Rudgea tanaosepala Sandwith (1933: 334)

Lachenaud, Olivier, Bruniera, Carla P. & Zappi, Daniela C., 2022, The Rudgea hostmanniana complex (Rubiaceae) in the Guiana Shield region, Phytotaxa 561 (3), pp. 219-242 : 237-238

8. Rudgea tanaosepala Sandwith (1933: 334) . Fig. 1F , 2F .

Type: — GUYANA. Simuni Creek , Rupununi River, 25 August 1931 (fl.), T. A. W. Davis in Forest Department 2149 (holotype, K! [2 sheets, K000447201 , K000447202 ]) .

Much branched shrub 2–7 m tall; twigs glabrous or minutely puberulous, 2–2.5 mm thick, soon covered with a pale straw-colored bark. Stipules 6.5–12 × 2–4.5 mm, glabrous or minutely puberulous, marcescent and soon corky, consisting of a short basal sheath 2–3.5 mm long (usually split at flower-bearing nodes) bearing on each side of the node one bifid lateral appendage 3–5.5 × 0.5 mm, and a central keel (4.5–)7–13 × 1–2 mm, the latter usually bifid for 2.5–4 mm long (rarely ± irregularly fimbriate) with each of the lobes divided in 3–5 linear appendages 1–2.5 mm long. Leaves opposite; petioles 0.1–0.7 cm long, glabrous or minutely puberulous; blades oblanceolate to narrowly elliptic, 7–20.7 × 1.8–7.2 cm, obtuse to rounded at base, gradually acuminate at apex, very thick, entirely glabrous, drying greyish-green; midrib concave or flat above; secondary veins 7–11 on each side of midrib, weakly ascending and forming loops 2–3 mm before margin; tertiary veins very lax and slightly prominent when dry (probably invisible when fresh); domatia absent. Inflorescences terminal, paniculate or rarely glomerulate, 0.8–4.4 cm long, erect, puberulous; peduncle terete, 0.1–2.4 cm long; flower-bearing portion 0.5–2.2 × 1.4–3.3 cm; secondary branches 3–4 per node, to 1.2 cm long, rarely absent; bracts 5–7 × 0.7–1.2 mm, linear to narrowly lanceolate, entire or with linear lateral teeth, sparsely and shortly puberulous outside. Flowers sessile, 5-merous, heterostylous, fragrant. Hypanthium obconical to almost cylindrical, 0.8 mm long, glabrous. Calyx tube extremely reduced, lobes linear, 3–5 × 0.7–1.2 mm, shortly and sparsely puberulous outside. Corolla white, hypocrateriform; tube narrowly infundibuliform, 6–7 mm long, 1–1.3 mm wide at base, 1.5–3 mm wide at mouth, glabrous outside, with a ring of dense short hairs at stamens insertion inside; lobes triangular to narrowly elliptic, 3.5–5 × 1–1.5 mm, puberulous outside at the apex, minutely papillose inside, with narrowly cylindrical (or rarely short and obtuse) dorsal cornicula (0.5–) 1–1.5 mm long. Stamens included in long-styled flowers, or exserted with filaments exceeding corolla mouth by 2–5 mm and anthers 2.2 × 0.4 mm in shortstyled flowers. Disk shortly cylindrical, 0.5 mm long, glabrous. Style exserted, 9–10 mm long in long-styled flowers, or included, 6 mm long, in short-styled flowers, lobes with papillose stigmatic surface. Fruits globose to ellipsoid, 7–11 × 7–11 mm when dry, dark brown (presumably immature) to red or orange (mature), glabrous, sessile, crowned with slightly accrescent persistent calyx 2.5 mm wide. Pyrenes plano-convex, hemi-ellipsoid or hemi-obovoid, 7–7.5 × 6.5 mm, dorsal side with 3 often very faint ridges mostly visible at the base, smooth between the ridges, ventral side smooth. Seeds with a deep T-shaped ventral furrow.

Distribution and ecology: —A species endemic to central Guyana ( Fig. 5 ), locally common in the middle Essequibo River basin; it grows in lowland forest on white or brown sand, sometimes along streams, at 80–500 m elevation.

Phenology: —Flowering specimens were collected in August and October–November; and fruiting specimens in February–April and September–October.

Notes: —This species was for a long time only known from the type (cf. Steyermark 1967: 407). It is now fairly well represented in herbaria, where most of the specimens had so far been mistaken for the closely similar and much more widespread Rudgea hostmanniana . The species is distinctive, within the R. hostmanniana complex, by its long and very narrow calyx lobes ( Fig. 2F ; Table 1 ); the secondary leaf veins are also less ascending than in other species, though a few specimens of R. cornigera approach R. tanaosepala in this respect.

