Angiosperms

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The angiosperms, or flowering plants (division Anthophyta or Magnolio-phyta), comprise more than 230,000 species and are thus by far the largest division of plants; they represent the dominant group of land plants today. In both vegetative and floral morphology the angiosperms are highly diverse. In size, for example, they range from the duckweeds (the genus Lemna), which are roughly one millimeter in length, to Eucalyptus trees, which are well over one hundred meters. Although all are characterized by the possession of flowers, these structures are also highly diverse in form and size. The smallest flowers are less than a millimeter in size (the flowers of duckweeds) while the largest flowers are approximately one meter in diameter (the flowers of Rafflesia). Features unique, or nearly so, to an-giosperms include the flower; the presence of seeds within a closed structure (actually a modified leaf) referred to as the carpel; the reduction of the female gametophyte to eight nuclei and seven cells; double fertilization (the

MAJOR ANGIOSPERM

Major Clades and Representative Families

GROUPS

Common Name

Number of Species in Family (approximate)

Eurosid

Rosaceae

Rose family

3,500

Fabaceae

Pea or legume family

17,000

Brassicaceae

Mustard family

3,000

Fagaceae

Beech or oak family

1,000

Cucurbitaceae

Pumpkin or gourd family

700

Euphorbiaceae

Spurge family

5,000

Juglandaceae

Walnut or hickory family

50

Begoniacae

Begonia family

1,000

Geraniaceae

Geranium family

750

Malvaceae

Cotton family

1,000

Euasterid

Cornaceae

Dogwood family

100

Ericaceae

Heath family

3,000

Lamiaceae

Mint family

3,000

Solanaceae

Tomato or potato family

2,500

Asteraceae

Sunflower family

25,000

Apiaceae

Parsley family

3,000

Hydrangeaceae

Hydrangea family

170

Caryophyllales

Cactaceae

Cactus family

2,000

Caryophyllaceae

Carnation or pink family

2,000

Aizoaceae

Mesembryanthemum family

2,300

Portulacaceae

Portulaca family

500

Polygonaceae

Buckwheat or rhubarb family

750

Magnoliids*

Magnoliaceae

Magnolia family

200

Lauraceae

Avocado or cinnamon family

2,500

Piperaceae

Pepper family

3,000

Myristicaceae

Nutmeg family

380

Annonaceae

Sweetsop family

2,000

Monocots*

Orchidaceae

Orchid family

18,000

Poaceae

Grass family

9,000

Arecaceae

Palm family

2,800

Araceae

Arum family

2,000

* Indicates major clades that are noneudicots; other major clades are eudicots.

morphology shape and form carpels the innermost whorl of flower parts, including the egg-bearing ovules, plus the style and stigma attached to the ovules gametophyte the haploid organism in the life cycle

A magnolia in bloom. Magnolias are basal angiosperms (plants thought to have evolved first) and are ancestors to both monocots and eudicots.

gymnosperm a major group of plants that includes the conifers genera plural of genus strobili cone-like reproductive structures zygote the egg immediately after it has been fertilized; the one-cell stage of a new individual endosperm the nutritive tissue in a seed, formed by fertilization of a diploid egg tissue by a sperm from pollen floristic related to plants gymnosperm a major group of plants that includes the conifers genera plural of genus strobili cone-like reproductive structures fusion of egg and sperm resulting in a zygote and the simultaneous fusion of the second sperm with the two polar nuclei, resulting in a triploid nucleus) and subsequent endosperm formation; a male or microgametophyte composed of three nuclei; stamens with two pairs of pollen sacs; and sieve tube elements and companion cells in the phloem. Nearly all angiosperms also possess vessel elements in the xylem, but vessel elements also occur in Gnetales and some ferns.

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