Travelling from Lüderitz in Southern Namibia to Alexander Bay in the coastal Richtersveld of the Northern Cape has not been easy for most of the past century due to diamond mining operations. While the region is opening up to tourism, news of interesting Geraniaceae reach us occasionally, however, the distribution of two otidias still remains obscure: P. ceratophyllum and P. albersii. In fact, until the publication of P. albersii as late as 2008 [1] it wasn’t clear there were two species at all.

In his trademark style, Clifton reviewed the history of these two taxa [2], with copious commentary and interesting detail. While meticulously researched, his insightful writing is mainly based on observations of herbarium specimens and cultivated plants – this was before citizen-science based platforms like iNaturalist emerged as major sources of photographic evidence directly from the habitat. I have lamented elsewhere the fact that pot-grown otidias often present themselves in shapes and forms that are entirely unrecognisable to anyone who has grown accustomed to seeing them in the habitat [3]. Their shapeshifting habit has led to many a taxonomical error in the not-so-distant past of armchair botanical taxonomy, particularly in this section of Pelargonium, often dismissed by growers as “difficult to ID”.

We do not want to dwell on this issue at all and simply need to accept that taxonomy always deals with data it has at hand. It is clear that habitat inaccessibility must lead to patchy data, which even Becker was not able to overcome entirely, having devoted his PhD entirely to section Otidia [4]. Becker reviewed hundreds of herbarium specimens, which is in itself a herculean achievement. It is no wonder that errors are made, given the poor state of some Otidia herbarium specimens (Fig. 1).

However, there are other issues that have earned this section its “difficult” adjective. 300 years ago, when many names for plants in this section emerged, botany was an altogether different science. The standards for naming plants that we have today did not exist then, and there are a number of dispensations that contemporary botany had to allow in order to deal with past taxonomical work. These were the times when new species were often described by those who may only have seen a pressed plant or a pot-grown plant, often in a country far away from Southern Africa. Plant descriptions were often comprised of a few sentences, if that, and locations were often given as broad-brush strokes, often deeply historical and in need of modern interpretation.

Fig. 1: A herbarium specimen of P. laxum ssp. laxum in the Schonland Herbarium. Many historical herbarium records of taxa in the section Otidia do not provide enough clues to enable identification: the above specimen was of a cultivated plant, meaning that the stem was probably etiolated. The flowers are now missing, as are the roots, which are also important for the identification of otidias. The specimen was identified as P. laxum on the basis of leaf pinnation and the collection location.

The (i) lack of clear habitat description, (ii) lack of plant descriptions focusing on relevant characters, (iii) lack of herbarium specimens and (iv) the descriptions and illustrations based on cultivated plants make deciphering the history and authorship of valid names in this section particularly difficult. To my mind, this is really what makes the section “difficult”.

P. ceratophyllum L’Her.

In 1789, L’Heritier describes P. ceratophyllum [5] and Clifton [2] helpfully provides the English translation from Latin as: “umbels multi-flowered, leaves pinnate with distant leaflets, fleshy, cylindrical, the lobes channelled and with 3 blunt teeth at tips.” In a letter to Aiton [6], L’Heritier provides “Cafraria” as the habitat of P. ceratophyllum. Historical maps from this time (Fig. 2) unfortunately do not help us to decipher where exactly the specimen was collected, based on L’Heritier’s “location”.

A few years later, the illustration of the plant then grown at Kew emerged [7], showing approx. 1-cm thick stems (judging on the basis of the size of the flowers, as depicted (Fig. 3). P. ceratophyllum rarely has such thin stems in habitat, so this feature must be a consequence of etiolation in sub-optimal growing conditions, which can be confirmed based on the long internodes, evident in the illustration.

The problem with this illustration and the description is that it is impossible to say with certainty whether the depicted plant is P. ceratophyllum or the much later introduced P. albersii. Both have thin stems in cultivation, (bi-)pinnate leaves with cylindrical pinnae, and short peduncles carrying few-flowered pseudo-umbels. We encountered exactly the same problem with the typification of P. laxum [8].

L’Heritier’s plant was cultivated from a cutting, brought to Europe by A. Hove in 1786. Had he mentioned whether the plant had tubers, we would have known for certain that it was P. albersii, as the absence of tubers is what consistently separates P. ceratophyllum from P. albersii, even in cultivation.

Fig. 2: Map of “Cafreria” in John Lodge’s “New Map of Africa from the Best Authorities” produced in the 1780s (exact date not known).

However, the fact is, that we do not actually know this. Curiously, Becker [1] claims “Corresponding to L’Heritier’s iconotype, the species from Lüderitz is obviously the typical P. ceratophyllum”, although he provides no clue on the basis of which such certainty is claimed. The vertically growing stems that develop in cultivation (Fig. 3) are potentially the character, on which basis we can assume that the illustrated plant is P. ceratophyllum, as the stems of P. albersii, even in cultivation, as usually much shorter and recurved, often horizontal.

Fig. 3: Redoute’s illustration of P. ceratophyllum for Geraniologia [6] and a cultivated plant in the author’s collection.

