Tristaniopsis planidisca Lannuzel 2023, sp. nov.

Tristaniopsis planidisca Lannuzel sp. nov. (Figs. 6, 7) Type:— NEW CALEDONIA. Province Sud. Yaté. Ouinné, 410 m, 21°58’26”S, 166°39’06”E, 20 October 2020 (fl., fr.), Lannuzel, Bruy & Gâteblé 376 (Holotype: NOU107436!, isotype: P00942253!). Diagnosis:— Tristaniopsis planidisca is the only species in the genus in New Caledonia having glabrous young leaves. It also differs from every other species by its large and flat yellow waxy staminal disc, very visible due to the flat hypanthium. Small tree, 2–6 m high, architectural model unknown. Plants hermaphrodite. Glabrous on vegetative parts, indumentum absent on young leaves. Bark gray, not peeling, fissured. Twigs rounded to slightly squared. Leaves spirally arranged; blades lanceolate, 7–15 × 2.3–3.5 cm, dark green adaxially, light green abaxially (in vivo), slightly coriaceous, glabrous; base attenuate; apex obtuse; margin entire. Venation brochidodromous; midrib impressed adaxially, prominent abaxially; secondary veins visible (in sicco), tertiary venation obscure. Petiole flattened adaxially, 10–15 mm × ca. 1.5 mm, green to reddish (in vivo). Inflorescences thyrsoid, axillary, with 9–14 flowers; primary inflorescence peduncle ca. 6 × 1.9 mm, flattened, without bracts, bracteoles widely triangular, ca. 1 × 0.5 mm, at secondary and tertiary axis axils. All inflorescence axes moderately pubescent. Flowers pentamerous; pedicel 2–4 × 1 mm, puberulous; hypanthium flat at anthesis, not extended beyond ovary summit, 2 × 2–3 mm, puberulous or with scattered hairs; calyx lobes spread, yellow (in vivo), triangular, 1.8 × 1.8 mm, with an obtuse apex, glabrous adaxially, puberulous abaxially; petals yellow (in vivo), orbicular, 1.5 mm in diameter, puberulent, with oil-dots; stamens yellow to orange (in vivo), 1–3 per fascicle, fused on ca. 0.9 mm, anthers 0.4 × 0.4 mm, filaments 1 mm long, fused on half the length, inserted on a flat waxy yellow staminal disc 3–4 mm in diameter. Ovary semi-inferior, 1.4 mm high, 1.8 mm in diameter. Style 1.1 mm long. Fruit a trilocular capsule, 5 × 5 mm. Seeds unknown. Phenology:—The species was observed flowering and fruiting in October, and seen in fruit only in April. Distribution and Ecology:—The species is known from two localities on the southern east coast of Grande Terre (Fig. 3). It was observed in high dense shrublands and low forests on ultramafic substrates. Etymology:— Tristaniopsis planidisca is named after the characteristic shape of its staminal disc. Species recognition:— Tristaniopsis planidisca is recognizable by its flowers with a flat hypanthium at anthesis, and the flat waxy yellow staminal disc. It is also the only Tristaniopsis species in New Caledonia that is glabrous in all sterile parts, including the young leaves. Conservation status:— Tristaniopsis planidisca is known from two populations, one of which is located on a mining concession that is soon to be exploited. The EOO calculated is 8 km ² and the AOO is 8 km ². Consequently, T. planidisca has been assigned a conservation status of Endangered (EN) B1 ab(i,ii,iii,iv,v)+2ab(i,ii,iii,iv,v) by the New Caledonian Red List Authority on 02/09/2022 (Endemia & RLA Flore NC, 2022). Additional specimens examined (Paratypes): — NEW CALEDONIA. Province Sud. Yaté: Ouinné, 415 m, 21°58’26”S, 166°39’06”E, 20 October 2020 (fl., fr.), Gâteblé, Bruy & Lannuzel 1240 (NOU107369); Yaté. Ancienne route à horaire, [22°08’38”S, 166°53’39”E], 08 August 2004 (fr.), Munzinger 2296 (NOU003844, P04682693).Published as part of Bruy, David, Lannuzel, Guillaume, Gâteblé, Gildas & Munzinger, Jérôme, 2023, Three new species threatened by mining activity in New Caledonia, pp. 228-240 in Phytotaxa 578 (3) on pages 236-238, DOI: 10.11646/phytotaxa.578.3.2, http://zenodo.org/record/752309