Naturalists and ecological professionals familiar with the Gippsland Region of Victoria might also be familiar with Eucalytpus strzeleckii K. Rule (Strzelecki Gum). If they are, they are probably aware of how notoriously difficult it is to differentiate from Eucalyptus ovata Labill. (Swamp Gum) as many of its key features are strikingly similar. And the ability to tell them apart is of particular importance because the Strzelecki Gum is threatened, listed as Vulnerable by the Environment Protection and Biodiversity Conservation Act Cth (1999) and the Swamp Gum, well, isn’t.
Here, we hope to give the amateur or aspiring ecologist or land manager a few pointers on identifying Strzelecki Gum, with respect to Swamp Gum.
About the author
Let me be clear, I am not a botanist. I am however a spatial ecologist with (at the time of writing) 20 years experience in terrestrial ecology. My early career saw me working directly in the conservation of Strzelecki Gum where I hand planted many thousands, and have since watched them develop, set seed and regenerate themselves. I have identified, mapped and measured tens of thousands for an assortment of conservation projects, and unfortunately have also identified and mapped many hundreds that were later condemned to be removed for an assortment of reasons. Much of this work is commercially confidential as is the way when you are engaged as a consultant, but at atleast one point in my career I had enough information and spare time on hand to conduct a survey and write it up for scientific publication (which you can access here).
This self flattering exercise isn’t to boast my Strzelecki Gum CV, but simply to give you confidence in the ramblings that follow. When it comes to Strzelecki Gums, I have seen it all.
One to one comparison - Strzelecki Gum to Swamp Gum
Like many things in botany (and probably zoology), once you are comfortable with identifying a species it becomes second nature. You can spot the species from a distance, but when asked “how do you know?”, you can’t quite answer. It isn’t often one thing, but a multitude of things. Where one diagnostic characteristic is inconclusive, another less obvious characteristic might be noticed. Many of these factors will be discussed in their own sub-sections below. But for now, here are some of the key features as they compare to Swamp Gum.
A comparison of key characteristics of Swamp Gum and Strzelecki Gum.
Note: Kevin Rule, the taxonomist that first described Strzelecki Gum in 1992 had a similar table in his paper, but I have opted to use the details from the Royal Botanic Gardens VicFlora site accessed in January 2023 as it is more likely to have included updated information.
Even those without a botany degree will notice that each row shares many of the same words, which is to say, they have very similar characteristics. The descriptions from Strzelecki Gum are often a bit longer, owing to a more detailed description in a more recent taxanomic revision, rather than being due to a specific point of difference in the species. And I can tell you from years of experience that not one characteristic is a sure-fire bet that you have a Strzelecki Gum - You need many positive indicators.
The new kid on the block
As recently as 2012, Eucalyptus bunyip Rule was first described. This is even more difficult (in my opinion) to tell apart from Strzelecki Gum, but because of its limited range (based on the current state of knowledge), it is less likely to come up. Pretty much if you are in the vicinity of Bunyip State Park, you may be dealing with the elusive Bunyip Gum. Otherwise, you are more likely to be faced with the distinction of Strzelecki Gum and Swamp Gum.
It is also worth noting that Strzelecki Gum is also very much likened to Eucalyptus brookeriana A.M.Gray but with the exception of the Otways population of Strzelecki Gum (that is noted as requiring further investigation) it usually occupies very different locations.
Differences
With all of that out of the way, let’s go over some of the key differences and describe them in non-botany talk. These are differences between Strzelecki Gum and Swamp Gum. It assumes you’ve already made the determination that you’re dealing with a Swamp Gum of some type.
And remember, never rely on a single trait to identify a Strzelecki Gum. Aim for multiple lines of evidence.
Glaucous new growth
Chief among the diagnostic features you’ll often hear is that Strzelecki Gum has glaucous new growth, or glaucous tips. In fact, the ‘other’ recognised common name for Strzelecki Gum is “wax-tip” which references this characteristic.
This description of glaucous growth is a conspicuous waxy residue that appears on the new leaves growing at the end of the stems. I use the term “waxy” because it is the term used by Kevin Rule in his 1992 description of the species but I think of it more like a powdery residue akin to what you’d find on latex gloves. Albeit, more of it. When you wipe the residue with your finger, it smears off showing the full gloss of the leaf underneath. So even if the residue is faint, you will see the distinct change when you rub it.
The wax is a whitish colour. Other descriptions say that it gives the new growth of Strzelecki Gum a “blueish” colour. Though, in my experience, this is offset but the reddish colour described in more detail below.
The glaucousness is a very strong indicator in that if you observe it (and the rest of the tree loosely matches that of a Swamp Gum), you likely have Strzelecki Gum. And although most Strzelecki Gums do have this trait, it is not impossible for it to be absent or so faint that you can’t observe it. For example, there may be new growth, but it lacks the glaucousness, or the tree simply does not have new growth at the time of assessment. Therefore, absence of this trait is not evidence that a tree is not Strzelecki Gum.
Bark colour
Both species can have some fibrous bark at their base, but for the most part, both are smooth barked. What differs is the colour of that smooth bark.
Now I’ll add here that bark is extremely variable from tree to tree. So on its own it is not a great indicator, but it is definitely one of those characteristics that you develop an eye for.
Compared to Strzelecki Gums, Swamp Gums bark ranges from fairly whitish/grey (though not as white as a Manna Gum), through to a soft yellowy grey. Occasionally it can be stricken with some darker patches of a grey/brown, but it doesn’t change the overall appearance of the bark from a distance. Strzelecki Gums are prone to much richer colours of the palettes described above. And while some dull coloured individuals can be found, they often have a richer, creamier yellowness to their bark. They display much more frequent grey/brown mottling all over and can sometimes have a rich red hue in some places looking a little pink from a distance.
