Rudgea approuaguensis 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 : 155-157

Rudgea approuaguensis O. Lachenaud , sp. nov. ( Fig. 1 )

Inflorescentiis glomerulatis et breviter pedunculatis, fructibus rubris et ellipsoideis, foliis glabris crassis venulis laxissimis, stipulisque margine fimbriatis dorso exappendiculatis et applanatis Rudgeae bremekampianae Steyermark (1967: 407) valde affinis, sed habitu humiliore (35 – 40 cm nec 1 – 4 m alto), caule breviter pubescente (nec glabro), foliis minoribus nervis lateralibus paucioribus, inflorescentiis ebracteatis (nec bracteis foliaceis conspicuis munitis), calyce breviore lobato et corolla breviore (tubo 6 mm longo nec 10 – 16 mm) conspicue differt.

Type: — FRENCH GUIANA. Haute Approuague , sur la Crique Calebasse au village Germain, 25 August 1968 (fr.), R.A.A. Oldeman B-1828 (holotype, P [P06839007]; isotypes, CAY [CAY021301], K [K001301358], L n.v., NY [NY03120147]) .

Subshrub, 35 – 40 cm tall, sparsely branched; terminal branchlets 2.5 – 3 mm thick, densely and shortly pubescent with patent hairs 0.3 mm long, soon covered with a corky buff-grey bark. Stipules consisting of two flat interpetiolar portions, broadly elliptic, 7 – 12 × 4 – 6 mm, with numerous marginal appendages 1.5 mm long and lacking dorsal appendages, externally puberulous, soon corky and easily damaged, hiding an internal sheath 1-3 mm long. Leaves opposite, petiolate; petioles 0.2 – 0.7 cm long, densely puberulous; blades elliptic or obovate, 7 – 13 × 2.6 – 4.6 cm, acute at base, shortly acuminate at apex, coriaceous, glabrous on both sides, drying olive green to greyish; midrib flat or concave above; secondary veins 9 – 12 on each side of midrib, rather ascending, not very prominent, forming inconspicuous loops 1.5 – 3 mm from the margin; tertiary veins laxly reticulate, slightly prominent when dry (possibly invisible in the fresh state); domatia absent. Inflorescences terminal, glomerulate, ca. 20-flowered, erect; peduncle terete, puberulous, 0.5 cm in flower, 1.5 cm in fruit; flowering part 0.8 cm in diameter in flower; no distinct ramifications or bracts. Flowers 5-merous, whether distylous unknown, sessile. Hypanthium tronco-conical, 0.3 mm, glabrous. Calyx cupuliform, 1 mm long, divided in short, round lobes for 1/3 or 1/2 of its length, densely ciliate. Corolla white; tube nearly cylindrical, 6 × 3 mm, glabrous outside; lobes triangular, 3.5 mm, not or hardly corniculate, minutely puberulous outside at the apex, otherwise glabrous. Stamens exserted just beyond the corolla mouth; filaments barely exceeding corolla mouth; anthers elliptic, 2 × 0.25 mm. Disk hemispherical, 0.5 mm long. Style included, 4.5 mm long, glabrous; branches 1.2 mm. Fruits ellipsoid, 12–13 × 8–9 mm when dry, round at apex, red, glabrous, sessile; calyx scar not enlarging. Pyrenes ellipsoid, 11.5 × 6.8 mm, dorsally smooth except for a slight median ridge in the lower half; seeds with a deep T-shaped ventral furrow.

Distribution and ecology: —Endemic to French Guiana; apparently restricted to the upper Approuague River ( Fig. 2 ). Occurs presumably in lowland forest, ca. 100 m in elevation, although the habitat is not precisely recorded.

Phenology: —Flowers were collected only once in July, at the end of the second rainy season, and fruits only once in August.

Conservation status assessment: —Endangered [EN B2ab(iii)]. Rudgea approuaguensis is endemic to French Guiana and is known from two specimens, 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. The area where it occurs is not protected, and illegal gold mining occurring along the Approuague River is a potential threat, which leads us to predict a decline in the extent and quality of habitat. The two occurrences represent two locations in the sense of IUCN, and the species qualifies for Endangered status according to the conditions B2ab(iii).

Notes: —This species closely resembles Rudgea bremekampiana Steyermark (1967: 407) , from French Guiana and northern Brazil (state of Amapá), and has been previously confused with it in herbaria. Both species have glomerulate inflorescences with a short peduncle, red, ellipsoid fruits, thick, glabrous leaves, and flat stipules (i.e., lacking a dorsal keel) with marginal appendages. Rudgea bremekampiana differs from R. approuaguensis by the glabrous stems, conspicuous bracts, and greater dimensions of all its organs (differences are summarised in Table 1 ).

It is not known whether the species is heterostylous, since only one collection bears flowers; these are too few to dissect, and the interior of the corolla tube is therefore not described.

Additional specimen examined (paratype): — FRENCH GUIANA. Fleuve Approuague , au Saut Grand Canori, 12 July 1968 (fl.), R.A.A. Oldeman 2765 ( CAY, P) .

Figures

FIGURE 1. Rudgea approuaguensis. A, fruiting branch; B, inflorescence and stipules; C, fruit; D, pyrene, dorsal view; E, seed, crosssection. A, C–E from Oldeman B-1828, B from Oldeman 2765. Drawn by O. Lachenaud.

FIGURE 2. Distribution of Rudgea approuaguensis (triangles), R. ayangannensis (stars) and R. graniticola (circles).