Solanum retroflexum Dunal, Prodr. [A. P. de Candolle] 13(1): 50. 1852

Saerkinen, Tiina, Poczai, Peter, Barboza, Gloria E., Weerden, Gerard M. van der, Baden, Maria & Knapp, Sandra, 2018, A revision of the Old World Black Nightshades (Morelloid clade of Solanum L., Solanaceae), PhytoKeys 106, pp. 1-223 : 1

13. Solanum retroflexum Dunal, Prodr. [A. P. de Candolle] 13(1): 50. 1852 Figures 40 , 41

Solanum retroflexum Dunal var. angustifolium Dunal, Prodr. [A. P. de Candolle] 13(1): 50. 1852.

Solanum retroflexum Type. South Africa. Eastern Cape: Graaff Reinet ( “Graafreynet”), 3000-4000 ft, 1838, J.F. Drège 7864b (holotype: G-DC [G00144331]; isotypes: K [K000414172], S [acc. # S-G-5707]).

Solanum retroflexum Dunal var. latifolium Dunal, Prodr. [A. P. de Candolle] 13(1): 50. 1852.

Solanum retroflexum Type. South Africa. Western Cape: Paarlberg, 1000-2000 ft, 1838, J.F. Drège 7864a (lectotype, designated here: G-DC [G00144331]; isolectotypes: BM [BM000943868], K [K000414175], P [P00341909]).

Solanum burbankii Bitter, Repert. Spec. Nov. Regni Veg. 12: 83. 1913, as ' Burbanki '.

Solanum retroflexum Type. Cultivated in Germany at Bremen, the seeds originally from Hamburg Botanical Garden thought to have been sent by Luther Burbank from United States of America. California, Santa Rosa (no specimens cited; no original material found); Cultivated in St. Louis, Missouri (USA) in the garden of Mr. Waldstein, seeds from Childs, 1 Sep 1909, Anon. [Waldstein] s.n. (neotype, designated here: MO [MO-3002957, acc. # 6651350]).

Solanum nigrum L. var. probstii Polg., Mitteil. Naturfor. Gesellsch. Solothurn 8: 71. 1928.

Solanum retroflexum Type. Switzerland. Solothurn: Degend. K.K. [= Wollkompost der Kammgarnfabrik Derendingen], [in protologue "22, 24, 26, 27"], 24 Aug 1926, R. Probst s.n. (syntypes; no herbarium cited; lectotype, designated here: BP [acc. # 485285]).

Solanum burbankii Bitter var. glabrescens Polg., Mitteil. Naturfor. Gesellsch. Solothurn 8: 72. 1928.

Solanum retroflexum Type. Switzerland. Solothurn: Degend. K.K. [= Wollkompost der Kammgarnfabrik Derendingen], [in protologue "22, 27"], 20 Oct 1922, R. Probst s.n. (syntypes; no herbarium cited; lectotype, designated here: BP [acc. # 485327]).

Type.

South Africa. Eastern Cape: Graaff Reinet ( “Graafeynet”), 3000-4000 ft, 1838, J.F. Drège 7864b (lectotype designated here: G-DC [G00144331]; isolectotypes: K [K000414172], S [acc. # S-G-5707]) .

Description.

