Post #20 Pelargonium brevipetalum N.E.Br.

Fig. 1 (header): The typical many-flowered pseudo-umbel of P. brevipetalum, originating from N of Matjiesfontein.

The section Otidia is one of the smaller sections of the genus Pelargonium, yet it has been attracting much debate and causing lots of confusion, quite disproportionately so, given that it consists of only ~16 species. There are many reasons that led to this situation. On the one hand, flowers are easily self-pollinated, meaning that locally, characters develop that could be seen as significant, and on the other hand, naturally occurring hybrids are well-known, indicating that pollination barriers between the taxa are low. This is exacerbated by the facts that (i) herbarium specimens often do not include all the plant parts needed for identification, (ii) drawings as well as herbarium specimens were often made of greenhouse-grown plants which may not resemble naturally grown specimens very well [1]. P. brevipetalum is one of the taxa that until recently remained unclear due to all the above.

Historical, morphological and DNA evidence

The Münster group, consisting of Dr Becker, Prof Dr Albers, Dr Röschenbleck and others, developed some level of clarity about this taxon based on DNA studies, indicating P. brevipetalum standing apart from the P. parviflorum taxa with its four potential subspecies. This data is shown in Becker’s PhD Thesis [2], but not available as a formal publication yet. Röschenbleck’s paper on phylogeny of the genus [3] considers P. brevipetalum as a good species on this basis. The issue is that the DNA studies appear to have been done on modern collections (A&B4462, A&B4463, both from close to Matjiesfontein), and not on the herbarium specimen formally associated with the name P. brevipetalum.

This would not necessarily mean a problem; however, the herbarium specimen K000074313 at Kew, collected by Pillans and that was used by N. E. Brown to publish the name [4], apparently consists of only two leaves and two pseudo-umbels [5]. Unfortunately, N. E. Brown’s description says nothing about the number of flowers per pseudo-umbel, which is the key morphological character that separates this taxon from P. parviflorum [2]. The herbarium sheet was seen by R. Clifton [5], however, he does not confirm the number of flowers per pseudo-umbel either.

The Münster group (who we know have consulted the herbarium sheet [5]) must have identified their collections A&B4462, A&B4463 as identical to the Pillans’s collection on the basis of the number of flowers per pseudo-umbel being up to 30, as opposed to P. parviflorum with the number of flowers per pseudo-umbel up to 15 only. Namely, in Chapter II.6 of his Thesis [2], Becker describes P. brevipetalum as:

“…as P. parviflorum J. C. Wendl. subsp. parviflorum but with up to 30 flowers per pseudo-umbel. Distribution: South Africa, Western Cape Province, Little Karoo, near Matjiesfontein.”

In 1994, Vorster [6] considered P. brevipetalum as synonymous with P. parviflorum. In their discussion of the parviflorum complex from 2005, Becker and Albers initially considered the same, as evident from the caption to Fig. 5C [7]. The same image appears again in Becker’s Thesis in 2006, in Fig. 1M on p. 91 [2], where it is already named P. brevipetalum.

In summary, the confusion surrounding the name P. brevipetalum and what taxon it represents, i.e. whether it is a species on its own or synonymous with P. parviflorum, has been dragging on for a while and seems to originate in the fact that the difference between the two taxa is apparently just in the number of flowers per pseudo-umbel – all the rest of the characters appeared to be the same. While the number of flowers per pseudo-umbel in P. parviflorum is highly variable, DNA studies confirmed that A&B4462 and A&B4463 are separated from P. parviflorum [2] and Becker must have confirmed that his collections were identical to Pillans’s herbarium specimen in order to be able to retain the name. However, a full account of this research is still missing as the second part of the Becker and Albers 2009 paper [8], focussing on the P. parviflorum complex, has still not been published.

