Pelargonium tetragonum, or the square-stemmed pelargonium, is a shrubby member of the Geraniaceae found in an inland strip of dry habitats paralleling the southern coast of South Africa. Its preference for dry, rocky and well-draining soils helps classify it as a xerophyte.
This species is characterized by its succulent square stems (tetra being the Greek prefix for “four”). Pelargonium tetragonum carries a pair of flowers upon its jointed stems; each flower has four petals with the upper petals larger than the lower. Petals are cream to pink in color with red streaks. These contrasting streaks serve as a nectar guide for its pollinators, who require a long tongue or beak to reach the nectar at the base of the extended floral tube (shown in the photograph). The evergreen leaves of this plant are hairy, fleshy, lobed, and dark green in color, with a dark central blotch (description inspired by Fogg’s 1964 work, Geraniums and Pelargoniums).
Among the two hundred or so members of Pelargonium, there is exceptional diversity in colour, size and morphology of the plants, flowers and leaves. Differences in flowers correlate with a difference in pollination syndromes. Species are variously pollinated by bees, long-proboscid hovering flies, butterflies, hawkmoths, and presumably by a small percentage by birds (see: Struck, M. 1996. Floral divergence and convergence in the genus Pelargonium (Geraniaceae) in Southern Africa: Ecological and evolutionary considerations. Plant Systematics and Evolution. 208:71-97.). From Struck’s paper, Pelargonium tetragonum is putatively pollinated by long-proboscid flies, as partly suggested by the length of the floral tube and several observations during the study.