Craterispermum sonkeanum Taedoumg & Hamon, 2013

Taedoumg, H. & Hamon, P., 2013, Three new species of Craterispermum (Rubiaceae) from the Lower Guinea Domain, Blumea 57 (3), pp. 236-242 : 240-242

Craterispermum sonkeanum Taedoumg & Hamon , sp. nov. — Fig. 3 ; Map 1

C. aristatum Wernham propter bracteas bracteolasque aristatas proximum, sed ab illo differt stipulis acicularibus, foliorum laminis multinervis (cum nervis lateralibus in 10–12 paribus, vs 5–6 paribus), floribus 4-meris (vs 5-meris), calycis lobis inaequalibus (vs aequalibus) et nervis tertiariis dense regulariterque reticulatis (vs laxe irregulatirque in C. aristatum ). — Typus: De Wilde JJFE, Arends, Louis AM, Bouman & Karper 98 (holo BR; iso MO, WAG), Cristal Mountains ,forest exploitation Leroy, 20 km NW of Asok (N0°53' E10°12'), 20 Jan. 1983 .

Etymology. The species is named after Professor Doctor Bonaventure Sonké, specialist of Rubiaceae and Director of the Plant Systematic and Ecology Laboratory in Higher Teacher’s Training College of the University of Yaoundé I in Cameroon, for his contribution to the knowledge of African Rubiaceae .

Shrub up to 3 m tall; all vegetative and generative parts glabrous; twigs greenish grey or brown, smooth but each internode with two decurrent ridges in line with the stipular tip. Stipules persistent; basal portion 2– 3 mm long; tip narrowly triangular, 4 –13 mm long. Leaves petiolate; petioles canaliculate, 5–10 mm long; leaf blades narrowly obovate 6.7–14 by 2 – 4.8 cm, subcoriaceous, greenish above, paler green below; base cuneate; apex acuminate-caudate, acumen 7–15 mm long; midrib prominent below; secondary venation slightly to moderately prominent on both surfaces, 10–12 pairs of secondary veins, secondary, inter-secondary and tertiary venation ± parallel and almost perpendicular to the midrib; quaternary venation ± obscure. Inflorescences pedunculate, axillary to slightly supra-axillary, borne 1– 2 mm above the nodes, paired, opposite, subcapitate, 9 –16 by 3 –10 mm, few-flowered; peduncle flattened, 3 – 4 mm long; bracts and bracteoles very congested, triangular to ovate with long aristate apex, sometimes sparsely ciliate; bracts 5 –9 mm long; bracteoles c. 4 mm long. Flowers presumed heterostylous (but only brevistylous morph known), 4-merous, sessile. Brevistylous flowers: calyx green; tube c. 1–1.5 mm long; lobes linear, opposite lobes equal in length, largest pair c. 2 mm long and smallest pair 1–1.2 mm long, margins densely ciliate, sparse collecters present in the sini. Corolla white; tube narrowly cylindrical, 5 – 6.5 mm long, sparsely to densely pubescent at throat and in upper half of tube inside; lobes c. 3 mm long, moderately to densely pubescent inside, tips acute and thickened. Stamens with anthers completely exserted from corolla tube, inserted in the throat, c. 1.3 mm long, white; filaments c. 1.3 mm long. Ovary c. 1 mm long. Style and stigma included in the corolla tube, c. 5.5 mm long; stigma bilobed, stigmatic lobes c. 1.5 mm long. Fruits sessile, subglobose, asymmetrical, 8– 7 mm diam (immature), crowned with persistent calyx, dark violet to black when ripe.

Habitat & Ecology — Craterispermum sonkeanum occurs in humid forest on terra firma. Altitude 185–750 m. Flowers: November to February; fruits recorded in: January, August and October.

Distribution — Craterispermum sonkeanum occurs in the continental part of Equatorial Guinea and in Gabon. The species is mostly collected from the National Park of Monte Alén and ‘Monts de Cristal’.

Conservation status — Endangered. See Table 1.

Critical remarks — Flowers and fruits are rare on the specimens of C. sonkeanum . Only a few brevistylous flowers were available and measurements were based on two of them.

Taxonomic affinities — Craterispermum sonkeanum and C. aristatum share long aristate bracts and bracteoles, short peduncles and subcapitate inflorescences. However, C. sonkeanum differs from C. aristatum by the following characters: stipules with long narrowly triangular tips in C. sonkeanum vs short and broadly triangular tips in C. aristatum , 10–12 pairs vs 5 – 6 pairs of secondary veins, 4-merous vs 5-merous flowers, unequal vs equal calyx lobes, closely and ± regularly reticulate vs laxly and irregularly reticulate higher order veins and by the smaller leaf blades (6.7–14 by 2– 4.8 cm in C. sonkeanum vs 11–25.5 by 4 –8 cm in C. aristatum ).

Additional specimens examined. EQUATORIAL GUINEA, Desmet, Nguema R & Nguema N 6 ( BRLU),transect de Monte Chocolate , 16 Nov.2002 ; Senterre & Ngomo 188 ( BRLU), SO du Parc National de Monte Alén, sur le transect ECOFAC de Mosumo , 10 Feb. 2001 ; Senterre & Ngomo 280 ( BRLU), SO du Parc National de Monte Alén, entre la station ECOFAC de Mosumo et Monte Boracho , 12 Feb. 2001 ; Senterre & Ngomo 582 ( BRLU), SO du Parc National de Monte Alén, sur le transect ECOFAC de Mosumo , 3 Feb. 2001 ; Senterre & Ngomo 2010 ( BRLU), SO du Parc National de Monte Alén, 2 km au NE du site de traversée du rio Uolo pour aller aux cataractas, 20 Jan. 2002 ; Senterre & Ngomo 3530 ( BRLU), N du Parc National de Monte Alén, à proximité du transect ECOFAC de Monte Chocolate , 21 Nov. 2002 ; Van Reeth 332 ( BRLU), Parc National de Monté Alén , transect de Mosumo, 30 Jan. 1998 . – GABON, Hallé N 818 ( P), Ngongolane , Monts de Cristal, 7 Aug. 1959 ; Hallé N 4434 ( P), Monts de Cristal , chûtes de Kinguélé, rivière Mbei, 15 Jan.1968 ; Leal, Nguema, Mounoumoulossi & Bissiemou 642 ( BR), Monts de Cristal , Mbe National Park, Mt Mbilan Plateau, 26 Oct. 2005 .

Note — The plants from Gabon show more conspicuous decurrent ridges on the young branches and stipules with a less-developed tip than the plants from Equatorial Guinea.

Figures

Map 1 Distribution of Craterispermum deblockianum (●), C. rumpi­ anum (▲) and C. sonkeanum (■). Based on the specimens cited in the text.

Fig. 3 Craterispermum sonkeanum Taedoumg & Hamon. a. Flowering branch; b. node carrying stipules and inflorescences with bracts,bracteoles and flower bud; c. calyx (brevistylous flower); d. corolla with anthers (brevistylous flower); e. young fruit (a, b: Desmet, Nguema R & Nguema N 6, BRLU; c–e: De Wilde JJFE, Arends, Louis AM, Bouman & Karper 98, BR). — Drawn by Antonio Fernandez.