Annual to perennial prostrate to erect herbs to 0.6 m tall, subwoody and branching at base. Stems sprawling, terete or ridged, 0.3-0.6 cm in diameter, if stems ridged the ridges sometimes spinescent, green to yellowish-brown, older stems straw coloured, not markedly hollow; new growth sparsely to densely pubescent with simple, spreading, uniseriate, translucent, glandular and/or eglandular trichomes, these 1-5(-8)-celled, 0.1-0.8 mm long; older stems glabrescent. Sympodial units difoliate, the leaves not geminate. Leaves simple, (0.5-) 1.5-7.5 cm long, 1.5-5.5 cm wide, rhomboidal to lanceolate, membranous, green, slightly discolorous, without smell; adaxial surface green, sparsely to densely pubescent with simple uniseriate trichomes like those on stem evenly spread along lamina and veins; abaxial surface slightly paler, more densely pubescent along veins and lamina; major veins 3-7 pairs; base truncate then abruptly attenuate along the petiole; margins shallowly toothed, the teeth rounded; apex acute, the tip sometimes rounded; petioles (0.5-) 1.5-3.5 cm long, sparsely to densely pubescent with simple uniseriate trichomes like those of the stems. Inflorescences 1.8-3.0 cm long, internodal, simple, sub-umbelliform, with 3-7 flowers clustered towards the tip of the rhachis, sparsely to densely pubescent with glandular and/or eglandular simple uniseriate trichomes like those on stems; peduncle 1.5-3.5 cm long, erect; pedicels 1.0-1.5 cm long, 0.3-0.6 mm in diameter at the base, 0.4-0.6 mm in diameter at the apex, recurving but not fully reflexed, pubescent like the peduncle, becoming woody, green or yellow-brown, articulated at the base; pedicel scars spaced 0-0.5 mm apart. Buds globose, the corolla 1/3 exserted from the calyx before anthesis. Flowers 5-merous, all perfect. Calyx tube 1.0-1.7 mm long, campanulate, the lobes equal, 1.0-1.5 mm long, less than 1 mm wide, oblong with rounded tips, green, sparsely pubescent with simple uniseriate trichomes like of the inflorescence. Corolla 11-16 mm in diameter, white, with a yellow basal star, stellate, lobed to 1/2-2/3 towards the base, the lobes 5.0-6.0 mm long, 2.5-2.7 mm wide, spreading to reflexed, densely papillate-pubescent abaxially with simple uniseriate trichomes, these denser on tips and margins. Stamens equal; filament tube minute; free portion of the filaments 1.2-1.5 mm long, glabrous or adaxially pubescent with tangled 6-8-celled simple uniseriate trichomes; anthers 1.3-1.8(-2.0) mm long, 1.0-1.5 mm wide, ellipsoid, yellow, poricidal at the tips, the pores lengthening to slits with age and drying, the connective becoming brownish in dry material. Ovary rounded, glabrous; style 1.9-2.2 mm long, slightly curved, pubescent with simple uniseriate trichomes 0.2-0.5 mm long in the basal 1/3 where included in the anther cone, exserted 0.5-1.5 mm beyond anther cone; stigma capitate, the surface minutely papillate. Fruit a globose berry, 6-10 mm in diameter, purple-black at maturity, the pericarp thin, matte with a glaucous cast; fruiting pedicels 1.0-1.5 cm long, 0.4-0.6 mm in diameter at the base, 1.0-1.2 mm at apex, becoming woody, recurving to deflexed, pale green to yellow-brown, spaced 0-0.5 mm apart, not falling with the fruit, remaining on the plant and persistent on older inflorescences; fruiting calyx not accrescent, the tube 1.0-1.5 mm long, the lobes 1.5-2.0 mm long, strongly reflexed. Seeds (5-)12-35 per berry, 1.6-1.8 mm long, 1.3-1.5 mm wide, flattened and tear-drop shaped with a subapical hilum, yellow to brown, the surfaces minutely pitted, the testal cells rectangular to pentagonal in outline. Stone cells absent. Chromosome number: 2n =4x=48 ( Henderson 1974; Randell and Symon 1976; Edmonds 1977, 1983; Symon 1981; Jacoby and Labuschagne 2006).

Distribution

(Figure 42 ). Endemic to southern Africa but has been introduced to Australia and was introduced as a garden plant to North America in the early 20th century and now globally available through commercial seeds from online sources under the name "Garden Huckleberry".

Ecology.

Grows in disturbed soil at watering holes, along dry watercourses, in shady places, in long grass, in Euphorbia candelabrum - Buxus zone, in dry hillsides and in disturbed areas along roads; between sea level and 1,800 (-2,300) m elevation.

Common names.

South Africa: mofhswe, nastegaal/nastergal, umsobo, gsoba, msoba ( Heiser 1969); Zimbabwe: m’Sungula, muSungu sungu.

Uses.

Berries used raw and for jam ( Viljoen 2011); leaves eaten as a pot-herb vegetable.

Preliminary conservation status

( IUCN 2016). Solanum retroflexum is widespread and can be assigned a preliminary status of LC (Least Concern; Table 7 ). Taking into account only collections from within the native range in Africa, the EOO is still very large (2,929,097 km2) and the assessment does not change.

Discussion.

Solanum retroflexum is a species that shows great variation in its indumentum, varying from nearly glabrous to densely pubescent with either eglandular or glandular trichomes. AFLP studies have shown that specimens of S. retroflexum with different indumentum types are genetically highly similar ( Manoko 2007, as S. hirsutum (Vahl) Dunal, here recognised as a synonym of S. memphiticum ). Developmental studies have shown that papillate glandular hairs are present on all young parts of Solanum plants ( Seithe 1962, 1979; see Morphology above), suggesting that, in the absence of other distinguishing features, glandular pubescence might not be taxonomically significant. We circumscribe S. retroflexum here to include both eglandular and glandular populations; this character is polymorphic in most species of morelloids in the Old World, perhaps due to genetic lability due to polyploidy.

