Cactus

-

Cactus, common name for the family comprising a peculiar group of spiny, fleshy plants native to America. The family contains about 1650 species, most of which are adapted to arid climates. The fruits of cacti are important sources of food and drink in many areas to which they are native. Because cacti require little care and exhibit bizarre forms, they are popular for home cultivation and are coming under increasing pressure as a result. More than 17 kinds of cacti now face extinction because of plundering by avid collectors and professional poachers, especially in the southwestern United States and northern Mexico.

Cactus plants usually consist of spiny stems and roots. Leaves are greatly reduced or entirely absent. Only in two genera are fully formed leaves present. The stems of cacti are usually swollen and fleshy, adapted to water storage, and many are shaped in ways that cause rain to flow directly to the root system for absorption. The roots form extensive systems near the soil surface, assuring that a given plant will absorb the maximum amount of water from a wide area; plants in deserts are usually widely spaced.

The most distinctive vegetative feature of cacti is the areoles, specialized areas on the stems on which stiff, sharp spines usually grow. Some cacti lack spines but have hairs or sharp, barbed structures called glocids on the areoles. Areoles develop from lateral buds on the stems and appear to represent highly specialized branches.

The flowers of cacti are often large and showy and occur singly rather than in clusters of several flowers. The perianth (floral tube) does not consist of sharply differentiated sepals and petals, but rather of a series of bracts (modified leaves), which gradually grade into sepals and finally into showy petals. The flowers have many stamens; the ovary is inferior and fused to the perianth. The fruits are often brightly colored and fleshy.

Scientific classification: Cacti make up the family Cactaceae. Cacti with fully formed leaves are classified in the genera Pereskia and Pereskiopsis. The night-blooming flowers and the saguaro plant are classified in the genus Cereus. The Christmas cactus is classified as Schlumbergera bridgesii.

See Pictures of Cactus

Comments

Post a Comment

Popular posts from this blog

Monocot and Dicot Seeds

-
Image
Monocotyledons (monocots) and dicotyledons (dicots) make up the two large groups of flowering plants, differentiated by their seed structures. Monocot seeds contain one cotyledon, or embryonic leaf. When these seeds germinate, the cotyledon remains below ground, absorbing nutrients from the endosperm, the starchy food supply in the seed. The coytledon transports these nutrients to the developing seedling. Dicot seeds contain two coytledons, which absorb and store the nutrients from the endosperm before the seed germinates. The cotyledons, thick with stored nutrients, emerge above ground during germination, and then transport the stored nutrients to the developing seedling. For a brief time, the cotyledons also serve as the first photosynthesizing leaves, but they wither and die when the true leaves emerge. related articles: flower flower variations in structure flower sexual reproduction flower pollination and fertilization flowering and the life cycle evolution of flowers angios
Read more

Gymnosperm

-
Image
Gymnosperm (Latin gymn-, “naked”; Greek sperma, “seed”), is a common name for any seed-bearing vascular plant without flowers. There are several types: the cycad , ginkgo , conifer , yew , and gnetophyte. Gymnosperms are woody plants, either shrubs, trees, or, rarely, vines (some gnetophytes). They differ from the other phylum of seed plants, the flowering plants (see Angiosperm ), in that the seeds are not enclosed in carpels but rather are borne upon seed scales arranged in cones. The gymnosperms are the most ancient seed plants; they appear to have arisen from fern ancestors in the Devonian Period. Cycads retain the most primitive characters of the extant seed plants. Gnetophytes are considered from morphological and molecular evidence to share a common ancestry with the flowering plants. Living gymnosperms are distributed worldwide, with a majority, particularly the conifers, in temperate and subarctic regions. Cycads and gnetophytes are mainly tropical to subtropical. There are ab
Read more

Cedar Tree

-
Image
Cedar (tree) is a common name for three or four species of large trees native to mountainous areas of North Africa and Asia. Cedar trees belong to the pine family, the members of which have needlelike leaves and, like all conifers, bear their seeds on scales clustered into cones. They differ from other members of the family in their evergreen four-angled leaves borne on short side-branches. The genus produces fragrant, durable, red-colored wood used in construction and cabinetry. The name cedar is also applied to other conifer trees with fragrant wood (see Cypress ). The well-known white cedar grows in swamps of the eastern United States and reaches a height of 24 m (80 ft). An arborvitae is also called cedar; western cedar and eastern white cedar are both important timber trees in the United States. Eastern red cedar, widespread in the eastern United States, is a juniper . A flowering tropical American mahogany is known as Spanish or West Indian cedar. Incense Cedar Native to wester
Read more