Jane Grows Garden Rooms

The controversy of classifying Commelina species in Australia.

My first recollection of this species is dominated by a catch of breath as I spied a delightful deep blue flower on my dam wall. This was followed by a resigned sigh, with a flower like that and the fleshy green stems it was probably an exotic invasive!

I put off identifying it which I do sometimes when I am enchanted by a new species. Often I find out that for the good of the biodiversity in my garden I must remove the plant.

A couple of months later I was browsing the Queensland Plant Identification Facebook Page when my eye caught the same blue flower! As I read through the discussion in the comments I was delighted to discover that it was native! Even better, the flower was more vibrant than its exotic cousin which also grows on my dam wall! I set out to isolate the populations of each species and started propagating the native to replace the exotic.

I starting finding it all around my neighbourhood and adding the identifications to iNaturalist. That’s where I discovered the true extent of the classification controversy!

In 2018, the native species in my garden was classified as Commelina cyanea, only a year later the Queensland Herbarium changed the classification of the plant to Commelina diffusa. I have no idea why or how this happened despite scouring the internet for an explanation.

In 2020, a botanist from the United States of America, changed many of my identifications to Commelina cyanea. Now I am at a loss, do I “agree” therefore making my identifications return to “research grade” or do I hold my ground? In my area the identification is correct, but just an hour’s drive South and I enter the state of New South Wales where it becomes incorrect.

To add insult to injury, if I follow Australia’s national standards, my identification is incorrect. Should I go with state or national standards? Both apply.

I still don’t have the answer so everything is sitting in stasis while I still use Commelina diffusa aligning my classification with my closest internationally recognised herbarium.

Who knew classification could be so complicated? It’s science and science is absolute right? Haha, this always makes me think of the words in Hamlet.

There are more things in heaven and Earth, Horatio, 
Than are dreamt of in your philosophy (William Shakespeare)

So let me share my current understanding of the Climbing Dayflower and some of its local relatives…

Also known as:

• Commelina cyanea (in New South Wales, possibly a different species, scientific analysis ongoing)
• Scurvy Plant
• Native Wandering Jew
• Creeping Christian
• Spreading Dayflower

Growing conditions:

• Part shade/Shade
• Tolerant of most soils
• Groundcover (can become invasive in good conditions)
• Suitable for rockeries and hanging pots
• Perennial in tropics and subtropics, annual in warm temperate climates

I use this plant for erosion control as it’s happy on a steep slope and provides great ecosystem services, like habitat for invertebrates and soil coverage as well as food for kangaroos, bandicoots and bettongs. It propagates easily from the brittle stem segments. Indeed if you try to remove it, you need to get every part of this plant or they will likely reappear.

Apparently, Captain James Cook gave this plant to his sailors to eat in order to prevent scurvy. The new leaf tips are reported to taste like bitter lettuce or baby spinach and also contain niancin, riboflavin and calcium.

A Factsheet published as a part of the Australian Tropical Rainforest Plants Edition 7 (RFK7) lists the following uses:

• Juice being used to cure wounds, for inflamed eyes, as part of an external remedy for bone fracture and as a digestive aid (Smith 1979).
• Women rub their hair with it in the Torres Strait area (Lawrie s.n.)
• Within China it is used as a medicinal herb with febrifugal and diuretic properties. A dye is also obtained from the juice of the petals for use in painting.

There are around 230 species in the Commelina genus and seven of them are native to Australia.

It’s distantly related to the other weed known as Wandering Jew, but it’s picked up the name due to their similar appearance. Thankfully, the blue flowers make it easily distinguishable from the white-flowered, toxic, invasive pest. It’s found in moist forests along the Eastern coast of Australia, Lord Howe Island and Norfolk Island.

Hairy Wandering Jew or Hairy Creeping Christian is Commelina benghalensis, which is, according to the Queensland Land for Wildlife, like the natives on steroids. It is an effective invader and will smother other plants, as it is a quick-growing and vigorous groundcover. It has naturalized in Queensland and Northern New South Wales, as well as some parts of the Northern Territory.

The other species found in South-East Queensland is Commelina lanceolata and it’s sometimes called Wandering Sailor and is easily confused when young with another Wandering Jew. It has much smaller leaves that are thin and pointed, hence the scientific name (lanceolata = lance-like).

All of these plants will regrow, in the right conditions, from any stem segment and if you try to remove them by hand they break apart and leave segments in the soil. They root from every nodule that touches the soil. This is not necessarily a problem with the slower-growing and less hardy natives, but the invasive Commelina has a tendency to survive dry periods and doesn’t die off as much in the cooler seasons.

On my dam wall and in one of my gardens the invasive exotic form has become quite a problem, so I have been pulling it out. It resprouts in my weed pile so I have to either bag and bin it or burn it. This is a shame because I like to reuse all the nutrients in my garden.

The natives can also smother plants but only if the conditions are “just right”.

So, why the fuss? Because the native species are awesome.

• They’re a food source for lots of native marsupials like bandicoots, bettongs and kangaroos.
• They attract native bees and provide habitat for other invertebrates.
• They quickly cover and protect bare soil in disturbed areas as well as preventing soil erosion.
• They are long-lived and edible.

Having said all that, what I love most about this plant are the deep blue flowers!

I have both the Commelina benghalensis and the Commelina diffusa on my block and I think I’ve found some Commelina lanceolata down the road. I am not confident about being able to distinguish the two native species yet but that’s not as important as being able to distinguish between the native and the invasive.

The invasive species has brown or white hairs, but the native species can also have white hairs, so brown hairs indicate the invasive. If your plant has white hairs you’ll have to find a flower to work out whether it’s the invasive pest or the native groundcover.

The native species have three petals of equal size, but the invasive pest has two larger petals and a small petal. Easy! Just make sure you check every day for flowers. They’re not called dayflowers for nothing and it took three days waiting for sections to flower for me to work out which patches were the friends and which were the foes.

What do you think? Should I follow the Queensland Herbarium or the rest of Australia?

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This story was originally published on Medium.com by the same author.

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