Talking about Leaves

Botanical jargon can seem off-putting to a beginner, but it is worth the trouble of learning a bit of it. Knowing some of the botanical words makes aware of what details about leaves to look for, and the more we know about what to look for, the more details we notice.

So let’s start with a few easy botanical terms, and what they mean.

Alternate or opposite leaves?
If you’re looking at a plant and wondering what it is, this is one of the first identifying features to look for.

Opposite simply means that the leaves are in pairs. Here is a specimen of a local climber with opposite leaves.


Stiff Jasmine, Jasminum simplicifolium - for more details on this plant see: https://toowoombaplants2008.blogspot.com/search?q=pearls

Alternate means the leaves are joined onto the twig (botanical term: branchlet) one at a time, not in pairs. The plant below has alternate leaves along its slightly zig-zagged branchlets.


Scrub Wilga, Geijera salicifolia - for more details on this plant see:
https://toowoombaplants2008.blogspot.com/search?q=bone-chilling.

Simple or Compound Leaves?

This is a little trickier. A simple leaf is never divided into leaflets. Simple leaves come in a lot of different shapes, but there is always is just a single leaf-blade, joined directly to the branchlet. The Jasmine and the Wilga above have simple leaves.
So does the plant below - and you will notice that they are opposite.


Red Olive-plum Elaeodendron australe var. integrifolium, - for more details on this plant see:
https://toowoombaplants2008.blogspot.com/search?q=olive-plum

Another local with simple, opposite leaves is this one.


Small Fruited Mock Olive, Notelaea microcarpa - for more details on this plant see:
https://toowoombaplants2008.blogspot.com/search?q=Rosenthal

This one has simple, alternate leaves:


Scrub Boonaree, Alectryon diversifolius - for more details on this plant see:
https://toowoombaplants2008.blogspot.com/search?q=dormitory

And here’s another one which also has simple, alternate leaves:

Breynia, Breynia oblongifolia.

Instead of being simple, leaves can be compound.
This means that the leaf is divided up into sub-leaves (botanical term: leaflets). This cam be confusing, because leaflets look rather like leaves!

The picture below shows ONLY THREE leaves. They are the kind called compound leaves, rather than simple leaves.


White Beetroot Tree Elattostachys xylocarpa - for more details on this plant see: 
https://toowoombaplants2008.blogspot.com/search?q=multiple-trunked

Two of its leaves are divided into five leaflets each, and the other leaf has only two leaflets.
You could mistake those leaflets for simple leaves, couldn’t you?



 White Beetroot Tree Elattostachys xylocarpa

The difference can be seen by looking at the join between the leaf-stalk and the branchlet. (The botanical term for this join is “axil”.) Can you see that there is a shoot coming from the axil? Only leaves have those shoots. There is never a shoot at the base of leaflets. The position of the shoot tells you that you are looking at compound leaves.
  
(And did you notice that this plant has alternate leaves?)

So does this one below - and its compound leaves are very large.

Deep Yellowwood, Rhodosphaera rhodanthema, - for more details on this plant see: https://toowoombaplants2008.blogspot.com/search?q=deep+yellowwood
 
Note the tiny shoot in the leaf axil, by my finger. The shoots in leaf axils are sometimes just very small points, so you need to look carefully for evidence that this is a compound leaf.

Also note the white sap oozing from the places where I have snipped off leaves, so I could show a clear photo of a single leaf. Relatively few trees have white sap, so this is an important identifying feature. (I washed my hands afterwards, an important precaution after handling this kind of plant.)

White beetroot tree and Deep Yellowood have the kind of compound leaves called pinnate leaves. Pinnate is a word about feathers. Can you see how the leaves in the photo above are arranged a bit like a feather - with a leaflets lined up on either side of the central rib, like the barbs of a feather? The central rib of the leaf is called the rachis. (Pronounced RAH-KIS) The strong central spine of a feather is a rachis, too.

Trifoliate Leaves
Here is another plant with compound leaves. In this case, its leaves are opposite.

Triple Leaf Jasmine, Jasminum didymum subsp. racemosum - for more details on this plant see:
https://toowoombaplants2008.blogspot.com/search?q=didymum
 
Despite its deceptive common name, it is the leaflets that are triple, not the leaves. If you look closely (double click on the photo) you can see the beginnings of shoots in the leaf axils.

Plants with compound leaves, having three leaflets arranged in this pattern are called “trifoliate” (or some people prefer “trifoliolate”, which is such a tongue twister that the word is dropping out of use, despite its being more correct). So the jasmine above has opposite, trifoliate leaves.

Here is another example of compound leaves which are trifoliate.

Tingletongue, Dinosperma erythrococcum. 
 
Can you see that there is a tiny shoot at the base of those trifoliate leaves? And that the leaves are opposite?

Now for a plant family - one with spikes.
A word that helps you identify quite a few of the trees in our local scrubs and dry rainforests is Sapindaceae, (Usually pronounced SAP-IN-DAY-SEE)
It is the name of a plant family, and we have an unusually large number of its members here in our local area. They all have alternate leaves. A few, (like the Scrub Boonaree) have simple leaves, but most of our local Sapindaceae have pinnately compound leaves.
Members of this family can be picked out from other plants with pinnate leaves by a small spike at the tip of the rachis, just where the top leaflet-stem joins on.


Scrub Boonaree, Cupaniopsis parvifolia. FAMILY: Sapindaceae

 You will also find spikes on the rachis-tips of a plant we looked at, earlier in this blog.

