Baissea atrobrunnea O. Lachenaud, 2022

Jongkind, Carel C. H. & Lachenaud, Olivier, 2022, Novelties in African Apocynaceae, Candollea 77 (1), pp. 17-51 : 18-22

Baissea atrobrunnea O. Lachenaud , sp. nov. ( Fig. 1 , 2 ).

Holotypus: GABON. Ngounié: Parc National de Waka , 1°06'23"S 11°09'49"E, 5.X.2007, fl. & fr., Boussengui-Nongo & Bouango 245 ( LBV!; iso-: BR!, MO) .

Baissea atrobrunnea O. Lachenaud resembles B. subrufa Stapf in its densely felted twigs and coriaceous leaves, but differs by its lower leaf surface being densely and persistently felted with chocolate-brown indumentum (a character unique in the genus), its longer pedicels (3.5–7 mm vs. 1.5–3 mm) and its lanceolate corolla lobes, 4–5 mm long and more than twice as long as the tube (vs. ovate, 1.1–2.2 mm long and 0.7–1.4 times as long as the tube).

Lianas 4 m tall, covered on most of its organs (except corolla and upper side of mature leaves) by a short and dense felt of dark brown more or less dendritic hairs ( Fig. 2 ). Branchlets cylindrical, 1.5 mm wide, brown-felted. Leaves opposite; blade elliptic, 10–13.8 × 2.3–3.5 cm, acute at base, acute or shortly acuminate at apex, thickly coriaceous, densely brown-felted

[SEM photo: I. van der Beeten]

on both sides when very young, upper side soon glabrescent and green, lower side with a persistent dark brown felt; midrib strongly impressed above, prominent below; secondary veins 4–6 pairs, widely spaced and strongly curved; tertiary veins hardly distinct; domatia absent; petiole 0.3–0.6 cm long, brownfelted. Inflorescences axillary and paired at nodes, laxly paniculate, 2–6.5 cm long, 10–25-flowered, brown-felted, branched from base; rachis 2–6.5 cm long, main branches 0.8–2.3 cm long; bracts minutely triangular, <0.5 mm long, obtuse at apex. Flowers 5-merous; pedicel 3.5–7 mm long, brown-felted. Calices with 5 imbricate ovate lobes c. 0.7 × 0.6 mm, acute to obtuse at apex, brown-felted outside, glabrous inside, with c. 5 small colleters at base. Corollas yellowish-white; tube broadly infundibuliform, 1.5–2 × 1–2 mm, inside with 5 prominent ridges alternating with lobes, glabrous outside, inside with a ring of deflexed hairs above stamens; lobes lanceolate, 4–5 × 0.7–1 mm, obtuse at apex, glabrous; flower bud cylindrical, obtuse at apex. Stamens fully included, inserted 0.3 mm above base of corolla tube, subsessile; anthers 2 × 0.4 mm, acute at apex, glabrous except puberulous connective. Pistils included; ovaries truncated cone-like, 0.5 mm long, densely villose at apex, 2-carpellate; styles 1.2 mm long, glabrous, with narrowly cylindrical base 0.2 mm long, fusiform median part 0.3 mm long and subulate stigma 0.7 mm long. Fruits consisting of 2 narrow, almost cylindrical follicles 16.5–18.5 × 0.6–0.8 cm, densely brown-felted, forming a very obtuse angle with each other; pedicel woody and thickened. Seeds not seen.

Distribution, ecology and phenology. – Only known from the type collection in central Gabon (Waka National Park); habitat not recorded but presumably evergreen forests. It is not known whether the species is truly rare, since its area of origin is little-prospected; however, it is presumably very local, having not been found elsewhere in Gabon during recent inventories (despite being readily recognisable on the field). Flowers and fruits were collected in October, corresponding to the onset of the first rainy season.

Conservation status. – Baissea atrobrunnea is endemic to Gabon and known from a single collection; its Extent of Occurrence (EOO) therefore cannot be calculated. Based on a 2 × 2 km cell size, its Area of Occupancy (AOO) is estimated as 4 km ², within the limit for “Critically Endangered” status under Criterion B2. Its only known occurrence is located within the Waka National Park, very close to the boundary of the park. With no precise data about its ecology, and considering that its area of origin is poorly explored, it is unclear whether the species is threatened or not, and it seems reasonable to include it in the “Data Deficient” [DD] category.

Notes. – This species is readily recognisable, even in the vegetative state, by its strongly discolorous leaves with a dark chocolate-brown underside; hence the specific name. Its closest relative is probably Baissea subrufa (see diagnosis for the similarities and differences). The peculiar indumentum of B. atrobrunnea and B. subrufa , which consists of inflated ramose hairs ( Fig. 2 ) is also found in the morphologically related genus Motandra , and it is a question whether the two genera are really worth keeping separate. They differ chiefly in the shape of their anther-tails, which are straight and acute in Baissea , curved and obtuse in Motandra . Oncinotis , also closely related, has anthers similar to Motandra but differs from both genera by the presence of coronal appendages between the corolla lobes at the rim of the tube.

Baissea campanulata (K. Schum.) De Kruif in Agric. Univ. Wageningen Pap. 85(2): 40. 1985.

 Oncinotis campanulata K. Schum. in Bot. Jahrb. Syst. 23: 227. 1896.

Lectotypus (designated by VAN DILST, 1995: 102 ): CAMEROON. Central Region: Yaoundé, s.d., Zenker & Staudt 19 ( BM [ BM000925817 ]!; isolecto-: NY) .

