Landolphia anthonii Jongkind, 2022

Jongkind, Carel C. H. & Lachenaud, Olivier, 2022, Novelties in African Apocynaceae, Candollea 77 (1), pp. 17-51 : 26-28

Landolphia anthonii Jongkind , sp. nov. ( Fig. 7 ).

Holotypus: GABON. Woleu-Ntem: 0.5 km E of Tchimbélé, 27.IV.1990, fl., Wieringa 778 ( WAG [ WAG.1610518]!; iso-: BR [ BR0000014318498 ]!, E, K, LBV [ LBV0000844 ]!, MO) .

Landolphia anthonii Jongkind resembles L. incerta (K. Schum.) J.G.M. Pers. with its axillary inflorescences, very short corolla tube (1.7–2 mm), long and narrow corolla lobes, and glabrous stems and leaves; but it has a more compact inflorescence, the anthers are not long acuminate but rounded at apex, the leaves are gland-dotted and with more prominent lateral veins below and the midrib of the leaf is channelled above, not prominent (when dried). In these characters it resembles L. ferrea J.G.M. Pers. , L. glabra (Pierre ex Stapf) Pichon and L. persooniana O. Lachenaud & Jongkind , but these species have a much longer corolla tube (6–13 mm).

Lianas large with tendrils and white latex. Branches smooth except for scattered and inconspicuous lenticels; branchlets 1–2 mm thick, glabrous, smooth. Leaves opposite, glabrous; blade narrowly elliptic or ovate, 6.5–9.5 × 2–3 cm, coriaceous, cuneate or rounded at base, caudate at apex, glandular dots conspicuous on lower leaf surface (1–4 per cm²), blackish when dried; midrib channelled above, prominent below; 12–17 pairs of secondary veins, forming an almost straight angle with

10 cm

midrib, alternating with (slightly) fainter parallel veins and connected by a slightly looping submarginal vein; tertiary venation laxly reticulate, invisible above and not very conspicuous below; petiole 4–6 mm long. Inflorescences axillary, cymose and highly contracted, up to 1.5 cm long (flowers included), 5– 7-flowered, glabrous; peduncle up to 3 mm long; bracts triangular to ovate, <1 mm long, ciliate. Flowers 5-merous; pedicel 1–1.5 mm long, glabrous. Calyx lobes imbricate, triangular to ovate, c. 1 × 1 mm, acute to obtuse at apex, ciliate, green. Corollas white, yellow in bud; tube 1.7 –2 mm long, ± cylindrical, glabrous on both sides; lobes 9–12 × 1.5–2 mm, hairy at base inside. Stamens subsessile, about half as long as corolla tube and inserted around mid-height, anthers almost 1 mm long, glabrous. Pistils 1.3–2 mm long, glabrous, ovary c. 1 mm long, ovoid with several longitudinal ridges, style absent or very short, pistil head c. 0.3 mm long with annular base and short stigmoid apex. Fruits unknown.

Etymology. – This species is named after Anthonius

J.M. Leeuwenberg (1930–2010), who first identified its type as a probable new species in 1992. Leeuwenberg was the leading expert on African Apocynaceae in his time, and contributed many generic revisions that have greatly advanced our knowledge of the family.

Distribution, ecology and phenology. – Occurs in the hill ranges of southern Cameroon (Akom II area) and Gabon (Cristal Mountains, Chaillu Massif) ( Fig. 8A ), in wet evergreen forests, at elevations of 500–1000 m. Flowers have been collected in March, April and July.

Conservation status. – Landolphia anthonii occurs in midaltitude forests (500–1000 m) in Cameroon and Gabon, and is known from four collections representing four distinct localities. Considering the still important forest cover in the areas where it was collected, we consider that these sites are still extant. Based on a 2 × 2 km cell size, its Area of Occupancy (AOO) is estimated as 16 km ², which falls within the limits for the “Endangered” status under Criterion B2. Its Extent of Occurrence (EOO) is calculated as 15,687 km ², which falls within the limit for “Vulnerable” status under Criterion B1. The only occurrence in Cameroon is in a protected area, CampoMa’an National Park. The three occurrences in Gabon are not protected (although one is very close to the limits of Monts de Cristal National Park, where the species may well occur) and have all been exposed to past and present forest exploitation; whether this represents a threat to the species is unclear, since little is known of its ecological requirements, and many liana species (including other Landolphia ) may actually benefit from moderate levels of forest disturbance. Also, as a tall liana with small flowers, the species is likely to be undercollected. With the two most remote localities more than 500 km apart this is even more likely. According to the limited data available at this moment, and using the IUCN criteria, we cannot reach a realistic threat category, and therefore L. anthonii is included in the “Data Deficient” [DD] category.

Notes. – The corolla tube of this species is among the shortest recorded in the genus, resembling that of Landolphia incerta (see the diagnosis for differences). However, in vegetative characters L. anthonii is closer to L. ferrea , L. glabra and L. persooniana ; all four species share small (usually <10 cm long), glabrous leaves with the midrib channelled above and the lateral veins inserted almost at a right angle, and also highly contracted inflorescences and very slender corolla lobes (their differences are summarised in Table 2). The distinction between L. anthonii and L. glabra is difficult in absence of flowers, although twigs of the latter are usually more strongly lenticellate. It is not known if there are additional differences in the fruits, since those of L. anthonii are not known; the label of Tchouto et al. 2853 mentions green fruits, but none are present on the WAG sheets.

and L. persooniana O. Lachenaud & Jongkind. Characters diagnostic for one species are in bold. L. anthonii L. ferrea L. glabra L. persooniana glabrous (rarely hairy sparsely to densely

Twigs glabrous glabrous on newest shoots) hirsute orange-brown to grey, dark brown, lenticels grey to dark brown,

dark brown, lenticels very

Older branches lenticels dense, bark dense and conspicuous, lenticels inconspicuous, sparse, otherwise smooth

strongly fissured otherwise smooth otherwise smooth

Glandular dots

present absent

on lower leaf surface

Corolla tube length

1.7–2 9.2–13

[mm]

Corolla tube

glabrous glabrous indumentum (outside)

Corolla tube hairy at the level glabrous

indumentum (inside) of the anthers present or absent present

6–10.8 5.5–8

dense, short ascending glabrous

hairs hairy at the level hairy at the level of the anthers of the anthers

Corolla lobe length 9–12, much longer 4.7–13, usually shorter

4.9–11, shorter than tube 9.5–18, longer than tube [mm] than tube than tube (rarely longer)

Ovary glabrous densely pilose densely pilose pilose at apex only

5.5–9.7, hairy (apex

4.6–7.2, hairy,

sometimes glabrous),

Style [mm] absent or very short very gradually 2.5–2.7, glabrous

abruptly narrowing

narrowing from ovary

from ovary

Figures

Fig. 7. – Landolphia anthonii Jongkind. A. Flowering branch; B. Leaf from below; C. Flower; D. Calyx lobe, inside; E. Bract, inside; F. Flower, opened. [Wieringa 778] [Drawing: H. de Vries]

Fig. 8. – Distribution maps. A. Landolphia anthonii Jongkind (triangles), L. persooniana O. Lachenaud & Jongkind (circles) and L. verrucosa Jongkind & O. Lachenaud (stars). B. Landolphia glandulosa (Pellegr.) Pichon (stars), L. obovata O. Lachenaud & Jongkind (circles) and Oncinotis gabonica O. Lachenaud (triangle).