Creeping wood-sorrel (Oxalis corniculata), in its anthocyanin form (producing red foliage — the species also comes in green). Sometimes cultivated as an edible, lemony green, its geographic origins are reported to be obscure. Although most sources suggest a Eurasian origin, the USDA lists it as native to the United States.
In Melbourne, O. corniculata is a reasonably frequent colonist of wall bases and pavements. This is another introduction of the 1864 Handasyde, McMillan catalogue for Melbourne.