Gymnosiphon mayottensis Cheek, 2020

Cheek, Martin & Traclet, Sébastien, 2020, Gymnosiphon mayottensis Cheek, sp. nov. (Burmanniaceae) a new species from Mayotte, Comoro Islands, Adansonia 42 (8), pp. 179-188 : 181-182

Gymnosiphon mayottensis Cheek , sp. nov.

( Figs 1-3 )

Gymnosiphon mayottensis Cheek , sp. nov. resembles G. longistylus (Benth.) Hutch. in the six long, filamentous, stigma appendages, two each arising from each of the three styles, also in the absence of an underground tuber or thickened rhizome; it differs in that the bracts are appressed to the rhachises, and about equal in length to them (not patent, and <1/4 as long), the outer tepals turn rapidly from white to translucent at anthesis (not remaining white), the inner perianth lobes are absent (not present and conspicuous), the stigmas are broader than long, held horizontally and are united along their lateral margins (not longer than broad, pendulous, free from each other along their lateral margins).

TYPUS. — Mayotte. Grande Terre, Chirongui , Bénara , bord de sentier, 567m, [–12.879241, 45.160691], sous-bois de forêt humide d’altitude, fl., 01. IV.2019, S. Traclet, A. Dimassi & E. Vennetier 665 (holo-, K [ K000593140 ]; iso-, MAO[MAO03189]; P, MO).

PARATYPI. — Mayotte. Grande Terre, Chirongui, Bénara, à droite du sentier, [–12.87921, 45.16077], bord de sentier de forêt humide, (fl., 24.III.2019, E.Vennetier 9 (MAO[MAO02677]); GrandeTerre, Chirongui, Bénara, au milieu du sentier, 560 m, [–12.878979, 45.160331], sous-bois de forêt humide d’altitude, spécimen le plus bas observé ce jour en fleur à 14h, pas d’autre individu sur la station, fl., 01.IV.2019, S. Traclet, A. Dimassi & E.Vennetier 666 (MAO[MAO03190]); GrandeTerre, Chirongui, Bénara, sur la petite colline du Cynorkis sp. blanc, 535 m, [–12.876430, 45.159233], fl., 07.IV.2019, E.Vennetier 12 (MAO[MAO02287]); Grande Terre, Mamoudzou, Majimbini, RF de Majimbini, 483 m, [–12.766693, 45.189309], forêt humide sur crête à Labramia mayottensis, Brexia madagascariensis, Grisollea myrianthea et Garcinia anjouanensis, fl., 03.V.2019, A. Dimassi & E. Vennetier 123 (MAO[MAO04114]).

DISTRIBUTION. — This species is known from Mayotte island at altitudes between 300 m and 600 m above sea level. Two stations are referenced: the largest one at Mount Bénara (area of station c. 13 ha) and a second at Mount Mtsapéré (area of station c. 8 ha). Photographs of what appears to be a similar but slightly different species have been seen from Moheli, but material has not yet been obtained so the specific identification remains uncertain.

HABITAT. — Old secondary tropical humid forest above 300 m, and primary forest 450-567 m primary altitude.

PHENOLOGY. — Flowering was observed in March, April and early May.

ETYMOLOGY. — The epithet refers to the island of Mayotte, from which the species was discovered and to which the species is endemic on current evidence.

