A new species of the Tricalysia atherura group
(Rubiaceae) from southwestern Cameroon
Bonaventure SONKÉ
Higher Teachers’ Training College, The University of Yaoundé I,
P.O. Box 047, Yaoundé, Cameroun.
bsonke@uycdc.uninet.cm
Laboratoire de Botanique systématique et de Phytosociologie,
Université Libre de Bruxelles,
50 Av. F. Roosevelt, C.P. 169, 1050 Bruxelles, Belgique.
David KENFACK
Limbe Botanic Garden, P.O. Box 437, Limbe, Cameroun.
rhiannonct@aol.com
Elmar ROBBRECHT
National Botanic Garden,
Domein van Bouchout, B-1860 Meise, Belgique.
robbrecht@br.fgov.be
KEY WORDS
Tricalysia atherura group,
Rubiaceae,
Korup National Park,
Cameroon.
ABSTRACT
A new species of Tricalysia (Rubiaceae) from Cameroon, Tricalysia achoundongiana Robbr., Sonké & Kenfack, is described and illustrated. The new
species belongs to the Tricalysia atherura group in section Tricalysia and
appears to be closely related to T. pangolina and T. vadensis.
MOTS CLÉS
Groupe de Tricalysia atherura,
Rubiaceae,
Parc National de Korup,
Cameroun.
RÉSUMÉ
Une nouvelle espèce du groupe Tricalysia atherura (Rubiaceae) du sud-ouest du
Cameroun.
Une nouvelle espèce de Tricalysia (Rubiaceae) du Cameroun, Tricalysia
achoundongiana Robbr., Sonké & Kenfack est décrite et illustrée ici. La nouvelle espèce appartient au groupe de Tricalysia atherura (section Tricalysia) et
semble très proche de T. pangolina et de T. vadensis.
ADANSONIA, sér. 3 • 2002 • 24 (2) : 173-177
© Publications Scientifiques du Muséum national d’Histoire naturelle, Paris.
173
Sonké B., Kenfack D. & Robbrecht E.
INTRODUCTION
The Korup National Park is a protected lowland rain forest area in the southwest of
Cameroon. The park extends 04°54’–05°28’N
and 08°42’–09°16’E and occupies a total of
125,900 hectares (GARTLAN 1989). The 50 ha
Korup Forest Dynamics Plot was established in
the park from 1997 to 1999, as a part of a world
network of long-term biological and socio-economic research within tropical forest coordinated
by the Center for Tropical Forest Science
(CONDIT 1998). Field methods included tagging,
mapping, identifying and measuring all stems of
free-standing trees and shrubs with diameter at
breast height (1.3 m) greater or equal to 1 cm.
The aim of identifying to species every single of
above 328,000 plant individuals led to some
interesting botanical findings, despite previous
works in this part of the park (N EWBERY &
G ARTL AN 1996; T HOMAS & G EREAU 1993;
GARTLAN et al. 1986). During the field work, one
of us (DK) drew attention to a remarkable
Tricalysia from the area. Subsequent collection of
flowering and fruiting material from the park and
its surroundings allowed a complete morphological examination, and comparison with herbarium
specimens at SCA, YA, BR, K and WAG revealed
that a new species was at hand, which is described
and named in this paper. We dedicate the new
species to Dr. ACHOUNDONG , director of the
Cameroon National Herbarium, who has always
advised and encouraged us (BS and DK).
When in fruit, Tricalysia achoundongiana is
immediately identified as a member of the
Tricalysia atherura group. This group of section
Tricalysia can be recognized by the character
combination fruits exceeding 15 mm in diameter
and having ± sclerified walls / bracteoles opposite
and fused to calyculi. Most species of the genus
have the same bracteole type but smaller fruits
with fleshy walls. The Tricalysia atherura group
and its features are discussed at length in another
current contribution (SONKÉ et al. 2002). The
densely hairy twigs of T. achoundongiana compare with only two other members of the
Tricalysia atherura group, T. pangolina and T.
vadensis. The former differs from the new species
by its long-pedicellate flowers and fruits, the lat174
ter by its 4-merous flowers and ribbed fruits. In
addition, the calyx of T. achoundongiana withers
in fruit and hence differs from all other species of
the Tricalysia atherura group. According to
ROBBRECHT’s scheme (1987: 64, table 1) of the
relationships in Tricalysia subgen. Tricalysia,
Tricalysia achoundongiana takes a position intermediate between T. pangolina and T. vadensis
(Fig. 1); it follows the trend of reduction (in
flower size and merousness, and number of
ovules) shown by T. vadensis, though in a less
extreme way.
Tricalysia achoundongiana Robbr., Sonké &
Kenfack, sp. nov.
