Monanthotaxis paniculata P.H.Hoekstra, 2014

Hoekstra, Paul H., Chatrou, Lars W. & Wieringa, Jan J., 2014, A new species of Monanthotaxis from Gabon with a unique inflorescence type for Annonaceae, Phytotaxa 186 (2), pp. 106-112 : 106-109

Monanthotaxis paniculata P.H.Hoekstra , spec. nov. ( Fig. 1 )

Type:— GABON. Ogooué-Ivindo: north of Koumameyong along SHM lumber roads, 0˚ 25’ N, 11˚ 55’ E, 31 January 1993 , McPherson 16123 (holotype: WAG!, isotypes: MO!, P!) .

Additional specimen examined: GABON, Estuaire: ca 20 km N of Libreville , 29 January 1987, Reitsma 2870 ( NY!, WAG!) .

Monanthotaxis paniculata resembles Monanthotaxis congoensis , but differs in the panicle-like inflorescence, instead of a raceme.

Liana to 20 m long; old branches dark, blackish, glabrescent with lenticels, young branches densely pubescent with appressed, ferrugineous-brown hairs 0.5 mm long. Petioles 4–8 mm long, 1.0– 1.5 mm wide, grooved adaxially, densely pubescent around. Leaf lamina 8.5–23.5 × 3.3–6.6 cm, length: width ratio 2.0–4.2, ovate to oblong-lanceolate, base cuneate to almost rounded with small linear black swollen base (see notes), apex acute to acuminate, acumen to 2.7 cm long, chartaceous, discolorous, young leaves adaxially with scattered appressed white hairs 1 mm long, glabrescent, abaxially glaucous or green, densely pubescent with appressed yellowish hairs 2 mm long, less densely in older leaves, secondary veins 9–16 on each side of primary vein, oblique, curving upwards, impressed adaxially, tertiary venation scalariform to somewhat reticulate, finely raised adaxially, abaxially only visible in older leaves. Inflorescence axillary or terminal, a 5.5–27.0 cm long panicle-like rhipidium with many flowers, peduncle 15–40 mm, rachis often multiple times bi- or trifurcate, densely pubescent with short ferrugineous hairs, 1–3 flowers in the axil of each bract; bracts lanceolate 1.0–8.0 × 0.5–1.5 mm, same indumentum as rachis; flower buds depressed-globose. Flowers bisexual; pedicels 5–29 × 0.4–0.8 mm, indumentum as rachis; sepals 3, 0.6–1.3 ×1.0– 1.5 mm, broadly ovate, outside densely pubescent with ferrugineous hairs, inside glabrous, apex acute; petals 6 in one whorl, yellowish or dull yellow, 2.7–3.0 × 1.5–2.0 mm, ovate, both inside and outside with short, appressed yellowish hairs; receptacle 2.0– 3.5 mm in diameter; stamens 12, in one whorl, inserted on a black hexagonal disc, 6 fertile stamens opposite to the petals, free at the base, obconic, 0.6 mm long, filaments 0.2 mm long, theca introrse/latrorse, connective appendage glabrous, truncate, kidney-shaped from above, 1.0 mm wide, not hiding anther cells, 6 sterile stamens alternating with inner stamens, 0.4 mm long, 0.5 mm wide, reduced theca-like structures 2, dorsal; carpels 14–24, 0.9 × 0.4 mm, ellipsoid, densely ferrugineous pubescent with 1 ovule, stigma bifurcate, 0.2 mm long, glabrous. Fruits unknown.

Etymology:— The specific epithet refers to the lax, many-flowered panicle-like inflorescence, which is unique within the family of Annonaceae .

Distribution:— Gabon, provinces Estuaire and Ogooué-Ivindo ( Fig. 2).

Ecology:— In forest fringe of a marshy savannah and along lumber roads, elev. 0– 500 m.

Phenology:— Flowers collected in the last week of January.

IUCN-conservation status:— A first assessment results in “Data Deficient”, since the extent of occurrence cannot be calculated with only two data points. However, in the last decades many collections have been made in Gabon, and for the revision we have seen almost all collections of Monanthotaxis in Gabon and surrounding countries. No other material has thus far been found. Therefore, the species seems to be genuinely rare (see also the discussion). Furthermore, both collections have been made in unprotected areas, one of which is in danger because of the expanding city of Libreville. The other collection has been made in a logging area, and therefore we suggest the status endangered: B2 ab(iii) for this species.

Notes:— A black swollen leaf margin at the base of the leaf is a common feature in many species of Monanthotaxis . In most literature, it is referred to as glands (e.g. Le Thomas 1969, Verdcourt 1971a). We are not sure if it is glandular tissue and until this is examined in more detail do not refer to it as such.

Figures

FIGURE 1. Monanthotaxis paniculata. A. Flowering branch. B. Flower bud. C. Flower bud with 3 petals removed. D. Petal from outside. E. Petal from inside. F. Stamen from inside. G. Stamen lateral view. H. Stamen from outside. I. Stamen from top. J. Staminode. K. Ovary. L. Leaf uppserside.A–K from McPherson 16123; L from Reitsma 2870. Illustrator: Esmée Winkel.