To pea, or not to pea

Ok, so, as I mentioned in the last post, I have just been on a botany field course, and so taking a little diversion from the evolution of life on earth to write about plants. (Got a bit distracted on the course, so forgot to finish writing this post, so apologies for the delay!)

This is a pea, we all know and eat these regularly, across the whole range of dining experiences, from high end restaurants to mushy peas and chips.

A pea plant (img from wikipedia)

This is the pea within the pod

Peas in the pod, ready to be eaten! (img from wikipedia)

The final image is of a pea plant in flower.

A pea plant (Pisum sativum) in flower. Image from Encyclopedia of Life

Peas are in the family Fabacae (from latin “faba” meaning bean, the word became fava over time, and broad beans are known as fava in Italy, they are also the type of bean that Hannibal Lector likes!)

In English, this family is known as the Pea Family, and the fruit they produce (the pea pods in the picture above) are known as legumes.  An alternative (less used now, but more common in the past) name for this family is Leguminosae.

This family is quite a big one, there are 19000 or so species (specific plants) within it.  I found one of the most interesting parts of the course I was just on was looking at a plant and thinking “How the hell did they know that was in the same family as this other plant”, and I am going to try to illustrate that a bit with this post, as well as try to explain how to recognise when a plant is in this family.

This family of plants has been around since the Paleocene era (approx 65-56 million years ago), and the 3rd and 4th images below show a modern Fabaceae plant, and a fossil one from the Paleocene.

Fossil plants compared with modern versions. The centre two images show a modern pea family plant, and a fossil one from the end of the Paleocene era. Image from American Journal of Botany

The modern species within this family are very diverse, and the following images are all of various plants within this family.  The first one is the gorse bush (Ulex europaeus, Ulex is the term Pliny the Elder used for heather (Pliny was an Ancient Greek guy who wrote one of the books which is on my very geeky “Must own this” list, Naturalis Historia) and europaeus means it is found in Europe), which is found on heaths, sandy dunes, and is an extremely annoying plant if you start wandering through some countryside and don’t spot the fallen thorns on the ground around it, or do not notice little bushes of it sprouting up as you climb through the edge of a forest.

Gorse Bush, very pretty, but very prickly! Image from http://www.cavinguk.co.uk/holidays/Pain2006/

This next picture is of course, the peanut (Arachis hypogaea,  hypogaea meaning underground), which, surprisingly is in the pea family!  The image afterwards is of the peanut plant in flower.

Peanuts. Image from Wikipedia

Peanut plant in flower. Image from Purdue Agriculture

The peanut is not actually a nut, it is a pod, like the pea pod, but it grows underground.  Once the flowers of the plant have been fertilised, the petals fall off, and the remaining part (the ovary, containing the seeds) develops a spike, and grows towards the ground, burying itself a few centimetres into the ground.  The picture below shows what remains of  a peanut flower after fertilisation.  The reddish brown pointy part is what will dig into the ground, and the whitish bit above it (wider than the stalk) is the ovary, and is where the peanut will develop from.

A Peanut plant after fertilisation, showing the end of the ovary growing towards the ground. Image from Wikipedia

The next picture is of the peanut just after harvesting, so you can see that the peanuts actually come up along with the roots.  It is a common idea that the peanut is part of the root, and not the fruit of the plant.  It is easy to see why people think this, because it does look exactly like that.

Peanut plant after harvesting. It is easy to see why many think the peanut is part of the roots. Image from Sagesite.com

Other plants that you may not expect to be in the pea family are liquorice, and clover (image below is of White Clover, the most common type, Trifolium Repens (Trifolium meaning 3 leaves, and Repens meaning creeping)).

White clover, known for its 3 leaves, and the difficulty in finding 4 leaved versions of it! Also associated with leprechauns. Image from Informedfarmers.com

So, I promised I would try to explain how you can tell something is in the pea family. Having just spent 5 days staring at lots of this family, when I was inserting the images for this post I thought “I cannot put these in, it is obvious that they are all in the same family”, but then I thought that it may not be so obvious if you have not just spent the best part of a week getting “pea-blindness” (Like snow-blindness, but caused by staring at various members of this family for too many hours a day with too little sleep the night before!)

So, the skeptical squirrel guide to identifying pea plants:

Firstly, hopefully it has a flower on it, this makes it very much easier!  Even with something like a clover, which does not initially look like it has the same flower, each clover head is made up of lots of small flowers, which have the same characteristics as other flowers from within this family. They look a bit like a side-on face with a sticking out tongue…..ok, maybe only a little bit, but definitely after some beers, and in the right light, they look like that!  The picture below shows the side view of a flower from this family, along with a diagram showing the parts of the flower.

Side view of a pea plant flower, and systematic diagrams. Image from Ohio State university

So, to be a bit more technical, you are looking for a flower with 5 petals, 1 large one at the top (the banner), 2 smaller ones sticking out in the middle (the wings), and 2 small ones at the bottom, forming a boat(ish) shape (the keel).  The Fabaceae  family has what are known as bilaterally symmetrical flowers, this means that if you cut them top to bottom, each half looks the same.  These flowers are very very distinctive, so once you know what they look like, if you see another one, you will recognise it immediately!

The other very distinctive feature of this family is the pods in which the seeds are held, they look like, well…., a pea pod.

Finally, if you have neither flowers nor seed pods, then it gets very annoying (and gave me a lot of headaches on the field course!), but, some plants within this family have very distinctive leaves, so can be recognised easily from those too.

Clovers, as mentioned earlier, have 3-leaves, or more correctly, a trifoliate leaf, which means it is one leaf, divided into 3 smaller leaflets, and the ones on clovers are very easy to spot.

Many Fabaceae plants have what are known as pinnate leaves, which means there are lots of small leaflets arranged along a small stalk, like in the picture below

A pinnate leaf. Image from UBC Biology 324 blog

At the end of the leaf in the picture above, there is a long curled stalky thing.  This is a tendril, and it is what the plant uses to climb. It wraps around another plant, a pole, anything it can grab onto.

A member of the Fabaceae family (Vicia sativa, or Common Vetch), the tendril is visible on the far right of the picture, extending from the leaf stalk. Image from wikimedia

This is just a very rough guide to how to spot a Fabaceae plant, but hopefully it is a bit helpful.  Tomorrow will be back to Cnidaria, plants will be in later posts, but, the land plants come along a whole lot later in our journey through evolution.

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