Englerophytum gigantifolium O. Lachenaud & L. Gaut., 2016

Gautier, Laurent, Lachenaud, Olivier, Burgt, Xander van der & Kenfack, David, 2016, Five new species of Englerophytum K. Krause (Sapotaceae) from central Africa, Candollea 71 (2), pp. 287-305 : 293-296

Englerophytum gigantifolium O. Lachenaud & L. Gaut. , spec. nova ( Fig. 3-5 ).

− Englerophytum letestui Aubrév. & Pellegr . in Not. Syst. Paris 16: 255. 1960; Fl. Gabon 1: 88. 1964 [nom. nud.]

Typus: GABON. Prov. Moyen-Ogooué: Mabounié, site base no. 2 , entre camp et débarcadère, 0°48’00”S 10°31’23”E, 73 m, 10.XI.2013, fl., Lachenaud 1253 (holo-: BRLU!; iso-: BR!, LBV!, MO!, P!, WAG!).

Englerophytum gigantifolium O. Lachenaud & L. Gaut. differs from other members of the genus by the combination of a 7- to 8-merous dark pinkish and bowl-shaped corolla with erect lobes, the stamens with filaments connate into a tube but anthers free, and the very large leaves (37.5-54 X 9-12.5 cm) with persistent stipules. The other species have the corolla either 5- or 10-merous, and the stamens with either both anthers and filaments connate, or both free.

A small understory tree, up to 6 m high, very ramose, with white latex; foliage clustered at the apex of the twigs, the latter 7-13 mm diam., shortly appressed-pubescent. Stipules paired, narrowly lanceolate with inrolled margin, 12-17 mm long, 1.5- 3.5 mm wide if flattened, not or weakly carinate at base, coriaceous, persistent, appressed-pubescent outside, glabrous inside. Leaves alternate, simple, entire, oblanceolate; petiole 20-30 mm long, 4-7 mm diam., longitudinally ribbed when dry, shortly appressed-pubescent; blade 37.5-54 cm long, 9-12.5 cm broad, broadest at 2 / 3 or 3 / 4 of its length, acute at base, rounded at apex or with a short blunt acumen <5 mm long, coriaceous and strongly discolorous; upper side green, glabrous; lower side coppery, with a dense immersed whitish indumentum intermingled with additional golden-brown medifixed trichomes; primary nerve in continuity of the petiole, canaliculate above, very prominent below and longitudinally ribbed when dry, appressed-pubescent; nervation brochidodromous and densely parallel, with numerous secondaries hardly distinct from the inter-secondaries and tertiaries, the nerves c. 1 mm apart, faintly raised above, more distinctly below, forming an angle of 60-75° with the primary nerve, then finally curving and anastomosing c. 1 mm from the margin. Inflorescences borne on the trunk, or on the branches up to the axils of the lower leaves, fasciculate, with 7-15 flowers pointing downwards; pedicels brown, 12-23 mm long and c. 1.3 mm in diameter at anthesis, appressed-pubescent. Calyx brown, consisting of 5(-6) imbricate and broadly ovate sepals, 3.5-4 mm long X 3-4 mm broad, obtuse at apex, appressed brown-pubescent outside (the inner ones often with a narrow hyaline glabrous area on the margin, fringed with short trichomes), glabrous inside. Corolla dark pinkish, glabrous, bowl-shaped; tube 2.5 mm long X 5 mm broad, ± hemispherical and gradually widening towards apex; lobes 7-8, triangular, entire, imbricate and erect, c. 4.5 X 3 mm, acute at apex. Stamens 7-8, opposite the corolla lobes; filaments connate into a short, white fleshy tube c. 1 mm long, in continuation of the corolla tube when seen from inside, and concealing the ovary; anthers beige, erect and free from each other at apex, sagittate, c. 4 mm long X 1.5 mm broad, apiculate with a short sterile appendage, extrorse and dehiscing longitudinally. Ovary subglobose, c. 1 mm, with 5-6 locules and 1 ovule per locule, densely hirsute with stiff trichomes directed upwards; style narrowly conical, 3 mm long, glabrous. Fruits unknown.