The species can be distinguished from other Old World morelloids based on the combination of characters of few-flowered inflorescences with 3-7 flowers, relatively long filaments (1.2-1.5 mm long) compared to anther length (1.3-1.8(-2.0) mm), strongly reflexed calyx lobes in fruit and matte purple-black berries that lack stone cells and drop without the pedicels. Leaf shape is generally rhomboidal, which is characteristic of the species and helpful in distinguishing it from closely related S. nigrum and S. villosum . Calyx lobes are generally longer than in S. villosum , S. scabrum or S. nigrum . It can be distinguished from the morphologically similar S. villosum based on its opaque purple-black fruit, its pedicels that remain behind after fruits drop, deeply stellate corolla with long corolla lobes and the long filaments as compared to anther length.

Solanum retroflexum is cultivated commercially in South Africa in KwaZulu-Natal and Free State for jam production ( Viljoen 2011) and farmers select individual plants with large berries to propagate for the next season. In one farm in KwaZulu-Natal, 10 tonnes of berries harvested were used to make 20,000 jars of “Umsobo” jam, most marketed in the Gauteng area. On other farms, S. retroflexum is cultivated along with S. chenopodioides and S. americanum and putative hybrid plants were found ( Viljoen 2011). Leaves of S. retroflexum are also produced under irrigation in Limpopo province, for the commercial market in the local area ( van Averbeke et al. 2007). The markets for both leaves and fruits are controlled by small scale rural traders in South Africa.

Solanum retroflexum is a tetraploid species with unclear parentage. Previous studies have suggested that one of the contributing parents of the tetraploid S. retroflexum is the diploid S. americanum ( Edmonds 1977), supported by crossing studies showing vigorous hybrids between the autotetraploid S. villosum derived from S. americanum and S. retroflexum ( Ganapathi 1987). Jacoby and Labuschagne (2006), however, reported that crosses of S. chenopodioides and S. retroflexum are much more successful than crosses between S. retroflexum and S. americanum . Ganapathi & Rao (1980) also reported weak chromosome pairing at low frequency in hybrids between S. retroflexum and S. americanum . Molecular studies suggest that either S. chenopodioides or S. nitidibaccatum are the likely parental species of S. retroflexum ( Jacoby et al. 2003; van der Walt et al. 2008; Poczai and Hyvönen 2011). Further molecular studies are needed to fully establish the parental species of S. retroflexum , but the current data from molecular and crossing studies suggests that S. chenopodioides or S. nitidibaccatum are the likely best candidates.

Solanum retroflexum or one of its close relatives has been suggested to have contributed to the origin of the hexaploid S. nigrum ( Ganapathi and Rao 1986c). Most current evidence suggests, however, that S. villosum and S. americanum were the parents of S. nigrum ( Edmonds 1979a; Ganapathi and Rao 1986b; Poczai and Hyvönen 2011).

In describing S. retroflexum , Dunal (1852) cited two elements; one from Saudi Arabia ("in Arabia circa Taifa") and the other from South Africa ("caput Bona Spei, Drege"). He then used two different collections held at G-DC to describe the varieties. The specimen from Saudi Arabia corresponds to S. villosum (P00055172), so we have used the flowering collection ( Drège 7864b) at G-DC (G00144331) that is also the holotype of var. Solanum nigrum angustifolium as the lectotype of S. retroflexum , making the two names homotypic.

Solanum burbankii was described from living material sent to Bitter ("colui ipso in horto Bremeno complures per annos e seminibus ab horto Hamburgensi acceptis" [grew in the Bremen garden for several years from seeds originally accepted from Hamburg]) and thought to have been from California ( Bitter 1913b) and thus, perhaps, from Luther Burbank himself. Bitter (1913b) cites no herbarium specimens in the protologue; if they were in either Bremen or Berlin, they were destroyed during the Second World War and we have found no specimens in Göttingen where some small fragments of collections are found ( Vorontsova and Knapp 2010). From the description of a somewhat pubescent plant ("utrinque sparsim breviter pilosa") with pruinose berries with no stone cells, in which the calyx lobes are strongly reflexed at fruit maturity, we are certain Bitter is describing a sparsely pubescent form of S. retroflexum . We have selected a neotype for S. burbankii from specimens grown in St. Louis, Missouri that were obtained from the original distributor of Burbank’s “wonderberry” seeds, J.L. Childs of New York. These specimens are almost certainly amongst those seen by William Trelease during his part in the newspaper war that was waged over the identity of the “wonderberry” in the early part of the 19th century (see Heiser 1969) and match the description well. Several collections grown in Mr. Waldstein’s garden are held at MO and we have chosen the sheet with the best fruiting material as the neotype.

