Plant Ecology and Evolution 151 (3): 442–448, 2018
https://doi.org/10.5091/plecevo.2018.1523
SHORT COMMUNICATION
Ixora kalehensis, a new Rubiaceae species
from the Democratic Republic of the Congo
Petra De Block
Meise Botanic Garden, Nieuwelaan 38, BE-1860 Meise, Belgium
Email: petra.deblock@meisebotanicgarden.be
Background – The rain forest genus Ixora currently comprises 37 species in Continental Africa. Within
the framework of a treatment of the genus for the Flore d’Afrique centrale, a new species is described from
D.R. Congo, despite its being known from only two specimens.
Methods – Standard methods of herbarium taxonomy are followed.
Key results – Ixora kalehensis De Block, a new species from the Central Forest District in D.R. Congo,
is described and illustrated. Ixora kalehensis remains under-collected and relatively poorly known but can
nevertheless easily be distinguished from other Ixora species. The most distinctive character is the colour
of the dried leaves: blackish on the upper surface and vivid brown on the lower surface. Other important
characters are the small-sized, compact and sessile inflorescences and the large tree habit. The species is
only known from two specimens collected in the 1950s and its preliminary IUCN status is Endangered (EN
B2ab(iii)). The lack of more recent herbarium material highlights that the collecting effort in D.R. Congo
remains substandard. It is hoped that the formal description of Ixora kalehensis will draw attention of
international and local collectors and will result in more material and greater knowledge of the species. The
description of this species brings the number of Ixora species to thirteen for central Africa (D.R. Congo,
Rwanda and Burundi) and to twelve for D.R. Congo. An identification key to the species of D.R. Congo
is provided.
Key words – Central Forest District, D.R. Congo, Ixora, Ixora kalehensis, preliminary IUCN assessment.
INTRODUCTION
Ixora L. is the only genus in the tribe Ixoreae (supertribe Ixoridinae, subfamily Cinchonoideae, family Rubiaceae). Previously, this tribe also contained a number of small satellite
genera, notably Captaincookia N.Hallé from New Caledonia, Doricera Verdc. and Myonima Comm. ex Juss. from the
Mascarenes and Versteegia Valeton from New Guinea and
the Solomon Islands. After phylogenetic studies by Mouly et
al. (2009a) these small genera were placed into synonymy
with Ixora.
Ixora is a large rain forest genus of shrubs and small trees
and has a pantropical distribution. A majority of its c. 530
species (Davis et al. 2009) occur in Asia and Oceania, but
Ixora is also represented in South and Central America and
in Africa. More than 85 species of Ixora occur in Africa, c.
half of those in Madagascar (De Block 2007, 2008, 2014a,
2014b), 37 in continental Africa (De Block 1998) and six
species in the Mascarenes and the Seychelles (Mouly et al.
2009b). In continental Africa, Ixora is easily recognized by
the following characters: petioles articulate; inflorescences
terminal, with branching trichotomous, articulate and bracteolate; flowers narrowly tubular, 4-merous; aestivation contorted; stigma bilobed; ovary bilocular with a single ovule
per locule; fruits drupaceous, containing two seeds; seeds
hemispherical or hemi-ovoid with a large adaxial excavation
(De Block 1998). The representatives from the Indian Ocean
Islands usually have the same characters but a few species
differ by lacking the articulate branching in the inflorescence
(e.g. I. pudica Baker from Mauritius) or by being 3–7-locular
with the stigma 3–7-lobed, and the seeds 3–7 per fruit and
not hemispherical or hemi-ovoid in shape (e.g. I. quadrilocularis De Block from Madagascar and I. borboniae Mouly &
B.Bremer, formerly known as Myonima obovata Lam., from
Mauritius and Reunion) (Verdcourt 1983, De Block 2014a).
In the most recent revision of the genus in continental Africa, 37 Ixora species were recognized and two further taxa
were mentioned as possibly new: Ixora sp. “Kalehe” from
D.R. Congo and Ixora sp. “Waka” from Gabon (De Block
1998). Ixora sp. “Kalehe” was only known from one specimen collected by Troupin in 1957 west of Lake Kivu.
