Isolona pleurocarpa
Tree up to 15-30 m high; d.b.h. to 40(-60) cm, fluted; bark thick, black with grey markings;; young branches drying black, glabrous; old branches dark grey, rugulose longitudinally, glabrous. Petioles 4-8(-12) mm long, ca. 1 mm in diameter, glabrous, leaf lamina inserted on side, broadly grooved adaxially. Leaf lamina 8.5-15.5 cm long, 3-6 cm wide, length:width ratio 2.5-3.5, narrowly elliptic to elliptic or narrowly obovate to obovate, subcoriaceous to papyraceous, glabrous, light green abaxially, dull dark green adaxially, base decurrent to narrowly cuneate, apex acuminate, acumen 1-1.5 cm long; midrib proximally depressed above, glabrous on both sides; secondary veins 9-12 pairs, uniformally curving upwards, glabrous on both sides. Rhipidium 1, on leafy branches. Flowering pedicels 10-20(-23) mm long, ca. 1 mm in diameter, glabrous. Lower bracts 2-6, ca. 1 mm long, ca. 1 mm wide, glabrous; margins with short appressed hairs. Upper bract inserted in the basal half of the pedicel, ca. 1 mm long, ca. 1 mm wide, glabrous; margins with short appressed hairs. Sepals 2-3 mm long, 2-3 mm wide, length:width ratio 0.6-1, depressed ovate to broadly ovate, base truncate, apex acuminate, glabrous, green, appressed against tube, falling in fruit; margins with short appressed hairs. Corolla bright green-white when immature, yellow with red tube at anthesis; tube (6-)9-15 mm long, lobe:tube ratio 1.6-3, verruculose when dried, glabrous; lobes 10-23 mm long, 5-10 mm wide, length:width ratio 1.6-3.5, narrowly ovate to ovate, narrowed at base, apex acute, glabrous, papyraceous, the margins undulate-wavy when dried. Receptacle ca. 4 mm in diameter. Stamens 1.7-1.9 mm long; connective shield ca. 0.2 mm long, glabrous, those of innermost row stretched and pressing against ovary wall. Ovary ca. 2.2 mm long, ca. 2 mm wide; stigma ca. 2.5 mm in diameter, sparsely covered with short erect hairs. Fruiting pedicels ca. 3 cm long, 3-4 mm in diameter, woody, rugulose in longitudinal lines, glabrous. Fruits ca. 5 cm long, ca. 4 cm in diameter, length:width ratio ca. 1.25, globose, apicule absent, conspicuously longitudinally 6-8 ribbed, rugulose all over, glabrous, green when immature. Seeds not seen.
Isolona pleurocarpa can be distinguished from other Isolona species by the following combination of characters: young leaves glabrous, leaf lamina inserted on the side, leaf lamina with a decurrent to narrowly cuneate base, the midrib is proximally depressed above, the corolla lobes are narrowly ovate to ovate with a narrowed base and an acute apex, and the margins of the corolla lobes that are undulate-wavy when dried. Isolona pleurocarpa resembles I. hexaloba in the shape of its corolla with which is was reduced in synonymy in the past. For a separation from I. hexaloba see that species (no. 10).
Fruits of I. pleurocarpa described here were based on a scan kindly provided by the Berlin Herbarium (B) and may not be completely accurate, but one can clearly see that the fruit of I. pleurocarpa is rounded and ribbed, whereas the fruit of I. hexaloba is conical and lumpy.
Diels (1907) based his description of I. pleurocarpa based on fruiting material only and was unsure if it belonged in Isolona as no flowers were available. With more material at hand, especially flowering material, its inclusion in Isolona is confirmed.
Although I. pleurocarpa and I. leucantha were published by Diels (1907) in the same article, I see no clear differences between them and reduce I. leucantha to a synonym of I. pleurocarpa. However, flowering material of I. leucantha (only represented by the type) is very scarce or in poor condition.
EN B2ab(iii). Isolona pleurocarpa is moderately represented in herbaria. Most of the collections come from a single locality (Bipindi) with a clear decrease in collections in recent years. It has only been collected in one forest reserve (Southern Bakundu in Cameroon) and one national park (Korup in Cameroon). The “endangered” category is thus deemed appropriate.
Western Cameroon and south-eastern Nigeria; in lowland rain forests; at 0-100 m altitude.