The Swiss botanist Rudolf Probst worked extensively on the adventive flora found around woollen mills in Solothurn (Switzerland) and sent much of his Solanum material to the Hungarian botanist Sandor Polgár, apparently both as specimens and as seeds. In his various publications ( Probst 1928, 1938), he quoted verbatim from Polgár’s letters, attributing both names and descriptions to Polgár for S. nigrum var. probstii and S. burbankii var. glabrescens . The numbers he cites in the protologues apparently refer to years of collection (e.g. "22, 24, 26, 27"), but we are not certain; because of the labels on specimens in BP seen and annotated by Polgár, we are assuming Probst sent herbarium specimens rather than seeds. We are therefore considering this material as lectotypes for these two names, both of which correspond to S. retroflexum . The letter quoted verbatim in the protologue of S. nigrum var. probstii is mounted on a sheet with a collection date (29 Jul 1929) later than the description, so we select another Probst collection from 24 Aug 1926 and annotated by Polgár (BP acc. # 485285) as the lectotype for this name. The specimen collected by Probst on 20 Oct 1922 (BP acc. # 485327) has elements of the text repeated in the protologue attached to it and we designate this as the lectotype for S. burbankii var. glabrescens .

Selected specimens examined.

Australia. New South Wales: Bouddi , 1970, Edmonds C 74 (K) ; Queensland: Somerset, Kentville , 28 Oct 1965, Henderson 123 (BRI, K) ; South Australia: Lower Eyre Peninsula, Sec [tion] 10, Hundred of Flinders , 13 Nov 1966, Alcock 1268 (AD); Pilli Waterhole, sect. 10, Hundred of Flinders , 27 Apr 1968, Alcock 2099 (AD, CANB, K) ; Victoria: Mildura, Hattah / Kulkyne National Park , 11 Feb 1989, Browne s.n. (AD) .

Botswana. Livingstone's Cave , Melepelele, 35 mi NW of Gaberone, 21 Apr 1974, Mott 236 C (K) .

Lesotho. Leribe: LHDA Phase 1A, 13 Jan 1996, Phillipson 4757 (MO); Basutoland, Dieterlen 157 (BM, K); Kolonyama plateau W border, 4 Oct 1969, Williamson 48 (K) .

Malawi. Southern: Blantyre, Ndirande Mountain , 2 May 1970, Brummitt 10323 (K) ;

Mozambique. Zambezia: Mocuba, ao km 40, estrada de Milange, 18 Mar 1943, Torre 4957 (MO) ;

Namibia. Erongo Mountains , 28 Jun 1916, Pearson 9834 (K) ; Khomas: Windhuk Bergland, regio Finkenstein , 13 Dec 1963, Seydel 3783 (A, K, MO) .

