Monocotyledon
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| Image:Hypoxis.jpg Hypoxis decumbens L. | ||||||
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Base Monocots: |
The Monocotyledons or monocots are an extremely important group of flowering plants, dominating great parts of the earth and with many economically important plants.
The largest monocot family is the Orchidaceae (orchids), with very complex (and striking) flowers, for highly specific insect pollination.
The second largest and perhaps more notable family, the Poaceae or Gramineae (true grasses), have evolved in another direction, becoming highly specialized for wind pollination. Grasses produce small flowers, which may be gathered in highly visible plumes (inflorescences).
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Name, characters
The traditional scientific name for this group is Monocotyledones, although recently, e.g. in the Cronquist system, it has been called Liliopsida (class, based on Lilium). As the monocots are a group above the rank of family there is a free choice of name; Article 16 of the ICBN allows either a descriptive name or a name based on a generic name. The traditional name Monocotyledones (some prefer Monocotyledoneae) derives from the fact that most members of this group have one cotyledon, or embryonic leaf, in their seeds. This as opposed to the (traditional) Dicotyledones which typically have two cotyledons. From a diagnostic point of view the number of cotyledons is neither a particularly handy nor reliable character.
Nevertheless, monocots are a distinctive group. One of the most noticeable traits is that a monocot's flower is trimerous, with the flower parts in threes or in multiples of three. For example, a monocot's flower could have three, six, or nine petals. Many monocots also have leaves with parallel veins.
Compared to Dicotyledons
Seeds: The embryo of the monocot has one cotyledon while the embryo of the dicot has two.
Flowers: The flower parts in monocots are multiples of three while in dicots are multiples of four or five.
Stems: In monocots, the stem vascular bundles are scattered, while in dicots there are in a ring.
Pollen: In monocots, pollen has one furrow or pore while in dicots they have three.
Roots: The roots are adventitious in monocots, while in dicots they develop from the radicle.
Leaves: In monocots, the major leaf veins are parallel, while in dicots they are reticulated.
Taxonomy
The monocots are considered to form a monophyletic group arising early in the history of the flowering plants. The earliest fossils presumed to be monocot remains date from the early Cretaceous period.
The APG II classification System, developed by the Angiosperm Phylogeny Group, recognises "monocots" as one of the two biggest groups in the Angiosperms (flowering plants), the other being the "eudicots", the remnant sometimes being called the "palaeodicots". Within the monocots, the APG II system recognizes ten orders of monocots and two families not yet assigned to any order, and divides these among the Base Monocots and Commelinids:
References and external links
- Chase MW, Soltis DE, Soltis PS, Rudall PJ, Fay MF, Hahn WJ, Sullivan S, Joseph J, Molvray M, Kores PJ, Givnish TJ, Sytsma KJ, Pires JC (2000). Higher-level systematics of the monocotyledons: An assessment of current knowledge and a new classification. In: Wilson KL, Morrison DA, eds. Monocots: Systematics and Evolution.. CSIRO, Melbourne. 3-16. ISBN 0643064370
- Tree of Life Web Project: Monocotyledons