All rights reserved. © 2018 Meise Botanic Garden and Royal Botanical Society of Belgium
ISSN: 2032-3913 (print) – 2032-3921 (online)
De Block, Ixora kalehensis, a new Rubiaceae species from D.R. Congo
In the framework of a flora treatment of Ixora for D.R.
Congo, Rwanda and Burundi (Flore d’Afrique centrale, see
Sosef 2016), the continental African material of Ixora at
the BR herbarium was revisited, inter alia to check if new
material was available for several under-collected species,
including I. hartiana De Block (known from three specimens in D.R. Congo), I. phellopus K.Schum. (known from
three specimens in D.R. Congo), I. nana Robbr. & Lejoly
(known from two specimens in D.R. Congo), and Ixora sp.
“Kalehe”. While very few Ixora specimens were collected
between 1998 and 2018, and no recent material was found
for the under-collected species, a second historical collection
(Gutzwiller 2506, collected in 1958) was located for Ixora
sp. “Kalehe”.
In this paper Ixora kalehensis is described as new to science. The species is illustrated and compared with closely
related taxa. Furthermore, a key to the Ixora species of D.R.
Congo is provided.
MATERIAL AND METHODS
Collections of the BR herbarium were studied, with specific
attention to specimens collected between 1998 (date of the
most recent revision of the genus) and 2018. Herbarium
acronyms follow Thiers (continuously updated). Terminology follows Robbrecht (1988), but leaf shape is described
according to the terminology of simple symmetrical plane
shapes (Anonymous 1962). Standard methods of herbarium
taxonomy are used (De Vogel 1987). Flowering and fruiting
periods are based on dates given on the labels of herbarium
material. Localities are cited as given by the collectors on the
specimen labels. Coordinates of localities were determined
using a botanical gazetteer of central Africa (Bamps 1982).
The distribution map was adapted from De Block (1998).
Preliminary conservation status was assessed by applying the
IUCN Red List Category criteria (IUCN 2018).
RESULTS
Ixora kalehensis De Block, sp. nov.
Resembling Ixora nana by the shape and size of the leaves,
the sessile, compact inflorescences with relatively few flowers and the corolla tube length; differing from this species by
the colour of the dry leaves (blackish above and vivid brown
below in I. kalehensis vs. greenish on both surfaces in I.
nana), the texture of the leaf blades (subcoriaceous in I. kalehensis vs. papyraceous in I. nana), the length of the petiole
and shape of the leaf base (petioles 0.4–1.2 cm long and their
bases cuneate to attenuate and never crispate in I. kalehensis
vs. leaves subsessile and long attenuate at the base with the
basal margins often crispate in I. nana), the presence/absence
of pubescence on the young shoots (glabrous in I. kalehensis
vs. moderately to densely covered with short erect hairs in I.
nana), the length of the first order axes and pedicels (up to 5
mm and 1.5 mm long, respectively, in I. kalehensis vs. first
order axes not developed and flowers subsessile in I. nana)
and the length of the corolla lobes (at least 6 mm long in I.
kalehensis vs. 4.5–5 mm long in I. nana). – Type: D.R. Congo, Province Kivu, Territoire Kalehe, vers km 110 sur route
Kavumu-Walikale, Irangi, réserve IRSAC, catena II à 120 m,
01°53′S 28°27′E, alt. 850–900 m, 8 Nov. 1957, fl., Troupin
4662 (holo-: BR; see electronic appendix 1).
Ixora sp. “Kalehe” (De Block 1998: 162).
Tree, up to 15 m tall (see remarks); young twigs glabrous,
smooth, drying blackish brown; older branches glabrous,
smooth, drying brown and somewhat glossy. Leaves with
petioles 0.4–1.2 cm long, glabrous; blades elliptic, narrowly
elliptic, obovate or narrowly obovate, 9.5–12 × 3–4.5 cm,
subcoriaceous, glabrous on both surfaces, drying blackish
above and vivid brown below; tip acuminate, with acumen
0.6–2.2 cm long; base cuneate to attenuate; midrib prominently raised below, dark brown; secondary nerves 9–12
on each side of midrib, dark brown or the same colour as
the leaf blade and hardly raised below; higher order nerves
inconspicuous on both surfaces; domatia absent; margins
not revolute when dry. Stipules glabrous, drying blackish;
sheaths triangular, 3–4 mm long, keeled; awns 2–4 mm long.
