Liliopsida

Monocotyledons or monocots are a group of flowering plants usually ranked as a class and once called the Monocotyledoneae. This taxonomic grouping is now named Liliopsida after the type genus, Lilium. Flowering plants not included in the Liliopsida are dicotyledons or dicots. These two broad groups are distinguished by the number of cotyledons, or embryonic leaves, in their seeds: dicots have two, and monocots have one.

The monocots are considered to form a monophyletic group which evolved from an early dicot. The earliest fossils presumed to be monocot remains date from the early Cretaceous period. The largest modern monocot family is the Orchidaceae (orchids), plants which have specialized in insect pollination. For this reason many species of orchids produce very complex flower structures. The second largest and perhaps more notable family, the Poaceae (true grasses), have evolved in another direction, becoming highly specialized for wind pollination. Grasses produce small, generally inconspicuous flowers.

Taxonomy

The APG II classification System, developed by the Angiosperm Phylogeny Group, recognizes ten orders of monocots and two families not yet assigned to any order, and divides these among the Base Monocots and Commelinids:

• Base Monocots
  • Family Petrosaviaceae
  • Acorus
  • Alismatales
  • Asparagales
  • Dioscoreales
  • Liliales
  • Pandanales
• Commelinids
  • Family Dasypogonaceae
  • Arecales
  • Commelinales
  • Poales
  • Zingiberales

Distinguishing traits

Monocots all share some traits. These traits can be used to distinguish a monocot from its close relative, a dicot. A monocot has a single cotyledon in its seed. Its gets its name, monocot because mono means one and a monocot has one cotyledon. Another distinguishing trait is that a monocot's flower is arranged in multiples of three. For example, a monocot's flower could have three, six, or nine petals. A monocot has leaves with parallel veins running down it.

References

• 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

External links

• Tree of Life Web Project: Monocotyledons