DESCRIPTION

Erect, probably perennial herb 7-9 cm tall above roots, above ground part c. 3-5 cm tall (Traclet et al. 665), glabrous, achlorophyllous, white when alive. Tuber(s) and swollen rhizome absent. Base of stem (only one seen) with loose rosette of 3-4 spreading, oblong, white reduced leaves, 0.8- 2 × 0.5 mm, apex obtuse. Roots c. 7, vermiform, to 5 mm long, c. 0.1 mm diam. Stem terete, erect, single, unbranched, c. 6 cm long, c. 1 mm in diameter, internodes 5-25 mm long. Scale-leaves cupular 0.5-0.6 mm diam., clasping the stem for 40-50% of its circumference. Inflorescence appearing subcapitate, 1-11-flowered, initially single-flowered, then cymose-biparous, with two equal but contracted branches. Bracts navicular (elliptic-oblong, concave), 1.5-1.6 × 0.5- 0.5 mm, adpressed to the rhachis (inflorescence axis), about as long as the internodes which they subtend, apex rounded. Pedicels 1.2-1.4 mm long. Flower white in bud, becoming translucent at anthesis, erect, actinomorphic, 3-4.5 mm long, 4(-5) mm wide at anthesis (flowers recorded open at 1400 hrs: Traclet et al. 665, 666), scent if present not recorded. Perianth tube 1.5-1.7 mm long, cylindrical, 1.3 mm wide, distal portion of tube above anther insertion as broad as the proximal portion. Outer tepals 3, oblong in outline, 1.5-1.8 × 1.2-1.3 mm, patent, with two slender lateral lobes, diverging from the main, central lobe by up to 45°, lateral lobes arising between the base and the distal half of the central lobe and in the same plane, 0.2-0.7 × 0.1 mm, apex obtuse. Inner tepals absent. Anthers inserted below the stigmatic head, c. 0.5 mm below the sinus between the outer perianth lobes, each 0.4-0.5 mm long, 1.5-1.7 mm wide, the two lateral, dithecal anthers globose, 0.5-0.7 mm diam., separated by 0.2-0.3 mm on the large, conspicuous connective. Style cylindrical, 1.5-2 mm long, 3-lobed at apex, stigmatic head 1.2 mm wide, the three stigmas horizontal, each lunate to bifurcate-broadly obtriangular, 0.4-0.6- 0.7 mm, each with a filiform appendage c. 2 mm long arising abruptly from the two sides, the appendages (probable pollen-receptive surfaces) extending along the outer perianth lobes. Ovary cylindric, outer surface lacking conspicuous ribs, 1.5-2 × 1.2-1.4 mm, unilocular, with 3 protoseptal, intruded parietal placentas, septal nectary glands six, globose, c. 0.2 mm diam., flanking the septae immediately below the junction with the perianth tube. Fruit indehiscent, lacking ribs, globose-ellipsoid, c. 1 × 1 mm, walls membranous, showing seeds; distal perianth tube remains subcylindrical, c. 1.5 × 1 mm. Seeds globose, 0.1-0.15 mm diam.

CONSERVATION STATUS

Despite the fact that all populations of Gymnosiphon mayottensis Cheek , sp. nov. are found in forest reserves, anthropogenic pressure still represents a strong threat on Mayotte. This is because traditional agriculture (slash-and-burn) is increasing everywhere, including inside the forest reserves. During the year 2013, the areas burned in forest reserves represented more than 76 ha (OFDM 2015). In addition, liana covers of the canopy by species such as Decalobanthus peltatus (L.) Simões & Staples ( Convolvulaceae ) regularly causes forest cover collapses and increases development of invasive alien species which threaten the ecosystem.

At the main station of the new species (Mount Bénara), less than 30 individuals were observed in a small area (13 ha). However, it is difficult to estimate accurately the size of the population because of the small size of the individuals which makes them inconspicuous. At the Mount Mtsapéré station, less than 25 individuals were found in small area (8 ha). According to the IUCN criteria ( IUCN 2012), using the IUCN-preferred grid cells of 4 km ², the area of occupancy is 8 km ², while the area of occurrence is difficult to calculate since only two points are known but is estimated as 9 km ², and the species is severely fragmented due to clearance of the forest habitat between the two sites. In addition, we estimate a decline in the area of occupancy, number of localities and habitat quality, and in the number of mature individuals. The number of mature individuals is less than 50. Therefore, we propose, using the IUCN (2012) standard, the assessment of this species as Critically Endangered (B1ab(i-iv), B2ab(i-iv), D) at the global and regional level ( Mayotte). It would be highly desirable for it to be the subject of a special protection statute. We recommend that a management plan to ensure the survival of this species is made and implemented. This should include a public sensitisation programme, annual monitoring of the Gymnosiphon population to determine trends in survivorship and threats, potentially increased guarding of the forest habitat, and seedbanking. Cultivation of achlorophyllous mycotrophic flowering species such as Gymnosiphon mayottensis Cheek , sp. nov. has never been achieved and so it is recommended that this is not attempted.

Figures

FIG. 1. — Gymnosiphon mayottensis Cheek, sp. nov.: A, habit; A’, detail showing base of stem and roots; B, branch of inflorescence with flower buds and detail of bract; C, dissection of large flower bud from B; D, open flower; E, perianth and stigmas (from photo); F, stamen and pair of lateral outer perianth lobes from bud dissected in C; G, stigmatic filament looped over lateral perianth lobe in bud dissected in C; H, fruit (dried). All drawn from S. Traclet 665 (MAO03189), liquid preserved, unless otherwise indicated. Drawn by Andrew Brown. Scale bars: A, 1 cm; A’, B, C, D, H, 2 mm; E, F, G, 1 mm.

FIG. 2. — Gymnosiphon mayottensis Cheek, sp. nov.: A, habit, whole plant with underground parts exposed; B, inflorescence viewed from above, note navicu- lar bracts; C, flower at anthesis viewed from above, note filamentous style arms; D, flower viewed from side, note the translucent tepals. Photos: A, Guillaume Viscardi; B-D, Étienne Vennetier.

FIG. 3. — Map of the global distribution of Gymnosiphon mayottensis Cheek, sp. nov. Map by Sébastien Traclet.