Inflorescences sessile, compact, with 15–45 flowers, c. 1 ×
1.5 cm (without corollas); axes, pedicels, bracts and bracteoles glabrous, drying reddish brown or blackish; first order
axes up to 0.5 cm long; first order bracts with the stipular
parts fused to an ovate blade (drying reddish-brown, 0.5–0.8
cm high) with a central awn (c. 3 mm long) and the foliar
parts either absent or forming small leaves (up to 1 × 0.2
cm); higher order bracts with stipular parts absent, the foliar
parts narrowly triangular and vaulted, up to 2 mm long. Ultimate flower triads with flowers subsessile or shortly pedicellate; pedicels up to 1.5 mm long; bracteoles present on most
pedicels, opposite at the base of the ovary, triangular, narrowly triangular or filiform, c. 0.5 mm long, tips acute. Mature flowers unknown; calyx tube c. 0.3 mm long; glabrous
outside, glabrous but with a ring of small colleters at the base
of the lobes inside; calyx lobes 4(–5), triangular or ovate, c.
0.5 mm long, glabrous outside, basal half moderately covered with appressed hairs inside, tips acute, bases not overlapping; corolla tube at least 15 mm long, glabrous outside,
basal half moderately to densely covered with erect hairs inside (except for the very base); lobes at least 6 × 2 mm, glabrous on both surfaces; stamens with filaments c. 1 mm long;
anthers at least 4 mm long; ovary 0.8–1.2 mm long, glabrous
outside; style glabrous, stigma lobes 1.5–2 mm long above a
c. 1 mm long thickened zone. Fruits: unknown. Fig. 1.
Habitat – In humid forest, altitude 850–1000 m.
Distribution – Only known from the eastern part of the Central Forest District in D.R. Congo, close to the Great Lakes.
Territoire Kalehe is located c. 50 km north of Bukavu in the
province of South-Kivu (fig. 2).
Phenology – Flowers: November; young fruits: January.
Vernacular names – Katangondo (dial. Kitembo; Troupin
4662); Nsamba (dial. Kirega; Gutzwiller 2506).
Etymology – The species is named for the locality in which
it occurs, notably Kalehe Territory.
Preliminary conservation assessment – Endangered (EN).
The extent of occurrence (EOO) of Ixora kalehensis cannot
be calculated because the species is only known from two
specimens. Its area of occupancy (AOO) was estimated to
be 8 km2 using a grid cell width of 2 km, which falls under
443
Pl. Ecol. Evol. 151 (3), 2018
the threshold of Critically Endangered status. Kalehe is located close to Lake Kivu and close to two National Parks,
Kahuzi-Biega National Park and Virunga National Park, but
no specimens of Ixora kalehensis are known from these protected areas. This densely populated region in eastern D.R.
Congo is highly perturbed by political instability and the two
National Parks are under severe threat of habitat destruction by local people, refugees and armed militias, under the
form of land clearing, poaching, tree cutting and artisanal
mining (UNESCO 2017a, 2017b). These difficult circumstances could explain the lack of recent herbarium specimens
for I. kalehensis, but would also suggest that the species is
threatened. The two known subpopulations of this species
represent two different locations, which falls within the Endangered status, and, despite the lack of recent data, we can
assess that the species is threatened by the destruction of its
habitat. We therefore assign a preliminary conservation status of EN B2ab(iii).
Remarks – Only two specimens are known for this species.
The first, Troupin 4662, is flowering and is described as a
dominant tree up to 15 m tall. The second, Gutzwiller 2506,
bears young fruits (as well as young buds) and is described
as a suffrutex of 60 cm tall.
The length of the corolla tube in mature flowers is unknown.
The flowers of Troupin 4662 seem close to maturity but the
anthers have not yet released the pollen inside the bud. Ixora
shows secondary pollen presentation (Puff et al. 1996): the
flowers are proterandrous with the anthers opening and depositing the pollen on the outside of the stigmatic lobes (receptaculum pollinis) just before the flower opens.
