On-line version ISSN 2311-9284
Print version ISSN 0006-8241
Bothalia (Online) vol.44 n.1 Cape Town 2014
M. Marianne le RouxI, II; John C. ManningIII, IV
INational Herbarium, South African National Biodiversity Institute, South Africa
IIDepartment of Botany and Plant Biotechnology, University of Johannesburg, South Africa
IIICompton Herbarium, South African National Biodiversity Institute, South Africa
IVResearch Centre for Plant Growth and Development, University of KwaZulu-Natal, South Africa
BACKGROUND: Field studies confirmed that unusually long-tubed populations of Pelargonium dipetalum from between Swellendam and Albertinia, Western Cape Province, South Africa, are a distinct ecotype adapted to pollination by the long-proboscid fly, Prosoeca longipennis. The geographical and morphological isolation of these populations suggests that they are reproductively isolated from short-tubed populations, which are pollinated by bees
OBJECTIVES: To determine and describe the floral variation in P. dipetalum, with a view to recognising the long-tubed populations at some taxonomic level
METHOD: All available collections were measured and compared
RESULTS: Populations of P. dipetalum were segregated into a short-tubed form with hypanthium 3 mm - 24 mm long and mostly pink petals that occurs from Betty's Bay to Knysna, and a long-tubed form with the hypanthium 34 mm - 54 mm long and consistently white petals that is restricted to a small area east of Swellendam between Suurbraak and Albertinia. We described the long-tubed form as the new subspecies P. dipetalum subsp. stenosiphon
CONCLUSION: The new subspecies increases our understanding of the diversity in P. dipetalum and represents a new taxon of conservation concern
The genus Pelargonium L'Her. ex Aiton (Geraniaceae) includes approximately 280 species distributed amongst 16 sections (Bakker et al. 2004). Section Hoarea (Sweet) DC., with ± 85 species occurring mainly in the winter rainfall region of South Africa (Marais 2014), is one of the largest sections in the genus. It comprises deciduous geophytes with carrot-shaped or turnip-shaped tubers covered with papery bark and a highly condensed stem with the leaves in a radical tuft and often dry at flowering (Marais 1994, 2014).
The section includes seven species with only the posterior two petals present, as opposed to the full complement of five petals commonly found in the genus (Manning & Goldblatt 2012; Marais 1994). Pelargonium dipetalum L'Her. is the only member of this alliance occurring along the southern coast in Western Cape Province and extends from Betty's Bay to Knysna. The hypanthium in P. dipetalum typically varies between 7 mm and 18 mm in length, but the species also includes a few populations east of Swellendam with exceptionally long hypanthia, 35 mm - 50 mm long. These populations were not recognised as a separate taxonomic entity by Marais (1994), who made no correlation between their distribution and their distinctly longer hypanthium. This variant was, however, identified by Manning and Goldblatt (2005) as representing a distinct morph adapted to pollination by the long-proboscid fly Prosoeca longipennis Loew (Nemestrinidae).
A recent study of the P. longipennis pollination syndrome by Newman, Manning and Anderson (2014) defined the guild (Fenster et al. 2004) as including mainly autumn-flowering species with unscented, white to pink flowers with long floral tubes. A population of the long-tubed morph of P. dipetalum included in the study confirmed that it is adapted to pollination by P. longipennis, whereas the short-tubed morph of the species is visited by bees.
We document the distribution and variation in hypanthium length and petal colour in P. dipetalum and confirm that the long-tubed populations represent a variant that is morphologically and geographically discontinuous from the typical populations. We recognise these populations as the new subspecies P. dipetalum subsp. stenosiphon.
Research method and design
Fieldwork was conducted in the Langeberg area (Western Cape Province, South Africa) and herbarium specimens from the Bolus Herbarium (BOL), Compton Herbarium (NBG) (including the South African Museum [SAM]) and the Pretoria National Herbarium (PRE) were studied (abbreviations according to Holmgren, Holmgren & Barnett 1990).
