Pelargonium tetragonum

And another entry written by Taisha:

Today’s photo of Pelargonium tetragonum was taken by Christopher Young (aka c.young@Flickr). Thank you, Christopher.

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 (illustration), 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.

Pelargonium tetragonum

6 responses to “Pelargonium tetragonum”

  1. Pygge Lord

    Beautiful photo!! I collect Pelargonium species and this is one of the really funny looking ones, with it’s weird fleshy square stems. I have mine hanging in a basket. Not sure how to keep it otherwise. It’s quite a fast grower and I highly recommend it as a potted plant, ornamental even without flowers. It’s a great family to collect due to the diversity and the xerophytes are my favourites. People just can’t believe it when you tell them it’s a ‘Geranium’ (we call them Pelargoniums in Swedish, so that is what I say). Then you walk over to next weird, totally different looking, plant and they ask what it is and it’s another Geranium – and so on. Not to forget the really big ones. Difficult to keep indoors during the winter, but well worth it, since they are great lookers oudoors in the summer. I have a cutting of P. hispidum and I can almost see it grow. Pelargoniums are great!!

  2. Lynn Cook

    Is seed, or plants, of Pelargonium tetragonum available in the USA?

  3. Edith

    Lack of knowledge question here. I thought a square stem implied mint family. How far off the mark (wrong) am I?
    Pretty flower!

  4. Anna

    I’m with Pygge on this one. Geraniums are great to collect. I like all the fragrant varieties too. I hail from Sweden and have noticed that the interest in Geraniums is much greater in Sweden than in North America. I wonder why? Thank you for the write-up Taisha!

  5. entire leaves

    Lynn I got seed from either Silverhill Seeds in South Africa or Chiltern in the UK (can’t remember which one). Pelargonium and Geranium seeds are pretty expensive though because it is difficult to collect.
    This one is easy to grow once it germinates. Very cool plant.

  6. misterF

    @Lynn Cook – I just purchased a potted Pelargonium tetragonum this past weekend at a Succulent Society sale in San Diego, CA.

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