In both specimens of this species the number of calyx
lobes varies between four and five. Flowers with five calyx
lobes are quite common.
Additional specimen examined – D.R. Congo: Central
Forest District, Territoire Kalehe, Turole, Bunyakiri, 02°04′S
28°34′E, alt. 1000 m, 2 Jan. 1958, fr., Gutzwiller 2506 (BR).
Figure 1 – Ixora kalehensis: A, flowering branch; B, stipule; C, triad (corollas removed); D, bracteole, ovary and calyx. From Troupin 4662
(BR). Drawn by A. Fernandez.
444
De Block, Ixora kalehensis, a new Rubiaceae species from D.R. Congo
DISCUSSION
Ixora kalehensis is only known from two specimens collected in 1957 and 1958. No recent material of the species
is available for study. This could be explained in part by the
fact that the species is a large tree up to 15 m tall (according
to the label on Troupin 4662), reducing the chances to observe flowering/fruiting and to collect it. However, the lack
of recent specimens also highlights the fact that D.R. Congo
remains severely under-collected (Hepper 1979, Campbell &
Hammond 1989, Taplin & Lovett 2003, Küper et al. 2006,
Stropp et al. 2016: figs. 3–5, Sosef et al. 2017: 8). The recent,
large-scale collecting expedition (“Boyekoli Ebale Congo
2010”) undertaken along the Congo River in 2010 by joint
Belgian scientific institutions considerably increased collections for some organisms (e.g. De Haan 2014, Cocquyt &
Taylor 2015), but was less fruitful for vascular plants. Collecting plant material in eastern D.R. Congo, where Ixora
kalehensis occurs, is difficult owing to political instability
and the presence of armed militia in the forests.
Despite the lack of recent observations/collections, the
preliminary conservation status of Ixora kalehensis is assessed as Endangered, since it is probable that the species
is under severe threat from anthropogenic actions. The two
localities in which the species was collected, (km 110 on
Kavumu-Walikale road and Bunyakiri) are close to the eastern part of Kahuzi-Biega National Park. This more mountainous region of the park is part of the Albertine Rift in the
Great Rift Valley and runs parallel to Lake Kivu; in contrast,
the much larger western region of the park is dominated by
lowlands and lower mountain ranges (Doumenge 1990). It is
possible that I. kalehensis occurs within the borders of Kahuzi-Biega National Park, at least in its mountainous eastern
part. Another protected area, Virunga National Park, is situated north of Lake Kivu and also forms part of the Albertine
Rift Valley. Although this park is located further away from
the two collecting localities of Ixora kalehensis, the species
may also occur there. Because of their outstanding natural
richness, both parks are listed as UNESCO natural world
heritage sites. However, the two parks are under severe threat
and are now designated as UNESCO natural world heritage
sites in danger (https://whc.unesco.org/en/danger/). They are
located in a densely populated region (for Kahuzi-Biega this
is true for the eastern highland sector), with most people depending on agriculture for their livelihood.
The forests in both parks are being cleared for wood production, charcoal production for neighbouring cities, as well
as for agriculture and grazing of livestock (Aveling 2010).
Anthropogenic pressure has increased strongly since the
1994 Rwandan Civil War when the parks were overrun by
refugees and armed militias, resulting in large-scale destruction of primary habitat (UNESCO 2017a, 2017b). Furthermore, Kahuzi-Biega National Park is subject to traditional
mining for gold, diamonds, coltan and tin whereas Virunga
National Park is potentially threatened because of the presence of large natural oil and gas reserves (Aveling 2010). Logistical problems include understaffing and insufficient funding to guarantee efficient protection of the remaining natural
vegetation. This creates dangerous working conditions for
the staff of both parks: e.g. to date, 175 Virunga park rangers
have been killed in the line of duty (Norton 2018).