Hypanthium length and petal colour were recorded for all specimens (Appendix 1). The shortest and longest values for hypanthium length were recorded for each herbarium collection, as well as the mean hypanthium length for all short-tubed and long-tubed collections, respectively.
The distribution map was compiled using the quarter degree reference system (Leistner & Morris 1976).
Populations of P. dipetalum are separable into two groups based on hypanthium length and petal colour. The common form corresponding with the type of the species has short-tubed flowers, with the hypanthium 3 mm - 23 mm long (9.7 mm ± 3.1 mm s.d.; n = 144) (Appendix 1; Figure 1), mostly pink petals (rarely white in populations near Knysna and Bredasdorp) (Figure 2) and a widespread distribution along the coast from Betty's Bay to Knysna (Figure 3). Three populations from slightly further inland between Suurbraak and Albertinia have consistently white petals and a significantly longer hypanthium 34 mm - 54 mm long (41.1 mm ± 9.0 mm s.d.; n = 8) (Figures 1-3; Appendix 1). There is no overlap in hypanthium length between the two variants.
The two variants are geographically separated and are morphologically distinct in hypanthium length and partially in petal colour, but we were unable to find any other differences between them. We accordingly treated the long-tubed populations as comprising a separate subspecies representing a distinct ecotype adapted to pollination by the long-proboscid fly P. longipennis.
Pelargonium dipetalum L'Hér., Geranologia, seu Erodii, Pelargonii, Monsoniae et Grieli historia iconibes illustrata: t. 43 (1792). Geranium dipetalum (L'Her.) Poir.: 744 (1812). Geraniospermum dipetalum (L'Her.) Kuntze: 95 (1891). Seymouria Vhéritieri Sweet: 77 (1824-1826), nom. illegit. superfl. pro P. dipetalum L'Her. Pelargonium Vhéritieri (Sweet) Don: 731 (1831). Type: Illustration in L'Heritier: t. 43 (1792) (icono.!).
Hoarea erythrophylla Eckl. & Zeyh.: 60 (1835). Pelargonium erythrophyllum (Eckl. & Zeyh.) Steud.: 285 (1841). Type: South Africa, [Western Cape], 'Rivier Zonder Einde apud villam Knoblauch (Zwellendam)', Ecklon & Zeyher 457 [S, lecto., designated by Marais: 245 (1994)-JSTOR image!; S, isolecto.-JSTOR image!] (JSTOR 2011a, 2011b).
Pelargonium nivenii Harv.: 271 (1860). Geraniospermum nivenii (Harv.) Kuntze: 95 (1891). Type: South Africa, [Western Cape], 'elevated places in Sweetmilk Valley [Soetmelksvallei]', Niven s.n. [S, holo.-JSTOR image!] (JSTOR 2012).
Geophytic herb up to 350 mm; tuber round to elongate, sometimes with a moniliform root. Stipules: subulate and adnate to petioles for two thirds of their length, 12 mm -37 mm χ 1 mm - 2 mm, ciliate. Leaves: erect; petioles 30 mm -200 mm long, rigid, hirsute with appressed or patent hairs; blades green or occasionally purple beneath, simple to irregularly pinnatisect to bipinnatisect, elliptic in outline, 20 mm - 120 mm χ 13 mm - 30 mm, acuminate, bases cuneate, lamina hirsute above and appressed-hirsute beneath. Inflorescence: 30 mm - 200 mm long, scape with 2-3(5) pseudo-umbels, each with (3)4-8(12) flowers; peduncles 25 mm -150 mm long, with glandular hairs interspersed with bristlelike hairs; bracts subulate, 3 mm - 7 mm χ 1 mm - 2 mm, hirsute beneath with distally appressed hairs; pedicels c. 0.5 mm long. Hypanthium: 3 mm - 54 mm long, reddish-brown, densely covered with glandular hairs interspersed with bristle-like hairs. Sepals: 5, lanceolate, acute, 5.0 mm -11.5 mm χ 1.2 mm - 4.0 mm, reflexed, green to reddish-brown, indumentum as for peduncle. Petals: 2 in posterior position, pink to white, usually with darker-coloured nectar guides, obovate to spathulate, 12 mm - 19 mm χ 3 mm - 7(-10) mm, emarginate, bases cuneate, recurved during anthesis. Stamens: white to pale pink, papillate; fertile stamens 5, posterior filament shortest, 6.5 mm - 11.0 mm long, lateral and anterior filaments 7.5 mm - 12.0 mm long, free filaments wine-red; staminodes 2.0 mm - 5.5 mm long; anthers dark red, 1.5 mm - 2.5 mm long, pollen orange. Gynoecium: pink; ovary 3 mm - 6 mm long; style 1.5 mm -6.0 mm long, lengthening during anthesis; stigma branches 1 mm - 3 mm long, wine-red. Fruit: bases of mericarps 5 mm - 8 mm long, eglandular, tails 20 mm - 31 mm long. Description based on Marais (1994, 2000).