Leaf shape
An example of lanceolate, ovate and elliptic leaf shapes.
You’ll notice in the table above that Swamp Gum juvenile leaves are described as “elliptic to ovate” whereas Strzelecki Gum is “lanceolate to ovate”. The adult leaves follow a similar pattern in their description in that Swamp Gum are “ovate to broadly lanceolate” whereas Strzelecki Gums are “ovate to lanceolate”. There’s not a heap of difference in those descriptions, but in other words, Swamp Gum leaves are rounder and in some circumstances almost totally circular, whereas Strzelecki Gum leaves are narrower.
This isn’t a great identifying characteristic if you’re new to spotting the species, but can be handy when you have one of each right in front of you as the distinction becomes more obvious. It is also a good one to keep in mind when considering …
Leaf size
Simply put, Swamp Gum leaves, particularly the new ones, appear bigger. This doesn’t match what the table above says as the longest Swamp Gum leaf is said to max out at 17 cm where as the Strzelecki Gum is 20 cm. And I’m not questioning those statistics obtained by people with far more botanical expertise than me, but it is why in the first sentence of this paragraph I said the leaves “appear” bigger.
Taking any two individuals from the two species may yield maximum leaf lengths similar to each other. Perhaps the Strzelecki Gum leaves are 15% longer as indicated by the table above. But because the Swamp Gums are often rounder, they have a much bigger surface area and just look huge. When seen side by side, it is actually comical how big Swamp Gum leaves can appear in relation to the apparent, dainty Strzelecki Gum leaves. Strzelecki Gum leaves, because of their more lanceolate shape, just look smaller, particularly on larger, older individuals.
Reddish new growth
Not often mentioned, and I’m probably committing a botanical sin by mentioning this, but Strzelecki Gum sometimes has reddish new growth. That is, the same new baby leaves that are glaucous, can also have a minor to very strong reddish colour. This isn’t always the case, as some Strzelecki Gums lack the colouring, but in my experience, Swamp Gum new growth is usually light green to slightly golden, meaning any reddish hue can be used as a positive indicator for Strzelecki Gum. Not only is the presence of this trait variable, but it is also influenced by the timing of the new growths, erm, growth.
Tree size and habitats
Tree size isn’t a great one because trees … grow. But when you’re looking at large, mature trees, Strzelecki Gums can dwarf Swamp Gums.
Both span habitat types ranging from emergent trees in swamps to dominant riparian forest trees, but Strzelecki Gum has a higher propensity for occupying taller forests that may be near or adjacent to damp and wet forests.
It is no exaggeration that the tree size of 40 m is listed for Strzelecki Gum above. Swamp Gums may exceed the 20 m metric listed in some cirumstances, but they will not get close to 40 m.
The examples pictured below are of more isolated trees that are a bit more “spreading” in form, but you can have instances where they are straighter forest trees.
Oil glands
As mentioned in the table above, the oil glands on Swamp Gum leaves are often not visible, compared to Strzelecki Gums which are usually obvious. Notice the words “often” and “usually”, because there is a lot of variation with this one. Nevertheless, to spot the difference, when you hold a leaf up to a strong light like the sun, you will see numerous oil glands throughout the Strzelecki Gum leaves which are less obvious and/or less numerous with the Swamp Gum.
Smell
I’ve left this one for last because it is often purported, but is so highly variable to almost be useless. Due to the difference in oil gland density mentioned above, Strzelecki Gum is said to have a stronger and more typically “eucalyptus oil” smell to it when the leaves are crushed in your hand. Whereas the Swamp Gum is described as being far milder and subtly sweet; more like a “box of apples”.
The smell is only useful when you have access to adult leaves, and you can compare one to the other. If you want to rely on it as a diagnostic feature, you would want to have the odors of each securely saved in your olfactory memory or have samples of one of each in your hands.
Though, remember to use different hands with your samples, and to smell the one you believe to be Swamp Gum first, as Strzelecki Gums smell can be so much stronger that it overwhelmes all other smells.
Similarities
Keep in mind that other characteristics that may be useful for the identification of eucalypts in the broader Swamp Gum group from other eucalypt groups are usually not useful for differentiating these species apart. For example, undulating (wavey) leaves are a distinct characteristic of all eucalypts in the Swamp Gum group, but is a shared characteristic between Eucalyptus ovata and Eucalyptus strzeleckii. Furthermore, the buds, fruit and flowers are all very similar between the two and not useful for diagnostic purposes. Kevin Rule, in his initial description of Strzelecki Gum does display a comparison of the buds and fruit highlighting the Strzelecki Gum buds are slightly more ovoid in their diamond shaped cross-section than Swamp Gum, but this is so minor and indistinguishable that I consider it more of an academic difference than anything.
So if you find some buds or fruit on the ground that come from a tree in question, they are not likely to help other than to tell you that you probably have something in the Swamp Gum group.
Making an identification of Strzelecki Gum
I’ve listed the characteristics in descending order of fidelity. That is, in my experience, those at the top of the list are stronger predictors than those at the bottom of the list.
You will always want to confirm more than one of the above listed diagnostic features to confirm a Strzelecki Gum. Even two may not be enough. And you may occassionally find that some characteristics, such as leaf shape, size or oil gland density are hard to obtain because the tree crown is too high forcing you to use other characteristics for identification.
Though it is reasonable to say that if you use the characteristics at the bottom of the list, you may want a couple more positive indicators than if you found some of the top ones.
If you are ever in doubt, you should always contact a specialist because these trees are threatened and protected and their identification and protection is critical for their conservation.
Need an ecologist to identify Strzelecki Gum? Reach out.