Question

What is the order of angiosperm include the maximum number of primitive angiosperm families?

Answer 1

Angiosperms

The angiosperms, or flowering plants, are the largest and most species-rich phylum of plants, with more than 250,000 species estimated.

Defining Characteristics

The term "angiosperm" derives from two Greek words: angeion, meaning "vessel," and sperma, meaning "seed." The angiosperms are those plants whose seeds develop within a surrounding layer of plant tissue, called the carpel, with seeds attached around the margins. This arrangement is easily seen by slicing into a tomato, for example. Collectively, carpels together with the style and stigma are termed the ovary, and these plus associated structures develop into the mature fruit. The enclosed seeds and the presence of carpels distinguish angiosperms from their closest living relatives, the gymnosperms , in which the seed is not enclosed within a fruit, but rather sits exposed to the environment. Some defining characteristics of angiosperms include flowers, carpels, and the presence of endosperm, a nutritive substance found in seeds, produced via a second fertilization event. However, some current studies suggest that endosperm is not unique to angiosperms.

Angiosperm flowers are generically characterized by having four whorls, or sets of organs: sepals , petals, stamens, and carpels. The carpels may be united or fused to form a compound pistil , and the number of stigma lobes may then be indicative of the number of carpels. The pistil also includes the stigma, on which pollen lands, and style, the tube leading to the egg. Stamens are separated into anthers, which produce pollen, and filaments. The mature ovary (part of the pistil containing the seeds) is termed a "fruit." Sepals and petals may be showy and colorful to attract pollinators, or may be quite reduced in wind-pollinated plants, such as grasses. Likewise, fruits may assume a wide variety of forms associated with mode of dispersal, such as fleshy fruits (for example, berries) dispersed by animals, and dry, winged fruits adapted for wind dispersal, such as the samaras of maple trees, which twirl like helicopters as they fall.

Evolution and the Angiosperms

The angiosperms are a relatively recent group of land plants, and are thought to have originated in the early Cretaceous, only 130 million years ago. The angiosperms increased dramatically in abundance during the Cretaceous. This sudden, dramatic appearance of large numbers of very diverse flowering plant species in the fossil record was referred to by English naturalist Charles Darwin as an "abominable mystery." It is postulated that coevolution with animal pollinators, especially insects, may have contributed to the explosion and abundance of angiosperm species which characterize the modern earth's flora. However, even today, it is not clear what group of nonflowering plants the angiosperms are most closely related to, or what the relationships of the early lineages of flowering plants are to one another. This is in part due to the extremely fast evolution of this group of plants, over a relatively short period of time, and the extinction of many closely related lineages of seed plants, some of which may be more closely related to the modern angiosperms than extant seed plant lineages.

Most contemporary studies, which are based on phylogenetic analysis of deoxyribonucleic acid (DNA) sequence data from as many as six different genes, suggest that the closest relatives of the angiosperms are the gymnosperms, which include cycads, Ginkgo, conifers (the group that contains the pines, spruces, firs, and relatives), and Gnetales (a group containing three ancient genera: Ephedra, the Mormon tea; Welwitschia, a bizarre plant of southwest African deserts; and Gnetum, a genus of mostly tropical vines). The origins of angiosperms are not well understood and remain problematic, in part because many seed plant lineages have already gone extinct. However, studies indicate that the earliest lineage of flowering plants, or basal angiosperms, may include the family Amborellaceae (with the single living species Amborella trichopoda, a shrub from the South Pacific island of New Caledonia). Other early diverging lineages of angiosperms include Nympheales, the water lilies; Illiciales, or star anise; a group called the magnoliids, which includes magnolias, laurels, and black pepper; and the very large group called the monocots . A final lineage, the eudicots , contains all other flowering plants and comprises the bulk (approximately three-quarters) of the flowering plant species.

Monocots, Dicots, and Eudicots

The angiosperms have historically been divided into two groups: the monocotyledons (monocots) and the dicotyledons (dicots). These terms derive from the number of seed leaves, or cotyledons , the plants have upon germination. Dicots have recently been shown not to be an evolutionarily natural group.

Answer 2

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Angiosperms: The flowering plants of the Kingdom Plantae are called the Angiosperms. They are the most diverse group of terrestrial- habitat plants. They are seed-producing plants.

Monocotyledons: The monocotyledons, also referred to as monocots. They are flowering plants or Angiosperms, which produce seeds containing only one cotyledon. Legumes are the best examples of monocotyledons.

Dicotyledons: The dicotyledons, also referred to as dicots. They are flowering plants or Angiosperms, which produce seeds containing two cotyledons. Grains are the best examples of dicotyledons