Homosporous

Spores are usually produced by the division of cells within a structure called a sporangium. In bryophytes and most ferns, horsetails, club mosses, and whisk ferns, spores give rise to the same kind of plants as the parents, which are thus called homosporous. But in a few of those just mentioned and in all seed plants, some spores grow into sexual plants (gametophytes) that produce male gametes (sex cells), while others grow into sexual plants that produce female gametes; parent plants producing such spores are called heterosporous. Spores that give rise to male gametophytes are called microspores; spores giving rise to female gametophytes are known as megaspores. In seed plants, male gametophytes are known as pollen grains, and female gametophytes are called embryo sacs. Thick-walled resting zygotes (cells formed by the union of gametes) resemble spores and are called zygospores or oospores.

Shrub

Shrub, short, woody plant, typically with several stems arising from or near the ground. Shrubs are perennial plants—that is, they live for at least three years. Although the distinction is often artificial, shrubs are generally shorter and have more stems than trees.

Shrubs grow wild in all but the coldest or driest regions of the earth. They may be evergreen (retaining foliage throughout the year) or deciduous (losing foliage each year). Shrubs are often planted to control erosion, the wearing away of topsoil by wind and rain, in exposed areas. Their variety of forms, foliage, flowers, fruits, and fragrance make them popular in gardens and as landscape plants. According to 20th century British botanist Stanley Whitehead, shrubs “have the stable, long-life qualities of forest trees without the embarrassment of the latter’s size. They match the floral beauty and grace of habit of herbaceous plants without their compelling need for support and attention.” Popular shrubs include the rhododendron, laurel, holly, dogwood, rose, and hydrangea.

Rhododendron

Rhododendron, common name for flowering plants of a genus of the heath family. The genus contains some 850 species, the majority of which are cultivated. Native to the temperate areas of the Northern Hemisphere, rhododendrons are most abundant in the Himalayas, southeast Asia, and the mountains of Malaysia. Cultivated species can now be found on all continents. Rhododendrons exhibit great variety in size, habit, and flower color. They range from small, ground-hugging shrubs to small trees, and from white to pink, dark-purple, or yellow flowers. Most species are evergreen—that is, they retain their foliage throughout the year. The deciduous species of rhododendron, those that lose all of their foliage each year, are known in horticulture as azaleas.

Scientific classification: Rhododendrons make up the genus Rhododendron of the family Ericaceae.

Heath

Heath, common name for a plant family comprising flowering plants that are widely distributed in both temperate and tropical regions of the world, and for its representative genus. The family contains about 3350 species, which are placed in more than 100 genera and include a large number of ornamentals. Important horticultural members of the family are rhododendrons and azaleas (see Rhododendron), heath, heather, madrona, mountain laurel, sweetbell, and sourwood. Various species produce such fruit as the blueberry, cranberry, and huckleberry. Briar pipes are made from burls of heath species native to the Mediterranean area.

Most members of the heath family are woody, often evergreen shrubs. Many are poisonous; indeed, many common cultivated species contain the toxin andromedotoxin, which causes vomiting and reduced blood pressure and may result in death if taken in large quantities. Azaleas, rhododendrons, sweetbells, and laurels all contain this compound.

The flowers are characterized by four or five sepals (outer floral whorls) and four or five petals (inner floral whorls) that are fused at the base to form a tube. The stamens (male floral organs) are usually twice as numerous as the petals, and the anthers (pollen-bearing structures) open by terminal pores rather than by longitudinal slits, as they do in most families of flowering plants. The ovary (female floral organ) is usually superior (borne above and free from the other floral parts).

Most members of the order to which the heath family belongs are woody plants, with small trees and shrubs predominating. Some tropical species are epiphytes (plants growing on other plants for support but not nourishment). A number of species, such as the Indian pipe, lack chlorophyll, the food-producing pigment that is found in most plants, and are parasitic, depending on other green plants for their nourishment.

Although the order is widely distributed, its members occur mainly in cooler areas. Thus, in tropical regions they are found mainly in mountainous areas. In addition, most members of the order occur in acid soils.

The seven other families of the order contain only a few species each and have limited economic importance as ornamentals. They are also used in local medicines.

Scientific classification: Heaths make up the family Ericaceae, of the order Ericales. The representative genus is Erica. The Indian pipe is classified as Monotropa uniflora in the family Pyrolaceae.

Blueberry

Blueberry, common name applied to several related shrubs (see Heath) and to their blue or black fruit. The lowbush, or swamp, blueberry and the highbush blueberry are the two most common species raised in the United States. The lowbush blueberry averages less than 1 m (less than 3 ft) in height; the highbush blueberry ranges from 1.8 to 6 m (6 to 20 ft). Although blueberries are cultivated in many regions of the world, large quantities of the shrubs grow wild. Mostly deciduous, the bushes bear sweet blue or black berries, which grow either singly or in clusters. Branches of the evergreen, also known as huckleberry greens, are used in flower arrangements and in other decorations.

Scientific classification: Blueberries belong to the family Ericaceae. The lowbush, or swamp, blueberry is classified as Vaccinium angustifolium, and the highbush blueberry as Vaccinium corymbosum.

Cranberry

Cranberry, common name for several species of low vines of a genus of the heath family, and for their small, sour, seedy fruit. The plants, which belong to the same genus as the blueberry, have drooping, pink flowers and small, thick, evergreen leaves. The small, or European, cranberry grows wild in marshlands of temperate and colder regions of Europe and North America. Most of the cranberry crop produced in the United States each year is canned as sauce or jelly or bottled as juice. The cowberry, or mountain cranberry, is common in both Europe and North America. It is gathered and sold in considerable quantity but is rarely cultivated. The highbush cranberry, with its clusters of white flowers followed by red berries, is a shrub of the honeysuckle family. Its fruit is sometimes used as a substitute for cranberries.

Scientific classification: Cranberries belong to the genus Vaccinium of the family Ericaceae. The small, or European, cranberry is classifed as Vaccinium oxycoccos; the large, or American, cranberry as Vaccinium macrocarpon; and the cowberry, or mountain cranberry, as Vaccinium vitis-idaea. The highbush cranberry belongs to the family Caprifoliaceae and is classified as Viburnum opulus.

Honeysuckle

Honeysuckle, common name for a plant family and for its representative genus. The family contains about 400 species of dicot flowering plants, including many ornamentals. It occurs mainly in the North Temperate Zone, particularly in China, but it also extends into tropical mountains. Its members are mostly shrubs or small trees, although some familiar members are herbaceous—for example, elderberry and some species of honeysuckle, such as Japanese honeysuckle. The leaves are opposite one another on the branch and lack stipules (leafy appendages at the leaf base); the calyx and corolla (floral whorls) have fused parts and arise from above the ovary (female flower part); and usually five stamens are borne on the inside of the corolla tube. The fruit is usually a berry.

The family contains many ornamentals, such as the honeysuckle, a genus of about 180 species of usually fragrant shrubs and vines—including the trumpet honeysuckle—more than 30 of which are cultivated; the elders; the arrowwoods; the abelias; and the weigelias. Some species of elder produce wood that has been used to make musical instruments, and the fruits and flowers of the genus are sometimes used to make wines and preserves. Japanese honeysuckle, introduced from Asia, has become a weed in eastern North America. It often kills the native vegetation by overshadowing it.

Scientific classification: Honeysuckles make up the family Caprifoliaceae. The representative genus is Lonicera. The Japanese honeysuckle is classified as Lonicera japonica and the trumpet honeysuckle as Lonicera sempervirens.