KEW BULLETIN (2017) 72: 31
DOI 10.1007/S12225-017-9699-0
ISSN: 0075-5974 (print)
ISSN: 1874-933X (electronic)
Ledermanniella yiben sp. nov. (Podostemaceae), Critically Endangered
at the proposed Yiben Reservoir, Sierra Leone
Martin Cheek1 , Xander van der Burgt1, Joseph Momoh2 & Aiah Lebbie3
Summary. Ledermanniella yiben Cheek is described from the Seli (Rokel) river bed at a single rapid to be flooded by
the proposed Yiben hydroelectric dam and reservoir in Sierra Leone. It is assessed as Critically Endangered using
the IUCN categories and criteria. The species appears to be unique among African Podostemaceae in bearing
dimorphic shoots having either cupuliform or short ribbon-like leaves.
Key Words. Dimorphy, extinction, homology, hydroelectric reservoir, point-endemic.
Introduction
In the course of a botanical baseline survey for the
proposed Yiben Hydroelectric Dam on the Seli River,
upriver of the Bumbuna Dam, Sierra Leone, in April
2016, the second and third authors encountered a
species of Podostemaceae, van der Burgt 1992. The
plants were scattered densely along the gneissic rock
bed of the river, then at its seasonal lowest level,
largely dry, and with only a small channel of moving
water, it being the end of the dry season. The plants
were 20 – 50 cm diameter, spaced at distances of up to
50 cm apart from each other, with bare gneissic base
rock in between, and appear restricted to the vicinity
of a single set of rapids.
The 8-ribbed, non-compressed, unilocular, terete
ovaries and fruits, each with two stigmas, the flowers
inverted within the spathellum and the absence of
flattened scale-leaves, indicate that this plant is placed
within the genus Ledermanniella Engl. in the sense of
Schenk et al. (2015), or, Ledermanniella subgenus
Ledermanniella in the sense of Cusset (1984).
Identification work at K failed to match van der Burgt
1992 with any known species of the genus (see Results,
below). Consequently in this paper it is formally
named as Ledermanniella yiben Cheek.
Podostemaceae are a pantropical family of annual
or perennial herbs. All species of the family are
restricted to rocks in rapids and waterfalls of clearwater rivers, and are therefore rheophytes. However
this very habitat is being increasingly exploited for
hydropower at some risk to the survival of the
Podostemaceae they contain (Schenk et al. 2015;
Cheek et al. 2015; Cheek & Ameka 2016). Most of
the African species of Podostemaceae are narrow
endemics, many being known from only a single
waterfall. New discoveries of species are still being
made frequently (Schenk et al. 2015; Cheek & Haba
2016; Cheek et al. 2015; Cheek & Ameka 2008, 2016;
Kita et al. 2008; Beentje 2005; Schenk & Thomas 2004;
Cheek 2003, Rial 2002). Important characters in
defining genera in Podostemaceae are the position
of the flower in the unruptured spathellum, and the
shape, and sculpture of the ovary. At species level,
important characters are the shape and relative
proportions of spathellae, stigmas, anthers, filaments,
gynophores, pedicels, and leaves.
The current generic classification of African
Podostemaceae is based on the framework established
by Cusset (1973, 1974, 1978, 1983, 1984, 1987). This
work has been compiled and updated by Rutishauser
(2004). Recently, combined morphological and molecular phylogenetic studies of African Podostemaceae
have shown that Ledermanniella (as delimited by
Cusset) is paraphyletic, including all other sampled
genera of Podostemaceae recognised in Africa. This
was revealed by Thiv et al. (2009), employing plastid
markers matK, trnD-trnT, rpoB-trnC in sampling 9
genera and 17 species of African Podostemaceae,
and Schenk et al. (2015), employing plastid markers
matK, trnL, rpoB-trnC, ndhF, rbcL and matR in sampling
10 genera and 27 species of African Podostemaceae.
In recent years the accumulated molecular phylogenetic data (Thiv et al. 2009; Schenck et al. 2015) has
shown that Ledermanniella subg. Phyllosma C. Cusset
Accepted for publication 25 April 2017. Published online 5 June 2017
1
Herbarium, Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AE, UK. e-mail: m.cheek@kew.org
2
Conservation and Wildlife Management Unit, National Protected Area Authority, Ministry of Agriculture, Forestry and Food Security, Freetown, Sierra Leone.