Etymology. – The species epithet refers to its exceptionally large leaves.

Distribution and Ecology. – Englerophytum gigantifolium is known with certainty only from the Mabounié region in West-Central Gabon, where it is not rare; but it is probably more widespread in western Gabon (see Notes). It grows in lowland forest on well-drained soils.

Conservation status. – Englerophytum gigantifolium is only known with certainty from a single location, where the forest is threatened by a mining project. A decline in the extent and quality of habitat, number of subpopulations and number of mature individuals is therefore expected. The new species is preliminarily assessed here as “Critically Endangered” [CR B2ab(iii,iv,v)], according to IUCN Categories and Criteria ( IUCN, 2012). It is however likely that more localities exist, and if this is confirmed, the new species should accordingly be downgraded to a lower Category.

Notes. – Englerophytum gigantifolium has quite distinctive flowers, which are unique in the genus in being 7- to 8-merous. The androecium is also unusual in having fused filaments but free anthers. The flowers are thus intermediate between those of the former genus Zeyherella (here included in Englerophytum ), with both anthers and filaments free, and those of Englerophytum s.s., with stamens united from the basis of the filaments to the tip of the connectives.

In vegetative characters E. gigantifolium differs very little from E. libenii : the stipules are not strongly keeled, and the leaves are of a richer coppery-rufous colour below, but since both species are little-collected, it is not clear how far these characters are reliable. No fruiting specimens have been collected yet, but they should be separable from E. libenii by the larger size of the calyx.

The invalid name E. letestui Aubrév. & Pellegr. is based on Le Testu 5801 ( Gabon, Ngounié, Sindara , 6.XII.1925, fr., P), a poor collection bearing only leaves and detached fruits, with unfortunately no calyces present at their base. This specimen could belong to either E. gigantifolium or E. libenii , though on geographical grounds the former is perhaps more likely. The fruits and seeds are closely similar to those of E. libenii .

The sterile collections Dauby et al. 2655 ( Gabon, Nyanga, E de la lagune Banio, à env. 20 km au NE de Ndindi et 20 km à l’E du débarcadère de Kayes, 3°38’36”S 11°09’47”E, 31.III.2012, BRLU) and 2830 ( Gabon, Ngounié, Zone de Mabounié , à env. 45 km au SE de Lambaréné, rive E de la Ngounié, 0°45’5”S 10°30’45”E, BRLU), closely match E. gigantifolium in vegetative characters, and very probably belong to this species (particularly the latter specimen, which comes from the same area as the type).

Figures

Fig. 3. – Distribution maps of the five new species of Englerophytum K. Krause. A. Englerophytum. paludosum L. Gaut., Burgt & O. Lachenaud; B. Englerophytum gigantifolium O. Lachenaud & L. Gaut. (squares) and E. sylverianum Kenfack & L. Gaut. (circles); C. Englerophytum libenii O. Lachenaud & L. Gaut. (squares) and E. ferrugineum L. Gaut. & O. Lachenaud (circles). Open symbols indicate specimens associated with doubt.

Fig. 4. – Englerophytum gigantifolium O. Lachenaud & L. Gaut. A. Leafy twig; B. Detail of the lower surface of the leaf, showing venation; C. Apex of twig with stipules and base of petioles; D. Inflorescence; E. Flower, side view; F. Flower, viewed from above; G. Flower, longitudinal section; H. Longitudinal section of corolla, with one stamen removed. [Lachenaud et al.1253, BR & BRLU] [Drawing: A. Fernandez]

Fig. 5. – Field photographs of Englerophytum gigantifolium O. Lachenaud & L. Gaut. A. Young inflorescence on trunk; B. Leaves; C. Inflorescence on twigs; D. Flowers. [Lachenaud et al. 1253] [Photos: O. Lachenaud]