Rudgea ayangannensis Steyermark (1967: 410)

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 : 157-159

Rudgea ayangannensis Steyermark (1967: 410) .

Type: — GUYANA. Mt. Ayanganna , NE side, 900–1100 m, 7 August 1960 (fl.), S.S. Tillett, C. L. Tillett & R. Boyan 45182 (holotype, NY [00133206]) .

Shrub, 2 – 3 m tall, much-branched; terminal branchlets 1 – 2 mm thick, glabrous, soon covered with a greyish bark. Stipules broadly ovate, 3 – 3.5 × 2.8 – 4.3 mm, shortly sheathing at base, round at apex, bearing a group of short dorsal appendages inserted below the apex, glabrous, soon fragmenting. Leaves opposite, petiolate; petioles 0.5 – 1 cm long, glabrous; blades elliptic, 5 – 10.3 × 2 – 4.2 cm, decurrent on petiole at base, acuminate at apex, slightly coriaceous, entirely glabrous, drying olive green to olive brown with the lower side paler, dull on both sides; midrib convex on both sides; secondary veins 8 – 9 on each side of midrib, inserted almost at a right angle, strongly curved, arching 1 – 3 mm from the margin; tertiary veins prominently reticulate below, concolorous, forming areolae ca. 2 mm in diam.; domatia absent. Inflorescences terminal, paniculate, 2 – 3 cm long; peduncle terete, 1 – 2 cm long, glabrescent; flowering portion 1 – 2 × 0.6 – 1.8 cm; main ramifications 4 per node, 0.4 – 0.8 cm long, minutely puberulous; bracts minute, triangular, 1.2 × 0.3 mm. Flowers 4-merous, whether distylous unknown, the lateral flowers of a triad with pedicels 1 – 1.5 mm long, the central one sessile. Hypanthium tronco-conical to subcylindrical, 0.7 mm long, puberulous. Calyx cupuliform, 0.2 – 0.5 mm long, minutely puberulous, with short triangular to subulate lobes. Corolla white; tube narrowly infundibular, 6 × 2.5 mm, minutely and sparsely puberulous outside towards the base, glabrous inside; lobes elliptic, 5 × 2 – 3 mm, obtuse at apex, papillose outside, glabrous inside. Stamens sub-included, inserted around the lower 1/3rd of the corolla tube; filaments 3 – 3.2 mm long; anthers elliptic, 1.2 mm long. Disk hemispherical, 0.6 mm long, glabrous. Style included, 1 mm long; branches 0.5 mm long. Fruits (only immature seen) ellipsoid, 4.5 – 8 × 4 – 6.5 mm when dry, yellowish green, glabrous, pedicels 3-7 mm long, calyx scar not enlarging, 1 – 1.5 mm broad. Pyrenes and seeds not seen.

Distribution and ecology: — This species is endemic to the highlands of western Guyana (Mt. Ayanganna and surroundings, Fig. 2 ), and occurs in mixed evergreen forest, at 1100 – 1650 m.

Phenology: — Flowering specimens were collected in August; and specimens with immature fruits in November.

Conservation status assessment: — Vulnerable (VU D2). Rudgea ayangannensis is endemic to the montane forests of western Guyana, 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. Both occurrences are in areas without official protection status. While their habitat is currently well preserved, and there is no evidence of a current threat from human activities, any stochastic events or future industrial (e.g. mining) projects in the area would represent a threat to the species. The two occurrences represent two locations in the sense of IUCN, and the species qualifies for Vulnerable status under criterion D2.

Notes: — The two collections cited in the protologue of this species, the flowering type Tillett et al. 45182 and the fruiting paratype Tillett et al. 45023 (K, NY), are not conspecific. The former has stipules without a dorsal keel (the appendages are inserted directly on the sheath), leaves with prominently reticulate tertiary veins, and inflorescences with the lateral flowers of a triad pedicellate. The latter has stipules with a dorsal keel exceeding the sheath, tertiary leaf veins hardly apparent, and sessile fruits; it appears to represent Rudgea graciliflora Standley (1936: 262) sensu lato, although its secondary leaf veins are more numerous (9-11 pairs) than usual for this species (5-8 pairs). Steyermark’s (1967) description is consequently based on a mixture (the details of the fruits, in particular, do not apply to R. ayangannensis ) and a new description is presented here. Apart from the type, only one collection has been seen that represents true R. ayangannensis . The species remains poorly known; no mature fruits have been seen, and it is not known whether its flowers are heterostylous (the only ones seen, on the type, have an included style).

Rudgea ayangannensis may be confused with both R. graciliflora , from which, in addition to the characters discussed above, it also differs in its much shorter corolla tube, and R. graniticola ; for differences with the latter, see that species.

Additional specimens examined: — GUYANA: Pakaraima Mountains , Mount Wokomung, summit ridge of Kamie-wah pinnacle NE to S pinnacle, “Little Ayanganna”, 5°04’N, 59°52’W, 17 November 1993 (imm. fr.), T. Henkel, R. Williams, S. Fratello & L. Williams 4471 (K, P) .

Figures

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