SHORT NOTE

 

Taxonomic status of Pelargonium reniforme Curt.

 

 

Janine E. Victor; Mmamphe Aphane

Biosystematics Research and Biodiversity Collections Division, South African National Biodiversity Institute, South Africa

Correspondence

 

 

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ABSTRACT

BACKGROUND: Pelargonium reniforme Curt. is a morphologically variable species that many authors have attempted to split or combine. Confusion relating to the differences between the two subspecies currently included under P. reniforme has impeded attempts to assess their conservation status. Pelargonium reniforme is closely related to Pelargonium sidoides; the two species are indistinguishable when not flowering and their distributions overlap in some areas
OBJECTIVES: With this study, we aimed to clarify the taxonomic status of the two subspecies of P. reniforme, which has relevance in terms of their conservation status
METHOD: Leaf shape, petiole length, internode length and flower colour were assessed by studying herbarium specimens of the two subspecies of P. reniforme and specimens of P. sidoides. Living specimens of the two subspecies were also examined in their natural habitat
RESULTS: The current investigation showed that the morphological characters used to distinguish the two subspecies of P. reniforme are too variable to separate them. Variation in some morphological characters may be related to environmental conditions
CONCLUSION: The recognition of the two subspecies of P. reniforme as distinct taxa is no longer justified

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Introduction

There are over 200 species of Pelargonium L'Her. ex Aiton in South Africa and comparatively few species elsewhere in the world (Vorster 2000). The genus Pelargonium is characterised by a zygomorphic flower with a nectariferous spur fused to the pedicel, five petals (rarely four or two), with the posterior petals larger than the anterior petals and 10 stamens, of which only two to seven are fertile (Van der Walt 1985).

There are 16 sections recognised in the genus (Bakker et al. 2004). Pelargonium reniforme Curt. is a member of section Reniformia (R.Knuth) Dreyer ex J.P.Roux (Roux 2013) and is distributed from Middelburg in Mpumalanga southwards to Riversdale in Western Cape and as far west as Mthatha in Eastern Cape. This species is a small shrublet with tuberous roots and pink to deep magenta flowers. Variation in P. reniforme in internode length, leaf shape and petiole length has led to several taxonomic opinions. Ecklon and Zeyher (1835) split P. reniforme into three distinct species of the genus Cortusina (DC.) Eckl. & Zeyh., namely Cortusina velutina Eckl. & Zeyh., Cortusina rubro-purpurea Eckl. & Zeyh. and Cortusina reniformis (Curt.) Eckl. & Zeyh., but these were reduced by Harvey (1860) to varieties as var. velutinum (Eckl. & Zeyh.) Harv., var. sidaefolium (Thunb.) Harv. and var. reniforme. Knuth (1912) later regarded var. velutinum as a synonym of P. reniforme and raised var. sidaefolium to species status as P. sidaefolium (Thunb.) Knuth, which is currently known as P. sidoides DC. In 1995, Dreyer, Marais and Van der Walt re-established the recognition of infraspecific taxa of P. reniforme by recognising P. reniforme subsp. velutinum (Eckl. & Zeyh.) Dreyer.

Pelargonium reniforme subsp. reniforme was applied by Dreyer, Marais and Van der Walt (1995) to plants with elongated internodes (5 mm - 12 mm), reniform leaves and petioles 5 mm - 50 mm long. This form, although sympatric with P. reniforme subsp. velutinum, is more abundant in the Port Elizabeth area, Eastern Cape, where it is restricted to drier coastal plains below 300 m.a.s.l. The form designated as P. reniforme subsp. velutinum has internodes of 1 mm - 7 mm in length and cordate or reniform leaves with petioles of 25 mm - 130 mm in length. Plants with characteristics corresponding to P. reniforme subsp. velutinum are, according to Dreyer et al. (1995), more abundant between Grahamstown and Queenstown, Eastern Cape. In all other respects the two subspecies are identical and their distinction is difficult.

