Monanthotaxis aestuaria P.H.Hoekstra, 2021

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 : 123-125

1. Monanthotaxis aestuaria P.H.Hoekstra , sp. nov. — Fig. 2 ; Map 2

Monanthotaxis aestuaria belongs to the M. schweinfurthii complex. It is distinguishable from the other species in this complex by the elliptic to oblanceolate leaves with attenuate to cuneate base,hardly visible tertiary venation, and yellow-brown branches densely covered with appressed, yellowish brown hairs. — Type: J. Floret 1456 (holo P ( P01967244 );iso LBV not seen, WAG0076149 ), Gabon, Estuaire, 5 km au NW de Mebba , 25 Sept. 1983. Paratype : G. D. McPherson 15091 ( LBV, MO, P, WAG), Gabon, Estuaire, along Remboué River, British Gas site, 10 m, 9 Jan. 1991 .

Etymology. Named after the province and habitat where the two known specimens have been collected (Estuaire, Gabon).

Liana; young branches densely covered with appressed, yellowish brown hairs c. 0.1 mm long, becoming glabrous; old branches yellowish brown to orange-brown. Leaves: petiole 3–9 mm long, 0.7–1.5 mm diam, grooved, indument as on branches; lamina elliptic to obovate or oblanceolate, 6–13 by 2.5–4.5 cm, 2 or 3 times longer than wide, chartaceous, not punctate, above glabrous except appressed, yellow hairs c. 0.1 mm long on primary vein, below densely covered with appressed, yellow hairs c. 0.1 mm long, base attenuate to cuneate, with a thickened black margin or with very thick, globose, black glands, apex acute to acuminate, acumen to 10 mm long; secondary veins 6–10 per side, sometimes hardly visible, slightly curving upwards, tertiary venation percurrent, hardly visible. Inflorescences axillary or c. 2 mm above axil, composed of 2–6-flowered fascicle-like rhipidia; sympodial rachis 3–10 mm long, densely covered with appressed, yellowish hairs c. 0.1 mm long; pedicels 6–10 mm long, 0.6–0.8 mm diam,

Map 2 Distribution of Monanthotaxis aestuaria P.H.Hoekstra (■) and M.atopostema P.H.Hoekstra (●, O uncertain det of M. atopostema ).

fruiting pedicels to 30 mm long and 0.7 mm diam, indument as on rachis; lower bracts broadly ovate to ovate, 0.6–1 by 0.6–0.8 mm, indument as on rachis; upper bract halfway up the pedicel, broadly ovate, 0.4–0.7 by 0.5–0.8 mm, indument as on rachis; flower buds globose to slightly ovoid. Flowers bisexual; sepals connate at the base, ovate to depressed ovate, 0.6–0.9 by 1.1–1.2 mm, apex obtuse, densely covered with hairs, persistent in fruit; receptacle c. 1.3 mm diam, flat; petals colour in vivo unknown, 6, in two whorls, base of inner petals visible in bud, outer petals ovate, c. 3.4 by 2.1–2.2 mm, outside densely covered with appressed, yellowish brown hairs c. 0.2 mm long, inside with yellow hairs at the apex and margins, inner petals narrowly elliptic, c. 3.2 by 1.1 mm, indument as on outer petals; stamens 9, in one whorl, free, obconical, 0.9–1 mm long, filaments c. 0.4 mm long, thecae extrorse, connective truncate, slightly prolonged inward, hiding thecae, glabrous, staminodes absent; carpels 6, subcylindric, c. 2.1 by 0.4–0.5 mm, densely hairy, ovules 6, lateral, stigma elongate, c. 0.7 mm long, glabrous. Monocarps 1–6, colour in vivo unknown, moniliform, 1–3-seeded, each part ellipsoid, 15–61 by c. 4 mm, verrucose, densely covered with appressed, pale green-brown hairs, apex apiculate, apiculum 1–3 mm long, stipes 3–6 mm long. Seeds unknown.

Distribution — Gabon (Estuaire).

Habitat & Ecology — In old secondary forest, clay soil. Altitude: c. 10 m. Flowering: September; young fruits: January.

Preliminary IUCN conservation status — Endangered (EN): B2ab(iii). AOO: 8 km 2. Only known from 2 collections from the Estuaire province in Gabon, both outside protected areas and under heavy threat of expanding villages or oil exploitation.

Notes — 1. Monanthotaxis aestuaria belongs to the Monanthotaxis schweinfurthii complex ( Fig. 1 , clade B) based on the flower and stamen morphology, but is one of the more easily recognisable species from this complex based on vegetative characters as denoted in the diagnosis.

2. G. D. McPherson 15091 has huge glands near the leaf base (see Fig. 2b ), which are absent in the type specimen. Also in related species, such as M. biglandulosa , the size of the basal leaf glands can vary largely between specimens .

Figures

Fig. 2 Monanthotaxis aestuaria P.H.Hoekstra. a. Habit of flowering branch; b. leaf base abaxially; c. young fruiting inflorescence; d. flower bud; e. flower with petals removed; f. cross section flower bud; g. outer petal, outside view; h. outer petal, inside view; i. inner petal, outside view; j. inner petal, inside view; k. stamen, side view; l. stamen, front view; m. carpel (a, d–m: J.J. Floret & A.M. Louis 1456, P; b–c: G.D. McPherson 15091, P). — Drawing by H. de Vries.

Fig. 1 Bayesian 50 % majority rule consensus tree of the genus Monanthotaxis. Asterisks at nodes indicate node support, i.e., *** Strong node support, ** moderate node support, * weak node support, see Hoekstra et al. (2018). The letters A to K with adjacent black bars indicate the clades. The triangles, circles and squares represent morphological characters of the species which are of some use to distinguis the clades. Green triangles = staminodes absent, red triangles = staminodes present. Green circles = petals in one whorl, red circles = petals in two whorls, yellow circles = petals in bud basally in one whorl, at the top outer petals overlapping the inner ones. Green squares = inflorescences extra-axillary or if cauliflorous also extra-axillary inflorescences present, red squares = inflorescences axillary, supra-axillary or cauliflorous, red and green squares = both extra-axillary and axillary inflorescences present.