Atractocarpus teamotuaitaui Mouly & Butaud, 2023

Mouly, Arnaud & Butaud, Jean-François, 2023, The French Polynesian Atractocarpus Schltr. & K. Krause (Rubiaceae): circumscription of A. tahitensis and description of A. teamotuaitaui sp. nov., both microendemic and critically endangered species in the Society Islands, Adansonia (3) 45 (10), pp. 151-159 : 158

Atractocarpus teamotuaitaui Mouly & Butaud , sp. nov.

( Fig. 4 )

Atractocarpus teamotuaitaui sp.nov. differs from the other Polynesian species A. tahitensis (Nadeaud) Puttock by its leaves shortly petiolate (2-3 mm vs 10-15 mm), with rounded to cordate lamina base (vs attenuate-cuneate), and long corolla lobes (ratio of the corolla lobe/corolla tube length: 2-2.5 vs 1.3-1.5).

TYPUS. — Society Islands, Tahiti. Tahiti Iti, Plateau de Taravao , Vallon Aoma , versant, 790 m, fl., 2.XII.2014, Butaud 3410 (holo-, PAP [ PAP015896 ]) .

PARATYPI. — Society Islands , Tahiti . Tahiti Iti, Taiarapu, Plateau de Taravao,fl.& fr., 25.X.2011, Florence, Butaud, Meyer, Jacq & Teamotuaitau s.n. (P, PAP) ; Plateau de Taravao , sur un replat sous une petite crête, 750 m, fl., 31.I.2008, Teamotuaitau 182 ( PAP [ PAP003752 ]) ; ibid., Teamotuaitau 183 ( PAP [ PAP003841 ]) ; Plateau de Taravao , replat sous une crête, 750 m, fr., 28.II.2008, Teamotuaitau 185 ( BESA, PAP [ PAP003842 ]) ; ibid., Teamotuaitau 186 ( PAP [ PAP003759 ]) ; Plateau de Taravao , petit replat sous une crête, 750 m, st., 28.II.2008, Teamotuaitau 187 ( PAP [ PAP003760 ]) .

PHENOLOGY. — The species seems to bloom from October to February and to produce mature fruits around October and November.

ETYMOLOGY. — The species is dedicated to the French Polynesian naturalist Walter Teamotuaitau who first observed the species in the field in 2008 and regularly monitors the population.

DESCRIPTION

Slender treelet 2-4 m high, up to 4 cm in diameter (at breast height); weakly branched, leaves concentrated toward the branch tips; the young branchlets glabrescent. Seedlings with reniform cotyledons, first leaves elliptic, markedly hairy on the margin. Stipules connate at the base, triangular, with a deep central costa, 7-10 mm long. Colleters cylindrical, 0.6- 1.1 mm long, c. 2 mm wide. Leaves opposite, elliptical-ovate to narrowly obovate, glabrous; petioles 2-3 mm long; lamina (70-) 130-310 mm long, (30-) 50-90 mm wide with acuminate apex and rounded to cordate base, glossy light green above, dull pale green below, chartaceous; secondary veins in 7-11 pairs at 50-60° to the midvein, raised below; tertiary venation reticulate and opaque; domatia absent. Inflorescences axillary, a solitary flower, or a perennial cyme contracted in a dwarf branchlet, c. 2-9-flowered. Flowers hermaphroditic, drooping; peduncles very short, c. 1-2 mm long per axis; bracts narrowly triangular, 1-2 mm long; pedicels 5-10 mm long, slightly puberulent. Hypanthium 3-4 mm long, cup-shaped, slightly puberulent. Calyx tube obconical, 2-3 mm long; lobes truncate, c. 0.5 mm long. Corolla tube 5-6 mm long, urceolate, c. 5 mm diameter at the widest point, slightly constricted distally, light green after anthesis.Corolla lobes lanceolate, 12-13 mm long, 3-4mm wide, glabrous, pure white above, greenish below. Stamens inserted at the base of the urceolate part of the corolla tube, filament 0.4-0.5 mm, anther basi-dorsifixed, 4-4.5 mm long, sagittate at base, acuminate by a sterile appendage, 0.2-0.3 mm long. Style included, 2-2.5 mm long, 0.4-0.5 mm wide, glabrous; stigmatic head oblong, deeply bifid, arms 2-2.5 mm long, 0.6-0.8 mm wide. Ovary bilocular, placentas 2, axile, multiovulate. Fruit erect, pale green when immature, turning yellowish-green, on a thickened pedicel 15-20 mm long, subspherical to ellipsoid, 18-33 mm long, 11-29 mm diameter, smooth, calyx persistent, nectary disc forming an umbo, 2-2.5 mm long, yellowish.Seeds laterally compressed; 3-4.5 mm in diameter.

DISTRIBUTION, ECOLOGY AND THREATS

The only known population is located on the sides of a ravine intruding the dissected Taravao plateau between 750 to 805 m, in a degraded hygrophilous/rain-forest vegetation on basaltic substrate, dominated by the invasive species Miconia calvescens DC. , Rubus rosifolius Sm. , Cecropia peltata L., Psidium cattleyanum Sabine , Spathodea campanulata P.Beauv. , Cestrum nocturnum L., Mikania micrantha Kunth , Cinchona pubescens Vahl , and the native Weinmannia parviflora G.Forst. , Crossostylis biflora J.R.Forst. & G.Forst. , Astronidium glabrum (G.Forst.) Markgr. , Cyathea spp. , Alstonia costata (G.Forst.) R.Br. , Fagraea berteroana A.Gray & Benth. , Metrosideros collina (J.R.Forst. & G.Forst.) A.Gray , Myrsine longifolia Nadeaud , Ficus prolixa G.Forst. , Glochidion spp. , Melicope spp. , Freycinetia sp. , Davallia spp. , Lepisorus spicatus (L.f.) Li Lang, Dicranopteris linearis (Burm.f.) Underw. , and Dryopteris sp. A few seedlings were observed from 2011 to 2013 but none since. Indeed, rats eat unripe fruits and seedlings, and can even gnaw through a mature individual (field observations by the second author).

Atractocarpus teamotuaitaui sp. nov. is endemic to the Society Islands and specifically to Tahiti Iti, on the Taravao Plateau. The species is known from a single population with c. 40 mature individuals in 2011 and only four remaining in 2022. It grows in forests highly infested by Miconia calvescens DC. , that exerts a high competitive pressure on native species, as documented in this locality for Psychotria species ( Meyer et al. 2003). Therefore, the species should be quickly assessed for the level of threat it faces, which corresponds to “Critically Endangered – CR”, based on the presence of a single population within a 50 × 50 m area, less than 50 individuals with a high mortality rate, with a permanent threat for the environment caused by the Miconia calvescens invasion in addition to other invasive plant species, rat predation, and possibly a fungal disease on the leaf buds.

Figures

FIG. 4. — Atractocarpus teamotuaitaui Mouly & Butaud, sp. nov.: A, leafy and flowering branch of the species, under the secondary vegetation cover; B, apical stipules; C, flower at anthesis; D, stipules and detail of the leaf-base at a ramification; E, unripe fruit on a branch with the congested leaf cluster. Photos by J.-F. Butaud.