Ixora kalehensis resembles I. nana (Robbrecht & Lejoly 1982, De Block 1998), another species from eastern
D.R. Congo, by the shape and size of the leaves, the sessile,
compact inflorescences with relatively few flowers and the
relatively short corollas. Both species occur in the Central
Forest District in humid rain forest. Ixora nana (electronic
appendix 2) is only known from Maiko National Park north
of the known localities of I. kalehensis. Ixora nana may occur at lower altitudes (500 m vs. 850–1000 m for I. kalehensis), but comprehensive data is lacking since both species are
only known from two specimens. The two species can easily be distinguished in dried condition by the colour of the
leaves: blackish above and vivid brown below in I. kalehensis vs. greenish on both surfaces in I. nana. Furthermore, I.
nana is a monocaulous dwarf (one-stemmed) or dwarf shrub
(few-stemmed) of 0.2–0.3 m tall, whereas I. kalehensis is a
dominant tree up to 15 m tall, at least according to the label
Figure 2 – Distribution map of Ixora kalehensis (adapted from De Block 1998).
445
Pl. Ecol. Evol. 151 (3), 2018
Key to the species of Ixora of D.R. Congo
1. Inflorescences distinctly pedunculate, 0.8–26 cm long........................................................................ 2
1’. Inflorescences (sub)sessile ................................................................................................................... 6
2.
Inflorescences compact, often consisting of three compact clusters; peduncle and axes densely covered
with short hairs; pedicels 0–3 mm long (rarely up to 5 mm long in case of reduction) ...................... 3
2’. Inflorescences lax; peduncle and axes usually glabrous; pedicels 0–18 mm long............................... 4
3.
Inflorescences erect; peduncles 1–10 cm long; corolla tubes (3.3–)4.9–7.2 cm long; ovary, calyx and
corolla tube glabrous or densely covered with short hairs outside; corolla lobes glabrous inside ........
..........................................................................................................................................I. brachypoda
3’. Inflorescences pendulous; peduncles (4–)10–26 cm long; corolla tubes (1.4–)1.8–2.5 cm long; ovary,
calyx and corolla tube glabrous outside; corolla lobes with a few hairs near the throat inside .............
................................................................................................................................ I. longipedunculata
4.
Inflorescences drooping or pendulous; peduncle 11.5–21.5 cm long; corolla lobes 12–15 mm long;
filaments 4–10 mm long; anthers 8–10 mm long.......................... I. aneimenodesma subsp. kizuensis
4’. Inflorescences erect; peduncle 0.8–5(–6.5) cm long; corolla lobes up to 10 mm long; filaments 1–2.5
mm long; anthers 3.5–6.5 mm long ..................................................................................................... 5
5.
Leaf blades 12–26.5 × 4.5–8 cm, usually densely pubescent below; inflorescences 8–12 × 13–17 cm
(without corollas) ................................................................................................................I. phellopus
5’. Leaf blades 6–12.5 × 2.5–4.5 cm, glabrous below; inflorescences 4.5–7.5 × 6–12.5 cm (without
corollas).................................................................................................................................I. hartiana
6. Inflorescences without corollas up to 1.5 × 1.5 cm.............................................................................. 7
6’. Inflorescences without corollas at least 2 × 2 cm, but usually much larger ......................................... 8
7.
Dwarf shrub, one- or rarely few-stemmed, 0.2–0.3 m tall; young twigs pubescent; leaves narrowly
obovate, subsessile, drying greenish, base long attenuate, basal margins often crispate; flowers
subsessile.................................................................................................................................... I. nana
7’. Large tree (see remarks); young twigs glabrous; leaves elliptic, narrowly elliptic, obovate or narrowly
obovate, shortly petiolate (petiole 0.4–1.2 cm long), drying blackish above and vivid brown below,
base cuneate to attenuate, basal margins not crispate; flowers with pedicels up to 1.5 mm long..........
............................................................................................................................................I. kalehensis
8.
Leaf blades narrowly elliptic, 0.5–1.7 cm wide; small shrub, ± 1 m tall, branching fastigiate .............
