Oxalis on waste ground in Condeixa, January 2012
January can be quite a pleasant month in central Portugal. It is not dull and rainy as the preceding months have been, nor is it as cold as February. There are many bright clear days. As for the countryside, it is unremarkable. The deciduous trees have lost (or are still losing) their leaves, but there are so many evergreens that the forests don’t look bare. Because it has been raining, grasses and weeds grow, so the ground is not bare either. But there is little colour, and very few plants are flowering. In our garden, we begin to see the birds coming to the bird table. The sparrows are always around, but at this season the robins, chaffinches and greenfinches become visible.
Oxalis pes-caprae is a herbaceous weed, forming conspicuous patches of bright green leaves, above which stand long-stalked heads of striking yellow flowers. Flowering in winter, it provides colour which is otherwise in short supply. The flowers and leaves fold down at night, and then spread out again in the day. It is most often seen along roadsides and on waste ground, and sometimes in grassland or olive orchards. Though it sets seed elsewhere in the world, in Europe it propagates itself only vegetatively, by small bulbs formed underground. After flowering, the above-ground plant disappears altogether for the hotter, drier part of the year. The bulbs are easily spread along roads and paths.
This plant is very characteristic of mild moist areas in Portugal not too far from the ocean. But it is not native to Portugal. It comes from South Africa, and has been introduced into most of the warmer parts of the world. Indeed, it is generally considered to be highly invasive, and also potentially harmful to livestock. In Portugal, however, it seems to be a relatively harmless weed, remaining confined to disturbed ground.
All above-ground parts of the plant contain oxalic acid (named after the plant genus Oxalis), giving a sour acid taste as in docks, sorrels and rhubarb. The only native Oxalis in Europe (Oxalis acetosella) is known as wood-sorrel, but there is no general English name for Oxalis species. O. pes-caprae is known as Bermuda buttercup, presumably because it was introduced there very early, but Americans call it sourgrass. Its Latin name refers to goat's foot because each of the leaflets of the clover-like leaves is divided into two oval lobes whose outline resembles a goat's foot print. In Portuguese, as in some other languages, it is referred to as a trefoil, "trevo", because of the clover-like leaves.
Gorse (Ulex spp.) is all over the place in Portugal, and lives up to its reputation of having some plants in flower at all times of year. The common gorse (Ulex europaeus) does occur around here, and mainly flowers later than January. What we see now is a local endemic, Ulex jussiaei, with quite large flowers mostly in long spikes and a low growing habit. It is common in the forests and mainly seen along roadsides. There are in fact some eight Ulex spp. which are endemic to Portugal or the western part of the Iberian peninsula. They are rather similar and difficult to distinguish without close examination, but their flowering periods are slightly different. The Portuguese name for this gorse is tojo-durázio, stiff gorse.