Six on Saturday: 5.9.20 Monocots & Dicots

For this weeks six I thought I would do a blog to aid with revision for my first RHS exam in a few weeks. Having had a look through past exam papers the differences between monocts and dicots is a regular exam question. Flowering plants (Angiosperms) are divided into two key groups moncots and discots. The course never really explains why this is important to know but it does give you a good idea of how a plant will grow, what leaves it will have. Some diseases may affect dicots but not monocots so it can be useful to be able to categorise the two.

1. Leaves

The leaves of monocotyledonous plants have parallel veins. They are usually strap-like in shape and have the stomata (where oxygen exits and carbon dioxide enters) are spread evenly between the top and bottom of the leaves. Grasses would be a good example of this. Here we have a hosta showing the parallel veins.

Whereas, dicotyledonous plants have spreading, reticulate (net-like) and branching veins. Here on the heuchera you can see the veins spreading out like a web. The stomata are located on the underside of the leaves.

2. Stems

Monocot stems have vascular bundles scattered around the stem with an epidermis one layer thick. They cannot undergo secondary thickening so they do not form woody stems. There are some exceptions such as palm trees and bananas that can form larger stems but these are exceptions that have developed different strategies than dicot stems for growing larger. So while something like a hosta may grow large leaves it does not develop a large stem. Here the agapanthus has the strap like leaves with a long stem but it cannot undergo secondary thickening to make it more stable.

Dicot stems have vascular bundles arranged in circles around the pith acting as a starch store. They can undergo secondary thickening. So, in general, most trees will be dicots.

3. Flowers

Monocot flower parts are arranged in multiples of 3. Irises and lilies are good examples of this.

Whereas, dicot flowers have parts arranged in multiples of 4 or 5.

4. Seeds

Monocot seeds have one cotyledon, thus the name monocot. The cotyledon is the embryonic leaf that the plant initially grows when first germinated. As it grows larger it forms the true leaves. In the case of monocots, as already said, strap-like.

In dicot seeds, they have two cotyledons. Here we have the two seed leaves of the dicot coneflowers, Echinacea purpurea.

5. Roots

In monocot roots are usually fibrous. They sometimes have an initial taproot that dies off quickly to be replaced by the adventitious fibrous roots. Whereas dicots can form a tap root system with a central thicker root growing down with roots branching off this. Then from the secondary roots smaller taproots may form. Here we have the fibrous roots coming off an onion.

6. Pollen grains

Monocot pollen is monosulcate. This means it has a single pore through the outer layer.

Whereas dicot pollen is tricolpate meaning it has 3 ridges through the outer layer.

I hope you have enjoyed me sharing some of my course knowledge. Hopefully, some of it may be accurate. One more weekend to go before the test so I have a bit more time to cram. Sorry if I don’t get around to reading everyone else’s sixes this week. Between starting my new job on Monday and preparing for my exam I am a bit busy. But it should settle into a nice routine after the exam. Enjoy your weekends.

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