Field observations

Looking at the succulent veld around Matjiesfontein, observations confirm that three closely related otidias are frequent in the area: P. carnosum ssp. ferulaceum, P. parviflorum and P. brevipetalum. It is thus interesting and perhaps unusual that the three taxa, all flowering in the summer, are distinct morphologically, and evidently, genetically as well. While the thick-stemmed P. carnosum ssp. ferulaceum are easy to distinguish and develop into significant shrubs up to 40-50 cm tall when not in flower, the other two species remain much smaller, usually 10-20 cm, rarely more. The most significant difference is in the petal length, these being white and longer than the sepals in carnosum, the petals are yellow and shorter than sepals in P. parviflorum and P. brevipetalum. However, as evident in Becker’s publication [7], P. parviflorum has light cream-yellow petals, while P. brevipetalum is shown to have light lemon-yellow petals, in addition, of course, to the many-flowered pseudo-umbels (Fig. 1).

Fig. 2: P. brevipetalum N of Nieuwoudtville.

Similar populations were found further north, N of Nieuwoudtville and E of Loeriesfontein. The shapes of leaves are the same as P. parviflorum, lamina lobes decurrent along the leaf rachis, with microscopic hairs that make the leaf margins appear whitish. In Fig. 3, a drought-stressed plant developed reddish leaf colouration, with pinnae margins rolled up to form an almost cylindrical shape. The photo was taken in 2017, at the height of the drought spanning almost a decade. In the middle of the unusually dry winter, these otidias represented one of the few plants with leaves, and were regularly grazed, even if hiding within shrubs.

Fig. 3: P. brevipetalum E of Loeriesfontein.

Field observations thus confirm a broader distribution of P. brevipetalum than previously assumed [2]. The morphological commonalities of the populations N of Matjiesfontein, N of Nieuwoudtville and E Loeriesfontein are the pale lemon-yellow petal colour and the high number of flowers per pseudo-umbel, both of which are different to what we currently understand is P. parviflorum. Other morphological characters appear to be the same for the two species.

Conclusion

Both morphology and DNA evidence indicate that A&B4462 and A&B4463 are distinct from P. parviflorum. While Vorster as well as Becker and Albers, initially, considered Pillans’s herbarium specimen as synonymous with P. parviflorum, Becker later appeared to confirm that A&B4462 and A&B4463 are consistent with Pillans’s specimen.

Once Becker’s research is formally published, the use of the name P. brevipetalum N. E. Br. for this interesting and long misunderstood taxon would appear to be justified.

By Matija Strlič, Ljubljana, Slovenia

Literature

1. M. Strlič: Otidias, or the Story of Dürer’s Rhino, Pelargonium Notes, #4 (2016).
2. M. Becker: 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, 2006.
3. J. Röschenbleck, F. Albers, K. Müller, S. Weinl, J. Kudla: Phylogenetics, character evolution and a subgeneric revision of the genus Pelargonium (Geraniaceae). Phytotaxa 159 (2014) 31-76.
4. N. E. Brown, Kew Bulletin of Miscellaneous Information (1909) 184.
5. R. Clifton: Pelargonium brevipetalum, Geraniaceae Group Associated Notes no. 80 (2015) 22.
6. P. Vorster: Taxonomy of the genus Pelargonium: review of the section Otidia, Proc. Int. Geraniaceae Symp., University Stellenbosch, 24-26 Sep 1990, p. 279.
7. M. Becker, F. Albers: Was ist Pelargonium parviflorum?, Avonia 23 (2005) 31.
8. M. Becker, F. Albers: Taxonomy and phylogeny of two subgroups of Pelargonium section Otidia (Geraniaceae). 1. The Pelargonium carnosum complex, Bothalia 39 (2009) 73-85.

Citation and Copyright

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ISSN 2464-014X.

This article was first published in Geraniaceae Group News #167. Cite as: M. Strlič: Pelargonium brevipetalum N.E.Br.. Geraniaceae Group News #167 (2022), pp 26-31.