Flowering plant

The flowering plants are one of the major groups of modern plants ,comprising those that produce seeds in specialized reproductive organs called flowers , wherethe ovulary or carpel is enclosed. These are known as angiosperms. In other seed plants ( Spermatophytes ), called gymnosperms , the ovule is not enclosed at pollination.

Origins

The first evidence of angiosperms appears in the fossil record approximately 140 million years ago, during the Jurassic period (203-135 million years ago). Based on current evidence, it is seems thatthe ancestors of the angiosperms and the Gnetophytes diverged from one anotherduring the late Triassic (220-202 million years ago). Fossil plants with someidentifiable angiosperm characteristics appear in the Jurassic and early Cretaceous (135-65 million years ago), but in relatively few and primitive forms. The great angiospermradiation, when a great diversity of angiosperms appear in the fossil record, occurred in the mid-Cretaceous (approximately 100million years ago). By the late Cretaceous, angiosperms appear to have become the predominant group of land plants, and manyfossil plants recognizable as belonging to modern families (including beech , oak , sycamore , and magnolia ) appeared.

Classification

The flowering plants are usually treated as a division ,formerly called the Angiospermatophyta or Anthophyta, but now called Magnoliophyta after the type genus Magnolia .Their classification has undergone considerable revision as ideas about their relationships change. The Cronquist system , proposed by Arthur Cronquist in 1981, isstill widely used but is no longer believed to reflect phylogeny. A general consensus about how the flowering plants should bearranged has only recently begun to emerge, through the work of the Angiosperm Phylogeny Group , who published an influential reclassification of the angiosperms in1998. An update incorporating more recent research was published as APG (2003).

Traditionally, the flowering plants are divided into the dicotyledons and monocotyledons (called dicots and monocots for short). This is basedmainly on the number of cotyledons or embryonic leaves within the seeds, butthere are a number of other differences. These groups are typically ranked as classes, formerly called Dicotyledoneae andMonocotyledoneae, but now respectively named Class Magnoliopsida and Class Liliopsida after thetype genus in each case.

Studies show that the monocots are monophyletic, and the dicots are paraphyletic to them. However, the majority belong to amonophyletic subgroup called the eudicotyledons or tricolpates,distinguished most notably by the form of the pollen. Since newer systems tend to avoid paraphyletic groups, these may be treatedas a separate class Rosopsida, or split into several different classes. The Magnoliopsida would then be restricted to the basaldicots or palaeodicotyledons , a paraphyletic group which may alsobe further divided.

The most diverse families of flowering plants, in order of number of species, are:

1. Asteraceae ( daisy family): 25,000species
2. Orchidaceae ( orchid family):18,000
3. Fabaceae ( pea family): 17,000
4. Poaceae (grass family): 9,000
5. Rubiaceae ( coffee family):7,000
6. Euphorbiaceae ( spurge family): 5,000
7. Cyperaceae (sedge family): 4,000

In the list above (showing only the 7 largest families), the Orchidaceae, Poaceae, and Cyperaceae are monocot families; theothers are dicot families. The total number of families in the Magnoliophyta is over 460.

Economic importance

Flowering plants provide a very high percentage of the base food for human use, whether directly or through livestock feed. Ofall the families of flowering plants, the Poaceae , or grass family, is by far themost important, providing the bulk of all feedstocks ( rice , corn ( maize ), wheat , barley , rye , oats , millet , sugar cane , sorghum ), with the Fabaceae , or legume family, in second place. Alsoof high importance are the Solanaceae , or nightshade family ( potatoes , tomatoes , and peppers, among others), the Cucurbitaceae , or cucumber family (also including pumpkins and melons ),the Brassicaceae , or mustard family (including rapeseed and cabbage ), and the Apiaceae , or carrot family. Many of our fruits come from the Rutaceae , or citrusfamily, and the Rosaceae (rose family, including apples , pears , cherries , apricots , plums , etc).

In some parts of the world, certain single species assume paramount importance because of their variety of uses. An example isthe coconut ( Cocos nucifera ) on Pacific atolls . Another example is the olive ( Olea europaea ) in the Mediterranean .

Flowering plants also provide economic resources in the form of wood , paper , fiber ( cotton , flax , and hemp , among others), medicines ( digitalis , camphor ), decorative and landscaping plants, and many,many other uses.

See also

• List of flowers
• How todistinguish a monocot from a dicot

References and external links

• Angiosperm Phylogeny Group (2003). An update of the Angiosperm Phylogeny Group classification for the orders and families offlowering plants: APG II. Botanical Journal of the Linnean Society, 141, 399-436. Available online
• Cronquist, Arthur. (1981) An Integrated System of Classification of Flowering Plants. Columbia Univ. Press, NewYork.
• Tree of Life Web Project - Angiosperms
• Oldest Known Flowering Plants Identified By Genes , William J. Cromie,Harvard Gazette, December 16, 1999.
• Stevens, P.F. (2001 onwards). Angiosperm Phylogeny Website at Missouri Botanical Garden.
• DeltaFamilies of Flowering Plants
• FlowerPictures