Family trees

When I started placing trees onto a map on Google My maps, it soon became apparent that I needed to place them in groups so that I could put different groups into different layers. It seemed natural to put related trees together. I thought putting Hornbeams with Whitebeams and Horse chestnuts with Sweet chestnuts would seem sensible; until I decided to check if they were actually related. They are not as closely related as their names would suggest. It sent me off on a course of finding out how the various trees in the park are related – or not.

In the end the layers on the map were partly decided by sheer weight of numbers and different families had to be grouped together. By that time, though, I had at least learned that certain trees belonged to certain families and some families had a lot of trees in them (as far as park trees are concerned) and other families had maybe just one.

There were some surprising discoveries in the way some of the trees were related and in the way some of the trees had barely any relatives in the park. Some, too, were expected like the Ginkgo as it is the only living species in its whole Phylum. A Phylum is a major division of living things, ranked just below a Kingdom. Depending on the characteristics of the living things they are put into smaller, more distinct, groups in the order Kingdom, Phylum, Class, Order, Family, Genus and Species. It is the last two which appear in the name of a given organism which in the case of this website is likely to be a tree such as an English oak, Quercus robur. Quercus is the genus and robur the particular species which makes it an English oak rather than a red oak which is in the same genus but is Quercus rubra or Q. rubra.

I had a simple idea to show, in a diagram, how the trees in the park were related. It turned out not to be that simple. Firstly, the naming system is not static. It was based on nineteenth century ideas but is now being updated to account for twentieth century science, particularly molecular biology. It is also now being revised for twenty-first century progress in science. So some names have changed. There is also a lot more sub-division of Genus and Species than I had expected. Then again when you think of all the cross-fertilsation of plants, grafting, cloning, hybridization it should not have been that unexpected.

Another simple factor that made it difficult was the ability to fit it all side by side on one page – near impossible and still be readable.

This is what I got if I put it all together.

Anything coloured in green is an individual species and it is one patch of green that I wanted to compare to another – how far away or how close was it? How far up and across did you have to go to make a connection or were they just next door to each other?

The top page is the easiest to deal with. It has no species in it and deals with the plant kingdom as a whole.

All trees are Tracheophytes but not all Tracheophytes are trees, some of them are ferns and some of them are Cycads which are not on this diagram. There are some tree ferns in the park. There are also examples of other plants in this diagram – mosses and lichens, for example, and there are plenty of those in the park, growing on trees, as shown below.

Tracheophytes are simply plants that have tubes and vessels to make up a circulatory system. Just like Humans have arteries, veins and lymph vessels, tracheophytes have vessels called xylem and phloem to move fluids around. In the case of trees the xylem becomes woody, not so for ferns and other soft plants.

Keeping it simple, follow the trees. Take the Conifers first (the Gymnosperms) simply because there aren’t as many of them and they are relatively simple in the way they sub-divide.

I’ve called this Level 2 because it is one level down from the Plant Kingdom. This diagram shows all of the park’s conifers (and the Ginkgo).

One group that stands out here is the Ginkophtya. It goes straight down to G. biloba with no branching and G. biloba is the only species in it. The naming of the different groups follows a pattern which is explained here.

So, apart from the Ginkgo most of the park’s conifers are fairly close cousins of each other, with only four distinct families.

Also one level down, the Angiosperms divide up in a more complicated manner and take up another four pages to complete.

Eudicots are a group based on seed type and pollen structure. Seeds can be single-leafed (monocotyledon) or double-leafed (dicotyledon). Eudicots are based on the previous ideas of dicotyledon plants. The reasoning and the differences between the groups is not the main interest here. The result of that work, though is what allowed the above diagram to be produced.

The Magnolias stand out as a separate branch of the Angiosperms very early on. It doesn’t take many steps to get from the top of the page to a species via Magnoliids. It’s the same via Proteales. The tree that caught my attention here was Platanus x hispanica, the London plane. Despite the shape of its leaves it has very little relationship to the sycamore and even its old name, P. acerifolia, is misleading to that connection. There is no relationship at all, bar a visual resemblance in their leaves. The other thing about thing which I learned is that the London plane is a hybrid.

