Monanthotaxis atopostema P.H.Hoekstra

Hoekstra, P. H., Wieringa, J. J., Maas, P. J. M. & Chatrou, L. W., 2021, Revision of the African species of Monanthotaxis (Annonaceae), Blumea 66 (2), pp. 107-221 : 127-128

4. Monanthotaxis atopostema P.H.Hoekstra — Map 2

Monanthotaxis atopostema P.H.Hoekstra in P.H. Hoekstra et al. (2016) 73. — Atopostema angustifolia Boutique (1951b) 121. — Popowia klainei Engl. var. angustifolia (Boutique) Le Thomas (1963) 291. — Monanthotaxis klainei (Engl.) Verdc. var. angustifolia (Boutique) Verdc. (1971b) 30, non Monanthotaxis angustifolia (Exell) Verdc. — Lectotype (designated here): J.L.P. Louis 15324 (lecto BR (BR0000008820334);isolecto BR0000008820358), Democratic Republic of the Congo, Orientale, à 20 km au Nord-Est de Yambao, 23 June 1939.

Shrub or liana, to 6 m long; young branches dark brown to blackish, sparsely covered with appressed, reddish brown hairs c. 0.1 mm long, soon becoming glabrous. Leaves: petiole 3–5 mm long, 0.9–1.1 mm diam, grooved, indument as on branches; lamina oblong-elliptic to narrowly so, 8.4–14 by 2.9–5.2 cm, 2–2.9 times longer than wide, chartaceous, not punctate, discolorous, shiny green above, dull glaucous green below, above densely covered with appressed, yellowish hairs when young, soon becoming glabrous, below sparsely covered with appressed, reddish brown hairs 0.1–0.2 mm long, soon becoming glabrous, base rounded, glands hardly visible, apex acuminate, acumen 10–35 mm long, primary vein often distinctly contrasting with darker petiole, secondary veins 5–8 per side, curving upwards, tertiary venation percurrent. Inflorescences cauliflorous or axillary, composed of solitary flowers or few-flowered fascicle-like rhipidia; sympodial rachis 0.8–5 mm long, densely covered with appressed, yellowish white hairs; pedicels 0–17 mm long, 0.3–0.4 mm diam, fruiting pedicels 0.6–1.8 mm diam, sparsely covered with appressed hairs, lower bracts ovate, c. 0.4 by 0.3 mm, indument as on rachis; upper bract in lower half of the pedicel, triangular to ovate, c. 0.7 by 0.4–0.8 mm, covered with appressed, yellowish hairs; flower buds ovoid. Flowers bisexual; sepals free, broadly to depressed ovate, 0.7–1 by 1–1.3 mm, apex acute, densely covered with appressed hairs, not persistent in fruit; receptacle 1.8–2.2 mm diam, flat; petals yellowish white, 6, in two whorls, base of inner petals visible in bud, outer petals broadly ovate, 2.9–3.4 by 2.6–3.2 mm, outside sparsely covered with yellow hairs, inside densely covered with yellowish hairs <0.1 mm long, inner petals elliptic, 2.5–2.9 by 1.3–1.9 mm, outside densely covered with very short hairs along the middle line, inside densely covered with hairs in the upper half, but the base glabrous; stamens 9, in one whorl, free, linear-oblong, c. 0.6 mm long, filaments c. 0.2 mm long, thecae latrorse, connective truncate, slightly prolonged inward and outward, not hiding thecae, glabrous, staminodes 6, alternating with the stamens, but not in front of the inner petals, c. 0.5 mm long, glabrous; carpels 15–20, ellipsoid, c. 1 by 0.4 mm, densely hairy, ovules 2 or 3, lateral, stigma subsessile, globose, 0.1–0.2 mm long, glabrous. Monocarps 1–6, red when ripe, narrowly ellipsoid, 18–30 by c. 7 mm, covered with appressed, reddish brown, short hairs, becoming glabrous, but longer persistent at stipe and apex, apex apiculate or rounded, stipes 3–6 mm long, grooved. Seeds 1 or 2, ellipsoid, 10–11 by 6 –7 mm, ochre-brown to reddish brown, apex apiculate or rounded, raphe not visible.

Distribution — Republic of the Congo (Pool), Democratic Republic of the Congo (Equateur, Orientale).

Habitat & Ecology — In tropical rain forests, swamp forests and riparian forests. Altitude: c. 470 m. Flowering: May, June, October; fruiting: February, March, May, August, October.

Vernacular names — Democratic Republic of the Congo: Lumwembe (Turumbu name) (JLP Louis 15324), Inaolo a Lumwemwe (Turumbu name) (RGA Germain 271).

Preliminary IUCN conservation status — Vulnerable (VU): B2ab(iii). EOO: 88 402 km 2, AOO: 28 km 2.This species is known from 9 collections and max 7 locations of which the majority are outside protected areas.

Note — Monanthotaxis atopostema is the only species of Monanthotaxis in Congo with oblong-elliptic leaves and cauliflorous inflorescences. It is very similar to M. couvreurii from Cameroon and M. aquila from Ivory Coast. It differs from M. couvreurii by the presence of 6 staminodes (vs staminodes absent), free stamens (vs connate) and in having more carpels (15–20 vs 9–12). For the differences with M. aquila see under that species.