Croton barrabeae Bruy, 2023

Bruy, David, Lannuzel, Guillaume, Gâteblé, Gildas & Munzinger, Jérôme, 2023, Three new species threatened by mining activity in New Caledonia, Phytotaxa 578 (3), pp. 228-240 : 229-233

Croton barrabeae Bruy sp. nov. ( Figs. 1 , 2 )

Type:— NEW CALEDONIA. Province Nord. Houaïlou: Cap Bocage , 180 m, 21°11’13.09”S, 165°36’25.6”E, 27 July 2010 (fl.,fr.), Barrabé & Rigault 1016 (Holotype: NOU034138 !, isotypes: NOU034137 !, P04844092 !) .

Diagnosis: — Croton barrabeae resembles C. cordatulus Airy Shaw but differs most notably from it by the habit (shrub to 1 m with leaves borne at the tip of the branches on short internodes, vs. a small tree to 4 m with leaves separated by longer internodes), the lamina pubescence (regular distribution of hairs, vs. very dense or uneven distribution), and the shape of the fruit (spherical vs. obovoid).

Branched shrub, 0.4–1 m high, 2–5.5 cm basal diameter, conforms to the Rauh architectural model ( Hallé et al. 1978) with orthotropic sigmoid branches and sometimes basal reiterates, with brown latex. Plants monoecious. Young stem brown (in vivo), densely covered with peltate and star-shaped hairs, gray-brown, 0.3–0.6 mm in diameter. Internodes 1–4 mm long. Stipules caducous, triangular, 0.5–1 mm long, 0.2–0.4 mm wide, black (in sicco), externally hairy at the base. Leaves spirally arranged; blades oval to elliptic, slightly conduplicated, 6–11.2 × 3.2–7.2 cm, rust colored when young and greyish green when mature (in vivo), chartaceous to subcoriaceous, regularly hairy adaxially and abaxially; base obtuse to rounded, rarely subcordate; apex obtuse; margin irregular; basal laminar glands 2 on either side of the petiole insertion, circular to elliptic, 0.2–0.4 mm in diameter, brown and shiny (in sicco). Venation brochidodromous; midrib not or barely raised adaxially, prominent abaxially, densely hairy; secondary veins (5–) 6–8 (–10) on each side of the midrib, raised adaxially and abaxially; tertiary venation obscure. Petioles without pulvinus, canaliculate adaxially, triangular in cross section, (1.2–) 1.7–3.5 (–4.1) cm long, 0.1–0.2 cm in diameter, rust colored to greyish (in vivo), densely hairy. Inflorescences in axillary raceme, with 0 (–1) ramification, androgyne or monogamous; inflorescence axis 1.7–4.2 (–5.1) cm, 1–2 mm in diameter, green (in vivo), sparsely to densely hairy; bracts triangular, green (in vivo), sparsely pubescent and ciliate at top. Staminate flowers hairy; pedicel 2–3.5 mm long, ca. 0.5 mm wide, green (in vivo); sepals (4–) 5, green (in vivo), ovate to oboval, domed, 1.5–2.5 mm long, 1–2 mm wide, with a rounded apex, densely ciliate at top and hairy abaxially; petals (4–) 5, white to yellowish white (in vivo), spatulate, domed, 1.5–2 mm long, 0.15–0.6 mm wide, with a rounded apex, densely ciliate at the top and hairy abaxially; stamens 8–10, hairy at the base, anthers ca. 0.5 × 0.5–0.6 mm, filaments 1.6–1.9 mm long, ca. 0.2 mm wide, pistillodes lacking. Pistillate flowers greenish (in vivo), sessile, sepals 5–6, triangular, 2–2.5 mm long, 1–1.5 mm wide, with a rounded apex, densely ciliate at the top and hairy abaxially; apetal; stigmas 3, 2–4-fides, yellow (in vivo); ovary spherical, 1.5–2.5 mm in diameter, densely hairy. Fruit a trilocular capsule, spherical, ca. 1.5 cm in diameter, exocarp rugulose, ochre (in sicco), regularly hairy, with persistent calyx and stigmas; seeds 1 per locule, carunculated, ca. 10 × 6 mm, brown (in sicco).

