encounter.
ANGIOSPERMS
Aloe Aloe vera has a long history of healing inflamed or damaged
tissue. For centuries, Aloe vera has been used to aide in the healing
of stomach disorders, ulcers, constipation, hemorrhoids, colitis, and a host of skin problems, including cuts, bruises, burns, and athlete's foot. The medicinally-active part of the plant is the yellowish, gelatinous sap that exudes when the succulent (juicy) leaves are cut. Most of you have probably used some kind of skin ointment that contained compounds derived from Aloe vera. Some research even credits Aloe vera with cancer fighting properties.
Ql. In addition to being succulent, Aloe vera leaves have a thick, waxy coating. In what kind of environment might these traits be most
beneficial to the plant?
India rubber tree(Ficus elastica) This species, a member of the fig
family, is native to Southeast Asia. We call a species native or indigenous when that plant (or animal) arrived in its geographical location without any assistance from humans. Plant seeds can arrive naturally in one of several ways: by floating on air or ocean currents, by rafting on top of a floating log, by hitching a ride stuck onto a migratory bird's feathers, or by being carried in a bird's digestive tract and subsequently being excreted. The milky sap produced by this species, known as latex, was once an important source of natural rubber. Its large, thick, oblong leaves may look familiar to you, because the species has also been cultivated for ornamental purposes as an indoor pot plant. Notice the sign attached to the trunk of this tree, indicating it is an Exceptional Tree protected by city ordinance. "Exceptional trees" by reason of age, rarity, location, size, aesthetic quality, endemic status, or historical and cultural significance may be designated as worthy of preservation. More than 100 trees have been designated as "exceptional" on Oahu; such trees are legally safeguarded from injury or destruction.
Q2. What is the minimum age of this tree? (Hint: look at the plaque on the tree)
FERNS
Ferns do not form flowers or seeds; instead they produce
reproductive bodies called spores. When the spores are mature
they are released and are spread by the wind. The spores germinate
when they land on sufficiently moist soil.
Laua'e Fern or Maile-Scented Fern (Phymatosorus grossus) Fern
leaves are called fronds. Turn a frond over carefully and observe the underside. Notice the patches of dots. These are the reproductive structures of a fern; they are called sporangia. Spores are produced in the sporangia by a process called meiosis. During meiosis, the number of chromosomes (the nuclear structures containing DNA) in a dividing cell is reduced by half. These spores then germinate to produce a tiny, heart-shaped plant that lays close to the moist ground. Following fertilization within this tiny plant, the embryo has the potential to grow into a new fern plant. The maile-scented fern is native to the Hawaiian Islands and to many other islands in the Pacific Ocean. Squash a little bit of the frond and smell it; it smells like maile, a native vine that is frequently used for making lei.
Exercise: Examine a laua' e fern frond and make a sketch to show the pattern of spores that you see.
Jack-in-the-box(Hernandia ovigera) You learned in lecture that
scientific names are sometimes given to commemorate
certain people. The genus Herandia ( in the family Hernandiaceae) is named after Francisco Hernand (1514-1578), a Spanish botanist who researched American natural history in the early era of colonial expansion. This species and its close relatives are native to Polynesia, Melanesia, and Micronesia, where the leaves, seeds, and bark are used in traditional herbal medicine. Like the Indian rubber tree, it has been declared an Exceptional Tree and is protected by city ordinance.
Q4. Look around the base of the tree and see if you can locate any fruits. How does the structure of the fruit suggest this tree's common name, Jack-in-the-box?
Exercise: Imagine that, like the Polynesian voyagers who
colonized Hawai'i, you are traveling to an unknown destination. You do not know what plants or animals may be present at your journey's end, and you must use precious water to keep alive the plants you bring with you during the journey. You must choose your plants wisely.
Q5. What purposes would you most want those plant species to serve you in your new home?
Kou (Cordia subcordata) Kou was probably brought to Hawai'i by early Polynesian settlers. When a species does not naturally occur in a particular geographic area, but has been brought there by humans (either deliberately or accidentally), we say it has been "introduced". Another term that is used to describe introduced species, particularly those that have become ecologically destructive, is "alien". Moreover, there is a special term for plants brought to Hawai'i by early Polynesians. Kou was prized primarily for its beautiful wood, which was crafted into calabashes, cups, and bowls. Because of its thick, wide crown of leaves, kou was also a favorite shade tree near home sites.
