Note #15 Pelargonium fergusoniae

Ferguson’s pelargonium is a curious geophyte from the southern part of the Western Cape Province, combining several unusual characters in a unique taxon. Like the majority of section Hoarea, it is a winter-growing, summer-flowering species, developing lax rosettes of leaves and showy, multi-flowered inflorescences. It can be found from the Hex River Valley to the Worcester basin, to across the almost entire Overberg, from Caledon to Riversdale. P. fergusoniae was described by Luisa Bolus in 1934 and named after E. Ferguson, with whom they first collected this species near Riversdale [1].

Flowers

Based on the flower characters, P. fergusoniae has been placed in the Attenuatum group of section Hoarea, containing taxa with long and narrow, ligulate (strap- or ribbon-shaped) petals with a length/width ratio >5 and very short stamens that are concealed within the flower (Fig. 1).

Fig. 1: P. fergusoniae, flower. Origin: W of Worcester.

Along with P. fergusoniae, the following species make up the group: P. attenuatum, P. angustipetalum, P. leptum, P. viciifolium, P. longifolium, P. undulatum, and P. longiflorum. The petals of P. fergusoniae are typically undulate (wavy), so a plant in flower can be confused with some of the above with similar flowers, particularly P. longifolium and P. undulatum, the distribution of which overlaps with that of P. fergusoniae at least in part.

There is a great variety in the length of the nectar tube (hypanthium), ranging from 15 to 42 mm. The markings on posterior petals vary a lot, and can range from prominent blotches to feather-like markings, on petals that are light yellow to cream in colour. The flower featured in Fig. 1 is of a plant originating from seeds from the vicinity of Worcester and has perhaps unusually strong markings.

It is not entirely clear what role petal margin undulation has, perhaps it makes it easier for insects to land on a flower. This feature is certainly not unusual in the section. Although it is occasionally used to separate taxa, undulation can be very weak and thus identification difficult.

Fig. 2: The moniliform root system of P. fergusoniae. Origin: S of McGregor.

Roots

P. fergusoniae has the typical moniliform root system (i.e. resembling a string of beads) – a system of interconnected tubers (Fig. 2). This is an important survival strategy, since if the central tuber is excavated, e.g. by a porcupine, a number of plants emerge the next season from the side tubers. The side tubers are ideal for vegetative propagation in collections as well, not just of this species but of the majority of hoareas.

Fig. 3: Adult leaves of P. fergusoniae, W of Worcester.

Leaves

As evident in Fig. 3, the leaves are palmate with sometimes just three main pinnae, but often these pinnae are subdivided into segments, occasionally very finely as well, a shape that is called palmately compound. It is the variety of shapes that sometimes makes it difficult to quickly identify P. fergusoniae in the field, as even on the same plant they often range from small, trefoil, Oxalis-like leaves to large, finely divided leaves resembling a number of other species, e.g. P. luteolum, P. gracillimum, P. attenuatum, P. angustipetalum, P. ternifolium, P. reflexum, or P. montaguense.

However, the petioles have an additional character of diagnostic value: they are strongly recurved, i.e. they start growing horizontally from the tuber, often underground, and recurve vertically at some distance from the main tuber. Of the above species, only P. ternifolium, P. reflexum, and P. montaguense share this character.

Fig. 4: A population of P. fergusoniae, S of Swellendam.

Relationships between P. montaguense and P. fergusoniae

The distribution area of P. montaguense is within that of P. fergusoniae, so the two species can be quite easily confused. The only clear difference is that P. montaguense has white petals that are a bit broader (length/width ratio 3.5–4.8), and has pollen that is pale yellow to white, as opposed to P. fergusoniae, where the pollen is dark yellow to orange. It should be said that the adult leaves of P. montaguense have finely segmented pinnae as well, in the same manner as those of P. fergusoniae, and not only palmately compound with three more or less even-sized obcordiform pinnae [2]. The two species appear quite a bit more related than suggested and perhaps their relative status might be revised in the future.

However, their habitats differ somewhat: P. montaguense is found on the rocky renosterveld slopes near Montagu, while P. fergusoniae prefers sandy renosterveld habitats. In addition, the former flowers in September/October, while the latter flowers from November to January.

Populations of P. fergusoniae

P. fergusoniae does not appear to be threatened and many healthy populations are documented in herbaria and on iNaturalist.