Phenology:—Flowers of Croton barrabeae have been observed in June and July, and fruits have been collected in July.

Distribution and Ecology:—This new species is only known from the southern flank of the Wêêŷuu valley (toponymy following Georep.nc) on the Cap Bocage peninsula, in Province Nord, between Houaïlou and Ponérihouen municipalities ( Fig. 3 ). It occurs in shrubby maquis dominated by Araucaria scopulorum de Laub. on ultramafic substrate, more specifically among peridotite blocks, at 180–191 meters elevation. Only about 20 adult individuals are known but intensive field survey in the area could potentially locate other individuals.

Etymology:—The plant is named in honor of Dr. Laure Barrabé, a botanist specializing in New Caledonian flora and the first to have collected this species along with Frédéric Rigault.

Species recognition:— Croton barrabeae is recognizable in the field by its shrubby habit, with orthotropic sigmoid branches bearing leaves on very short internodes. It is also the only New Caledonian Croton species with spherical fruit and a regular distribution of hairs on the lamina.

Conservation status:— Croton barrabeae is only known from one population located on a mining concession a few dozen meters from the active mining site. The population equates to one unique locality sensu IUCN since all individuals could be affected by a single threatening event. Only about 20 mature individuals are known to date. The EOO calculated is 4 km ² and the AOO is 4 km ². Consequently, C. barrabeae has been assigned a conservation status of Critically Endangered (CR) B1 ab(iii,v)+2ab(iii,v) by the New Caledonian Red List Authority on 28/09/2022 (Endemia & RLA Flore NC, 2022).

Additional specimens examined (Paratypes): — NEW CALEDONIA. Province Nord. Houaïlou. Cap Bocage, creek Wêêy ̂uu, 191 m, 21°11’13.1”S, 165°36’25”E, 23 June 2021 (fl.), Bruy & Lannuzel 2033 ( MPU1379610 , NOU107771 , P) ; Cap Bocage, creek Wêêy ̂uu, 188 m, 21°11’12.7”S, 165°36’24.4”E, 23 June 2021 (fl.), Bruy & Lannuzel 2034 ( BM, G, K, MPU1379613 , NOU107772 , NOU107773 , P) ; Cap Bocage, creek Wêêy ̂uu, 191 m, 21°11’13.1”S, 165°36’25”E, 23 June 2021 (fl.), Bruy & Lannuzel 2035 ( NOU107774 ) ; Cap Bocage, sous la concession Aurore , 21°11’13.0”S, 165°36’24.8”E, 23 June 2021 (fl.), Lannuzel & Bruy 490 ( NOU108190 , P) .

Figures

FIGURE 1. Pictures of Croton barrabeae. A—Habit; B—Flowering branch; C—Detail of the pubescence on the abaxial surface of the leaf; D—Staminate flowers; E—Pistillate flower and staminate buds; F—Fruit in sicco (Barrabé & Rigault 1016). Photographers: Lannuzel G. & Bruy D.

FIGURE 2. Drawing of Croton barrabeae. A—Flowering branches; B—Adaxial (left) and abaxial (right) sides of the leaf; C—Base of the blade; D—Detail of a laminar gland; E—Peltate hair; F—Inflorescence and its axillary leaf; G—Staminate flower; H—Abaxial (left) and adaxial (right) sides of a staminate flower’s sepal; I—Abaxial (left) and adaxial (right) sides of a staminate flower’s petal; J—Stamen; K—Pistillate flower; M—Abaxial (left) and adaxial (right) sides of a pistillate flower’s sepal; N—Fruit; O—Seed. Illustrator: Ramon L.

FIGURE 3. Distribution map of Croton barrabeae (black large dots), Geijera tartarea (black pentagons) and Tristaniopsis planidisca (grey squares). The T’s represent the locality of the type specimens for each species. The black triangles represent the two highest mountains in New Caledonia. The small black dots represent the main cities in the South Province and the North Province. Grayed areas represent ultramafic substrates (from DIMENC/SGNC-BRGM 2010).