Cyperus stroudii Gray, A. & Stott, 2017

Cyperus stroudii Gray, A. & Stott View in CoL , sp. nov.

Type:— ASCENSION ISLAND, between White Hill and Weather Post: approx. 1 km SW of Spire Beach , on flat, area composed of shallow soils derived from weathered volcanic debris, -7.944987, -14.3221200, 160 m, 21 July 2010, (Holotype: E, A. Gray s.n.! GoogleMaps AG101! GoogleMaps AG102! GoogleMaps ).

Caespitose perennial, mean height of 3.1 cm with a range of 1.6 to 9.4 cm in the type locality (n = 30), in cultivation plants achieve a greater height of up to 17 cm. Leaves, bracts, stems, and rays green to glaucous-green when fresh and glaucous when dry, papillate throughout. Rhizome horizontal and short up to 5 mm long. Culms diameter when dry 0.3–0.6 mm and 0.6–0.9 mm when fresh, trigonous but rounded, papillose and only slightly scabrous towards the inflorescence. Leaves In the type locality, mean leaf length is 3.2 cm with a range of 0.5 to 6.0 cm, and up to 1 mm wide, again leaves larger in cultivation 7 to 22 cm long, v-shaped, coriaceous, the margins and keel scabrid; sheaths brown. Inflorescence bracts leaf like 2–3, 0.6–1.7 wide and 1–13 cm long, the margins and keel scabrid, either slightly ascendant or descendant. Simple contracted ovoid inflorescence 10–20 mm diameter. Spikelets 6–10, 1–2.5 mm long, (rather finely spaced, concealing the short rachis), oblong-ellipsoid to oblong lanceolate, compressed; rachilla approximately 0.25 mm wide, successive spikes 1 mm apart; Glumes lanceolate 4 nerved when dry but appearing one nerved when fresh, pale green becoming reddish brown when ripe, persistent, 1–3 mm long, 1–2 mm wide, ovate, slightly mucronate. Stamens 3; filaments 1–3 mm long (at maturity of Nutlets); anthers (0.8–1.2) yellow. Styles and stigmas roughly equal in length 1.5, ca. 3 mm long in entirety. Nutlet about 0.6–2 mm long, 0.2–1 mm wide, trigonous, broadly obovoid, apex sub-acute, the base tapering from the middle, sessile, papillose, and brown. See Figures 4 View FIGURE 4 and 5 View FIGURE 5 .

Phenology: collections were made in July and the majority of plants were in flower which appears to occur rapidly after germination and throughout the year.

Habitat: Figure 3 View FIGURE 3 shows the type locality, an area of dry xeric gravel, sandy soil derived from weathered volcanic material, 300 m. There are few other native species in the area except Aristida adscensionis Linnaeus (1753: 82) and Psilotum nudum ( Linnaeus 1753: 1100–1101) Palisot de Beauvois (1805: 112) and introduced plants dominate the vegetation including Psidium guajava Linnaeus (1753: 470) , Juniperus bermudiana Linnaeus (1753: 1039) , Cyperus owanii Boeckeler (1878: 29) .

Distribution: endemic to the island of Ascension.

Conservation Evaluation: Cyperus stroudii is known only from Ascension Island from a single locality, occupying a very small area that is declining in quality due to encroachment by invasive species. Using IUCN (2012) criteria we would preliminary evaluate C. stroudii as Critically Endangered B2ab(iii)+2ab(iii).

Etymology: named for Stedson Stroud of St Helena who has dedicated many years to the conservation of the endemic and native plants of Ascension and St Helena. Stedson also aided in the collecting of material and his company in the field has always been a privilege.

Notes: Cyperus stroudii is in Cyperus sect. Turgiduli (C.B.Clarke) Kük. ( Kükenthal 1935 –36; Wilson 1991; Larridon et al. 2011). Morphologically , Cyperus stroudii is most similar to C. appendiculatus (Brongn.) Kunth , a species of the islands of the South Atlantic ( Ascension, Fernando de Noronha , Trindade ). These two species are sympatric on Ascension. In the type locality, C. stroudii can be quickly distinguished in the field because of its diminutive size, moving further afield it can be difficult to distinguish from C. appendiculatus because of the presence of intermediates and microscopic examination is required. The degree of any hybridisation and or environmental influence in the intermediate population has yet to be determined but should be a focus of a future revision of the entire C. appendiculatus group. The conservation of C. stroudii is also in need of some urgent action. The single population is extremely vulnerable to invasive species and stochastic events that could easily render the population extinct. A small ex situ collection exists in Edinburgh but we would recommend further seed collection and the establishment of on island cultivated material as well as a collection housed in the Millennium Seed Bank.