Haec species subgeneris Tricalysiae propter fructus cum
parietibus scleroticis et bracteolas in calyculis cupularibus
connatas nullo dubio Tricalysia atherurae et T. vadensi
proxima; a priori floribus sessilis, a posteriori foliorum
laminis cuneatis et floribus 5-6-meris differt.
TYPUS. — Sonké 2315, Cameroon, Korup National
Park, fl. 18 Nov. 1999 (holo-, BR!; iso-, BRLU!, K!,
P!, SCA!, YA!).
Shrub up to 10 m tall; young twigs puberulous. Leaves with interpetiolar stipules triangular,
fused at base, protruded into an awn up to
10 mm long, puberulous outside; petioles up to
12 mm long, puberulous; leaf-blades elliptic or
lanceolate, 14-18.5 × 5-9 cm, glabrous except for
the midrib puberulous above and beneath,
papyraceous, base cuneate, apex acuminate, acumen 9-11 mm long; lateral nerves 5-6 on each
side of the midrib; intersecondaries few, difficulty
visible, parallel and ± perpendicular to lateral
nerves.
Inflorescences 3-flowered, sessile, congested;
bracts and bracteoles fused into cups (‘‘calyculi’’),
sitting in one another, the upper ones embracing
the ovaries; 1-2(-4)-toothed or truncate cups per
flower, and a basal 4-toothed cup embracing the
flower triplet; calyculi puberulous outside and
covered with colleters inside. Flowers 5-6-merous, sessile. Calyx puberulous outside and covered with colleters inside, tube 2.5 mm long and
1.5 mm wide, with (4-)5-6 short triangular teeth.
Corolla white, sparsely hairy in- and outside;
tube c. 4 mm long; lobes c. 3.5 mm long, with
ADANSONIA, sér. 3 • 2002 • 24 (2)
Tricalysia atherura group (Rubiaceae) from Cameroon
Fig. 1. — Modification of ROBBRECHT’s (1987: table 1) scheme of relationships in the group of Tricalysia atherura, including the
newly described T. lejolyana (SONKÉ et al. 2002), le and T. achoundongiana, ac. Two letter abbreviations of other species and numbering of characters corresponding to ROBBRECHT (1987): bf, T. biafrana - ld, T. lasiodelphys - at, T. atherura - pg, T. pangolina va, T. vadensis / 11a, flowers pleiomerous - 11b, 5-6-merous - 11c, 4-merous; 12a, flowers large - 12b, small; 13a, ovules many 13b, ovules 4 - 13c, 2 collateral; 14a, style and anthers hairy - 14b, glabrous; 18a, flowers on long pedicels - 18b, flowers sessile.
The arrows represent postulated changes of states of characters.
triangular tip. Stamens attached to throat;
anthers subsessile with their bases included, c.
3.3 mm long, each with a shortly triangular,
hairy, apical, sterile appendage. Ovary pubescent,
more densely than the calyx, with two 4-ovulate
placentas; style pubescent, c. 5 mm long except
its lobes 1 mm long. Fruits ± spherical, 1.8 cm in
diameter, sparsely pubescent, colour at complete
maturity unknown; calyx withered, leaving a conspicuous scar on top; seeds four, ± having the
shape of a quarter of a sphere, up to 8 mm long,
with long comma-shaped hilum; coat glossy,
chestnut brown. — Fig. 2.
PARATYPES. — Sainge & Mambo 277, Cameroon,
Korup National Park, 05°03’N, 08°53’E, fr., 21 Jan.
2000 (BR!, MO!, SCA!); Thomas & Mambo 4239,
Cameroon, Mundemba town, 05°58’N, 08°55’E, fl.,
June-July 1984 (BR!, MO!, WAG!).
H ABITAT. — The area in which Tricalysia
achoundongiana occurs supports a closed-canopy
evergreen forest with patches of secondary
growth, classified by L E TO U Z EY (1985) as
Atlantic-Biafran evergreen forests, rich in
Caesalpiniaceae. This forest has a well-defined
structure with a high degree of local endemism
ADANSONIA, sér. 3 • 2002 • 24 (2)
(e.g. T HOMAS & G EREAU 1993; G EREAU &
KENFACK 2000). The area lies at 50-100 m above
sea level and is flat to gently undulating with
numerous small creeks in shallow valleys. Using
the mean elevation, slope angle and convexity,
the Korup Forest Dynamics Plot was divided into
seven habitat categories, namely riverside, low
gully, high gully, low flat areas, bench, ridge top,
steep slopes. The new species obviously avoids
steep slopes and swampy areas, and seems to be
associated to low flat areas, river banks and
bench.
