Commelinas are a group of groundcover herbs commonly referred to as dayflowers due to the fact that the delicate flowers only last a day or so.
In south-east Queensland (SEQ) there are three species of Commelina that all have a similar looking small, but brilliant, blue, three-petalled flower. There are two native Commelinas, Blue Commelina (Commelina diffusa) and the Queensland Wandering Sailor (Commelina lanceolata). Then there is the introduced weed, Hairy Commelina (Commelina benghalensis). There are a couple features that will help you tell the natives from the weed.
Many Land for Wildlife folk will be familiar with Blue Commelina as it is extremely common and grows prolifically as a spreading groundcover anywhere with moist shady conditions. In the right conditions it grows so quickly and densely that it is considered by some as a nuisance weed of manicured garden beds and veggie patches and is commonly mistaken for a weed in the bush. It is a valuable groundcover in the bush because it can seal up an area of bare soil after weed control or a disturbance to help inhibit weed regrowth. It quickly provides habitat for invertebrates on the forest floor. It has weak stems with soft fleshy leaves up to 7cm x 15mm in size. The stems lying along the ground will eagerly take root as it spreads, but tend to die back during the dry season.
Queensland Wandering Sailor is Blue Commelina’s daintier cousin. It has a similar growth habit but is far less vigorous, far less common and is restricted to rocky and well drained sites in eucalypt forests. Living up to its botanical name Commelina lanceolata has longer and more ‘lance-like’ leaves than Blue Commelina, growing up to 12cm x 15mm in size.
Hairy Commelina hails from Africa and Asia and is a notable environmental weed smothering the ground layer in waterways, disturbed bushlands and crops in Australia. It grows like Blue Commelina on steroids. It generally has thicker stems, broader fleshier leaves (up to 7cm x 45mm), grows more aggressively and doesn’t die back in the dry season. The common name, ‘Hairy’, is a little misleading as all three Commelina species can have fine white hairy stems and leaves. The hairs used to identify this weed species are the dark reddish-brown hairs on the leaf sheath, unfortunately they are not always dark and can be white like the two native species.
The sure-fire way to tell the natives apart from the weed is to have a close squiz at the flowers. Blue Commelina and Queensland Wandering Sailor have three petals of equal size. On Hairy Commelina the upper two petals of the flower are the same size, with the lower petal being much less prominent.
Next time you see beautiful little blue flowers on the forest floor take the time to make sure you are enjoying a native Commelina and not the invasive weed. If you have the weed Hairy Commelina, small infestations can be controlled manually with the knowledge that any stem fragment left lying around can take root. Large infestations may need specialist herbicide advice so please talk to your local Land for Wildlife Officer or refer to the recommendations in the SEQ Ecological Restoration Framework. Taking action early will help make sure that this invasive dayflower has seen its day.
Conservation Partnerships Officer
City of Gold Coast
References & Further Reading
Global Invasive Species Database.
Leiper G, Cox D, Glazebrook J & Rathie K (2017) Mangroves to Mountains. 2nd Ed. Logan River Branch, Native Plants Qld.
LucidMobile (2019) Weeds of South East QLD and Northern NSW. App free version.
SEQ Catchments (2012) South East Queensland Ecological Restoration Framework: Manual.