The closely allied Pelargonium sidoides differs from P. reniforme in having black or very dark purple flowers. It is usually indistinguishable from P. reniforme when not flowering, in having an identical habit and leaves that are similar in shape and size, usually cordate and velvety. The distribution of P. sidoides overlaps with that of P. reniforme but is wider, the species occurring throughout Eastern Cape, Lesotho, Free State and southern Gauteng (Van der Walt & Vorster 1988).

Medicinal use and conservation status

Some Pelargonium species are valued by traditional healers for their medicinal uses. The roots or extracts of roots of both P. sidoides and P. reniforme are used to treat diarrhoea, bronchitis, stomach ailments and respiratory tract infections (Watt & Breyer-Brandwijk 1962). Both species play an important role in traditional medicine and are therefore subject to occasional harvesting for local use, but P. sidoides is harvested at a much larger scale for export to Europe for use in the manufacture of a number of medicinal products (Brendler & Van Wyk 2008).

The conservation statuses of the two subspecies of P. reniforme are listed as 'Not Evaluated' (South African National Biodiversity Institute [SANBI] 2013a, 2013b), as the difficulty in distinguishing between them hinders data collection for conservation assessments. There is concern about the conservation status of P. reniforme as it can be harvested along with P. sidoides where the two occur sympatrically because of their morphological similarity. The conservation status of P. reniforme is thus currently listed as 'Near Threatened' as a result of suspected widespread overharvesting (Raimondo et al. 2012). The conservation status of P. sidoides is 'Least Concern' because, although it is heavily harvested, it is a very widespread and common species (De Castro et al. 2012). The clarification of morphological differences between the two subspecies of P. reniforme is regarded as a high priority by the Threatened Species Programme (D. Raimondo pers. comm., 29 May 2012) so that the conservation status can be properly assessed. We therefore investigated the species in an attempt to resolve the taxonomic problem. Morphological comparisons were made between the two subspecies, as well as with the nearest relative, P. sidoides, to clarify taxonomic uncertainty and subsequently contribute to the conservation of this species. The possibility that variation in some morphological characters is related to environmental conditions was also investigated by observing specimens of both subspecies of P. reniforme in their natural habitat.

 

Research method and design

Specimens (101 in total) of both subspecies of P. reniforme from the National Herbarium in Pretoria (PRE), all wild-collected and covering the entire geographical range of the subspecies, were studied to assess morphological variation between the two subspecies. A total of 15 specimens were previously identified as P. reniforme subsp. reniforme and 86 as P. reniforme subsp. velutinum. In addition, 140 specimens of P. sidoides from PRE were investigated in order to determine whether similar variation occurred in this species. The diagnostic characters distinguishing the two subspecies - that is, the lengths of the petioles and the internodes, as well as the leaf-shapes - were recorded for each specimen. A digital image of the holotype of P. reniforme subsp. velutinum from the Herbarium at the Swedish Museum of Natural History, Stockholm (S) was also examined. Observations of both subspecies were made in the area between Humansdorp, East London and Queenstown.

 

Taxonomic treatment

Pelargonium reniforme Curt. in Curtis's Botanical Magazine 14: 493 (1800); Pers.: 229 (1806); Desf.: 457 (1809); Willd.: 703 (1809); Ait.: 171 (1812); Haw.: 307 (1812); Sweet: t. 48 (1820); DC.: 666 (1824); Hoffmg.: 95 (1824); Loudon: 574(1829); Don: 737 (1831); Steud.: 289 (1841); Harv.: 300 (1860); Knuth: 447 (1912); Pole-Evans: 672 (1937); Watt and Breyer-Brandwijk: 454 (1962); Batten and Bokelman: 89 (1966); Smith: 381 (1966); Clifford: 237 (1970); J.J.A. van der Walt: 40, Figure (1977); Webb: 69 (1894); Dreyer, Marais and Van der Walt: 325 (1995). Cortusina reniforme (Curt.) Eckl. & Zeyh.: 77 (1835). Geranium reniforme (Curt.) Andr.: 108 (18000; Poir.: 751 (1812); Steud.: 679 (1840). Geraniospermum reniforme (Curt.) Kuntze: 95 (1891). Iconotype: Curt.: t. 493 (1800).

