Soursob

Soursob is a perennial herb that grows from an underground bulb, producing clusters of small bulbils around the parent bulb each season. The leaves are trifoliate, resembling clover, with each leaflet heart-shaped to inverted-triangular in outline and mid-green, often marked with small purplish spots on the upper surface. Leaves and flower stalks arise directly from the bulb at ground level on long stalks, giving the plant a low, rosette-like habit typically 10 to 30 cm tall. The flowers are bright yellow, five-petalled and funnel-shaped, borne in clusters of several blooms atop slender stems held above the foliage.

The plant reproduces almost entirely by vegetative means in Australia, rarely setting viable seed. A single parent bulb can produce numerous small bulbils each year, and these are readily spread by cultivation, soil movement, mowing equipment and floodwater. The main bulb sits several centimetres below the surface, with fine roots and a cluster of bulbils forming around it, making the plant difficult to remove completely by hand pulling or shallow cultivation.

Soursob is widespread across southern Australia, particularly in Western Australia, South Australia, Victoria, New South Wales and Tasmania. It grows actively through the cooler, wetter months of autumn, winter and spring, then dies back and becomes dormant over summer as the foliage senesces and the bulb and bulbils persist in the soil.

It is a significant weed of pastures, orchards, vineyards, turf, garden beds and disturbed ground, where it competes with desirable plants for light, moisture and nutrients during its active growing season. Because the bulbs and bulbils survive dormancy and resist mechanical control, effective management usually relies on repeated foliar herbicide applications timed during active growth, combined with measures to prevent bulbil spread through soil, mulch and machinery.