..............................................................................................................................................I. fastigiata
8’. Leaf blades any shape, at least 2.5 cm wide; shrub or tree, branching not fastigiate .......................... 9
9. Inflorescence axes and pedicels glabrous........................................................................................... 10
9’. Inflorescence axes and pedicels pubescent (sometimes only sparsely) at least in the upper part of the
inflorescence....................................................................................................................................... 12
10. Leaf blades drying pale greyish or fawnish green; ovaries and calyces drying fawnish; calyx lobes
truncate with central acumen; pedicel of the central flower in a triad usually distinctly shorter than the
pedicels of the lateral flowers; dyads often present ......................................................... I. mildbraedii
10’. Leaf blades usually drying (dark) brown; ovaries and calyces drying brown; calyx lobes widely
triangular to ovate with rounded to acute tips; pedicel of the central flower in a triad not distinctly
shorter than the pedicels of the lateral flowers; dyads absent .............................................................11
11. Leaves drying bronze brown above; pedicels (0–)2–10 mm long; bracteoles filiform .........................
........................................................................................................................................I. praetermissa
11’. Leaves drying dark brown above; pedicels 0–2 mm long; bracteoles broadly ovate at the base with
long filiform tips ....................................................................... I. laurentii (atypical glabrous variant)
446
De Block, Ixora kalehensis, a new Rubiaceae species from D.R. Congo
12. Leaves drying pale greyish of fawnish green; pedicels of the lateral flowers in a triad 6–10 mm long,
pedicel of the central flower usually distinctly shorter; dyads often present; anthers 6–8 mm long .....
.............................................................................................I. mildbraedii (atypical pubescent variant)
12’. Leaves drying (dark) brown; pedicels of the lateral flowers in a triad 0–4 mm long, that of the central
flower not markedly shorter; dyads absent; anthers 3–6 mm long .................................................... 13
13. Leaf blades drying dark to blackish brown above, paler brown underneath; stipular sheaths 1.5–2.5
mm long; bracteoles broadly ovate at the base with long filiform tips; calyces turbinate, lobes broadly
ovate with rounded to obtuse tips, their bases not overlapping; style glabrous; pedicels 0–2(–5) mm
long .......................................................................................................................................I. laurentii
13’. Leaf blades drying brownish; stipular sheaths 3–7 mm long; bracteoles narrowly triangular to
filiform; calyces tubular, lobes truncate with central acumen or irregularly truncate, their bases often
overlapping; style pubescent especially in its lower half; pedicels 0–4(–6) mm long .............I. seretii
information on Troupin 4662. As mentioned above, the habit
data on the label of Gutzwiller 2506 reads “suffrutex, 60 cm
tall”. Further differences between the two species are given
in the diagnosis above.
With the description of Ixora kalehensis, the number of
Ixora species in D.R. Congo increases to twelve. Ixora brachypoda DC. is widespread in tropical Africa and widely collected from D.R. Congo. Ixora longipedunculata De Wild.,
I. nana and I. seretii De Wild. are endemic to D.R. Congo,
their distribution centered in the Central Forest District. Ixora
laurentii De Wild. and I. mildbraedii K.Krause are mostly
known from D.R. Congo with a few specimens collected from
surrounding countries such as the Central African Republic,
Republic of the Congo or Uganda. The other Ixora species
occurring in D.R. Congo are I. aneimenodesma K.Schum.
subsp. kizuensis De Block, I. fastigiata (R.D.Good) Bremek.,
I. hartiana, I. phellopus and I. praetermissa De Block. All are
known from very few specimens from D.R. Congo. Except
for I. praetermissa, which is common in Gabon, these species have only rarely been collected (even outside the Flore
d’Afrique centrale area), which results in taxonomic uncertainty. In Rwanda and Burundi, a single Ixora species occurs:
I. burundiensis Bridson, an Afromontane species occurring in
the region of the Great Lakes. Besides these native species,
two Asian Ixora species, I. coccinea L. and I. chinensis Lam.,
are cultivated in central Africa.
SUPPLEMENTARY DATA
Supplementary data are available in pdf at Plant Ecology and
Evolution, Supplementary Data Site (https://www.ingentaconnect.com/content/botbel/plecevo/supp-data) and consist
of the following: (1) scanned holotype of Ixora kalehensis
(BR); and (2) scanned holotype of Ixora nana (BR).
