Rudgea jadinii 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 : 168

Rudgea jadinii O. Lachenaud , sp. nov. ( Fig. 7-8 )

Stipulis brevis apice fimbriatis dorso exappendiculatis, foliis glaberrimis venulis inconspicuis et corollae tubo longe et anguste cylindrico Rudgea graciliflora Standley (1936: 262) similis, sed differt inflorescentiis glomerulatis (vs. breviter ramosis), staminibus et stylo in corollae tubo inclusis, et calyci lobis majoribus 1.5-2.5 mm longis (vs. 0-1 mm longis).

Type: — FRENCH GUIANA: Route de Kaw , pk 33, sentier vers les grottes, 4°33’N, 52°13’W, 4 December 2000 (fl.), F. Billiet & B. Jadin 7459 (holotype, CAY [CAY014902]; isotype, BR [BR000000907386]) .

Shrub, much branched, or small tree, to 6 m tall; terminal branchlets 1 – 1.5 mm thick, glabrous. Stipules 2 – 3 × 2 – 3 mm, glabrous, marcescent and soon corky, consisting of a truncate to round basal sheath 0.5 – 2 mm long (usually broken at flower-bearing nodes), bearing on each side a dorsal keel with 4 early caducous terminal appendages <1 mm long. Leaves opposite, petiolate; petioles 0.3 – 1 cm long, glabrous; blades elliptic, 6.5-12.2 × 3-6.4 cm, obtuse to acute at base, abruptly acuminate for 0.5 – 1.5 cm at apex, coriaceous, entirely glabrous, drying olive green to blackish; midrib concave or flat above, secondary veins 7 – 10 on each side of midrib, flat above, weakly ascending, forming conspicuous loops 1.5 – 4 mm from the margin, tertiary veins inconspicuous or very lax; domatia absent. Inflorescences terminal, glomerulate, 5 – 15-flowered, sessile or with peduncle <0.4 cm long, glabrous; bracts triangular to elliptic, 2.5 – 3.5 × 0.7 – 1.5 mm, entire or minutely toothed, glabrous at base and shortly pubescent at apex. Flowers sessile, 5-merous, whether distylous unknown. Hypanthium tronco-conical, 0.5 mm long, glabrous. Calyx lobed nearly to the base; lobes narrowly ovate, 2 – 2.3 × 0.5 – 0.8 mm, glabrous at base, minutely and sparsely pubescent at apex, alternating with minute colleters in their sinuses. Corolla white; tube very narrowly cylindrical, 6.5 – 10 × 0.1 – 0.15 cm, glabrous outside, pubescent at distal 1.5 cm inside; lobes narrowly elliptic, 8 – 12 × 1.5 mm, with short rounded dorsal appendages near apex, glabrous outside except the minutely puberulous appendages, papillose inside. Stamens included, inserted 4 mm below corolla mouth, subsessile; anthers narrowly elliptic, 3 × 0.4 mm. Disk cylindrical, 0.5 mm long, glabrous. Style included, glabrous, 6.5 cm long, branches 2.5 mm. Fruits unknown.

Distribution and ecology: —Endemic to northeastern French Guiana, where known from the Kaw Mountain Range and the Nouragues inselberg ( Fig. 9 ); in the former locality it occurs in low forest on lateritic crust, in the latter presumably in a similar habitat but on granite. The species appears to be very rare; the first author was unable to find it in the type locality, despite visiting the site on several occasions at various times of the year.

Phenology: —Flowering specimens were collected twice in December, at the beginning of the first rainy season, which represents a flowering peak for most shrubby Rubiaceae in French Guiana.

Conservation status assessment: —Endangered [B2ab(iii)]. Rudgea jadinii is endemic to French Guiana and is known from two collections representing two occurrences. Its extent of occurrence (EOO) is therefore not calculable, and its area of occupancy is estimated to be 8 km ², within the limit for Critically Endangered under subcriterion B2. One of its occurrences is protected in the Réserve Naturelle des Nouragues. The other, on the Kaw Mountain, has no official protection status, and is potentially threatened by touristic development, forest exploitation and/or mining activities (mining projects in the area were abandoned in 2008 but may resurface in the future), which leads us to anticipate a decline in habitat extent and quality. The two occurrences represent two locations in the sense of IUCN, and the species qualifies for Endangered status under the conditions B2ab(iii)

Notes: — Rudgea jadinii resembles R. graciliflora , from which it differs by the glomerulate inflorescence, flowers with anthers and style both included, and calyx lobes 1.5 – 2.5 mm long, while R. graciliflora has shortly branched inflorescences, distylous flowers with either style or anthers exserted, and the calyx truncate or with lobes <1 mm long. The corolla tubes of R. jadinii are 6.5 – 10 cm long, which are much longer than in specimens of R. graciliflora from the Guianas, which are 2 – 5.2 cm long and represent the typical form of the species. However, some collections of R. graciliflora from western Amazonia have the corolla tube length comparable to that of R. jadinii . These have been originally described as R. klugii Standley (1936: 164) ; their status may have to be re-assessed, but this is outside the scope of this paper. Rudgea graciliflora belongs to the informal “ lanceifolia clade” ( Bruniera 2015) which includes species from the Guianas and the in Amazon basin, and R. jadinii probably belongs there as well.

It is not known whether R. jadinii is heterostylous; the only flowers seen have the style and anthers both included, the latter well above the former.

Eponymy: —This species is named in memory of the Belgian botanist Bernard Jadin (1948–2012), collector of the type and of many other French Guianan plants, together with his wife Frieda Billiet - who is remembered in Philodendron billietiae Croat (1995: 24) .

Additional specimen examined (paratype): — FRENCH GUIANA. Station des Nouragues , entre les croisements H XXII et I XXII, 27 December 1988 (fl.), D. Loubry 100 ( CAY) .

Figures

FIGURE 7. Rudgea jadinii.A, flowering branch; B, terminal bud; C, inflorescence (corollas fallen) and stipules of the upper node (already damaged); D, calyx and bract; E, corolla; F, calyx and style; G, apex of a flower bud; H, upper part of the corolla in longitudinal section. From Billiet & Jadin 7459. Drawn by O. Lachenaud.

FIGURE 8. Rudgea jadinii. Flowers. From Billiet & Jadin 7459. Photo: F. Billiet.

FIGURE 9. Distribution of Rudgea jadinii (circles) and R. leucocarpa (triangles).