White Beetroot Tree Elattostachys xylocarpa.  FAMILY: Sapindaceae

We’d better have a closer look


 White Beetroot Tree, Elattostachys xylocarpa. FAMILY: Sapindaceae

And here's another member of the Sapindaceae family.



Pitted Coogera, Arytera foveolata. FAMILY: Sapindaceae
 
The spikes at the tip of the rachis, of its pinnately compound, alternate leaves, are rather blunt.
 
 
Pitted Coogera, Arytera foveolata. FAMILY: Sapindaceae


Looking at the back of the Beetroot Tree's leaflets, you can notice another interesting feature.


White Beetroot Tree, Elattostachys xylocarpa.

There are little hairy pits, at each junction of a side vein with the main central vein,. These pits are called domatia. The word means “little homes”, and that’s exactly what domatia are.

White Beetroot Tree, Elattostachys xylocarpa.
 
Domatia are good investments for the trees that have them. They have evolved these structures so they can be landlords. Small mites move in, and “pay their rent” by preying on small insects which would otherwise eat the leaves.

Some species of plants have them, and some don't. Where domatia are present, they give another clue to the identity of the plant.

These leaves also have domatia.

Pitted Coogera, Arytera foveolata. 

You could easily overlook them, couldn't you? If you double-click on the photo they will be easier to see, and now that you know the word, domatium, perhaps you will look with more interest at the backs of leaves and leaflets.

And I hope that you will be more aware of whether leaves are alternate or opposite, and whether they are simple or compound. If they are compound, you can look to see whether they are trifoliate or pinnate. If they are pinnate you can check  whether they are members of the Sapindaceae family.

What else can you learn about leaves?

The Perfect Windbreak

Scrub Wilga
Geijera salicifolia
Family: RUTACEAE
It was so cold on the Darling Downs west of Toowoomba yesterday! The weather report told us the maximum temperature was 14°, and there was a dry, bone-chilling breeze.

However at Irongate Reserve, in the sunny clearings sheltered by the scrub, the weather was delightful. The little birds and butterflies were going about their business as usual, and we felt we could ignore the wind, which was merely providing the musical accompaniment, singing its she-oak song well above our heads.
One of the most effective windbreak trees at Irongate is the scrub wilga.
(Don't confuse it with the very narrow-leaved common wilga, Geijera parviflora, which also occurs at Irongate, but is better known from the plains further west).
The scrub wilga’s great virtue is the density of its dark-green canopy, which it maintains year-round and through the worst droughts. Like so many of our dry rainforest/vine scrub species, scrub wilgas have very deep roots which make use of deep-down groundwater. This lets them be even more resilient in droughts than some of our toughest eucalypts. Over the last few years we have seen Eucalypts dying in paddocks west of Toowoomba, while the nearby “scrub trees” were looking as lush and green as ever.
Here are some roadside specimens growing near Mt Tyson, showing the typical canopy-to-the-ground formation of younger trees, which makes them such good windbreaks. As you can see, they are very happy snuggling up close to the mountain coolibah Eucalyptus orgadophila, making a little clump with obvious bird-appeal.



This garden-grown specimen at Gowrie Junction is known to be 27 years old.






With age, the plants develop into pretty little shade trees. I had thought that pruning by cattle must help with the shape (as pruning by sheep does with the common wilga) but I have been assured by a cattle farmer that cattle won’t eat the leaves of scrub wilgas. They are often left in paddocks as shelter for cattle.
This one has had a hard life, with the soil around it well-compacted by stock.
Paddocks in this district were first cleared about 1880, and it is possible that this tough little tree has been roughly this shape and size for 120 years or so. With many of our vine scrub tree species, growth in tough conditions is very slow indeed, and some very old trees are deceptively small. If this one became part of somebody’s garden, and its soil give a bit of extra care, it would probably start to grow again.
Like many of our local native trees, scrub wilgas are very long-lived. The one at the foot of this article grows at at Gowrie Junction. It has never been dated, but could well be 300 years old.
Don't believe the story - usually told as a justification for planting foreign species - that Australian natives are "short-lived"! (It's partly true, of course. The short-lived species are indeed short lived!!! However, only someone who doesn't know much about Australian natives could think that Australia is more richly endowed with short-lived species than any other part of of the world.)
I imagine, though, that a gardener who wanted a little shade tree, could discourage the early tendency to low branching, by judicious use of the secateurs.
Scrub wilgas have a long flowering season. They were beginning to come out in early April, and are at their best around the district in June and July. They are a mass of flowers at Irongate at present, providing food for insects, which in turn provide useful over-winter food for many little birds. The shiny black seeds which follow will provide a further food source.
Botanists tells us that there two varieties (a broad-leaved one, var. latifolia, and a narrow-leafed one, ver. Salicifolia) however here above the Great Dividing Range we notice that there seems to be a continuum. Close to the range they are broad-leafed, and as we move west they become progressively narrower in the leaf.






This is what the leaves look like at Highfields....











...and this is a photo I took at Jondaryan in April. Note the much narrower leaves....









...while the ones at Irongate are somewhere in between.

This picture shows the deep grey twiglets, which, together with the dark canopy, give the whole tree a rather dark look from the far. This must be part of the reason why the local common name for this tree is “black alley”.




The crushed leaves have a delicious plum-pudding smell. This plant is in the same family as citrus trees, and like them is a host plant for our largest native butterfly, the orchard butterfly (Papilio aegeus).
I am told that the butterflies grow larger on their native host plants than they do on introduced citrus species.
Irongate Reserve is in Wallingford Road, between Pittsworth and Mt Tyson.