The other tree of interest is the Ash tree (Fraxinus excelsior) which is in a family giving it closer ties to Olive trees, Jasmine, Lilac, Forsythia and Privet than Beech or Oak as I had previously imagined.

Following Core Eudicots we are now at level 3. First there are a whole lot of close cousins linked via Asterids and a different set linked via Saxifragales but the Rosids split into two sub-divisions that become more complex. Although it takes another three pages to tease them out, they are still on a par with the Asterids and Saxifragales – but with more sub-divisions.

As the name suggests, Rosids are a group of plants related in some way to roses. There are a huge number of them and the first sub-division is into Eurosids i and Eurosids ii. Eurosids i has a further subdivision that leads on to the Rosaceae which may be said to be the ‘true’ roses; at least that’s the family which includes the roses you would expect to see in a florist’s shop around Valentine’s day.

It’s easiest to deal with the group Eurosids ii first as it is a smaller group. Nothing obviously rose-like to the untrained eye but to a botanist there must be some characteristics in common with other Rosids.

One surprise here was the very close connection between the Acers (maples) and the Horse chestnut. It means that Horse chestnuts are more closely related to a Sycamore than to a Sweet chestnut. Despite the difference in shape of the leaves between a sycamore and a Horse chestnut, there must be more than a mere coincidence that their leaves are both arranged in groups of five – five points on the sycamore leaf and five leaflets in a group on the Horse chestnut leaf. The Sweet chestnut is in the other main group of the Rosids, Eurosids i.

Although it’s a common tree, in the park, the European Lime Tilia x europaea is the only one from its particular family. It is a hybrid of the large-leafed lime and the small-leafed lime.

No real surprises here, just a matter of following the many sub-divisions. Remember this is not a complete picture, it just represents what is found in the park. Even then bits are missing, such as Hazel trees, as they weren’t on the database. Hazels (Corylus avellana) should go alongside Carpinus in the Coryloideae sub-family.

From this diagram we can see that Oaks, Beeches and Chestnuts are closely related. So are Poplars and Willows. Birch, Alder Hornbeams and Hazels are closely related. Of all the above, though, Poplars and Willows have the least connection to the others – but closer than a Maple or a Lime.

The Elm (Ulmus) and the Mulberry (Morus) have only one representative in the park. The Rosaceae have many; and that excludes the flower beds!

The organisation of these groupings has changed and some changes are very recent (2001, 2007) but for my purposes it identifies two Tribes, the Amygdaleae and the Maleae. The Amygdalyeae contains all the cherry trees. I believe the distinction is in the type of fruit – the cherry group have drupes. That is a stone fruit; the fruit contains a stone, having a hard shell inside which, lies the seed. The maleae, on the other hand, have pomes, where the seeds are in a core surrounded by fleshy fruit – just think of an apple. The fleshy part will vary and the number of seeds will vary. Compare an apple to a rose-hip; both pomes but quite different. A Hawthorn berry will be a pome as the Hawthorn is in the Maleae tribe (Crataegus monogyna) but the berry has only one seed and the fleshy part is not that thick – it’s also not a berry in the strictest sense. But the important thing is that a Hawthorn tree is closely related to Apple trees and Roses and very closely related to Medlars. Medlars have been re-named from Mespilus germanica to Cretaegus germanica. The renaming of plants is according to APG iii and for a while I am sure both old and new names will happily co-exist. I only mention it because I found I was re-directed to new names when searching to find out about various trees.

Another Genus in this diagram is Sorbus and this includes the Whitebeam, Sorbus aria that I had previously thought was connected to Hornbeams. Distant cousins at best. But they are closely related to the Rowan or Mountain ash (Sorbus aucuparia). What was previously called the Swedish whitebeam (Sorbus intermedia) is now given a separate genus Scandosorbus and is re-named Scandosorbus intermedia. Like-wise Sorbus torminalis becomes Torminalis glaberrima.

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