Monanthotaxis zenkeri 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 : 213

79. Monanthotaxis zenkeri P.H.Hoekstra — Fig. 35 ; Map 45

Monanthotaxis zenkeri P.H.Hoekstra in Hoekstra et al. (2016) 98. — Type: G.A. Zenker 3495a (holo G00308331 ;iso BR0000013211349 , E00624356 , HBG, K, L.1759466, MO3726267 ), Cameroon, South Province, Bipinde, probably Oct. 1907.

Probably a liana; young branches brown, densely covered with erect, reddish brown hairs 0.3–0.4 mm long, becoming glabrous; old branches dark brown. Leaves: petiole 3–6 mm long, 0.7–2.3 mm diam, terete, indument as on branches; lamina obovate to elliptic-obovate 4.7–20.1 by 2.3–9.5 cm, 2–2.3 times longer than wide, subcoriaceous to chartaceous, not punctate, young leaves above sparsely covered with erect, yellow-brown, short hairs, becoming glabrous, below densely covered with erect, yellow-brown hairs 0.4–0.5 mm long, base rounded, with thickened margin, apex obtuse to acute, secondary veins (8–)10–12 per side, first straight, halfway curving upwards, tertiary venation percurrent. Inflorescences axillary, 1–3-flowered rhipidia; sympodial rachis 0–2 mm long, densely covered with ascending to erect, reddish brown, short hairs; flowering pedicels 4–6 mm long, 0.4–0.5 mm diam, densely covered with ascending to erect, short hairs; lower bract strongly reduced or absent; upper bract in the lower half of the pedicel, ovate, 0.6–0.8 by 0.5–0.8 mm, densely covered with hairs; flower buds globose. Flowers bisexual; sepals slightly connate at the base, depressed ovate to shallowly triangular, c. 1 by 1.5 mm, apex obtuse, densely covered with appressed, yellow hairs; receptacle c. 1.5 mm diam, flat; petals colour in vivo unknown, 6, in two whorls, outer petals broadly ovate, 2–3.1 by 2.1–2.5 mm, outside and margins of inside covered with appressed, yellowish, short hairs, base and centre of inside glabrous, inner petals rhombic, 1.8–2.4 by 1.3–1.6 mm, outside and apex of inside densely covered with yellow hairs; stamens 35, in three or four whorls, free, linear-obconical, 0.7–0.8 mm long, filaments c. 0.4 mm long, thecae extrorse, convergent apically, hiding the connective, sparsely hairy, staminodes absent; carpels c. 16, subcylindric to narrowly ellipsoid, 1.1–1.4 by c. 0.3 mm, densely hairy, ovules 4 or 5, lateral, stigma curved, elongate to subglobose, c. 0.2 mm long, glabrous, except for some hairs at the base. Monocarps and seeds not seen.

Distribution — Cameroon (South Province).

Habitat & Ecology — In forest. Flowering: October.

Preliminary IUCN conservation status — Critically Endangered ( CR): B2 ab(iii). AOO: 4 km 2. Only known from the type collection, more than 100 years old, from an unprotected area. It can be extinct .

Note — Monanthotaxis zenkeri has unique stamens within the genus. It is the only species with the combination of hairy thecae on top and a relative short filament. Besides this, it can be distinguished from the other species of Monanthotaxis with thecae on top by the dense indument of erect, reddish brown, short hairs.

Figures

Fig. 35 Monanthotaxis zenkeri P.H.Hoekstra. a. Habit; b. leaf abaxially; c. flower bud; d. flower with petals removed; e. old flower; f. stamen, side view; g, h. stamen, outside view; i. stamen, inside view; j. carpel (all: Zenker 3495a, G). — Drawing by H. de Vries.