ACKNOWLEDGMENTS
Antonio Fernandez (BR) is acknowledged for making the
line drawing of Ixora kalehensis. Nuno Veríssimo Pereira
(BR) is thanked for extracting Ixora information from BGBase. I thank two anonymous reviewers, as well as Natacha
Beau and Elmar Robbrecht, for their helpful remarks on a
previous version of this paper.
REFERENCES
Anonymous (1962) Systematics Association committee for descriptive biological terminology. II. Terminology of simple symmetrical plane shapes (chart 1). Taxon 11: 145–156. https://doi.
org/10.2307/1216718
Aveling C. (2010) World Heritage in the Congo Basin. Paris,
UNESCO World Heritage Centre.
Bamps P. (1982) Flore d’Afrique centrale (Zaire - Rwanda - Burundi). Répertoire des lieux de récolte. Meise, Jardin botanique
national de Belgique.
Campbell D.G., Hammond H.D. (1989) Floristic inventory of tropical countries. The status of plant systematics, collections, and
vegetation, plus recommendations for the future. New York,
New York Botanical Garden.
Cocquyt C., Taylor J.C. (2015) New and interesting Surirella taxa
(Surirellaceae, Bacillariophyta) from the Congo Basin (D.R.
Congo). European Journal of Taxonomy 133: 1–15. https://doi.
org/10.5852/ejt.2015.133
Davis A.P., Govaerts R., Bridson D.M., Ruhsam M., Moat J.,
Brummitt N.A. (2009) Global assessment of distribution, diversity, endemism, and taxonomic effort in the Rubiaceae. Annals of the Missouri Botanical Garden 96: 68–78. https://doi.
org/10.3417/2006205
De Block P. (1998) The African species of Ixora (RubiaceaePavetteae). Opera Botanica Belgica 9: 1–218.
De Block P. (2007) Three new Madagascan Ixora species (Rubiaceae) with flowers up to 25 cm long. Nordic Journal of Botany 25:
75–84. https://doi.org/10.1111/j.0107-055X.2007.00111_7.x
De Block P. (2008) Synopsis of the uniflorous Madagascan Ixora
(Rubiaceae) species belonging to section Microthamnus. Belgian Journal of Botany 141: 141–156.
De Block P. (2014a) Synopsis of the multilocular Ixora species (Rubiaceae) in Madagascar. Phytotaxa 162: 121–133. https://doi.
org/10.11646/phytotaxa.162.3.1
De Block P. (2014b) Eight new species of Ixora (Ixoreae - Rubiaceae) from Madagascar. Plant Ecology and Evolution 147:
237–255. https://doi.org/10.5091/plecevo.2014.927
447
Pl. Ecol. Evol. 151 (3), 2018
De Haan M., Cocquyt C., Tice A., Zahn G., Spiegel F.W. (2014)
First records of Protosteloid Amoebae (Eumycetozoa) from the
Democratic Republic of the Congo. Plant Ecology and Evolution 147: 85–92. https://doi.org/10.5091/plecevo.2014.883
De Vogel E.F. (1987) Manual of herbarium taxonomy: theory and
practice. Indonesia, UNESCO.
Doumenge C. (1990) La conservation des écosystèmes forestiers du
Zaire. Gland & Cambridge, IUCN.
Hepper F.N. (1979) Second edition of the map showing the extent
of floristic exploration in Africa south of the Sahara. In: Kunkel
G. (ed.) Taxonomic aspects of African economic botany: Proceedings of the IX Plenary Meeting of AETFAT, Las Palmas de
Gran Canaria, 18–23 March, 1978: 157–162. Las Palmas, Perez
Galdoz.
IUCN (2018) Guidelines for Using the IUCN Red List Categories
and Criteria. Version 13. Available from http://www.iucnredlist.
org/technical-documents/red-list-documents [accessed 1 Apr.
2018].