Until Becker separated P. albersii in 2008 [1], the literature dealt with a mix of ceratophyllum and albersii characters, on the basis of which it is often impossible to tell, which of the two species is being written about. However, we will point at a few examples and address this confusion later. Becker had access to a much more comprehensive database, and correctly took a combination of characters into account, including the roots, when describing a species. Although an occasional error creeps in, his work can be considered as a sea-change.

Based on Becker’s work, we now understand that the population of otidias growing in the immediate vicinity of Lüderitz, in an area no more than 10 km x 10 km, is P. ceratophyllum (Fig. 4). The herbarium specimens that he has seen indicate the possible presence of P. ceratophyllum further down the coast, however, there are no recent observations of it close to Alexander Bay, while the coast between the two towns, as already discussed, is rarely visited. It could be assumed, therefore, that the distribution of P. ceratophyllum is limited to a very small area around Lüderitz. Hopefully, future research will dispute this statement, but for the time being, it appears to be valid.

Fig. 4: The distribution of P. ceratophyllum and P. albersii, according to Becker [4]. (“oder” in German means “or” in English).

Fig. 5: P. ceratophyllum growing in an exposed location close to the ocean.

Fig. 6: a large shrub of P. ceratophyllum growing in a sheltered location.

The landscape around Lüderitz is incredibly inhospitable and frequently wind-swept by strong Atlantic winds. In exposed areas this results in plants with low, arrested growth (Fig. 5). The branches are typically a couple of centimetres thick and plants do not develop underground tubers. In sheltered locations, P. ceratophyllum can grow into huge, thick shrubs – the plant in Fig. 6 was about 50 cm in diameter and frequently branched – this was photographed in the town suburbs, growing in a depressed location on a cliff.

P. albersii M. Becker

The population of otidias inland from Alexander Bay, around Beauvallon, comprises either the unmistakeable P. klinghardtense, which usually grows close to rocky outcrops, or miniature plants, usually no taller than 10 cm, sparsely branched, and always with underground tubers. The stems are usually thinner than 1 cm and are often entirely covered by sand, such that only the leaves and flowers are visible. This is P. albersii, the distribution of which stretches at least half-way northwards towards Lüderitz (Fig. 4). It has not been found along the coast south of Alexander Bay, although van der Walt and Vorster [9] refer to a possible observation at Spektakel Pass, which would be hugely surprising, as P. albersii is a coastal species, growing in deep sand.

In both species, the thin peduncles are red and short, which easily separates the two species from the rest of the section (with the exception of P. crithmifolium, which also has red peduncles). However, in P. albersii, the inflorescence is branched more frequently and apparently bears more, up to 8 consecutive pseudo-umbels. However, this can be observed in P. ceratophyllum as well, so cannot be a characteristic feature.

Fig. 7: Left: P. albersii in habitat inland from Alexander Bay. Right: in cultivation.

The petals in both species are similarly shaped, recurved, often much longer than the tepals, with wine-red markings. P. ceratophyllum has white sepals, while those of P. albersii can be slightly yellowish (Fig. 8). The petal size, shape and colour are thus not distinctive. However, the flowers of P. albersii have a distinctive citrussy smell, as opposed to P. ceratophyllum, which are not scented.

Fig. 8: The flowers and the thin, wiry peduncles of P. albersii. The branched inflorescence remains of inconspicuous height.

Becker also claims that the leaves of P. albersii are covered in short glandular hairs, whereas those of P. ceratophyllum are in addition covered in thick, recurved hairs. In reality, and as already noticed by Clifton [2], the leaves of both species carry the same indumentum.

The shapes of the laminas are very similar. The (bi-)pinnatifid leaves have cylindrical pinnae and the petiole, as well as the leaf rachis and the pinnae have a central groove. The similarities and differences are summarised in Table 1.

 

Tab. 1: Characters of P. ceratophyllum and P. albersii.

	P. ceratophyllum	P. albersii
Roots	Tubers absent	Tubers present
Stems	(in cultivation: 10-)20-30 mm, with persistent remains of petioles. Plants typically up to 20(-30) cm tall	(in cultivation: 3-)5-10 mm, with persistent remains of petioles. Plants typically up to 10(-20) cm tall.
Stipules	Triangular
Leaves	(Bi-)pinnatisect, succulent. Pinnae cylindrical, terminal pinnae often incised at the end. Petiole, rachis and pinnae with a central groove. Lamina (10-)20-40(-60) x 10-20(-40) mm, petiole up to 40 mm. Indumentum: short glandular hairs and recurved non-glandular trichomes
Inflorescence	Borne terminally on branches, peduncle and central rachis red, thin (<2 mm), sparsely branched with up to 8 pseudo-umbels with up to 4 flowers
Pedicel and hypanthium	Similar in length, 4-15 mm
Petals	5, linear, ovate, auricled, white in P. ceratophyllum or white to yellowish in P. albersii. Ears hairy. As long as, but typically longer than sepals. Posterior petals with feather-like wine-red markings.
Scent	Absent	Citrussy smell

 

A herbarium specimen (BM649394) of P. albersii was named by Dinter in 1929, however, this was not accompanied by a description. Therefore, his name P. hospitans needs to be considered as synonymous with P. albersii.