The inflorescences in R. tanaosepala are quite variable; they are usually well-branched, but sometimes the ramifications are very short or absent (e.g. Hoffmann et al. 1488; Maas et al. 5885). Specimens from the south of the range, including the type, have usually glabrous vegetative parts (rarely the twigs are sparsely puberulous) and corolla lobes with narrowly cylindrical, 1–1.5 mm long dorsal cornicula. The more northern specimens (Ek et al. 602, 772; Maas et al. 5885) have minutely puberulous twigs, stipules and petioles, and corolla lobes with shorter and broader dorsal cornicula, ca. 0.5 mm long; it is possible that they represent a separate infraspecific taxon.

Records of R. tanaosepala from French Guiana ( Funk et al. 2007) are based on misidentified collections of the recently described R. glomerulata Zappi & O. Lachenaud ( Lachenaud et al. 2022: 159) . The latter differs from R. tanaosepala and other species of the R. hostmanniana complex by its stipules lacking dorsal appendages, large and deeply laciniate bracts 9–28 × 2.5–3.5 mm, longer corolla tube, 18 – 20 mm long that is entirely glabrous within, longer calyx tube 1.5 – 4 mm long, bipartite disk, yellow to yellow-orange fruits, and densely pubescent twigs, petioles and abaxial side of leaf veins.

A collection from the Bakhuis Mountains, in Suriname, Bordenave, Doerga, van Troon & James 8619 (BBS n.v., CAY) resembles the variants of Rudgea tanaosepala with glomerulate inflorescences, but has smaller leaf blades, 5–7 × 0.8–1.7 cm, and stipules with four subequal dorsal appendages on each side and no dorsal keel. It presumably represents a new species, but the material is very poor, with only leaves, hypanthia and calyces.

Specimens Examined: — GUYANA. Iwokrama Rainforest Reserve, Iwokrama Mts , 4°20’N, 58°50’W, 22 November 1995 (fl.), D. Clarke & B . Hoffmann 584 ( CAY, U); Iwokrama Rainforest Reserve, Moco Moco II Creek, 20 mi. SW of Kurupukari on Kurupukari – Annai road, 4°25’N, 58°49’W, 24 March 1996 (fr.), D. Clarke 1431 ( CAY, U); Iwokrama International Rainforest Reserve , Iwokrama Mts , 4°19’N 58°47’W, 22 September 1996 (fr.), D. Clarke 2492 ( CAY, K, U); Iwokrama Rainforest Reserve , Iwokrama Mountains , 4°19’N, 58°47’W, 22 September 1996 (fr.), D. Clarke 2516 ( CAY, U); Iwokrama Rainforest Reserve , N of Surama , 4°10’N, 59°03’W, 20 May 1995 (fr.), C. Ehringhaus 126 ( CAY); Mabura region, West Pibiri compartment, 5°20’N, 58°30’W, 28 November 1992 (fl.), R. C. Ek 602 ( U); Mabura region, Pibiri compartment, main road, 5°01.95’N, 58°37.73’W, 20 March 1993 (fr.), R. C. Ek, B. Gravendeel, B. Robers & M. Elsinga 772 ( U); Region Potaro-Siparuni, Annai – Karupukari road, 18 km N of Surama village cut off, 0.5 km W of road, 4°14’N, 58°56’W, 29 April 1992 (imm. fr.), B . Hoffman, T . Pennington & C . Capellaro 1488 ( CAY, U); Mabura Hill , 5°19’N 58°38’W, 27 November 1981 (fl.), P. J.M. Maas, A . Mennega & B . J . H. ter Welle 5885 ( U); Iwokrama Reserve, Essequibo watershed, Georgetown–Lethem road, Mount Daniel transect, 4°28’26”N, 58°47’05”W, 27 February 1995 (fr.), P . Mutchnik 973 ( K) .

Figures

FIGURE 1. Stipules in the Rudgea hostmanniana complex.A, R. bolivarensis; B, R. coussareoides; C, R. cornigera; D, R. hostmanniana subsp. hostmanniana; E, R. maypurensis; F, R. tanaosepala. A from Mutchnick 1620 (K), B from Diaz et al. 7727A (K), C from Schulz 7539 (U), D from Lachenaud 1011 (BR), E from Williams 12972 (K), F from Clarke & Hoffman 584 (U). Drawing by O. Lachenaud.

FIGURE 2. Calyx and corolla in the Rudgea hostmanniana complex.A, R. bolivarensis, calyx; B, R.coussareoides, calyx; C, R. cornigera, flower bud; D, R. hostmanniana subsp. hostmanniana, flower bud; E, R. maypurensis, flower bud; F, R. tanaosepala, flower bud. A from Henkel 5675 (U), B from Liesner 24924 (K), C from Procter 4769 (U), D from Lachenaud 981 (BR), E from Plowman 13733 (K), F from Clarke & Hoffman 584 (U). Drawing by O. Lachenaud.

FIGURE 5. Distribution of Rudgea billietiae (black triangles), R; bolivarensis (grey circles), R. cornigera (black squares), R. pungens (grey squares) and R. tanaosepala (grey triangles).