Monanthotaxis zenkeri P.H.Hoekstra, 2016

Hoekstra, Paul H., Wieringa, Jan J. & Chatrou, Lars W., 2016, A nonet of novel species of Monanthotaxis (Annonaceae) from around Africa, PhytoKeys 69, pp. 71-103 : 95-97

Monanthotaxis zenkeri P.H.Hoekstra sp. nov. Figs 5 , 14 , Table 5

Type.

CAMEROON. South Province , Bipinde, probably October 1907, G.A. Zenker 3495a (holotype: G [G00308331!]; isotypes: BR [BR0000013211349!], E [E00624356!], HBG!, K!, L [L.1759466!], MO [3726267!]) .

Diagnosis.

The only other two species of Monanthotaxis with the anther cells convergent apically hiding the connective are Monanthotaxis bicornis (Boutique) Verdc. and Monanthotaxis filamentosa (Diels) Verdc., it differs from both in having small flowers and further can be distinguished from the first by the almost glabrous leaves with cuneate base and having only 15 stamens, while Monanthotaxis filamentosa has long erect hairs on the stems and pedicels and has ovate to ovate-lanceolate flower buds with much longer petals.

Description.

Probably a liana. Young branches brown, densely covered with reddish brown, erect hairs 0.3-0.4 mm, old branches dark brown, cylindrical, glabrescent with few lenticels. Leaves: petioles 3-6 × 0.7-2.3 mm, indumentum as branches; lamina 4.7-20.1 × 2.3-9.5 cm, length:width ratio 2.0-2.3, obovate to elliptic-obovate, base rounded, with thickened margin at base, apex obtuse to acute, subcoriaceous to chartaceous, adaxially glabrescent, young with a few short erect yellow-brown hairs, midrib impressed with short erect yellow-brown hairs, lower surface with dense erect short yellow-brown hairs, venation eucamptodromous, secondary veins (8-)10-12, first straight halfway curving upwards, tertiary venation scalariform. Inflorescences axillary, a 1-3-flowered rhipidium; sympodial rachis 0-2 mm with dense short ascending to erect reddish brown hairs; flowering pedicels 4-6 × 0.4-0.5 mm, with dense short ascending to spreading hairs; lower bract strongly reduced or wanting; upper bract in the lower half of the pedicel, ovate, 0.6-0.8 × 0.5-0.8 mm with dense hairs; flower buds rounded; sepals 3, slightly connate at base, 1.1 × 1.5 mm, broadly ovate to broadly triangular, apex obtuse, with dense yellow appressed hairs; receptacle 1.5 mm in diameter, flat; petals 6 in two whorls; outer petals, 2.0-3.1 × 2.1-2.5 mm, ovate, short appressed yellowish hairs on the outside and inside along the margins, glabrous at base and center of the inside; inner petals 1.8-2.4 × 1.3-1.6 mm, rhombic, with dense short yellow hairs on the outside and apex of the inside; stamens 35 in 3 to 4 whorls, free, linear-obconic, 0.7-0.8 mm long, filaments 0.4 mm long, anther cells extrorse converging apically and hiding the connective, with hairs at edges of the anther cells, staminodes 0; carpels ca 16, 1.1-1.4 × 0.3 mm, subcylindric to ellipsoid, with dense hairs, ovules 4-5, lateral, stigma curved, elongate to subglobose, 0.2 mm long, glabrous, but long hairs at base of stigma. Fruits: unknown.

Distribution.

Cameroon, South province. Figure 5 .

Ecology.

Forest.

Phenology.

Flowering in October.

Conservation status.

Proposed IUCN Red List Category: Critically Endangered (CR): B2ab(iii), only known from the type collection, which was collected more than a hundred years ago in an unprotected area. Actually, the species may well be extinct already.

Etymology.

Named after G.A. Zenker, who collected many specimens of Monanthotaxis in Cameroon from the end of the 19th and the beginning of the 20th century. The types of seven species of Monanthotaxis were collected by him.

Discussion.

Sprague and Hutchinson (1916) noted that they had seen the specimen Zenker 3495a, but felt reluctant to describe it because of the immature flowers on the specimens in the Kew herbarium. However, the flowers are fully developed on the specimens of G and HBG where the flowers are open, some of which have lost the petals already.

Monanthotaxis zenkeri is one of three species of Monanthotaxis with anther cells converging at the apex of the stamen. It can be distinguished easily from the other two species by the small flowers and dense short erect hairs on the young branches and leaves (Table 5 ). Vegetatively, this species is quite similar to Monanthotaxis diclina (Sprague) Verdc. which also is densely covered with short reddish brown hairs. However, the flowers are very different, Monanthotaxis diclina has unisexual flowers, the female inflorescences are cauliflorous and the male inflorescences axillary. Furthermore, the stamens are very different as Monanthotaxis diclina has 6 stamen in one whorl with the anther cells latrorse and an external whorl of 12 staminodes.

Figures

Figure 5. Distribution map of Monanthotaxis couvreurii (red diamonds), Monanthotaxis latistamina (blue squares), Monanthotaxis tripetala (green triangles) and Monanthotaxis zenkeri (black asterisk).

Figure 14. Monanthotaxis zenkeri P. H. Hoekstra. A-J drawn from the type (Zenker 3495 a). A Habitus B Leaf underside C Flower bud D Flower with petals removed E Old flower F Stamen lateral G-H Stamen outside I Stamen inside J Carpel. Illustration by H. de Vries.