The various species of yellow flowered Oxalis are extremely difficult to ID to species, even in the hand. Apart from counting the number of flowers in the flower clusters, measuring petal length, looking at the shape of the paired leaf lobes and the distance between the apex of the lobes!!, hairiness and direction of the hairs on the leaf stalks, the presence, size, and shape of leafy outgrowths at the bases of the leaf stalks, and size, shape, and type of hairs on the fruiting bodies, you have to look at the roots, whether it produces underground bulbils or not, and whether the bulbils are close to the oarent at the ends of above-ground runners.