Pteridocalyx appunii Wernham (1911: 318)

Delprete, Piero G., 2019, Notes on calycophyllous Rubiaceae. Part V. A succinct overview of genera with calycophylls, and a revision of Pteridocalyx (Sipaneeae) with observations on distyly and calycophyll variation, Phytotaxa 391 (1), pp. 81-92 : 87-89

Pteridocalyx appunii Wernham (1911: 318) . ( Figs. 1–3 )

Type:– GUYANA. “Demerara” [Potaro-Siparuni Region, Upper Potaro River], Kaieteur Falls [5°10’N, 59°28’W], [date unknown] 1872 (fl,

fr), C. Appun s.n. (holotype BM barcode BM 000099002). = Pteridocalyx minor Wernham (1913: 218) , syn. nov. Type:– GUYANA. Potaro-Siparuni Region, [Upper] Potaro River, “Sheenabowa” [Chenapou Village, 4°55’N, 59°34’W, ca. 470 m],

September–October 1881 (fl), G. S. Jenman 1282 (holotype K barcode K 000173940).

Shrub or treelet, 1–2 m tall, commonly with a central, thin stem, sparsely branched towards the top ( Fig. 2A ); young branches reddish, densely appressed-strigose; older stems and branches pale gray, glabrate. Stipules ovate to narrowly triangular, 2.2–3 × 4 − 6 mm, entire or bifid at apex, sometimes entire at early stage and becoming bifid at later stage, appressed-pubescent to appressed strigose-pubescent, the apical teeth (when present) to 1.5 mm long. Leaves with petioles 1.5 − 5 mm long, appressed-strigose-pubescent; blades elliptic to elliptic-lanceolate, 9–16 × 3 − 5.5 cm, acute to decurrent at base, acuminate at apex, chartaceous, shiny and dark green above and dull pale green below when fresh, pale brown above and olive-green below when dry, sparsely pubescent above, pubescent below, midrib and secondary veins sericeous-pubescent below; secondary veins 10 − 12 on each side of midrib. Inflorescence cymose during early stage of anthesis, expanding during and after anthesis ( Figs. 2B, 2C, 2E ), appressed-pubescent, with 1 − 3 pairs of lateral branches; lateral branches 2 − 6 cm long when fully expanded, dichotomously branched, with one flower at the base of each bifurcation, ultimate branchlets scorpiod (more evidently so when fully expanded); bracts subtending branchlets lanceolate, 2–4 × 0.5 − 1 mm, appressed-pubescent; bracteoles subtending flowers 1–2(– 3) per flower, linear-lanceolate, 1 − 3 × 0.2 − 0.7 mm, appressed-pubescent. Flowers sessile (rarely sub-pedicellate), secundiflorous, erect. Hypanthium oblong-obovoid, 1.5 − 1.7 mm long, acute-decurrent at base, round to truncate at apex, appressed strigose-pubescent. Calyx tube absent (lobes free) or extremely reduced (to 0.2 mm long); smaller lobes white when fresh, cream-white to beige when dry, linear to linear-lanceolate, 2 − 4.5 × 0.4–0.7 mm long, sparsely appressed strigose-pubescent outside, margins hispidulous; expanded, petaloid lobes (calycophylls) 1–2 per flower, sometimes with 1–2 additional less expanded lobes ( Fig. 3 ). Calycophylls varying in size and shape within the same inflorescence, pure white when fresh, cream-white to beige when dry, palmately veined; smaller calycophylls without a distinguishable stalk, linear, narrowly oblanceolate to narrowly oblong-oblanceolate, 4.5 − 9.5 × 0.8 − 1.5 mm, acute at apex, sparsely hispidulous along veins and sometimes at margins, with 3 veins (including midrib); larger calycophylls with stalks 2 − 5 mm long, sparsely appressed strigose-pubescent outside, blades narrowly elliptic, elliptic to ovate, 4 − 15 × 5 − 10 mm, acute, obtuse to round at base, acute to obtuse at apex, lamina glabrous, sparsely hispidulous along veins and sometimes at margins, with 5–7 veins (including midrib). Corolla 14 − 19.5 mm long, tube pale brown or white and brownish at medial portion, lobes pink, with a basal white triangle of glandular hairs on adaxial side at base (the rest glabrous), forming a white star-like pattern (with the 5 lobes) at mouth ( Fig. 2D ); tube narrowly cylindrical, slightly wider at mouth, 10.5–14 mm long, 0.7–0.9 mm wide for most length, 1.3–1.5 mm wide at mouth, appressed strigose-sericeous outside, sparsely puberulent below stamens, antrorsely pubescent at the portion surrounding the stamens, and with sparse moniliform hairs above the stamens inside; lobes oblong-ovate to ovate, 3.5 − 5.5 × 1.7–3 mm, obtuse to acute at apex, glabrous outside, with a basal triangular area of glandular hairs inside, the rest glabrous. Long-styled flowers: stamens inserted at 3 − 4 mm from base of corolla tube; filaments 0.5–1 mm long; anthers linear, 1.8 − 2 × 0.2 − 0.3 mm, acute at both ends; style about the same length as corolla tube (tip of branches exserted) or barely exserted, 11 − 15 mm long, glabrous; style branches linear, 1 − 1.2 mm long, densely papillose when receptive. Short-styled flowers: stamens inserted at 5.5 − 6 mm below corolla mouth (about the middle of corolla tube); filaments 0.3 − 0.5 mm long; anthers linear, 2.5 − 2.7 × 0.2 − 0.3 mm, acute at both ends; style included, 6 − 6.5 mm long, glabrous; branches narrowly lanceolate, 1.5 mm long, acute, adaxial surface densely papillose when receptive. Capsules oblong-ellipsoid to narrowly oblong, 6 − 14 × 2 − 3 mm, acute-decurrent at base, round to truncate at apex, crustaceous, sparsely strigose-sericeous, pale green when young, turning pale brown when dry. Seeds 0.3–0.4 mm in diam.

