Rudgea itoupensis O. Lachenaud, 2022

Lachenaud, Olivier, Bruniera, Carla P. & Zappi, Daniela C., 2022, Six new and a little-known species of Rudgea (Rubiaceae-Palicoureeae) from the Guianas, Phytotaxa 531 (3), pp. 154-174 : 166-167

Rudgea itoupensis O. Lachenaud , sp. nov. ( Fig. 6 )

Inflorescentiis pendulis dense globosis bracteis valde laciniatis munitis discoque bipartito ab omnibus congeneribus differt Rudgea glomerulatae excepta, a quae distinguitur bracteis externis brevioribus et latioribus 7 × 7 mm (vs. 9 – 28 × 2.5 – 3.5 mm) calycibus non excedentibus et corollae tubo minore 11.5 mm longo (vs. 18 – 20 mm).

Type: — FRENCH GUIANA: Sommet Tabulaire [Mount Itoupé], zone sud, ca. 50 km SE de Saül, 22 August 1980 (fl.), J.J. de Granville 3550 (holotype, CAY [CAY077712]; isotype, CAY [CAY077713]) .

Shrub 3 m tall, much-branched; terminal branchlets 1.5 – 2 mm thick, densely appressed-pubescent. Stipules consisting of two flat interpetiolar portions, narrowly ovate, 9 – 16 × 3 – 4 mm, deeply laciniate with ca. 13 marginal appendages 4 – 9 mm long and lacking dorsal appendages, pubescent, soon corky and eventually caducous, surrounding an internal sheath 2 mm long bearing ca. 4 lateral appendages 2 mm long in the axils of the petioles. Leaves opposite, petiolate; petioles 0.5 – 1 cm long, appressed pubescent; blades narrowly elliptic, 9.5 – 15.5 × 1.9 – 3.7 cm, acute at base, gradually long-acuminate at apex, papyraceous when dry, glabrous above and shortly appressed hairy beneath with hairs denser on the veins, drying dark grey-brown, midrib convex on both sides, secondary veins 9 – 12 on each side of midrib, weakly ascending, forming rather conspicuous loops 1 – 2 mm from the margin, tertiary veins prominent and forming a moderately lax reticulum (ca. 2 mm) in the dry state; domatia absent. Inflorescences terminal, nodding, capitate and hemispherical, many-flowered, densely appressed-pubescent; peduncle terete, 1.3 – 4.5 cm long; flowering portion 1.1 – 1.5 cm in diam., no distinct ramifications; bracts green, not exceeding the calyces, the basal ones 7 × 7 mm, deeply and irregularly laciniate for about 2/3 of their length, the upper ones almost linear and pinnatifid, 3.5 × 0.4 mm, all densely appressed hairy outside and glabrous inside. Flowers sessile, (4 –)5-merous, apparently distylous (see Notes). Hypanthium tronco-conical, 1 mm, pubescent. Calyx deeply cupuliform, pubescent outside, tube 2.5 – 4 mm long, lobes initially triangular and acute at apex, 1 mm long, but very soon damaged, becoming ± round and scariose at margin. Corolla white; tube narrowly cylindrical, 11.5 × 1 mm, glabrous outside and inside; lobes triangular, 3 mm, broadly corniculate at apex, glabrous on both sides except the cornicula minutely puberulous. Stamens included with their apex just reaching corolla mouth in long-styled flowers; anthers linear, 3.5 × 0.5 mm, dorsifixed. Disk bipartite, cylindrical to slightly conical, 1 – 1.3 mm long, glabrous. Style included, glabrous, 10 mm long and almost reaching corolla mouth in long-styled flowers, or 3.8 mm long in short-styled flowers, branches 0.8 – 1 mm long. Fruits unknown.

Distribution and ecology: —Endemic to French Guiana ( Fig. 4 ); apparently restricted to Mount Itoupé (also known as Sommet Tabulaire) in the central Inini-Camopi chain. Collected only once in submontane forest, at 750 m elevation.

Phenology: —Flowers collected once in August.

Conservation status assessment:—Vulnerable (VU) (D2). Rudgea itoupensis is known from a single collection near the summit of Mount Itoupé in south-central French Guiana, where it occurs in submontane forest. Its extent of occurrence (EOO) is therefore not calculable, and its area of occupancy (AOO) is estimated to be 4 km ², within the limit for Critically Endangered under subcriterion B2. Its only known location, which lies in the Parc Amazonien de Guyane, is very remote and difficult to access, and unlikely to be directly impacted by human activities. However, considering its very restricted range and particular habitat, the species may be at risk from any stochastic events (and possibly from future climatic changes). Being known from a single location, it qualifies for Vulnerable status under criterion D2.

Notes: —This species is very close to Rudgea glomerulata , described above, from which it differs by the shorter and relatively much broader bracts, not exceeding the calyces, and a shorter corolla tube; both species are apparently endemic to French Guiana, but have different ranges and habitats ( Table 2 ). They share dense and more or less pendulous inflorescences with deeply laciniate bracts, narrowly elliptic leaves with a sparsely hairy lower surface, a well-developed calyx tube, and a bipartite disk, while all other Rudgea species in the Guianas (and, as far as we know, elsewhere) have an entire disk.

The only collection seen includes both long- and short-styled flowers (the latter with the corollas fallen off and only the style remaining) that are on separate branches, which were presumably collected from different individuals.

Figures

FIGURE 4. Distribution of Rudgea glomerulata (squares) and R. itoupensis (star).

FIGURE 6. Rudgea itoupensis. A, branch with young inflorescence; B, stipules; C, outer bract, seen from inside; D, inner bract, seen from inside; E, longitudinal section of calyx and disk; F, same, with persistent style (short-styled flower); G, flower bud; H, same in longitudinal section (long-styled flower); I, corolla (long-styled flower); J, style (long-styled flower). From Granville 3550. Drawn by O. Lachenaud.