Pelargonium dipetalum subsp. dipetalum
Petals pale to dark pink, rarely white; hypanthium 3 mm - 17(-23) mm long (Figure 2a).
Subsp. dipetalum occurs from Betty's Bay eastwards to Belvedere near Knysna (Figure 3a).
Additional specimens seen
WESTERN CAPE.-3418 (Simonstown): Kogelberg Forest Reserve above road to Oudebosch farm, (-BD), 30 Mar. 1971, Boucher 1487 (NBG); Kogelberg State Forest, halfway between first turn and first bridge, left of road to Oudebos, (-BD), 02 Mar. 1992, Kruger 407 (NBG, PRE); Fairy Glen, firebreak, (-BD), 12 Mar. 1970, Boucher 1186 (NBG); Hangklip, Betty's Bay, north-east corner of plot 3009 near boundary with school plot 2759, (-BD), 04 Mar. 1999, Forrester 1310 (PRE); Betty's Bay, (-BD), 05 Feb. 1963, Levyns 11417 (BOL); Betty's Bay, lower mountain slopes above Anna's Hof, (-BD), 21 Feb. 1989, Rourke 1924 (NBG). 3419 (Caledon): Central koppie, Haasvlakte, Houhoek, (-AA), 29 Jan. 1988, Boucher & Stindt 5373 (NBG); Houhoek, Houtech terrain, (-AA), 13 Apr. 1988, Boucher & Stindt 5395 (NBG); Houhoek, Houtech terrain, (-AA), 16 Apr. 1988, Boucher & Stindt 5396 (NBG); Elgin, Caledon, (-AA), 24 Apr. 1943, Compton 14523 (NBG); Houhoek, at hotel, (-AA), 04 Apr. 1892, Guthrie 2225 (NBG); near Palmiet River, Oudeburg, (-AA), 26 Apr. 1943, Leighton 503 (PRE); Houhoek, (-AA), 12 Apr. 1896, Schlechter 667 (PRE); Houhoek, (-AA), 12 Apr. 1896, Schlechter 7561 (BOL); Elgin, at the Bridge, Caledon, (-AA), 06 Mar. 1926, Smith 2539 (PRE); Caledon, hill north of Baths, (-AB), 31 Mar. 1922, Marloth 11085 (NBG, PRE); Kleinmond, kloof north-west of Heuningklip, (-AC), 28 Apr. 1948, De Vos 941 (NBG); Driebosch, Kleinmond, Caledon, (-AC), 01 Mar. 1943, Marais s.n. (NBG); Suikerboskop east of Bot River Lagoon, (-AC), 25 Apr. 1975, Oliver 5798 (NBG, PRE); Kleinmond, (-AC), 22 Apr. 1922, Stokoe 1327 (BOL); Groot Hagelkraal near Pearly Beach, (-AC), 16 Mar. 1983, Van Wyk 1154 (NBG); Happy Valley, Riviersonderend Mountains, (-BA), 12 Apr. 1941, Compton 10665 (NBG); flats at foot of Riviersonderend Mountains near Neethlings Farm, (-BA), 29 Apr. 1950, Wilman 978 (PRE); Riviersonderend Mountains, (-BB), Apr. to May 1950 [without day], Lewis SAM63209 (PRE); Zonderend near Olifantsbos, (-BB), 01 Apr. 1922, Marloth 11090 (PRE); Riviersonderend, (-BB), 30 Apr. 1950, Middlemost 1509 (NBG); foothills of Riviersonderend Mountains, (-BB), Apr. to May 1950 [without day], Stokoe 63208 (PRE); Sandies Glen near Sandfontein, north-east sandstone slope of Koueberg, (-BC), 18 Mar. 1977, Hugo 908 (NBG, PRE); 4 km north-west of Napier, near Quarry Kop, (-BD), 31 May 1995, Dreyer 525 (PRE); Skoenmakers River, ± 10 km west of Napier, (-BD), 18 Mar. 1977, Thompson 