Morphological observations: – Wernham (1911: 318) described the calyx tube of Pteridocalyx appunii as “ 3–4 mm long”; however, in the type specimen the calyx tube is either absent (lobes free) or up to 0.2 mm long, as in all other specimens studied. The difference between Wernham’s measurements and those presently observed might be due to the fact that British botanists in those days included in what they called “calyx tube” both the hypanthium and the unlobed portion of the calyx. However, nowadays most botanists distinguish the hypanthium from the calyx (and eventually supply the corresponding measurements), and divide the lobed calyx into calyx tube (excluding the hypanthium) and calyx lobes.

Wernham (1913: 218) separated Pteridocalyx minor from P. appunii by the stipules entire (vs. divided at apex in P. appunii ), calycophyll blades 4 × 5 mm (vs. 11 − 13 × 7 − 9 mm), and corolla tubes 16 mm long (vs. 10 − 11 mm long). However, although he described P. minor as having “corolla tube 16 mm long, 1 mm wide, lobes 5.5 × 2 mm ”, the holotype specimen at K has corolla tube 11 mm long and lobes 3.5 × 1.5 mm, which largely correspond to the measurements supplied by him (and here confirmed) for P. appunii , i.e., “corolla tube 10–11 mm long, lobes 4–5 × 2 mm.” ( Wernham 1911: 318).

In addition, personal observation of natural populations, and detailed analysis of numerous herbarium specimens recently collected, demonstrated that the stipules can be either entire or bifid on the same branch ( Fig. 1B–C ), often entire when young and becoming bifid at later stage.

Finally, petaloid calyx lobes (calycophylls) can be one or two per flower, sometimes with one or two additional less expanded lobes, and can vary in shape and size within the same inflorescence ( Fig. 3 ), with blades ranging from narrowly elliptic, elliptic to ovate and 4 − 13 × 5 − 9 mm within the same inflorescence. The largest ones are found on the basal flowers and the smaller ones on the distal flowers of the same inflorescence branch. In conclusion, all morphological characters used by Wernham to distinguish P. minor from P. appunii are widely overlapping, and the two taxa are here treated as conspecific.

Distribution and ecology: –Endemic to the Upper Potaro River basin, above and below Kaieteur Falls, central Guyana, at 200–500 m altitude. According to herbarium specimen labels and personal field observations, it grows in shady areas, usually in the understory of tall forests, in alluvial or lateritic soil, either seasonally inundated, e.g., mora forest [dominated by Mora excelsa Bentham (1839: 210) ], or not inundated, e.g., bulletwood forest [dominated by Manilkara bidentata (A.P. de Candolle 1844: 204) Chevalier (1932: 270) ].

