Sesuvium portulacastrum subsp. persoonii Sukhor., 2018

Sukhorukov, Alexander P., Nilova, Maya V., Erst, Andrey S., Kushunina, Maria, Baider, Claudia, Verloove, Filip, Salas-Pascual, Marcos, Belyaeva, Irina V., Krinitsina, Anastasiya A., Bruyns, Peter V. & Klak, Cornelia, 2018, Diagnostics, taxonomy, nomenclature and distribution of perennial Sesuvium (Aizoaceae) in Africa, PhytoKeys 92, pp. 45-88 : 67-71

Sesuvium portulacastrum subsp. persoonii Sukhor. subsp. nov.

Sesuvium pedunculatum sensu Sieber (in herb.) non Pers.

Diagnosis.

Differs from the autonymous subspecies by the absence of rampant ramification, clearly petiolate leaves (petioles 5-10 mm long) that are usually less than three times as long as wide (all blades including those of upper leaves ovoid or oblong, 20-40 × 10-15 mm) and 3-9 mm thick.

Holotype.

Republic of Cape Verde, Sal Island, 2 km W of Santa Maria town, 16.590246, -22.924272, sandy depressions near the sea, 30 Aug 2015, A.P. Sukhorukov 59 (MW0595660! iso - BR, G, K).

Description.

Sprawling glabrous perennial herb (the shoots are often partially buried by sand and appear to be separate plants) with ramification not rampant; stems rooted or not, roundish, greenish or more often red (Fig. 15A, B ), 3-5 mm in diameter, ascendent (not creeping); leaves opposite, petiolate; petioles 5-10 mm, reddish or green, broadened basally, leaf blades oblong, 20-40 mm long (the leaves on the shortened shoots are smaller), 10-15 mm wide, 3-9 mm thick, entire, green or reddish (Fig. 15C ); flowers solitary in the leaf axils (each node bears one flower from one of the opposite leaves), ~10 mm in diameter, with two hyaline glabrous bracteoles; pedicels 3-5 mm, accrescent at fruiting stage up to 10(15-20) mm long; perianth bifid, apically acutish, green abaxially and pink adaxially (Fig. 15D ), without prominent red glands at the tip of the segments; stamens ~50, pink, slightly shorter than perianth, filaments 5 mm long, anthers 0.4-0.6 mm long; ovary turbinate, with (2)3-4 stigmas; seeds ~20, black, roundish, ~1 mm across, completely covered with a funicular aril; seed surface smooth or slightly uneven.

Etymology.

The subspecies is named after Christiaan Hendrik Persoon (1761-1836), botanist and mycologist, who described several Sesuvium species.

Ecology.

Sandy beaches near the sea and seasonally flooded, saline plains on the landward side of the coastal dune belt.

Flowering and fruiting.

All year round, but most abundantly from September to May (at least in the Cape Verde Islands).

Taxonomic and nomenclatural notes.

Franz Wilhelm Sieber labelled his Sesuvium collections from Senegal as S. pedunculatum Pers. The use of this name for the African material is very confusing but explained here.

The name was published by Persoon (1806), who provided a very short diagnosis mentioning pedicellate flowers (not petiolate leaves!) and noted that the species originates from India. It is assumed that Persoon probably did not see the plant in the wild. A specimen was found in the De Candolle herbarium (G-DC) that contains three fragments of different origin: two fragments of S. portulacastrum from the Caribbean and one fragment of Sieber’s collection from Senegal (1825) named S. pedunculatum . However, the material kept at G-DC is not a type of S. pedunculatum , but only one of the duplicates sent by Sieber to different herbaria.

