Sesuvium ayresii Marais, Kew. Bull. 32(2): 483 (1978)

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 : 56-57

Sesuvium ayresii Marais, Kew. Bull. 32(2): 483 (1978) Fig. 8

Holotype.

MAURITIUS [main island], Fort William, Sep 1860, Ph.B. Ayres s.n. (K000076290! iso - LE!).

Description.

The description of S. ayresii was provided by Marais (1978). The most indicative characters of this species are small (up to 25-28 mm long, but usually smaller) terete or semi-terete leaves and (sub) Sesuvium sessile flowers (see Marais 1978, Hartmann 2002). Additionally, Marais (1978) reported a smaller number of stamens (12-20) that have never been observed in S. portulacastrum (stamens more than 30). The smaller seed size (~1 mm) of S. ayresii compared with S. portulacastrum ( Marais 1978) seems to be an insignificant diagnostic trait. Leaf shape and leaf size are very variable, sometimes within a given individual.

Ecology.

Sesuvium ayresii usually grows on coral rocks, basalts or calcarenites ( Marais 1978), but it also can be encountered on sandy seashores, like many other species of the genus. The records of Sesuvium from the calcarenite islets of Les Bénitiers ( Johnston 1894) and Rochers des Oiseaux ( Johnston 1895) probably belong to S. ayresii . Sesuvium ayresii is reported as the only member of the genus in the Mascarenes ( Marais 1990).

Additional specimens examined

(Fig. 14 ). MAURITIUS [main] Island: Gris Gris, [no date, before 1932], Vaughan 653 (MAU 0017795); Rocky coast near Rivière des Anguilles, 8 Dec 1962, Edgerley S. n. (MAU 0017801); Post Lafayette, east coast, 11 Jan 1973, Lorence 189 (K, MO324309 ); estuary of Black River, 10 Sep 1981, L. Averyanov 446 (MHA); Mer Rouge, 13 Mar 2004, Pynee et al. s.n. (MAU 0012461); Cap Malheureux, 26 Apr 2004, Pynee S. n. (MAU 0017803); Albion, 10 Nov 2011, Pynee S. n. (MAU 0009004); Rivulet Terre Rouge Bird Sanctuary, 01 Sep 2017, Baider CB 2729 & V. Florens (MAU 0023815); Mauritius [islets] Island: Gunner’s Quoin or Quoin de Mire, 1871, Horne 129 (K); 06 Aug 2007, Baider CB 677 & V. Florens (MAU 0023819); 07 Aug 2007, Baider CB 701 A & V. Florens (MAU 0023820); 07 Aug 2007, Baider CB 701 B & V. Florens (MAU 0023821); Ile de la Passe, 26 Oct 1888, Johnston s.n. (E00651982); 29 Nov 2003, Baider CB 588 & V. Florens (MAU 0023826); Ile aux Fouquets, 4 Nov 1962, Rountree s.n. (MAU 0017798); Ilot Marianne, east coast, 13 May 1956, Vaughan s.n. (MAU 0017796); 18 Jan 1975, D. Lorence 1059 (K, MAU 0017800); 28 Nov 2007, Baider CB 551 & V. Florens (MAU 0023822); 31 Jul 2007, V. Florens s.n. (MAU 0023823); Ilot Sancho, south coast, 15 Aug 1974, D. Lorence 943 (K, MAU 0017799); Ile D’Ambre, 21 Dec 2003, Baider CB 783 A & V. Florens (MAU 0023827); 21 Dec 2003, Baider CB 783 B & V. Florens (MAU 0023828); Ilot Bernache, 21 Dec 2003, Baider CB 814 & V. Florens (MAU 0023829); Ilot Gabriel or Gabriel Islet, 20 Apr 2006, Pynee S. n. (MAU 0017804, MAU 0017805), 06 Aug 2007, Baider CB 1942, V. Florens & D. Hammond (MAU 0023825); Ile aux Fous, 01 Aug 2007, V. Florens & D. Hammond s.n. (MAU 0023824); Rodrigues [main] Island: Plaine Coral, Jul 1970, Cadet RO 218/2604 (MAU 0017807); 1874, Balfour s.n. (E00651981, K); Rodrigues [islets] Island: Frigate Island , Jan 1963, Staub s.n. (MAU 0017806); Ile Gombrani, 10 Jan 2004, Baider CB 932 & V. Florens (MAU 0023817); Ile aux Crabes, 13 Jan 2004, Baider CB 1036 & V. Florens (MAU 0023818); Ile aux Cocos, 15 Jan 2004, V. Florens s.n. (MAU 0023816) .

General distribution.

Endemic to the Mascarenes.

Conservation status.

The species should be considered Near Threatened (NT) according to the IUCN red list criteria ( IUCN 2017). This assessment is based on the species’ EOO of 24,241 km2 and AOO of 68 km2; together with other factors including the species’ habitat being restricted to seashores affected by salt spray, fragmentation of the populations and a high probability of losing sites in the near future due to habitat transformation (construction of hotels, improvement of seashores by removal of vegetation, dumping of refuse in the coastal belt), especially on mainland Mauritius. Only a few of the populations are located in areas with some degree of protection such as Nature Reserves or National Parks (one on Rodrigues; nine on Mauritius), most of them being on small islets. Some records are over 50 years old and need to be updated to determine any decline in its geographic distribution. Competition with invasive alien plants seems not to be a serious problem for this species, although sea-level rise is reducing the area of suitable habitat.

Figures

Figure 8. Sesuvium ayresii: A the only species growing on the islet (Ile aux Fous, Mauritius, 1 August 2007) B clumps on sandy beach (Ilot Gabriel, Mauritius, 6 August 2007) C an individual clump on calcarenite (Ile de la Passe, Mauritius, 3 February 2007) D close-up of a flower (Rivulet Terre Rouge Bird Sanctuary, Mauritius, 1 September 2017). Photographs by F. B. V. Florens.

Figure 14. Distribution map of Sesuvium ayresii (stars) and S. portulacastrum subsp. portulacastrum (circles, mapped only for Africa).