Conservation status: –VU (Vulnerable). Until recently Pteridocalyx was a genus known by only a few historical collections made in 1872, 1881 and 1907, preserved in the BM and K herbaria. A gathering of 1992 remained unidentified until recently. All these collections are from the Upper Potaro River basin, above and below Kaieteur Falls (located within the Kaieteur National Park), central Guyana, which is an area botanically poorly collected. During my field expedition of 2016, I observed several populations of approximately 100–200 individuals along the trails bordering the Potaro River and its affluents, near the Chenapou Village, in forests seasonally inundated or never inundated. Because of the difficult terrain in the forests away from the forest trails, the only populations that I examined are those bordering the rivers. Therefore, the AOO (Area of Occupancy) of this taxon is difficult to estimate, and the EOO (Extent of Occurrence) is less than 20,000 km 2. Although this monospecific genus is endemic to the Upper Potaro River basin, no imminent threats were detected in 2016, as the forests bordering the rivers surrounding the Chenapou Village are fairly well preserved (i.e., selective logging of certain large trees), even though they do not have any official conservation status. In addition, the only way to access the area surrounding the Potaro River above Kaieteur National Park is by canoe, which renders impossible any considerable timber exploitation (aside from the sparse extraction by local indigenous community) in this portion of the river, including the forests surrounding the Chenapou Village. In conclusion, because of the small populations observed and the relatively restricted area of occurrence, this taxon is here treated as Vulnerable (VU) based on criterion D1 of IUCN (2012, 2017).

Phenology: –Flowering specimens were collected in June, September, October and November; collections with flowers and capsules were made in June.

Additional specimens examined:– GUYANA: Potaro-Siparuni Region, Potaro River, Holmia [ca. 4°58’N, 59°35’W], November 1907 (fl), A. W. Bartlett 8763 ( K) ; Potaro-Siparuni Region (Region 8), Upper Potaro River, Chenapou Village , trail from village to Karisparu Landing , tall Mora forest seasonally inundated, on alluvial soil, 4°58’40”N, 59°34’14’’W, 450 m, 12 June 2016 (fl), P. G. Delprete & P. Benjamin 12813 ( BRG, CAY, K, MG, MO, NY, US), 12814 ( B, BBS, BR, BRG, L, P, US), 12815 ( BRG, CAY, K, MG, NY, P, US) ; Potaro-Siparuni Region, Upper Potaro River, Chenapou Creek Mouth (affluent of Potaro River ), secondary forest, on lateritic soil, 4°58’25”N, 59°34’47’’W, 420 m, 13 June 2016 (fl), P. G. Delprete & P. Benjamin 12824 ( BRG, CAY, GB, L, MG, MO, NY, RB, W) ; Potaro-Siparuni Region, Upper Potaro River, Chenapou Village, Paramakatoi trail, parallel to Chenapou Creek , going from Chenapou Village to Paramakatoi Village , bulletwood forest on lateritic soil, never inundated, 4°57’26’’N, 59°35’01’’W, 440 m, 14 June 2016 (fr), P. G. Delprete & P. Benjamin 12836 ( BRG, CAY, G, MO, NY, RB, US) ; Potaro-Siparuni Region, Micobe , mixed forest on brown and white sand, shady places, 5°20’N, 59°30’W, 200 m, 20 October 1992 (fl), S. Tiwari & A. Mengarini 487 ( BRG [3 sheets], CAY) .

Figures

FIGURE 1. Pteridocalyx appunii. A. Branch with inflorescence. B–C. Stipule shapes present on the same branch. D. Flower in anthesis. E. Dissected long-styled flower, with stamens inserted at basal portion of corolla tube. F. Dissected short-styled flower, with stamens inserted at distal portion of corolla tube. G. Mature capsule with calycophyll fallen off. A–E: drawn from P.G. Delprete & P. Benjamin 12813 (CAY); F: drawn from P.G. Delprete & P. Benjamin 12824 (CAY); G: drawn from P.G. Delprete & P. Benjamin 12836 (CAY). Illustration by Piero Delprete.

FIGURE 2. Pteridocalyx appunii. A. Habit. B. Inflorescences, side view.C. Inflorescence, top view. D. Corolla, top view. E. Inflorescence and infructescence from the same plant. Photos by Piero Delprete.

FIGURE 3. Pteridocalyx appunii. Calycophyll variation within the same inflorescence branch.A. Basal flower. B–D. Intermediate flowers, from base towards distal portion. E. Distal flower. A–E: drawn from P.G. Delprete & P. Benjamin 12813 (CAY). Illustration by Piero Delprete.