Küper W., Sommer J.H., Lovett J.C., Barthlott W. (2006) Deficiency in African plant distribution data – missing pieces of the
puzzle. Botanical Journal of the Linnean Society 150: 355–368.
https://doi.org/10.1111/j.1095-8339.2006.00494.x
Mouly A., Razafimandimbison S.G., Florence J., Jérémie J.,
Bremer B. (2009a) Paraphyly of “Ixora” and new tribal delimitation of Ixoreae (Rubiaceae): Inference from combined
chloroplast (rps16, rbcL, and trnT-F) sequence data. Annals
of the Missouri Botanical Garden 96: 146–160. https://doi.
org/10.3417/2006194
Mouly A., Razafimandimbison S.G., Khodabandeh A., Bremer B.
(2009b) Phylogeny and classification of the species-rich pantropical showy genus Ixora (Rubiaceae-Ixoreae) with implications of geographical monophyletic units and hybrids. American Journal of Botany 96: 686–706. https://doi.org/10.3732/
ajb.0800235
Norton E. (2018) In Memoriam: Deadliest attack on Virunga Staff
in Park’s recent history brings total ranger deaths to 175. Available from https://virunga.org/alliance/rangers-project [accessed
10 Apr. 2018]
Puff C., Robbrecht E., Buchner R., De Block P. (1996) Survey of
secondary pollen presentation in the Rubiaceae. Opera Botanica
Belgica 7: 369–402.
Robbrecht E. (1988) Tropical woody Rubiaceae: Characteristic features and progressions; Contributions to a new subfamilial classification. Opera Botanica Belgica 1: 1–271.
448
Robbrecht R., Lejoly J. (1982) Une espèce nouvelle d’Ixora (Rubiaceae – Coffeeae) du Zaire. Bulletin du Jardin botanique national
de Belgique 52: 487–489. https://doi.org/10.2307/3667902
Sosef M.S.M. (2016) Producing the Flore d’Afrique centrale,
past, present and future. Taxon 65: 937–939. https://doi.
org/10.12705/654.54
Sosef M.S.M., Dauby G., Blach-Overgaard A., van der Burgt X.,
Catarino L., Damen T., Deblauwe V., Dessein S., Dransfield J.,
Droissart V., Duarte M.C,. Engledow H., Fadeur G., Figueira
R., Gereau R.E., Hardy O.J., Harris D.J., de Heij J., Janssens S.,
Klomberg Y., Ley A.C., Mackinder B.A., Meerts P., van de Poel
J.L., Sonké B., Stévart T., Stoffelen P., Svenning J-C., Sepulchre P., Zaiss R., Wieringa J.J., Couvreur T.L.P. (2017) Exploring the floristic diversity of tropical Africa. BMC Biology 15:
1–15. https://doi: 10.1186/s12915-017-0356-8
Stropp J., Ladle R.J., Malhado M., Ana C., Hortal J., Gaffuri J.,
Temperley W.H., Skøien J.O., Mayaux P. (2016) Mapping ignorance: 300 years of collecting flowering plants in Africa.
Global Ecology and Biogeography 25: 1085–1096. https://doi.
org/10.1111/geb.12468
Taplin J.R.D., Lovett J.C. (2003) Can we predict centres of plant
species richness and rarity from environmental variables in subSaharan Africa? Botanical Journal of the Linnean Society 142:
187–197. https://doi.org/10.1046/j.1095-8339.2003.00164.x
Thiers B. (continuously updated) Index Herbariorum: a global directory of public herbaria and associated staff. New York Botanical Garden’s Virtual Herbarium. Available from http://
sweetgum.nybg.org/science/ih/ [accessed 1 Apr. 2018]
UNESCO (2017a) State of Conservation: Virunga National Park
(Democratic Republic of the Congo). Available from https://
whc.unesco.org/en/soc/3509 [accessed 1 Apr. 2018].
UNESCO (2017b) State of Conservation: Kahuzi-Biega National
Park (Democratic Republic of the Congo). Available from https://whc.unesco.org/en/soc/3506 [accessed 1 Apr. 2018].
Verdcourt B. (1983) Notes on Mascarene Rubiaceae. Kew Bulletin
37: 521–574. https://doi.org/10.2307/4109725
Manuscript received 21 Jun. 2018; accepted in revised version 8
Oct. 2018.
Communicating Editor: Elmar Robbrecht.