D I S T R I BU T I O N . — The new species here
described is endemic of the Lower Guinea
Domain of the Guineo-Congolian Region, which
is the centre of diversity of the genus Tricalysia
and of the Tricalysia atherura group (ROBBRECHT
1987, fig. 11).
C ONSERVATION STATUS . — The species is
widely distributed in the southern part of the
Korup National Park, as shown by a field
inventory in the 50 hectares Plot, but is not yet
sufficiently documented by collections. Despite
of past intensive botanical surveys of Cameroon
coastal forest, the new species is known so far
only from Korup and surrounding areas. This
175
Sonké B., Kenfack D. & Robbrecht E.
B
2 mm
2 mm
J
2 mm
H
1 mm
A
0,5 mm
C
E
1 cm
1 mm
G
F
D
Fig. 2. — Tricalysia achoundongiana Robbr., Sonké & Kenfack: A, habit of a flowering twig; B, pair of interpetiolar stipules at twig
apex; C, inflorescence (two corollas fallen off); D, ovary crowned by calyx and the two calyculi of the central flower in C laid open
(hairiness not depicted, except for the colleters inside the upper calyculus); E, style; F, two views of a placenta; G, fruit; H, its cross
section; J, seed.
176
ADANSONIA, sér. 3 • 2002 • 24 (2)
Tricalysia atherura group (Rubiaceae) from Cameroon
area is less than 20,000 km2. Thus T. achoundongiana, following the Red Data criteria of
IUCN (2001), should be classified as “VU B”.
Acknowledgements
The 50 ha Plot was established with the support of
the International Cooperative Biodiversity Group
(ICBG) through the Center for Tropical Forest
Science (CTFS) and the Bioresource Development
and Conservation Program - Cameroon (BDCP - C).
We wish to thank the International Foundation for
Science for continuing to support the research on
Rubiaceae in Cameroon of the senior author, BS (IFS
D/2165-2). B. SONKÉ’s visit in Europe in 2001 was
supported by the project DIVEAC; thanks are due to
Prof. J. LEJOLY (Laboratoire de Botanique systématique et de Phytosociologie, Université Libre de
Bruxelles), main promoter of this project. BS is also
indebted to Dr. M. CHEEK for the facilities offered at
K during his visit. We are indebted to M. SAINGE of
the Korup Forest Dynamics Plot for collecting fruiting
material of the novelty and to J. ROSSEEL and P.M.
SEME (ECOFAC-Cameroon) for their assistance.
REFERENCES
C ONDIT R. 1998. — Tropical forest census plots.
Springer-Verlag and R. G. Landes Company,
Berlin, Germany, and Georgetown, Texas.
GARTLAN S. 1989. — La conservation des Écosystèmes
forestiers du Cameroun. Gland, Suisse et Cambridge,
Royaume-Uni, UICN.
GARTLAN J.S., NEWBERY D. MCC., THOMAS D.W. &
WATERMAN P.G. 1986. — The influence of topography and soil phosphorus on the vegetation of Korup
Forest Reserve, Cameroon. Vegetatio 65: 131-148.
G EREAU E.R. & K ENFACK D. 2000. — Le genre
Uvariopsis (Annonaceae) en Afrique tropicale, avec
la description d’une espèce nouvelle du Cameroun.
Adansonia, sér. 3, 22: 39-43.
IUCN (2001). — IUCN Red List Categories: Version
3. 1. IUCN Species Survival Commission, IUCN,
Gland Switzerland and Cambridge, U.K. 23 pp.
LETOUZEY R. 1985. — Notice de la carte phytogéographique du Cameroun au 1:500000: 4) Domaine
de la forêt dense humide toujours verte. Institut de
la Carte Internationale de la Végétation, Toulouse.
N EWBERY D. M C C. & G ARTLAN J.S. 1996. — A
structural analysis of rain forest at Korup and
Douala-Edea, Cameroon. Proc. Roy. Soc. Edinburgh
104B: 177-224.
ROBBRECHT E. 1987. — The African genus Tricalysia
A. Rich. (Rubiaceae): 4. A revision of the species of
sectio Tricalysia. Bull. Nat. Plantentuin Belg. 57: 39208.
SONKÉ B., CHEEK M., NAMBOU D.M. & ROBBRECHT
E. 2002. — A new species of Tricalysia A. Rich.
(Rubiaceae) from western Cameroon. Kew Bull. 57:
681-686.
T HOMAS D.W. & G EREAU E.R. 1993. — Ancistrocladus korupensis (Ancistrocladaceae): A new
species of liana from Cameroon. Novon 3: 494-498.
Manuscript received 15 November 2001;
revised version accepted 20 August 2002.
ADANSONIA, sér. 3 • 2002 • 24 (2)
177