Isolona thonneri (De Wild. & T. Durand) Engl. & Diels, Monogr. Afr. Pflanzenfam. 6: 83, 1901

Couvreur, Thomas L. P., Dagallier, Leo-Paul M. J., Crozier, Francoise, Ghogue, Jean-Paul, Hoekstra, Paul H., Kamdem, Narcisse G., Johnson, David M., Murray, Nancy A. & Sonke, Bonaventure, 2022, Flora of Cameroon - Annonaceae Vol 45, PhytoKeys 207, pp. 1-532 : 149-151

Isolona thonneri (De Wild. & T. Durand) Engl. & Diels, Monogr. Afr. Pflanzenfam. 6: 83, 1901

Fig. 40 ; Map 5G

≡ Monodora thonneri De Wild. & T. Durand, Bull. Soc. Roy. Bot. Belg., Compt. Rend. 38: 12, 1899.

= Diospyros oblongicarpa Gürke, Bot. Jahrb. Syst. 43: 200, 1909. Type. Cameroon. South Region, Bipindi, Zenker G.A. 3471, 1908: holotype B n.v.: isotype: K[K000199009]; US[US03899523]; WU[WU0040298].

Type.

Democratic Republic of the Congo. Equateur; Massanga ( près de Monveda), Thonner F. 104, 24 Sep 1896: lectotype, designated by Boutique (1951b), p. 263, sheet here designated: BR[BR0000005113330]; isotypes: BR[BR0000005112715, BR0000005113040] .

Description.

Tree to shrub, 3-10 m tall, d.b.h. up to 25 cm; stilt roots or buttresses absent, trunk not fluted. Indumentum of simple hairs; old leafless branches glabrous, young foliate branches glabrous. Leaves: petiole 3-8 mm long, 1-2 mm in diameter, glabrous, grooved, blade inserted on the side of the petiole; blade 11-20 cm long, 4-7.5 cm wide, elliptic to obovate, apex acuminate, acumen 1-2 cm long, base decurrent to cuneate, coriaceous to subcoriaceous, below glabrous when young and old, above glabrous when young and old, concolorous; midrib raised above, above glabrous when young and old, below glabrous when young and old; secondary veins 9 to 12 pairs, glabrous below; tertiary venation reticulate. Individuals bisexual; inflorescences ramiflorous on old or young foliate branches, axillary. Flowers with 9 perianth parts in 2 whorls, 1 to 2 per inflorescence; pedicel 5-18 mm long, ca. 1 mm in diameter, glabrous; in fruit 8-10 mm long, 3-4 mm in diameter, glabrous; bracts 3 to 7, several basal and one upper towards the lower half of pedicel, basal bracts ca. 1 mm long, ca. 1 mm wide; upper bracts ca. 2 mm long, 1 mm wide; sepals 3, valvate, free, 2-3 mm long, 1-2 mm wide, ovate, apex acute, base truncate, dark green, glabrous outside, glabrous inside, margins flat; petals basally fused, tube 3-6 mm long, inner and outer whorl not differentiated, equal; lobes 14-31 mm long, 3-5 mm wide, linear to lorate (strap-shaped), apex acute, green, margins flat, glabrous outside, glabrous inside, pendulous; stamens numerous, in 3 to 4 rows, ca. 2 mm long, broad; connective discoid, glabrous; staminodes absent; carpels fused into a single structure, ca. 2 mm long, stigma bilobed, slightly capitate, sparsely pubescent. Fruit syncarpous, sessile, 40-60 mm long, 20-35 mm in diameter, ellipsoid, apex rounded, glabrous, smooth, not or faintly ribbed, color unknown; seeds not counted, 15-18 mm long, 8-9 mm in diameter, ellipsoid; aril absent.

Distribution.

A central African species, known from Cameroon to Gabon and the Democratic Republic of Congo; in Cameroon known from the South and East regions.

Habitat.

An infrequent species; in lowland rain forests, near rivers and swamps. Altitude 450-750 m. a.s.l.

Local and common names known in Cameroon.

None recorded.

IUCN conservation status.

Least Concern (LC) ( Cosiaux et al. 2019w).

Uses in Cameroon.

None reported.

Notes.

Isolona thonneri is characterized by long, narrowly elliptic to linear and glabrous corolla lobes. In the absence of flowers, it is hard to distinguish from I. dewevrei .

Specimens examined.

East Region: Pres de Banana 10 km ENE de Moloundou, 2.08°N, 15.28°E, 17 April 1971, Letouzey R. 10682 (P,WAG,YA); near Ndongo ca 45 km WNW of Moloundou, 2.16°N, 14.83°E, 15 March 1973, Letouzey R. 12085 (K,P); Près Ndongo à 45 km WNW de Moloundou, 2.15°N, 14.86°E, 16 March 1973, Letouzey R. 12111 (BR,K,P,WAG,YA); près Ndongo à 40 km WNW de Moloundou, 2.15°N, 14.86°E, 16 March 1973, Letouzey R. 12115 (BR,K,P,WAG,YA). South Region: Colline Ongongondje près Akonekye 15 km NW d’Ambam, 2.46°N, 11.16°E, 23 March 1970, Letouzey R. 10205 (BR,COI,K,P,WAG,YA); Inselberg d’Akookas pres du village d’Akookas 38 km au sud est d’Ebolowa, 2.71°N, 11.27°E, 15 March 2001, Parmentier I. 1943 (BRLU,WAG); Inselberg d’Akookas pres du village d’Akookas 38 km au sud est d’Ebolowa, 2.71°N, 11.27°E, 15 March 2001, Parmentier I. 1961 (BRLU,WAG) .

Figures

Map 5. A Isolona congolana B Isolona cooperi C Isolona dewevrei D Isolona hexaloba E Isolona pilosa F Isolona pleurocarpa G Isolona thonneri H Isolona zenkeri I Letestudoxa bella. White borders represent region limits in Cameroon; green patches represent protected areas (see methods and Suppl. material 1: Fig. S 1).

Figure 40. Isolona zenkeri A flowering branch B flower C fruit. Isolona campanulata D flowering branch; E flower E corolla lobe opened G fruit. Isolona thonneri H flowering branch I flower J fruit A from Le Testu 5117 B from Le Testu 8001 C from Klaine 2675 D-G from Aubreville 6 H, I from Vrydagh 34 J from Lebrun 2032. Drawings by Helene Lamourdedieu, Publications Scientifiques du Museum national d'Histoire naturelle, Paris; modified from Le Thomas (1969 b, pl. 67, p. 359).