The sap of some aloe plants can be processed for medical use. Powdered aloe juice is a laxative, and aloe vera gel soothes burned and frozen skin. Other species give rise to rope-quality fiber, fine thread, and dyes.
The larger species of arborvitae serve the timber industry, while the smaller species are cultivated in gardens. Arborvitae produce a balsamic resin, thought to have medicinal ability to increase blood pressure and reduce fever.
The cacao tree produces a fruit from which cocoa is derived. Following harvest the fruit is fermented to give the cocoa seed, or bean, its distinctive flavor. Cocoa, containing approximately 20 percent protein, 40 percent carbohydrate, and 40 percent fat, is high in nutritive value. Côte d’Ivoire, Ghana, Nigeria, and Brazil are leaders in cocoa production.
The spice known as cinnamon has been cultivated for centuries and is a popular aromatic and flavoring ingredient in foods, soaps, and medicines. A cinnamon farmer typically strips the bark off the stems of a cinnamon tree and collects the calyx from the base of each yellowish-brown cinnamon berry (shown at center). Fragrant cinnamon oil results from distilling the bark and calyx, and cinnamon sticks are made from the tightly rolled and dried bark of the stems.
The flower of the common dandelion, which belongs to the genus Crepis, is not a single flower but rather a composite made up of a large number of very small flowers. Although usually considered a troublesome weed, the dandelion’s leaves are edible if collected early in the spring before they become bitter.
The common foxglove is grown for decorative and medicinal purposes. The flowers contain glycosides (chemicals that affect heartbeat and pulse), which can be extracted from the leaves and used to regulate and strengthen a person’s heartbeat. However, if plant materials containing glycosides are directly consumed by humans, nausea, abdominal pain, diarrhea, and heartbeat and pulse abnormalities can result. If consumed in large enough quantities, glycosides can cause convulsions and death.
The ginseng plant, found in greatest abundance in the American tropics and the Indo-Malaysian archipelago, is grown primarily for its root, which is used as an additive in cooking and as a stimulant. According to folklore, extracts of the ginseng root can be used effectively as an aphrodisiac and as an aid in prolonging youth.
Vital in brewing malt liquors and popular as ornamentation, the American hop vine is a perennial climbing herb cultivated in the northern temperate zone. Female hop plants produce the conelike pendulous catkins seen here. The catkin, containing overlapping leaf bracts and fruit, is the portion of the plant used in brewing. A fine yellow powder called lupulin or hop flour covers the catkin and gives the hop its bitter flavor and aroma.
This snow gum sits atop Mount Spectacular in Victoria, Australia. Eucalyptus species are some of the most important trees in western Australian forests. In addition to their importance to the lumber industry, extracts from their bark are used in the manufacture of various dyes and drugs. Many species of eucalyptus are called gum trees for the resin that oozes from them.
The American licorice is one of a number of perennial herbs of the pea family. Licorice flavoring used in making candy and sweeteners is extracted from the roots. This plant grows well in sunny locations in deep, fertile, well-drained soils.
Included in the onion family are several species of garlic, genus Allium. The strong-smelling and tasting bulbs of these plants are used in pickling and cooking, and their curative powers have been celebrated for centuries. Among garlic’s most ardent fans are the residents of Gilroy, California, where garlic-flavored ice cream is a favorite at the annual garlic festival.
Variegated Holly Leaf
The green color in a normal holly leaf is due to the uniform distribution of the dominant photosynthetic pigment chlorophyll. In a variegated holly leaf this important pigment is reduced or lacking altogether in certain parts of the leaf, as indicated by the yellow color. Variegated leaves generally do not survive in the wild due to this pigment deficiency.
Cultivated celery, Apium graveolens, dates from 17th-century France. Its branching stalks and feathery leaves are reminiscent of the related herb parsley.
Cultivators grow coriander, an herb related to carrots, anise, parsely, and dill, primarily for its aromatic leaves and seeds. The leaves, used as a spice known as cilantro, are a common ingredient in Latin American and Asian cooking. The seeds contain an oil that is extracted and used in the preparation of some liqueurs.
The seed, leaf, stem, and bulb of the fennel plant, Foeniculum vulgare, are used in cooking. A long-standing favorite among cultivated plants, fennel was declared a garden essential by Charlemagne in ad 812.
The pomegranate, native to parts of tropical Asia but now grown throughout the world, is cultivated for its seeds and rind. The seeds are surrounded by a sweet, edible pulp. The rind, though inedible, has derivatives that are used in medicinal applications and tanning processes.
The opium poppy’s green, unripe seed capsule, revealed when the flower petals drop, contains a milky sap that is the source of opium. To collect the sap, slits are made along the circumference of the seed capsules, enabling the milky sap to ooze out and dry. It is then scraped from the capsules, pressed into cakes, and dried to form the rubbery, yellow-brown opium. Natural derivatives of opium include morphine and codeine, used extensively in medicine as sedatives and pain killers. Heroin is a synthetic derivative of morphine. Morphine and codeine are habit forming. Heroin, which is especiallly addictive, is illegal in the United States.