3487 (NBG); Koks River, near entrance to farm, (-DA), 11 Mar. 1979, Hugo 1606 (NBG); Groot Hagelkraal, Hagelkraal River area, north-east of farmstead, (-DA), 18 Apr. 1975, Oliver 5895 (NBG); beacon 147, hills just north-west of Elim, (-DA), 29 Mar. 1971, Oliver 3344 (NBG); Hagelkraal, poort near Hagelkraal River, (-DA), 10 Mar. 1979, Thompson 3917 (NBG); on road from Elim to 'Die Dam', (-DA), 22 Mar. 1982, Van Wyk 801 (NBG); flats north-west of Soetanysberg, Rietfontein Private Nature Reserve, (-DB), 25 Feb. 1994, Beyers 224 (NBG); Bredasdorp, Rietfontein, (-DB), 13 Apr. 1978, Esterhuysen 34910 (BOL); near Mierkraal, south-west of Bredasdorp, (-DB), 14 Mar. 1977, Hugo 823 (NBG); 4 miles [6.44 km] west of Elim, Bredasdorp, (-DB), 18 Feb. 1951, Maguire 845 (NBG); Vogel Valley, (-DB), 23 Apr. 1897, Schlechter 1867 (PRE); Koks River, north-west of Buffeljagts Mountain, (-DC), 17 Mar. 1978, Hugo 1197 (NBG). 3420 (Bredasdorp): De Hoop Nature Reserve, flats north of station, (-AD), 17 Mar. 1977, Hugo 881 (NBG); De Hoop Farm, (-AD), 1971 [without day or month], Van der Merwe 2015 (NBG); De Hoop, Potberg Nature Reserve, (-BC), 16 Feb. 1979, Burgers 1810 (NBG); De Hoop, Hamerkop, (-BC), 29 Jan. 1985, Fellingham 869 (NBG); Zoetendal's vlei, east of Soetanysberg, (-CA), 25 Mar. 1982, Fellingham 398 (NBG), Uyshoek, 7 km due north of Arniston, (-CA), 15 Mar. 1977, Hugo 840 (NBG, PRE); Eiland's Valley between Bredasdorp and Skipskop, (-CA), 16 Mar. 1978, Hugo 1174 (NBG); hill near Bredasdorp, (-CA), [without date], Leighton NBG 671/33 (BOL); De Hoop, Moerasfontein at second gate from main road, (-CA), 31 Jan. 1985, Van Wyk 2171 (NBG); De Hoop, Buffelsfontein, along road to Ryspunt, (-CB), 18 Mar. 1985, Van Wyk 2208 (PRE); Uitvlugt, south slopes of Bredasdorp, (-DA), 16 Mar. 1978, Boucher 3775 (NBG). 3421 (Riversdale): Still Bay ridge north of rifle range, (-AD), 15 Feb. 1979, Bohnen 5071 (NBG, PRE); Schoemanshoek in Albertinia, the Fisheries Road, (-BA), 14 Mar. 1978, Boucher 3720 (NBG); Cauca se Laagte, south of Albertinia, (-BC), 20 Mar. 1975, Oliver 5717 (NBG, PRE); Albertinia, Gouriqua/ Ystervarkpunt, (-BC), 20 Jan. 1987, Willemse 65 (NBG). 3422 (Mossel Bay): Mossel Bay, near new town extension at Golden Rendezvous Hotel, (-AA), 29 Mar. 1987, Vlok 1855 (NBG); Knysna, Belvidere, (-BB), Feb. 1921 [without day], Duthrie 500 (BOL, PRE, SAM). 3423 (Knysna): Knysna, (-AA), 20 Feb. 1955, Adamson D331 (PRE); Knysna, (-AA), Mar. 1921 [without day], Breyer 25210 (PRE); Knysna, (-AA), Feb. 1921 [without day], Breyer 23973 (PRE); Knysna Heads, (-AA), Feb. 1922 [without day], Fourcade 2018 (BOL). Without precise locality: Caledon division, Purcell 45919 (SAM).
