Note #12 Pelargonium polycephalum in habitat

Fig. 1 (Header image): Although the petals of P. polycephalum are mostly white, clones with striking red stripes on all five petals were found at Karrachab Poort in August 2019.

 

Like many other taxa of the section Otidia, Pelargonium polycephalum is not particularly well understood. Many plants circulate collections under this name but usually turn out to be something else and not the “multi-headed pelargonium”. On the day I saw my first plant, I was so fixated on finding Pelargonium pachypodium that I wasn’t really looking at large shrubs at all.

Yet as is often the case, the plants I was looking for did not share my plans and remained hidden (I was really keen to find LAV25716 at Karrachab Poort – not seen again after Lavranos). So, although P. polycephalum easily grows to 1 m tall, and was plentiful right next to the road, I was as stunned when I saw the first plant as if it were a super-small miniature (Fig. 1).

The multi-headed pelargonium

P. polycephalum is not rare in nature and grows at higher altitudes in Namaqualand, mostly in the Northern Cape. Its distribution stretches from the central Richtersveld to the Kamiesberge at altitudes up to 1200 m. Becker and Albers [1] grouped P. polycephalum with P. adriaanii and P. carnosum into the so called P. carnosum complex of species due to similarities in the flower structure. A closer relationship with P. carnosum was clear already very early: Harvey namely described the taxon as P. ferulaceum var. polycephalum in 1860 and Knuth only later elevated it to the species rank. According to DNA studies, it appears most closely related to P. adriaanii, however [2].

It can grow into sizeable shrubs with 5-cm thick upright stems adorned with dry remains of petioles, not unlike P. paniculatum, with which it can be easily confused when not in leaf. However, both P. carnosum and P. parviflorum complexes can be easily separated from the rest of the section on the basis of the hypanthium:pedicel length ratio. This is 2-10 for taxa of the above complexes, and 0.1-1 for the rest of the section. The only species that deviates from this “rule” is P. adriaanii, which is easily recognisable otherwise. Petals of species in the P. parviflorum complex are all mostly the length of sepals or shorter, and mostly yellowish, so the two groups of taxa can be easily distinguished.

Fig. 2: The stems of P. polycephalum can be up to 5 cm thick and are covered with short remains of dry petioles. This is reminiscent of P. paniculatum, however, this can only be found closer to river Orange and is particularly widespread just north of the river in southern Namibia.

P. polycephalum has succulent leaves covered with microscopic hairs, a character it shares with P. carnosum ssp. ferulaceum. However, their laminas are different: the leaves of P. polycephalum are irregularly pinnatilobate. Its best known character is the compact nature of pseudoumbels, which is due to particularly short pedicels and hypanthia, in combination with a significant number of flowers per flower-head.

Fig. 3: Pelargonium polycephalum inflorescence structure. X denotes a pseudoumbel that finished blooming. After [2].

The most important character, however, is the structure of the inflorescence: in all other species of the complex, the inflorescence develops vertically, with the youngest flowers developing on the top of the inflorescence when the oldest might already be fruiting. In P. polycephalum, the inflorescence (Fig. 1) develops horizontally away from its vertical axis such that almost the entire inflorescence is in flower at the same time. Since an inflorescence is branched 4-5 times, and 10-15 flower heads develop at each node, each with ~10 flowers, a flower spike can easily carry 500 flowers at the same time!

Its period of flowering is relatively short and extends from August to September. This is much earlier than the rest of the section Otidia taxa that share the same distribution, and thus seems to represent a stable barrier to cross-pollination. The other related and early flowering species, P. adriaanii, is geographically well separated.

Fig. 4: An aged inflorescence showing the typical structure as per Fig. 3, with all the flowers open almost at the same time.

Karrachab Poort

I’d not be truthful if I said that this lazy pass between Eksteenfontein and Lekkersing in the central Richtersveld is easy to get to. Yes, there is a road. Yes, it doesn’t look too far away from either settlement. But anyone trying to navigate even these relatively gentle slopes (let alone the more “serious” passes in the National Park nearby) will surely agree that the roads across the entire Richtersveld have recently deteriorated so much that even this pass requires a good measure of patience.

And yet, it is so worth visiting! This is a typical succulent karoo veld type, one of those habitats with randomly scattered weathered stones where succulents are found in each and every crack, and where pelargoniums are amongst the taller shrubs providing shelter for other plants, as if this was all one large botanical garden. There are plenty of pelargoniums here, P. crithmifolium mostly occupying open locations along with P. dasyphyllum, P. spinosum, P. echinatum, as well as Monsonia ciliata and M. l’heritieri. All of these are among the larger shrubs, with P. karooicum and P. tenuicaule hiding within them. On the other hand, P. polycephalum grows in slightly more level and sheltered conditions at the foothills along the road.

One normally leaves such places of extraordinary beauty with a firm conviction to return as soon as possible: there is never enough time to explore and enjoy the rough beauty of the Richtersveld. But the short August days impose their own restrictions on a daily itinerary and with a 2.5-h drive back to our accommodation ahead of us, the time to return came all too quickly.

By Matija Strlic, Ljubljana, Slovenia.

Literature

  1. Becker, M., Albers, F. (2005): Pelargonium adriaanii (Geraniaceae), a new species from the Northern Cape Province, South Africa. Botanische Jahrbücher für Pflanzengeographie und Systematik 126, 153-161.
  2. Becker, M. (2006): Revision der Pelargonium-Sektion Otidia (Geraniaceae) aus dem Winterregengebiet des Südlichen Afrikas und Bewertung evolutiver Strategien der Pelargonien aus der Capensis, PhD Thesis, Westfällische Wilhelms-Universität Münster.

Citation and Copyright

© The Author. This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
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ISSN 2464-014X.

Cite as: M. Strlic: Pelargonium polycephalum in habitat, Pelargonium Notes, #12 (2020).

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