= Baissea laurentii De Wild., Not. Pl. Ut. Congo 2: 253. 1908. Holotypus: D.R. CONGO. Province Orientale: Romée, I.1906, fl., M. Laurent 1362 (BR [ BR0000008824615 ]!; iso-: BR [ BR0000008825032 , BR0000008824622 ]!, YBI [ YBI169747992 ] image!).

= Baissea goossensii De Wild., Pl. Bequaert. 5: 417. 1932. Holotypus: D.R. CONGO. Province Orientale: Barumbu, V.1921, fl., Goossens 1670 (BR [ BR0000008824929 ]!; iso-: BR [ BR0000008824653 ]!, MO-2415948 image!).

Distribution and ecology. – Widespread from Côte d’Ivoire to central D.R. Congo; occurs in forest edges, usually along rivers, up to elevations of 1200 m.

Notes. – Baissea campanulata is here considered in its narrow sense, excluding B. congensis and B. subsessilis that were both placed under synonymy by VAN DILST (1995) . Differences between the three taxa are summarised in Table 1. Baissea campanulata is the most widespread of the three; its range locally overlaps with B. subsessilis in western Cameroon. No material has been seen from Nigeria; specimens from this country cited in the revision by VAN DILST (1995) correspond to B. subsessilis .

The inflorescences in Baissea campanulata can be terminal or axillary, often in the same branch; terminal inflorescences are always lax, while axillary ones are usually congested (but can be laxer, e.g. in Le Testu 8852, L. Dubois 136 or J. Léonard 1172). Some specimens (Breteler et al. 8944, M. Laurent 1362, J. Léonard 1172, Mandango 2879) also show a remarkable dimorphism in size and shape of corolla lobes: the flowers from terminal inflorescences (and sometimes from the upper leaf axils) have remarkably long and narrow, almost linear corolla lobes up to 18 mm long, while those borne lower down on the twigs have the corolla lobes much shorter and triangular, not exceeding 5 mm long.

Baissea concinna Stapf ex Hutch. & Dalziel, Fl. West Trop. Afr. 2: 45. 1931.

Lectotypus (first-step designated by VAN DILST, 1995: 110 ; second-step designated here): LIBERIA. Grand Bassa: Grand Bassa (= Buchanan), 9.IV.1896, fl., Dinklage 1630 (K [K000233867]!; isolecto-: A [A00078659] image!, K [K000233868, K000233869]!, Z [Z-000000982] image!) .

Distribution and ecology. – Restricted to Liberia and southwestern Côte d’Ivoire ( Fig. 3 ), where it occurs in wet evergreen forests near the coast.

Notes. – Both HUBER (1963) and VAN DILST (1995) treated this species as a synonym of Baissea lane-poolei , but the two taxa differ in inflorescence characters and also in ecology. Baissea concinna has a lax inflorescence and most flower pedicels are> 4 mm long; it grows in wet evergreen forests near the coast. Baissea lane-poolei has a congested inflorescence and flower pedicels up to 4 mm long; it grows in semideciduous forests or gallery forests, usually in hilly inland areas ( Fig. 3 ).

The first author did see both species in the field in their current known distribution. Nevertheless, both species were never observed in the other forest areas of Liberia despite several visits.

VAN DILST (1995: 110) cited the holotype at K. Three specimens are desposited in K and the specimen K000233867 annotated “ holotype ” by van Dilst in 1993 is here formally designated as the lectotype.

Additional specimens examined. – LIBERIA. Sino: Greenville, 18.III.1948, fl., Baldwin 11560 (K).

CÔTE D’IVOIRE. Tabou: 13 km NW of Tabou, 12.IV.1974, fl., Breteler 7386 ( WAG); close to Pata-Idié, 11.IV.2000, fl. bud, Jongkind & Assi-Yapo 5081 ( WAG) .

and B. subsessilis (K. Schum.) Stapf ex Hutch.& Dalziel. Characters diagnostic for one species are in bold. B. campanulata B. congensis B. subsessilis glabrous or with short

Indumentum of twigs densely and shortly tomentose densely villose sparse hairs glabrous between nerves Indumentum villose all over glabrous between nerves (or rarely with very short of lower leaf surface (more densely so on nerves) sparse hairs)

Leaf base cordate to rounded rounded to obtuse cordate to rounded terminal and/or axillary, if axillary

Inflorescences mostly axillary, always lax mostly axillary, always lax then usually congested yellow or white, sometimes

Colour of corolla white turning red white or pale yellow turning red

Corolla tube shape cylindrical or funnel-shaped urceolate funnel-shaped glabrous except below Pubescence glabrous except below densely pubescent (except base) the sinuses of the lobes (rarely of corolla tube (outside) the sinuses of the lobes with very sparse hairs between)

Length

2–18 (flowers often dimorphic) 2.5–5 7–13

of corolla lobes [mm]

Distribution Côte d’Ivoire to D.R. Congo Gabon, Angola ( Cabinda) Nigeria, SW Cameroon

& Dalziel (circles) and B. lane-poolei Stapf (triangles).

Figures

Fig. 1. – Baissea atrobrunnea O. Lachenaud. A. Flowering branch; B. Flower; C. Calyx (with one lobe removed) and ovary; D. Corolla (opened) showing pistil and stamens inside; E. Corolla (opened) with stamens still attached to the pistil; F. Fruit. [Boussengui-Nongo & Bouango 245] [Drawing: A. Fernandez]

Fig. 2. – Baissea atrobrunnea O. Lachenaud. Detail of the lower leaf surface trichomes. [Boussengui-Nongo & Bouango 245]

Fig. 3. – Distribution map of Baissea concinna Stapf ex Hutch.