In Leiden (L), where the largest collection of Persoon’s types is deposited, one sheet with two different plant fragments and without any information about their locality (L1693369) was found with the label " Sesuvium pedunculatum Lam." (!) (Fig. 16 ). Lamarck’s authorship of this species is clearly wrong (see Lamarck 1817: 141). The plant fragment on the left side of the herbarium sheet shows typical characteristics of the leaf shape found in S. portulacastrum subsp. persoonii , but it is named by Ch. H. Persoon as S. portulacastrum . The right fragment on the sheet belongs to the autonymous subspecies of S. portulacastrum . According to Persoon’s identification, his new species ( S. pedunculatum Pers.) is indeed a synonym of the typical S. portulacastrum that has been recorded in India at least since the 17th century, probably as an alien species (BM, K and L). Sesuvium pedunculatum was treated as a variety under S. portulacastrum (as S. portulacastrum var. pedunculatum ) by Cambessedes (in Saint-Hilaire 1829), who described this variety from temperate South America (!) as "les fleurs sont un peu plus grandes, et portées sur des pédoncules longs de deux à trois lignes" [the flowers are slightly larger, with the pedicels two to three lines long]. Furthermore, the synonymisation of S. pedunculatum and S. portulacastrum is confirmed by reference of Persoon ( Persoon 1806) to the very clear drawing in Lamarck (1793) showing the shoot, flowers and fruits of typical S. portulacastrum . This image in Lamarck (1793) was chosen as the lectotype of S. pedunculatum by Hartmann (2002) and it is treated by her as a synonym of S. portulacastrum . Her opinion was accepted by Bohley et al. (2017). The authors also agree with Hartmann (2002) and Bohley et al. (2017) about the merger of S. pedunculatum with S. portulacastrum [ Sesuvium portulacastrum subsp. portulacastrum ].

Sesuvium portulacastrum subsp. persoonii is morphologically similar to S. repens Willd., a species found in coastal areas of the Indian subcontinent (E! G! K!). Both species possess distinctly petiolate leaves, but the latter species has much smaller (usually up to 20 mm long) leaves and shortly pedicellate flowers (pedicels at fruiting stage up to 6 mm long). Sesuvium portulacastrum always has tapered leaves with indistinct petioles up to 3 mm long. Additionally, the leaf thickness in S. portulacastrum subsp. persoonii varies from 3 to 9 mm and the leaves are especially thick (terete, almost roundish) in plants growing in saline depressions. In contrast to that, S. portulacastrum subsp. portulacastrum plants seen in the wild or in cultivation possess thinner (1.5-4 mm) leaves, in accordance with previous measurements ( Bohley et al. 2017). Besides, plants with clearly petiolate leaves ( S. repens and S. portulacastrum subsp. persoonii ) have never been found in the Americas.

Additional specimens examined

(Fig. 17 ). CAPE VERDE: São Nicolau Island, Praia Branca, 1851, C. Bolle s.n. (E00651990); Sal Island , Santa Maria , 19 Oct 1934, M. Dinklage 3192 (BM, BR0000013828158); Sal Island , 1934, A. Chevalier 44288 (P04602231); Boa Vista Island , Santa Monica beach, 15.981955, -22.831910, 10 Jan 2016, A. Sukhorukov s.n. (MW) ; GAMBIA: [Upper River Region] Keneba , Sep 1952, D.S. Bertram s.n. (K) ; GUINEA-BISSAU: Cacheu Region, S. Domingos sector, Candemba , 15 Apr 1997, M.A. Diniz & A.E. Gonçalves 1777 (K) ; MAURITANIA: [Dakhlet Nouadhibou Region] Cape Arguin, Dalmas, 5 May 1895, herb. E. Drake 6 (P04602228); Cansado, 1901, A. Gruvel s.n. (P04602226); Port Etienne [Nouadhibou], 12 Apr 1908, anonym s.n. (P04602227) ; SENEGAL: [without exact location] 1825, Sieber 19 (E000651984; G00660404; K; LE; M; P05196607); [without exact location and year] Sieber 112 (LE); [without exact location] 1859, Perrotet 366 (G); St. Louis , 1902, A. Chevalier 3469 (P04602206); Dakar, Hann beach, common, 23 May 1947, J.T. Baldwin 5754 (K); St. Louis , 23 Jul 1960, J.D. Kesby 20 (K); St. Louis , 14 Nov 1984, P. Bamps 7642 (BR0000013827533); Poumekhor, saline depression, common, 2 Feb 1966, J. Audru 3200 (P04602214); Joal-Fadiouth, 25 Jun 1973, P. Geissler 6538 (G) .

General distribution.

The authors are still not sure whether this overlooked subspecies is native to West Africa. Plants with such habit are known from the seashores near Chennai, India (Anand Kumar, pers. comm., with an image sent to AS), but are not represented in any herbaria. One sheet from "Peninsula Indiae Orientalis" (herb. Wight 963, L1693577) corresponds to the African specimens of S. portulacastrum subsp. persoonii (labelled as " S. portulacastrum var.") in leaf shape.

