Erythroxylum choungiense, E. Bidault, Traclet & M. Pignal, 2022

Bidault, Ehoarn, Traclet, Sébastien & Pignal, Marc, 2022, Novelties in Erythroxylum P. Browne (Erythroxylaceae) from the Comoros Archipelago: two new, range-restricted and threatened species, and notes on the Mount Choungi biogeographical singularity, Adansonia (3) 44 (21), pp. 215-228 : 219-222

1. Erythroxylum choungiense E.Bidault, Traclet & M.Pignal, sp. nov.

( Figs 1 ; 2 )

Ab aliis speciecibus Erythroxylorum Insulae Comorianae Madagascaraeque species nova facile differt conspicuis cordatis ad basem curvinervisque foliis (vs cuneata rectinervaque et angulos ad apicum).

TYPUS. — Mayotte. Grande Terre, Kani-Kéli , Choungui , peu avant le sommet du Mont Choungui , 450 m, 12°57’25”S, 45°08’02”E, fl., fr., 30.XI.1997, J.-N. Labat & O. Pascal 2920 (holo-, P [ P00080562 ]! ; iso-, G, K, MAO [ MAO00616 ]!, MO, WAG) .

PARATYPI. — Mayotte. Grande Terre, Chirongui , Choungui , Mlima Choungui , fl., 16.XI.1995, O. Pascal 209 ( MAO [ MAO01945 ]!; P [ P00143108 ]!) ; fr., 29.XII.1995, O. Pascal 286 ( MAO [ MAO01948 ]!; P [ P00143107 ]!) ; 593 m, fl., 17.VI.1996, O. Pascal 593 ( MAO [MAO01944]!, P [ P000780170 ]!) ; Réserve forestière de Choungui , fr., 28.XI.2002, F. Barthelat, F. Melki & B. Ali Sifari 1100 ( MAO [ MAO00618 ]!; P [ P00339177 , P00339178 ]!; K; MO) ; 18.XI.2002, F.Barthelat, P.Hoffman, H. Ralimanana. M. Mchangama & B. Ali Sifari 1084( MAO [ MAO00619 ]!; P [ P00339195 ]!) ; 03.I.2004, F. Barthelat, G. Viscardi & N. Parras 1260 ( MAO [ MAO00620 ]!; P [ P00437926 ]!). — Grande Terre, Kani-Kéli , Choungui , sommet du Mlima Choungui , 500-640 m, 12°57’52”S, 45°7’55”E, fr., 30.XII.2000, J.-N. Labat & F. Barthelat 3349 ( MAO [ MAO00617 ]!; P [ P00209805 ]!) ; plateforme 2 , fr., 09.IX.2014, V. Guiot 3 ( MAO [ MAO00433 ]!) ; au-dessus du sentier avant le plateau dans le sous-bois, 537 m, 12°57’26.30”S, 45°08’02.18”E, st., 02.I.2019, S. Traclet & A. Abdallah 591 ( MAO [ MAO02187 ]!; P [ P000780169 ]!) ; plateforme (point de vue) du sentier qui monte au padza, 504 m, 12°57’27”S, 45°08’02”E, fr., 02.I.2019, S. Traclet & A. Abdallah 593 ( MAO [ MAO02189 ]!; P [ P000780168 ]!) ; 06.II.2019, S. Traclet 651 ( MAO [ MAO02283 ]!; MO; P [ P01069781 ]!) ; dans les pentes ouest avant de traverser le padza à fougères, 538 m, 12°57’25”S, 45°08’01”E, fr., 02.I.2019, S. Traclet & A. Abdallah 598 ( MAO [ MAO02194 ]!; P [ P000780167 ]!) ; pente à l’ouest du sentier montant au sommet, 533 m, 12°57’26”S, 45°08’02”E, fr., 06.II.2019, S. Traclet 640 ( MAO [ MAO02272 ]; P [ P000780166 ]!) ; 524 m, 12°57’26.20”S, 45°08’01.38”E, fr., 06.II.2019, S. Traclet 645 ( MAO [ MAO02277 ]!; P [ P000780165 ]!) ; 512 m, 12°57’27”S, 45°08’01”E, fr., 06.II.2019, S. Traclet 652 ( G; MAO [ MAO02284 ]!; P [ P01069782 ]!) ; 468 m, 12°57’28.87”S, 45°08’00.79”E, fr., 06.II.2019, S. Traclet 653 ( MAO [ MAO02287 ]!; P [ P01069783 ]).

ETYMOLOGY. — The specific epithet refers to Mlima (Mount) Choungi, to which the species is endemic.

HABITAT AND DISTRIBUTION. — Erythroxylum choungiense sp. nov. is restricted to submontane nepheliphilous shrubland with Buxus madagascarica Baill. and Olea capensis subsp. macrocarpa (C.H.Wright) Verd. ( Boullet 2005; Fadul 2011), where it occurs locally in a south-southwest oriented ravine, along with Eugenia choungiensis Byng & N.Snow , Cynometra mayottensis Labat & O.Pascal , Cassipourea ovata Tul. , Chionanthus cordifolius Labat, Pignal & O.Pascal , et Securinega durissima J.F.Gmel. This species is only known from Mayotte island, at altitudes between 470 and 580 m. Only a single locality is known, near the top of Mount Choungi.