South Africa. Eastern Cape: turnoff to Carlisle Bridge from Grt Riebeek East Rd , Grahamstown grid, 31 Mar 1974, Bayliss BRI-B-761 (A, K); Annes Villa, Zuurberg, 2 Oct 1975, Bayliss 7182 (A, MO); Graaff Reniet, Bolus 50 (F, K); SA Nr camp site 1 km E of Steilkop, New Agatha Forest Reserve, 21 Apr 1971, Scheepers 54 (EA) ; Free State: Fauresmith, Apr 1937, Henrici 3080 (K); Mequatling's Nek , Apr 1972, Jacobs 8533 (K) ; Gauteng: Pretoria, Carlisle Bridge, Albany , 2 Apr 1978, Bayliss 8679 (MO); Burttholm, Verreniging, 25 Apr 1918, Burtt Davy 17658 (K); Magaliesberge, Pretoria District , 8 Jun 1955, Schlieben 7009 (F, K, MO) ; KwaZulu-Natal: 2829 (Harrismith) Drakensberg, Royal Natal National Park , 19 Jan 1987, Goldblatt & Manning 8416 (MO); Drakensberg Range, Tugela Valley & Mont-aux-Source, 3 Apr 1934, Humbert 14849 (MA); Distr. Alexandra, Station Dumisa, Campbellson, 17 Dec 1912, Rudatis 1805 (W); Ngome, 15 Dec 1969, Strey 9409 (E, EA, K) ; Limpopo: Duiwelskop, grid no. 3219CA, Clamvillham District, 15 Oct 1983, Bean 1366 (MO); New Agatha Forest Reserve , nr campsite 1 km E of Steilkop, 21 Apr 1971, Múller & Schespere 54 (K) ; Mpumalanga: Ermelo, Nooitgedacht Research Station , 19 Jan 1976, Balsinhas 2901 (K, MO); Namaqualand, Klipfontein, 23 Dec 1949, MacDonald 117 (BM); Bei der Stadt Lydenburg, Mar 1884, Wilms 1022 a (BM, E) ; North West: head of Helskloof, Hottentosparadyskloof, 28 Aug 1977, Thompson & Le Roux 134 (K); Magaliesberg , Jackson’s kiln, 28 Feb 1957, Vueeden 97 (K) ; Northern Cape: Westeljike bellings van Rebunie, Calvinia, 27 Dec 1977, Hanekom 2499 (K); Namaqualand, Ai-Ansi , 1 Jan 1950, MacDonald 137 (BM) ; Western Cape: Pro Spei (Cape of Good Hope), 1771, Banks & Solander s.n. (BM); Nr drift of Cayman’s River, George, Barkly s.n. (BM); Table Mountain , Burchell 856 (K); Simon's Bay , Cape of Good Hope , 1853, Wright s.n. (GH) .

Swaziland. Ukulula , Mbabane Dist, 13 Mar 1955, Compton 25011 (K) .

Zambia. Central: Copperbelt: Kitwe , 15 Jan 1960, Fanshawe, F-5353 (K) ; Northern: Kaloswe, Koloswe , 16 Jul 1930, Hutchinson & Gillett 3767 (K) ; Zimbabwe. Owelo Teachers College , 11 Nov 1966, Biegel 1413 (K); Vumba, Clouds Downs, 29 Feb 1960, Head 170 (BM); sin. loc, Hislop Z-155 (K); Bulawayo, Jan 1898, Rand 171 (BM) ; Bulawayo: Bulawayo , garden, 9 Oct 1946, Best 499 (K) ; Harare: Harare, Salisbury Expt. Station, 26 May 1943, Arnold 10206 (K); Harare, Salisbury Botanic Garden , 30 Jan 1969, Muller 743 (K) ; Manicaland: Umtali, Nuza plateau, Mutasa Distr. , Oct 1934, Gilliland 974 (BM, K); Nyanga , Inyanga Distr. , 11 Jan 1931, Norlindh & Weimarck 4199 (BM, MO) ; Mashonaland Central: Mazowe, southern Rhodesia, Mazoe , Umvukwes , Ruorka Ranche , 17 Dec 1952, Wild 3961 (MO) ; Mashonaland East: Pasture Research Station, Marandellas , 28 Mar 1934, Brain 10574 (MO) ; Masvingo: Victoria, Rhodesia , 1909, Monro 1024 (BM) ; Matabeleland North: Makoholi Experiment Station, Victoria District , 13 Mar 1978, Senderayi 226 (K) ; Matabeleland South: Matobo, Farm Beana, Kobila , Apr 1957, Miller 4341 (K); Gwanda, Tuli Experimental Station Reservior in pasture block, 16 Jan 1965, Norris-Rogers 599 (K) ; Midlands: Sable Park, QueQue District , 13 Mar 1978, Chipunga 168 (MO) .

Figures

Figure 40. Solanum retroflexum A Habit B Flower. Drawing by M. L. Szent-Ivany, first published in Symon (1981), courtesy of the Board of the Botanic Gardens and State Herbarium (Adelaide, South Australia), reproduced with permission.

Figure 41. Solanum retroflexum A Habit B Glandular indumentum present in some individuals C Flowers D Mature, slightly ovoid dull black-purple fruits with reflexed calyx lobes (A, C Nijmegen acc. A 1450022; B Nijmegen acc. 944750163; C Nijmegen acc. A 14750023; D Nijmegen acc. A 14750025). Photos by S. Knapp and G. van der Weerden.

Figure 42. Distribution of Solanum retroflexum in the native range in Southern Africa (black circles) and in its non-native range (white squares).