Pelargonium tetragonum L'Hér.
Common names: square-stemmed pelargonium
With its square, jointed, succulent stems, this fascinating pelargonium could easily mislead the casual observer into mistaking it for a member of the Euphorbia family.
Pelargonium tetragonum is a plant adapted to grow in dry habitats (xerophyte). It branches from the base and if supported by other vegetation, will reach a height of 2 m. The plant tends to sprawl, but can be successfully grown as a pot specimen. Pelargonium tetragonum is distinguished by its almost leafless, three- to four-angled, jointed and succulent stems. When present, the leaves are fleshy, palm-shaped and sometimes have red zonal markings.
The very attractive cream to pink flowers occur in pairs on the flower stem. Each flower has four petals, with the upper two significantly larger than the lower pair. The large upper petals are streaked with red. The flowering time is from September to December.
Distribution and habitat
Pelargonium tetragonum is only found in dry habitats within a strip parallel to, but inland from the South African south coast, extending from Worcester to Grahamstown. This distribution thus extends from the winter rainfall region in the west to the summer rainfall area in the east.
Derivation of name and historical aspects
The specific name, tetragonum, is derived from the Greek words tetra (four) and gonia- (angled) and refers to the characteristic square-shaped stem. The genus Pelargonium consists of over 200 species, of which some 80% occur in southern Africa. Of these, approximately 80% are found in the southwestern Cape. The misnomer 'geranium' refers to the hybrids derived from south African pelargoniums, and now extensively grown throughout the world.
Unlike many other pelargoniums, this species does not produce aromatic oils. However, the attractive flower and unusual growth form make this a worthwhile addition to any pelargonium collection.
Growing Pelargonium tetragonum
P. tetragonum favours arid, rocky habitats, and will rot if over-watered. It is therefore best suited to well-drained and dry situations in the garden, and thus an excellent choice for a water-wise garden. It is easily propagated from stem cuttings using river sand as the rooting medium. Dipping the cuttings in a rooting hormone will increase the chances of success. Keep the river sand damp during the rooting process, but do not over-water. (Liesl van der Walt, Kirstenbosch pers. comm.)
Dr. Andy Moore
Kirstenbosch National Botanical Garden
Plant Type: Shrub
SA Distribution: Eastern Cape, Western Cape
Soil type: Sandy
Flowering season: Spring, Early Summer
Flower colour: Pink
Aspect: Full Sun
Gardening skill: Average