PHENOLOGY. — Flowering material has been collected in June (Pascal 593) and from November to December. Fructification starts at the end of November and extends through February, with a peak of fruit maturation at the end of January.

CONSERVATION STATUS. — Erythroxylum choungiense sp. nov. is endemic to Mayotte and known from 17 collections made between 1995 and 2019, only 10 of which provide precise geographical coordinates, although all of them came from the same area on Mount Choungi. These collections represent a single extant subpopulation, and while the total number of individuals has not been counted, the population size is estimated to exceed 50 individuals. Using a 2 × 2 km cell size, the AOO of this species is estimated to be 4 km 2, below the upper threshold for “Critically Endangered” status under Red List Criterion B2. Calculation of the EOO would yield a lower value than the AOO, so the EOO is therefore calculated to the AOO (4 km 2), below the upper threshold for “Critically Endangered” status under Criterion B1. All occurrences are located within the recently created National Natural Reserve No. 328 (Réserve Naturelle Nationale des Forêts de Mayotte). The single subpopulation is nevertheless threatened by touristic activities, including uncontrolled hiking to the summit of Mount Choungi, which induces a decline in the quality of the habitat of this species. As a consequence, the 10 occurrences represent a single location (sensu IUCN 2012; IUCN Standards and Petitions Committee 2019) with respect to the most serious plausible threat (touristic activities). Based on this threat, we infer a past, current and a future continuing decline in the extent and the quality of its habitat. This species is thus assessed as Critically Endangered [CR B1ab(iii)+2ab(iii)].

DESCRIPTION

Shrub to 3 m tall, densely branched, with numerous short branches. Branches 2-5 mm in diameter, arranged alternately, silver-brown, finely striated; branches vinous when young, with numerous, elongated, yellowish lenticels 0.8-1.8 mm long; internodes 2-24 mm long on short branches. Cataphylls scarce, restricted to the youngest portion of stems, usually by 2(or 3) in the 1-2.5 cm portion of stem above each leaf, triangular, symmetrical, 1.8-2.2 × 2-2.4 mm, with two conspicuous longitudinal straight wings and a third wing between the two others, only visible in the apical half. Stipules caducous, often present on youngest leaves, 2-2.5 × 2- 1.2 mm, triangular, asymmetrical, the longest margin to 2 mm, the shortest to 1.2 mm, apex joining the opposite stipule, base thickened, keel winged, straight, margins entire. Petiole 1.5-2.5 × 0.7-1 mm, subterete. Leaf blade (28-)45-60(-85) × (14-)22-29(-42) mm, chartaceous, usually ovate to elliptic, rarely obovate, base cordate, margins slightly revolute, apex acuminate, acumen rounded, 1-3 mm long, blade red when immature, discolorous when mature, medium-green (silver-green when dry) adaxially, light green (light brown to ochre when dry) abaxially, the midrib lighter green to yellow (prominent when dry) adaxially, prominent abaxially, 8-11 secondary veins per side, regularly arched, most evident on lower leaf surface. Inflorescences comprising 1- to 4-flowered fascicles borne in the axils of cataphylls; bracteoles 3-4, c. 1.2 mm long, triangular, concave. Flowers borne on a pedicel 10-13 mm long. Calyx: 2-3.5 mm high, 4-7 mm wide; lobes 5, 2-2.5 × 1.5-1.8 mm, triangular to rounded, apex acuminate, united for about one fourth of their length. Petals white, oblong, 4.5-5 × 2-2.5 mm, slightly recurved at anthesis, finely striated; ligule 1.5-2 mm, oriented towards the center of the flower, margin undulate, 2-lobed, the lobes triangular. Staminal cup smaller than calyx, margin entire. Short-styled flowers: stamens white subequal, 5.5-6 mm long; anthers 0.7 × 0.7 mm, suborbicular; styles 3, 3-3.2 mm long, free. Long-styled flowers: stamens white, unequal, antisepalous filaments 3.8-4 mm long; antipetalous filaments 3-3.5 mm long; anthers 0.7 × 0.7 mm, suborbicular; styles 3, 5.5-6 mm long, free. Fruit a drupe, green to orange with longitudinal red lines to red, 9-12 × 6-9 mm when mature, ovoid, pointed at apex, surface smooth; pedicel 11-16 mm long. Seed similar in shape, 7-10 × 5-6 mm when mature, finely striated longitudinally.

Figures

FIG. 1. — Erythroxylum choungiense E.Bidault, Traclet & M.Pignal, sp.nov.:A, habit (dry);B, habit (fresh);C, detail of leaf venation; D, long-styled flower; E, shortstyled flower; F, short-style flower with corolla fallen; G, mature fruit; H, seed; A, C, D-F, Guiot 03 (MAO), B, G, H, no voucher. Drawings by Ludivine Longou. Scale bars: A, B, 2 cm; C, 3 mm; D, E, 1 mm; F, 2 mm; G, H, 1 mm.

FIG. 2. — Erythroxylum choungiense E.Bidault, Traclet & M.Pignal, sp. nov.: A, habit; B, terminal leaves with red young leaves; C, long-styled flower; D, shortstyled flowers; E, upper surface of leaves and immature fruits; F, mature fruit and seed; G, lower surface of leaves showing cordate base; A, B, E-G, photos by S. Traclet, C, D, photos by V. Guiot.