Reports of the occurrence and frequency of S. portulacastrum subsp. persoonii in West Africa until the early 20th century are inconsistent. The first reference for West Africa originates from Forster (1789, sub S. portulacastrum ) who cited it for Santiago Island (Cape Verde Archipelago). Schmidt (1852) thought that this record was doubtful, because this plant was not mentioned by other travellers. However, Hooker (1849) reported Sesuvium as a common plant on seashores of the adjacent Senegal. F.W. Sieber was the first to collect the specimens of S. portulacastrum subsp. persoonii (collections from Senegal in early 19th century, identified as S. pedunculatum ). Other specimens, named as S. portulacastrum and collected in mid-19th century in Cape Verde ( São Nicolau Island) and Senegal (without exact location), are stored in the herbaria E and G, respectively. Sesuvium portulacastrum subsp. persoonii (under the names S. pedunculatum or S. portulacastrum ) had not been reported amongst the most common plants in the checklists for West African plants until the early 20th century (e.g. Engler 1910). Chevalier (1920) cited Sesuvium portulacastrum subsp. persoonii (sub S. portulacastrum ) for West Africa (Mauritania and Senegal), with subsequent records for Santiago and Sal Islands (Cape Verde), where it grows spontaneously on the seashores and in saline depressions ( Chevalier 1935). M. Dinklage (collections from 1934, kept at BM!) noted the common and abundant Sesuvium populations on sandy beaches in Santa Maria village (Sal Island, Cape Verde). Recently, S. portulacastrum subsp. persoonii has been reported for several islands of Cape Verde Archipelago: Boa Vista, Mayo, Sal, Santiago and São Vicente ( Gilli 1976, Gonçalves 1995, Arechavaleta et al. 2005, all as S. portulacastrum ).

All populations of perennial Sesuvium seen by the first author (AS) in Cape Verde belong to S. portulacastrum subsp. persoonii . It is common at least in the southern part of Sal Island on the sandy beaches and seasonally flooded saline depressions by the seashores near Santa Maria and in pristine landscapes in Boa Vista (e.g., Santa Monica beach in the southern part of the island). In Sal Island, S. portulacastrum subsp. persoonii is often a characteristic species of such habitats together with other dominant plants of coastal communities, such as Arthrocaulon franzii (Sukhor.) Piirainen & G.Kadereit (≡ Arthrocnemum franzii Sukhor.), Suaeda vermiculata Forssk. ex J.F.Gmel., Tetraena fontanesii (Webb & Berthel.) Beier & Thulin (≡ Zygophyllum fontanesii Webb & Berthel.) and Cistanche phelipaea (L.) Cout. Based on the specimens seen, it is concluded that Sesuvium portulacastrum subsp. persoonii is present on the seashores and saline depressions in (semi)arid territories of West Africa (Cape Verde, Gambia, Guinea-Bissau, Mauritania and Senegal) as a geographically separated form of S. portulacastrum .

Conservation status.

Sesuvium portulacastrum subsp. persoonii is common on sandy inland plains on Sal and Boa Vista islands (Cape Verde). Herbarium labels refer to it as a very characteristic plant of seashore communities in Senegal. Currently the construction of new buildings close to the coast is drastically damaging the natural landscapes, especially on Cape Verde Archipelago ( Romeiras et al. 2016, Sukhorukov and Nilova 2016) and may negatively affect the number of populations. However, at present, as there is doubt about the origin of this new subspecies (if it is native to the region), it should not be assessed for the IUCN Red List until more data is available.

Figures

Figure 15. Sesuvium portulacastrum subsp. persoonii: A general view of the plant (of red colour) in saline depressions near the seashore, together with the subshrub Arthrocaulon franzii B S. portulacastrum subsp. persoonii on the seashore dunes C closer look at an individual D close-up of the flower. Photographs by A. Sukhorukov (A-C Sal Island, Cape Verde, August 2015) and A. Konstantinova (D Sal Island, Cape Verde, January 2016).

Figure 16. A specimen kept in Leiden (L 1693369) and probably seen by Persoon, containing both Sesuvium portulacastrum subsp. portulacastrum (right) and S. portulacastrum subsp. persoonii (left) from different locations (America and West Africa, respectively).

Figure 17. Distribution map of Sesuvium portulacastrum subsp. persoonii (circles) and S. verrucosum (stars).