Texan dichondra a welcome mirage in summer

Talking Plants is resuming normal transmission! I'm back in the seat at Royal Botanic Gardens Victoria and back on the look out for flowers, gardens and other botanical treats to serve up each week.

Today, we'll ease back into things with a plant from the desert regions of southern USA and Mexico, reaching Europe (at least in dried, pressed form) in the early nineteenth century. I see it every day, in my backyard, but until I sat down next to it in a low chair, in late February, I hadn't noticed the flowers.

The silvery leaves of our Dichondra argentea 'Silver Falls' tumble from an old colander (competing with the rather rampant Ivy-leaf Toadflax, Cymbalaria muralis), and they look their best when our climate is a little more like tropical America, in our Melbourne summer.

The silver sheen is due to a covering of downy hairs which also covers the flowers, which along with their tiny dimensions (less than 5 mm across) makes them, as the Missouri Botanical Garden Plant Finder puts it, 'insignificant'. They are 'not showy', as the same site explains. All true but they are rather cute if you can get close enough.

In the following picture, you can just see the two capsules that follow the flower, providing the genus name 'dichondra', which means two grains (the grains being the ovaries or resulting capsules in fruit). 'Argentea' means silvery and I'm presuming I should use the cultivar name 'Silver Falls' for our specimen, a variant happy to dangle from a basket, or colander. 

The species Dichondra argentea was collected and named by the famous German ecologist, Alexander Humboldt and French botanist, Aimé Bonpland, after their journey through Latin America between 1799 and 1804 (the German botanist Carl Wildenow formally described the species, from their information, in 1809).
It was a good find. The genus Dichondra is a small one, currently thought to have only 15 species, most of which have creeping stems that can send down roots at the point where the kidney-shaped leaves arise. The distinctions between species can be fine but presumably the silvery sheen made this one stand out from the (small) crowd. 

Dichondra species are mostly found in the tropics but here in Victoria we have Dichondra repens, Kidney Weed, a species found naturally in I think every State in Australia (including the even more temperate Tasmania). There is possibly a second species in the north of Victoria and in other States, called 'sp. 1' in VicFlora and 'sp. A' in the Flora of New South Wales, plus the sometimes weedy Dichondra micrantha from North America and east Asia.

Interestingly, the rest of the genus is found in the Americas: North America has eight species, South America about seven. It's an odd world distribution but that's the way it is. Dichondra is in the family Convolvulaceae, with Blue Morning Glory (Ipomoea indica) and Silverbush (Convolvulus cneorum), as well as the sweet potato (Ipomoea batatas). The family as a whole is spread all over the world, apart from the colder extremities in both Hemispheres.

Dichondra argentea is a good tough plant for our impending climate in Melbourne but I do note that it didn't survive a trial on an un-irrigated roof garden in Texas. It also gets a little shy during winter but should pull through.