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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19 thoughts on “Six on Saturday: 5.9.20 Monocots & Dicots”

  1. Right, I think I’m ready for the moncots and dicots section of the exam – once I’ve read through that several more times. The best of luck with the revision. I was always a last minute, late into the night reviser and I still have nightmares about it. Great close up photos by the way.

    Liked by 1 person

    1. Bit nervous about whether I can get it all answered in time. I’ve tried to revise this over a good period as there is so much for this first one. The next ones are shorter. I’ve got an assignment that will be a bit rushed after this but want to focus just on the exam first.
      Stole the wifes macro lens for a lot of the pics this week so I could illustrate it.

      Liked by 1 person

  2. What an interesting Six on Saturday…please continue this botanical theme. I am learning lots, and will probably refer back to this as I observe my plants more closely. You’ve obviously understood the subject well, so hope you have the opportunity to use this in your exam.

    Liked by 1 person

  3. Well, we all think you should pass with flying colours! Very interesting and beautiful photos again. As a teacher, I refused to wish the students luck, they were talented enough without it, as you clearly are!

    Like

  4. I did botany at A level around 1970, so all of it rang a bell except the bit about pollen. If I’d been set the question yesterday I would have struggled to get beyond a couple of items though. I suspect I could identify most things correctly as monocots or dicots without being sure why I thought they were, so I must have absorbed something.

    Liked by 1 person

    1. The pollen wasn’t covered by the course to be fair that was from my own reading. It’s been on most papers. Sometimes just for a few marks other times for a good chunk. It isn’t in the syllabus to identify ones but looking at past papers it has come up so I figure it’s worth me having a few examples to mind.

      Like

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