Hala(Pandanus tectorius) Hala is primarily a coastal tree. You can find it growing in nearly every coastal area in Hawai'i. There are many species of the genus Pandanus in Hawai'i. All of them except the species Pandanus tectorius have been introduced; Pandanus tectorius is native to Hawai'i. Notice the stem-like structures growing out of the trunk to the ground. These structures are actually roots, and are called prop roots.
Q6. What function do you think prop roots have for the hala tree?
Hala was an important plant in ancient Hawai'i. The leaves were woven into fine mats that were used for house flooring. You may be
familiar with lauhala bracelets (the Hawaiian word for leaf is "lau").
Look for some lauhala weaving the next time you visit a local craft fair. Hala leaves are good for weaving because they have long, strong fibers that run in a parallel direction down the length of the leaf. If you wish, pick up a leaf and try separating the leaf into narrow segments. Be careful of the spines on the margins of the leaves!
The fruit of the hala tree somewhat resembles a pineapple. See if there are any fruits developing on the tree you are observing, or if there are any dried fruits on the ground. The dried fruits were used by ancient Hawaiians as paint brushes for dying kapa (bark cloth), and the prop roots were used for their healing powers. Modern scientists have also found that these roots carry useful medicinal chemicals.
There are a number of Hala trees used for landscaping on the UH
Manoa campus. The next time you attend Biology 101 lecture,
notice the Hala trees lining Spalding Hall just outside the lecture room.
GYMNOSPERMS
Gymnosperm means "naked seed". Unlike the seeds of flowering
plants, which are enclosed in a protective fruit, the seeds of gymnosperms are more exposed and unprotected. Many types of gymnosperms produce their seeds in cones, and these types are referred to as "conifers". Pine, spruce, cedar, and fir trees are examples of conifers. There are no gymnosperms native to Hawai'i. All the conifers that you see g rowing in Hawai'i have been introduced from elsewhere.
Queensland kauri(Agathis robusta) Think of the conifers that your
family may use as Christmas trees or other decoration at
Christmastime. The "needles" are the photosynthetic portion of those
trees. Most conifers have thin, compressed "needles". Some conifers,
however, have broad leaves instead of needles; the Queensland kauri is a broad-leafed conifer. The genus (and family) to which this tree belongs is native to the southern hemisphere; this species is native to Australia.
Look on the ground around the base of the tree and notice the
numerous triangular-shaped scales. Before falling from the tree, each
scale carried a single seed, and was packed into a compact structure
called a "cone" with other scales. If the ground around the tree has not been too disturbed recently, you may be able to find a cone that has not yet disintegrated. Look into the tree to see if you can locate any developing cones. This species bears separate male and female cones; your Instructor may be able to locate examples of each. The wood from this species is prized for interior finishing and furniture, and the resin from the bark is used to make varnish.
Q7. In terms of evolution, which do you think came first: the gymnosperms or the angiosperms?
STILL MORE ANGIOSPERMS
Crown flower(Calotropis gigantea) The crown flower shrub is native
to tropical Asia. Depending on the time of year that you visit this plant, you may (or may not) be able to witness the white or lavender crown-shaped flowers. The flowers have become popular in Hawai'i for use in leis. In its native Indonesia, the plant has been used medicinally. Like many plant derived medicines, proper dosage of the physiologically-active plant parts is important, and in excess they may be poisonous. Just as the crown flower plant has been introduced to Hawai'i, so, too, is the chief insect herbivore (plant-eater) that feeds on the leaves of this plant: the Hawaiian monarch butterfly. Adult monarchs preferentially lay their eggs on crown flower plants; when the eggs hatch, the leaves provide a ready and abundant food source for the growing larvae, or caterpillars. The caterpillars may incorporate some of the poisonous chemicals from the plant into their own animal tissue, making them distasteful to potential predators such as birds. This relationship between the crown flower plant and the monarch butterfly, both of them introduced to Hawai'i, makes an interesting example of how non-native species may ecologically adapt to their new home. While neither the crown flower plant nor the monarch butterfly have become "pests" in Hawai'i, keep in mind that many introduced species are not nearly as harmless; indeed, the ecological effects of alien species are presently considered to be the primary threat to the preservation of native Hawaiian plants and animals.