by Sammy Stein

Created on: March 30, 2009

The major difference between a monocotyledon (monocot) and a dicotyledon (dicot) is that a dicot has two cotyledons and a monocot one. The cotyledon is the seed endosperm contained within the testa (seed coat). If you take the large seed of a dicot like a bean and remove the seed coat you will see the endosperm divides into two halves. In a monocot, there is only one part. In monocots, there is only one seed leaf, which is the embryonic leaf found in the endosperm which will develop into the plumule (first leaf). In a dicot, there are two seed leaves.

As well as this, there are other differences. Monocots and dicots both have vascular tissue which consists of phloem which carries sugars manufactured in the leaves to all parts of the plant and xylem, which is conductive tissue taking water and dissolved minerals to all parts of the plant from the root hairs. In monocots, the vascular tissue is scattered in the stems but in dicots, the vascular tissue forms distinctive rings.

Dicots have a specialised meristematic tissue called cambium which sits between the xylem and phloem. Annualy, the cambium divides to create xylem on the inside and phloem on the outside (which is where aphids are seeking to get their stylets to feed on the sugars in the phloem). Monocots do not possess cambium. The cambium layer is formed each year in perennials and creates secondary thickening of stems. It also gives trees their 'rings' of annual growth.

The root systems of dicots and monocots are different as well. Monocots tend to have a wide ranging network of fibrous roots whereas dicots have a long tap root with wide roots coming off.

Monocot leaves are strap like with entire margins (think grasses an dlilies) whereas dicots have leaves which may be divided and the margins may be entire but are usually lobed like oak, serrated or divided.

The venation in the leaves is different in monocots and dicots. In a monocot, the venetation is parallel but in a dicot the venation forms networks or meshes and is said to be reticulate.

The pollen grains of monocots tend to be smooth with a single pore but a dicot's pollen has furrows, pits and may have several pores.

The flowers of monocots vary but often have their petals in multiples of two whereas a dicot usually has them in threes or fives.

Many monocots grow from the base such as grasses but dicots often have a stem before side branches and leaves are produced.

Identifying monocots and dicots can seem like it might be hard as there are many plants in each category but once you understand the few defining features of each, it becomes easier. Monocots are thought to be a later evolution than dicots, which may be surprising but the simpler anatomy is actually more efficient in using energy and growing quickly. They can also withstand grazing, burning and disease better than many dicots.

There you have it - mono or dicot? Now you should know!

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