Massularia stevartiana Sonké, Bidault & Droissart, 2015

Sonké, Bonaventure, Bidault, Ehoarn & Droissart, Vincent, 2015, Taxonomic revision of the genus Massularia (Rubiaceae, Gardenieae), with a new species from Central Africa, Phytotaxa 203 (3), pp. 263-270 : 267-269

2. Massularia stevartiana Sonké, Bidault & Droissart sp. nov. ( Fig. 1 , 3 ).

Type: — GABON. Mabounié, NE du campement, 00°45’36,1’’ S, 10°36’6,8’’ E, 112 m, 04 February 2013 (fl), B. Sonké, E. Bidault, D. Ikabanga, E. Akouangou, J.- N. Boussiengui 6188 (holotype MO!, isotypes BR!, BRLU!, LBV!, P!, WAG!, YA!).

Massularia stevartiana Sonké, Bidault & Droissart sp. nov. is similar to Massularia acuminata because of the remarkable anisophylly on some nodes of the branches; absence of domatia; pseudo-axillary inflorescences, inserted at alternate nodes; floral buds acute and twisted, and differs from it by its leaf blades 6–9 × 1.2–2.4 cm (vs 15–32 × 5–12.5 cm), 5–9 pairs of secondary veins (vs. 12–16), flowers 4-merous (vs. (4–)5-merous), corolla tube 6–10 mm long (vs. 11–20 mm long).

Shrub or small tree 4–5 m tall; young stems slender, ca. 4–5 mm in diam., puberulous; older stems with pale brown bark. Stipules persistent, entire, triangular, 3–4 × 2 mm, pubescent on both sides. Leaves opposite, sometimes anisophyllous; petioles (3–) 5–8 cm long, glabrous; blades narrowly obovate, 6–9 × 1.2–2.4 cm, cuneate at base, glabrous, usually short- acuminate at apex (acumen 6–10 mm long), drying darkish green to pale olive-brown, paler below; midrib impressed above, puberulous; secondary veins 5–9 on each side of the midrib, ascending at +/- 45°, puberulous; tertiary veins inconspicuous; domatia absent. Inflorescences pseudoaxillary, pedunculate, 4–10 mm long; bracts fused into a cup 2 mm long. Flowers 4-merous, short-pedicellate, pedicels ca. 0.8 mm long. Hypantium 10 mm long. Calyx tube 5–6 mm long, teeth narrowly acute, sparsely pubescent. Flower buds acute, twisted. Corolla pale pink to red; tube 6–10 mm long, glabrous; lobes ca. 6 mm long, acute, glabrous. Stamens included; anthers ca. 4.8 mm, attached at the middle, acute, glabrous; ovary 2-locular; style exserted ca. 2 mm beyond the corolla mouth, grooved on the upper, glabrous. Fruits unknown.

Distribution & ecology:— Lower Guinea Domain. Massularia stevartiana is sparsely distributed from Cameroon, Central African Republic and Gabon ( Fig. 2 ); in closed canopy forest.

Conservation status:— IUCN Red List Category: Endangered [EN B2ab(ii,iii)]. The extent of occurrence (EOO) of Massularia stevartiana is estimated to be 126,556.613 km 2 (i.e. greater than the 20,000 km 2 upper limit for vulnerable status under criterion B1) and its area of occupancy (AOO) is about 12 km 2 (which falls within the limits for endangered status under criterion B2). Only one collection has been made inside the boundaries of a protected area (Dja Fauna Reserve). The main threat for the species is logging and mining activities which negatively influence the quality of its habitat. Based on these threats and because only three localities are currently known, and the continuous decline of vegetation in the area, extent and/or quality of his habitat can be projected.

Etymology:— The specific epithet honours Dr Tariq Stévart, of the Missouri Botanical Garden, who is an internationally recognized taxonomist, specialist of the Flora of Central Africa and mostly of the Orchidaceae family.

Discussion:— Field collections of Massularia stevartiana were undertaken by B. Sonké and E. Bidault in 2013. However, its first collection dates back to 1947, with a collection by C. Tisserant. The second specimen was collected in 2002 in the Dja Reserve. The collected material clearly belong to Massularia on the basis of the blackish colour of the specimens in the dried state; shrubby habit; stipules with triangular lobes; remarkable anisophylly on some nodes of the branches; absence of domatia; pseudo-axillary inflorescences (i.e., one inflorescence per node), inserted at alternate nodes; floral buds acute and twisted; 2-locular ovary with small, fleshy placentas attached near the middle of the septum; style exserted.

The discovery does not match the description of the only known species of the genus, Massularia acuminata ( Keay 1963; Hallé 1970). The material clearly differs from the typical species, particularly in its narrowly obovate and smaller leaves, and smaller flowers. The small leaves and the small 4-merous flowers can distinguish the novelty at first glance. Massularia acuminata has larger leaves with numerous secondary veins and generally 5-merous flowers with a larger corolla. A few quantitative characters complete the diagnostic features: Massularia stevartiana is a small shrub, up to 5 m tall, small leaf blades, with usually less than 10 secondary veins each side of the midrib, and corolla lobes shorter than the tube. The main differences between the two species are summarized in Table 1.

Additional specimens examined (paratypes): — CAMEROON. 12 km E Somalomo, 07 November 2002, B.

Sonké, C. Nguembou, A.P. Davis & O. Morrin 2862 (BR, BRLU, K, MO, SCA, WAG). CENTRAL AFRICAN REPUBLIC. Boukoko, 18 October 1974, C. Tisserant 367 (P).

Figures

FIGURE 1. Vegetative and floral morphology of Massularia.A–C. M. acuminata (B. Sonké, E. Bidault, D. Ikabanga, E.Akouangou, J.-N. Boussiengui 6189); D–F. M. stevartiana (B. Sonké, E. Bidault, D. Ikabanga, E. Akouangou, J.-N. Boussiengui 6188).

FIGURE 2. Distribution of Massularia based on herbarium specimens studied.

FIGURE 3. Massularia stevartiana. A, flowering shoot; B, node showing stipule with the base of petioles; C, Portion of midrib and lateral nerve; D, Stipule; E, flower-bud; F, flower; G, calyx and ovary; H, section through corolla; I, stamen; J, style with stigma.A–D, F–I, from B. Sonké, E. Bidault, D. Ikabanga, E. Akouangou, J.-N. Boussiengui 6188; E, from B. Sonké, C. Nguembou, A.P. Davis & O. Morrin 2862. Drawn by Antonio Fernandez.