The beautiful blue flowers of Commelina (Commelina cyanea), also known as Scurvy Weed, are appearing around the region in large numbers at the moment. There isn't that much blue in the plant world, relative to other colours, so it's always pleasant to see a plant with such delightful bright blue flowers.
And Commelina is a very common plant, growing in a wide range of conditions in local woodland and forests, and often appearing unbidden in gardens. It is a weak trailing perennial herb that grows low to the ground, with pointed lance-shaped leaves. It may easily go unnoticed until the flowers appear.
Commelina gets its other common name, Scurvy Weed, from the fact that early European colonists ate its leaves to prevent or alleviate scurvy. (This is widely reported but I have not found original documentation. For example, the Little Eco Footprints blog run by Dr Tricia Walker mentions it, as well as a few other Commelina facts.)
The context I encounter Commelina most often is people asking about how to tell it from the dreaded weed Trad (Tradescantia fluminensis), which is in the same family – yes, the Commelinaceae family! They have similar form and habits, and somewhat similar leaves. The easiest way is when the plant is in flower; Trad's flowers are white, and so are impossible to confuse with Commelina's beautiful blue flowers.
But a plant may not be in flower when you see it, and that adds complexity! The leaves of Trad are often broad-lanceloate, whereas the Commelina leaves are lanceolate or even narrow-lanceolate. Trad leaves often have a purple tinge on the underside, and they're often but not always darker than those of Commelina.
Finally, Trad as a plant is more brittle than Commelina, and will easily break apart into many separate lengths and pieces (this is part of its super power as a weed, as each part can grow into a separate plant).
But wait, there's more! There are more local plants that look a bit like Commelina, and a bit like Trad, and to add insult to injury (or rather to add confoundment to confusion), these ones have white flowers. Twin-flowered Aneilema (Aneilema biflorum) and Aneilema (Aneilema acuminatum) both occur in local forests, Twin-flowered Aneilema preferring damp situations and a bit more sun. Both Aneilemas can be confused with Trad, though both have narrower leaves and the inflorescences (flower heads), although white, are both a bit different from Trad's.
It can take quite a while to 'get your eye in' on these species. For more details and photos of Trad, this NSW Weedwise page is excellent.