Cortusina velutina Eckl. & Zeyh.: 77 (1935). Pelargonium reniforme var. velutinum (Eckl. & Zeyh.) Harv.: 300 (1860). Pelargonium reniforme subsp. velutinum (Eckl. & Zeyh.) Dreyer, in Dreyer, Marais and Van der Walt: 328 (1995). Type: SOUTH AFRICA. Eastern Cape: 'campestriis ad fluvium "Zwartkopsrivier" et collibus in "Adow" [Addo] (Uitenhage)', Ecklon & Zeyher 598 (S, holo. - digital image!).

Description

Comparison of diagnostic characters of the two subspecies

Based on field observations as well as morphological comparison of herbarium specimens, P. reniforme subsp. velutinum was found to have internodes that were variable in length and a range of petiole lengths overlapping with those of subsp. reniforme (Table 1). This finding contradicts the descriptions given by Dreyer et al. (1995) to distinguish the two subspecies.

Character variation was plotted on a scatter plot chart (Figure 1), which shows that all variation overlaps in both subspecies. This implies that these characters cannot be used to distinguish the two subspecies. The petiole length of subspecies velutinum overlaps completely with that of subspecies reniforme and this characteristic is therefore also not useful to distinguish the two subspecies. Most of the specimens with characteristics that correspond with subspecies velutinum have cordate leaves; although, there are a few that are reniform. All specimens corresponding to subspecies reniforme have reniform leaves. Figure 1 shows that variation in the leaf shape is not correlated with petiole length or internode length and therefore this character is too variable to reliably be used to distinguish subspecies.

 

 

Pelargonium sidoides is vegetatively similar to the descriptions given in Dreyer et al. (1995) for subspecies of P. reniforme; however, one consistent characteristic of P. sidoides is the short internodes (usually 1 mm but never longer than 3 mm in length), whereas the internode length in P. reniforme varies between specimens. The other consistent difference between the two taxa is the flower colour, as described above.

 

Influence of habitat on morphology

Although specimens with the form P. reniforme subsp. reniforme are concentrated around Port Elizabeth, observations of plant characteristics in this area revealed that a possible cause for variation is the microhabitat in which the plant was growing. Plants growing in the shade of dense grass in the Port Elizabeth area tended to have both longer internodes (as in subsp. reniforme), as well as longer petioles (as in subsp. velutinum). It is possible that availability of nutrients, water and sunlight affects internode and petiole lengths, which could explain much of the variability of these characteristics in P. reniforme.

 

Conclusion

The findings of this study show that it is not possible to reliably distinguish between P. reniforme subsp. reniforme and P. reniforme subsp. velutinum and we recognise a single variable species for all populations.

 

Acknowledgements

The Botanical Education Trust is gratefully acknowledged for the funding received to enable this project to be carried out. We are grateful to Dr John Manning and Mr Tony Dold for discussions and comments on the manuscript. Two anonymous reviewers are gratefully acknowledged for improvements to the manuscript.

Competing interests

The authors declare that they have no financial or personal relationships that may have inappropriately influenced them in writing this article.

Authors' contributions

M.A. (SANBI) examined herbarium specimens and took measurements under the training and guidance of J.E.V. (SANBI). M.A. contributed to writing of the manuscript and collated background information. J.E.V. undertook fieldwork, contributed to writing the manuscript and editing it and supervised the project.

 

References

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Correspondence:
Janine Victor
Private Bag X101
Pretoria 0184, South Africa
Email: j.victor@sanbi.org.za

Received: 24 June 2013
Accepted: 13 June 2014
Published: 10 Oct. 2014