The populations close to Worcester (Figs. 1, 3) are quite unusual in that the posterior petals are extremely prominently marked. They grow side by side with a large population of P. luteolum, and can be difficult to identify during the winter vegetative period due to the obvious similarities in the leaf shapes.

The populations S of McGregor occur in dense renosterveld (Fig. 2) in the company of several other hoareas: P. rapaceum, P. luteolum, P. radiatum and P. pilosellifolium. The leaves vary in size significantly, from small ternate leaves to large palmatisect ones.

There are significant populations S of Swellendam, where the plants grow in the open in deep sand – these are easily the biggest plants of P. fergusoniae I have seen, also growing in the densest colony (Fig. 4).

Fig. 5: Compton herbarium specimen 145436, unidentified Hoarea from Buitenverwagting (3320 CA Montagu), collected by M. B. Bayer.

An interesting Compton herbarium sheet with an unidentified hoarea (Fig. 5) indicated a possible relationship with P. fergusoniae, however, the pressed plants appear to be extremely small, with the leaves having only three entire pinnae and the petioles appear not to be recurved. An enquiry revealed that the farm Buitenver-wagting (S of Touws Rivier) has been turned into the Drie Kuilen Nature Reserve, where the manager kindly indicated the locality of the unusual taxon (Fig. 6).

Upon closer inspection, it became evident that this is P. fergusoniae, growing in deep sand in a very open grassy landscape, with leaves mostly in the juvenile state, though with some adult leaves as well.

Fig. 6: Leaves of P. fergusoniae at the Drie Kuilen Nature Reserve, with an Oxalis flower.

By Matija Strlic, Ljubljana, Slovenia.

Acknowledgements

The current Drie Kuilen Nature Reserve manager, Charl Steenkamp, and the previous manager, Kevin Jolliffe, as well as Florent Grenier, are gratefully acknowledged for having helped with research into the Drie Kuilen population of P. fergusoniae.

Literature

  1. Marais, E. M. (1994). Taxonomic Studies in Pelargonium, Section Hoarea (Geraniaceae), Ph. D. Thesis. University of Stellenbosch, South Africa.
  2. Marais E. M. (2017), Three new geophytic species of Pelargonium (Geraniaceae) from the Western Cape Province, South Africa and their relationships within section Hoarea. South African Journal of Botany 113, 261-269.

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.

This article was first published in Geraniaceae Group News #158. Cite as: M. Strlič: Pelargonium fergusoniae. Geraniaceae Group News #158 (2020), pp 22-29.

2 thoughts on “Note #15 Pelargonium fergusoniae

  1. Donovan Kirkwood says:

    I had a look over the description – really useful thank you and I will add it as an online reference on our sun.gardenexplorer.org species description. But I would strongly disagree with the article statement under populations that this species is not threatened – apart from the SA Red List status of Endangered, http://redlist.sanbi.org/species.php?species=1976-123, the few (not many – most observations are clustered in a small area within Bontebok National Park S of Swellendam) populations indicated by reliable Research Grade iNat observations are all on insecure habitat that consists of tiny remnants or marginal habitat where it occurs on De Hoop Nature Reserve. These rare sandier parts of Critically Endangered lowland Renosterveld habitat are still disproportionately rapidly losing habitat compared to not threatened habitats such as most montane areas (NBA 2018 provides copious terrifying evidence of this). Someobservations extending into the Karoo are more doubtful in ID confidence IMO, but also on locations subject to ongoing agricultural development. The observations on Worcester sandy flats will be gone within the next 10 years due to inevitable and rapid urban expansion there sadly. Basically there are extremely few remaining populations of a species that would have once been widespread and abundant (as per the many older herbarium records), definitely warranting En or CR status when you also look at the species’ habitat status and trends in my opinion.

    • admin says:

      Thank you Donovan – that’s a very helpful response. The pops referred to in the article appear to be stable and have been observed several times over the last decade, but it is absolutely certain that most of these habitats are generally endangered. I believe that one of the reasons for the lack of reliable observations in iNat is that a pop needs to be observed twice, as for successful ID, both leaves and flowers are necessary (as is the case with many hoareas), so the small number of research-grade obs is perhaps not truly indicative of its distribution? Cheers, Matt.

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