Pelargonium dipetalum subsp. stenosiphon J.C.Manning & M.M.le Roux, subsp. nov.
Type: SOUTH AFRICA. Western Cape: (3421) Riversdale: 2 km west of Dekriet siding on main road, (-AB), 10 Apr. 1979, Bohnen 5551 (NBG, holo.).
Petals white; hypanthium 35 mm - 54 mm long (Figure 2b).
Subsp. stenosiphon is localised along the southern foothills of the Langeberg west of Swellendam, between Suurbraak and Albertinia (Figure 3b).
Unlike subsp. dipetalum, which is relatively widespread and partially protected in nature reserves, subsp. stenosiphon has a much more limited range. The taxon is recorded from an area 90 km χ 20 km in extent, much of which is under pressure from agricultural activity. No known populations are formally protected and the conservation status of the subspecies needs to be assessed.
Additional specimens seen
WESTERN CAPE.-3420 (Bredasdorp): Swellendam, Zuurbraak [Suurbraak], (-BA), 01 Mar. 1930, Thode A2301 (NBG, PRE). 4321 (Riversdale): flats west of Dekriet siding west of Albertinia, (-AB), 19 Mar. 1975, Oliver 5692 (NBG).
The two subspecies of P. dipetalum are distinguished by hypanthium length and mostly also by petal colour (Figure 1 and Figure 2). The flowers in subsp. dipetalum are usually pale to dark pink, but two populations, one near Bredasdorp and the other at Belvedere near Knysna, have white flowers, and the hypanthium ranges from 3 mm to 23 mm long. The petals in subsp. dipeatlum are always marked with dark nectar guides. In contrast, the petals in subsp. stenosiphon are consistently white with only faint nectar guides and the hypanthium is 35 mm - 54 mm long.
The floral differences between the two subspecies of P. dipetalum are associated with a shift in pollination system from bee-pollination in the typical ecotype to pollination by the long-proboscid fly P. longipennis in subsp. stenosiphon.
In an analogous situation, Becker and Albers (2010) recently described P. alternans subsp. longicalcar M.Becker & F.Albers (2010) for populations from the Outeniqua Mountains in the Little Karoo differing from the other two subspecies in having a longer hypanthium [(12-)18 mm - 36 mm long in P. alternans subsp. longicalcar versus 3 mm - 9 mm in subsp. alternans and subsp. parviinflorescens M.Becker & F.Albers (2010)]. The long-tubed subspecies in this species is also thought to be pollinated by a long-proboscid fly and has undergone evolutionary changes similar to those documented for P. dipetalum subsp. stenosiphon.
Amida Johns kindly provided the image of P. dipetalum subsp. dipetalum, taken in the Kogelberg Nature Reserve.
The authors declare that they have no financial or personal relationships that may have inappropriately influenced them in writing this article.
M.M.l.R. (South African National Biodiversity Institute) and J.C.M. (South African National Biodiversity Institute) collectively performed the research. J.C.M. conducted the fieldwork and provided input during the compilation of the manuscript; M.M.l.R. compiled the manuscript.
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Marianne le Roux
Private Bag X101
Silverton 0184, South Africa
Received: 19 May 2014
Accepted: 17 Sept. 2014
Published: 08 Dec. 2014