Sabicea crystallina subsp. engongensis Zemagho, O.Lachenaud & Sonké, 2017

Zemagho, Lise A., Liede-Schumann, Sigrid, Lachenaud, Olivier, Dessein, Steven & Sonke, Bonaventure, 2017, Taxonomic revision of Sabicea subgenus Anisophyllae (Ixoroideae, Rubiaceae) from Tropical Africa, with four new species, Phytotaxa 293 (1), pp. 448-450 : 448-450

6b. Sabicea crystallina subsp. engongensis Zemagho, O.Lachenaud & Sonké , subsp. nov. ( Fig. 14 )

Type :— EQUATORIAL GUINEA. Parc national de Monte Alén, dalle rocheuse d’Engong, 5 km W of village d’Engong, 11 May 2002, I. Parmentier & P. Esono 2732 (holotype BRLU!) .

Sabicea crystallina subsp. engongensis differs from the typical subspecies in having the calyx and corolla lobes densely pubescent outside (vs. glabrous or nearly so).

Stems, petioles and upper side of leaf blade glabrous. Stipules 13–20 x 2–4 mm. Bracts 3–3.5 x 0.7–1.2 mm, bracteoles 4–6.5 x 0.5–1 mm. Calyx tube glabrous or sparsely villose outside; lobes 3–5.5 x 0.8–1.2 mm, slightly widening at the apex, pubescent outside with sparse woolly hairs all over and stiff hairs ca. 0.8 mm long mostly on the margin. Corolla tube glabrous outside, the lobes densely villose with stiff hairs ca. 1 mm long.

Etymology:— The name of the subspecies derives from its only known locality, the Engong rock slab in Equatorial Guinea.

TAXONOMIC REVISION OF SABICEA SUBGENUS ANISOPHYLLAE

Phytotaxa 293 (1) © 2017 Magnolia Press • 31 32 • Phytotaxa 293 (1) © 2017 Magnolia Press

ZEMAGHO ET AL.

Distribution: —Lower Guinea Domain. Endemic to Equatorial Guinea and known from a single rocky outcrop in the Monte Alén National Park ( Fig. 13 ), slightly outside the distribution of the typical subspecies.

Habit and ecology: —Low shrubby formations (“manteau arbustif”) on rocky outcrops, ca. 1100 m in altitude.

Conservation status:—IUCN Red List Category: Vulnerable [VU D2]. This taxon is known from a single population (sensu IUCN 2012), therefore its extent of occurence is not calculable. Its area of occupancy is estimated as 4 km 2, within the limit for Critically Endangered under criterion B2. Its only location is in the Monte Alén National Park, and does not seem currently threatened by human activities, so there is no evidence of a decline. However, due to its extremely limited range, the taxon is vulnerable to any stochastic event, and qualifies for Vulnerable under criterion D2.

Phenology: —Flowering in May.

Notes: —Only the type specimen bears flowers; a second collection from the type locality, Parmentier & Nguema 110, lacks flowers and fruits.

Additional specimen examined (Paratype):— EQUATORIAL GUINEA. Parc national de Monte Alén, dalle rocheuse d’Engong , 5 km à l’Ouest du village d’Engong, 2 July 1999, I. Parmentier & N. Nguema 110 ( BRLU) .

Figures

FIGURE 13. Distribution of Sabicea crystallina subsp. crystallina and S. crystallina subsp. engongensis.

FIGURE 14. Sabicea crystallina subsp. engongensis. A, flowering branch; B, detail of stem with two successive nodes showing the stipules, reduced leaves and base of normal leaves; C, flower bud with two bracteoles; D, long-styled flower; E, section of long-styled flower. From Parmentier & Esono 2732 (A, C–E), Parmentier & Nguema 110 (B). Drawing by Hans De Vries.