Pelargonium cordifolium (Heart leaf pelargonium)
I just adore the flowers on this species pellie, and its preference for dappled shade makes it super for planting under trees or beneath large shrubs. It will flower throughout the warm weather with a distinct flush in spring and again in autumn if the soil isn't too dry. It does prefer a lightly moist soil, although it can tolerate drier soils, it will enter a stasis until conditions more amenable to growth and flowering return. While its reputed to grow over a metre high in its native habitat, it hasn't got larger than 50cm high in my drier garden. I give it a light prune after flowering to encourage denser growth (gets a little leggy without this), and aside from this maintenance, it's an easy and pretty species pelargonium for dappled shade.