 Period of Uncertainty

Most of the sources before, and some literature after 2008, confused the two taxa and conflated them into one, perhaps occasionally with other taxa that could potentially be seen as similar. We will not review all of this literature here, instead, we will point at some sources that are more frequently consulted.

Fig. 9: Curtis’s illustration of (probably) P. albersii, Bot. Mag. t. 315 (1795).

Readers may know the illustration of P. ceratophyllum in Curtis’s Botanical Magazine of 1795, plate 315 (Fig. 9), which exhibits some artistic liberties, such as a branched pedicel and the apparently two inflorescences emerging from the tip of the same stem. The stems also appear unnaturally smooth – this is a character associated with neither P. ceratophyllum nor P. albersii. It is difficult to know what taxon the illustration depicts but given that the stems are very thin (1/2 the width of a flower, so ca. 5 mm), one could assume that this illustration depicts P. albersii. This could only mean two things (given that Kew was the source of the illustrated plant): either Hove collected both P. ceratophyllum and P. albersii and these were illustrated for L’Héritier and Curtis, respectively, or (if the same actual plant) the illustrators took a lot of artistic licence. We may never know, but given that Becker has used L’Héritier’s illustration to identify P. ceratophyllum and introduced P. albersii, we should probably stick to this view, for the sake of nomenclature stability.

In 1990, Vorster [10] readily recognised P. ceratophyllum in Redoute’s illustration (Fig. 3), similarly to Becker [4]. However, in contrast to Becker, it is clear from Vorster’s description that he actually meant P. albersii (which had not been described yet, of course): “the excellent accompanying figure leaves no doubt about the identity of the species. It comprises dwarf plants with short and thin aerial branches…” He also refers to yellowish petals, which are characteristic of P. albersii. This is perhaps not surprising, given that in Pelargoniums of Southern Africa, vol. 2 [7], Ward-Hilhorst’s illustration depicts P. albersii. However, it is also clear that van der Walt and Vorster conflated the two taxa, as they were aware of populations at both extremes of distribution: “In the vicinity of Lüderitz it occurs on low rock outcrops, often wedged in cracks where the plants attain their maximum size.” Similarly, Clifton, despite his extremely useful insight, didn’t seem to have been able to confidently identify the taxa, as he identified P. ceratophyllum as P. dasycaule, cf. p. 22 [2].

Conclusion

Despite the confusion in the literature, mostly prior to 2008, there is now good clarity in relation to the characters of two closely related species: P. ceratophyllum and P. albersii. They can easily be separated on the basis of stem thickness, presence of tubers and flower scent. While the stem thickness in cultivated plants varies and could lead to confusion, the other two characters are stable.

There is, of course, a third closely related taxon, i.e. P. dasycaule. We will address it in a future contribution.

By Matija Strlic, Ljubljana, Slovenia.

Literature

1. Becker M. (2008), Pelargonium albersii, a new species of Pelargonium section Otidia (Geraniaceae). Schumannia 5, 157-168.
2. Clifton R. (2014), Pelargonium section Otidia, Typification and Verification Notes for ceratophyllum, P. albersii, P. dasycaule, P. dasycaulon and P. hospitans. Geraniaceae Group Associated Notes: no. 75.
3. Strlič M. (2016), Otidias, or the Story of Dürer’s Rhino, Pelargonium Notes, #4.
4. Becker (2006), Revision der Pelargonium – Sektion Otidia (Geraniaceae) aus dem Winterregengebiet des südlichen Afrikas und Bewertung evolutiver Strategien der Pelargonien aus der Capensis. PhD Thesis, University of Münster.
5. L’Héritier de Brutelle C. L. Aiton (1789), Hortus Kewensis, ed. 1, vol. 2, p. 422.
6. Clifton R. (2011), The L’Heritier Project: The Partial Text of Geraniologia. Geraniaceae Group Associated Notes: no. 56
7. L’Héritier de Brutelle C. L. (1792), Geraniologia, Didot, Paris, plate 13.
8. Strlič M. (2018), The Laxum Conundrum, Geraniaceae Group News #150, pp 15-24.
9. Van der Walt J. J. A., Vorster P. J. (1981), Pelargoniums of Southern Africa, vol. 2, Juta, Cape Town, pp. 27-29.
10. Vorster P. J. (1990), Proceedings of the International Geraniaceae Symposium, University of Stellenbosch, 24-26 September 1990, reprinted by the Geraniaceae Group, 1994, pp. 279-294.

Citation and Copyright

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

ISSN 2464-014X.

This article was first published in Geraniaceae Group News #170. Cite as: M. Strlič: P. ceratophyllum and P. albersii – Two Lesser-Known Sister Otidia Species. Geraniaceae Group News #170, pp 16-28.