3
National Herbarium of Sierra Leone, Department of Biological Sciences, Njala University, Njala, Sierra Leone.
© The Author(s), 2017. This article is an open access publication
31 Page 2 of 7
(1984) merits elevation to genus level as the
resurrected genus Inversodicraea Engl. The transfer of
names to effect this was recently completed (Cheek &
Haba 2016). The generic status of the remaining
African taxa is not clear, since most of the recognised
African genera are embedded within the remainder of
Ledermanniella (formerly Ledermanniella subg.
Ledermanniella). Additional molecular sampling and
analysis of taxa is needed to resolve relationships
further.
A most remarkable feature of van der Burgt 1992 is
that the shoots arising from the massive, long,
branched main stems are dimorphic in their leaves
and phyllotaxy. The two shoot types are:
1. Vegetative shoots of distichous phyllotaxy with
narrowly ribbon-like and slightly channelled leaves.
2. Fertile shoots terminating in a spathellum
subtended by opposite and decussate, very inconspicuous, cupuliform leaves.
These features are treated at length in the Discussion
section.
Methodology
Abundant herbarium material, with photographs,
was collected as van der Burgt 1992. Duplicates were
deposited in Sierra Leone at FBC and SL and once
authorisations had been obtained, the specimens
were exported to K for identification by specialists,
with other specimens resulting from the baseline
botanical survey of the proposed Yiben dam area.
Here it was examined with a Leica Wild M8
dissecting binocular microscope fitted with an eyepiece graticule measuring in units of 0.025 mm at
maximum magnification. The drawing was made
with the same equipment with a Leica 308700
camera lucida attachment.
The key used to attempt identification of the
specimen was that of Cusset (1984). The specimen was
compared with authoritatively named reference material
at K, or illustrations and descriptions, of every known
species of Ledermanniella. The format of the description
follows Cusset (1984). All specimens cited have been
seen. The conservation assessment follows the IUCN
(2012) standard. Herbarium codes follow Index
Herbariorum (continuously updated). Plant names and
authorities follow IPNI (continuously updated).
Results
The first couplet of the key to the species of
Ledermanniella subg. Ledermanniella of Cusset (1984) is
“Leaves with sheath very enlarged, cupuliform, membranous” (lead 1), vs “leaves with sheath non
cupuliform” (lead 2). Ledermanniella yiben is unusual,
possibly unique, in having both types of structure on
the same plant.
© The Author(s), 2017. This article is an open access publication
KEW BULLETIN (2017) 72: 31
If the first lead of couplet 1 is taken, we are led
to the second couplet, the first lead of which fits
our material: “blade reduced to a small mucron on
the back of the sheath; flowers sessile on the
thallus” leading to Ledermanniella aloides (Engl.) C.
Cusset. However, van der Burgt 1992 (L. yiben)
differs from this species in that it appears to lack
an extensive thallus, but possesses instead massive
lengthy aerial stems (Fig. 1), which do not occur in
L. aloides. It also differs in that the cupuliform
leaves lack stipules and that the mucro (reduced
blade) is rarely seen, while in L. aloides stipules are
present and the blade, while reduced, is conspicuous in over 90% of the leaves. The new species also
differs in having one stamen (vs two in L. aloides)
and in having short, sterile shoots with ribbon-like
leaves (absent in L. aloides).
If the second lead of couplet 1 is followed (“leaves
with sheath non cupuliform”) and we set aside the
cupuliform leaves seen in our material, Ledermanniella
yiben keys out to couplet 14, by virtue of the bases of its
ribbon-like leaves being non-cupuliform, the leaf
apices being entire, the leaves arising along the length
of a well-developed stem, leaves less than 2 cm long,
and stamens one, closely matching the lead to
L. jaegeri C. Cusset of Mt Loma (Sierra Leone):
“Leaves filiform, base not enlarged, 3 – 5 mm long,
stamen shorter than the ovary, pollen in dyads”.
Despite the fact that in van der Burgt 1992 (L. yiben)
the stamen is longer than the ovary, L. jaegeri seems to
be the species which most closely matches it. However,
the differences, set out in Table 1 below, are so
numerous that there is no doubt that they are
different species. Accordingly, the species represented
by van der Burgt 1992 is formally described and named
below as Ledermanniella yiben.
Ledermanniella yiben Cheek sp. nov. Type: Sierra
Leone, Koinadugu Distr., proposed Yiben Reservoir
area, large rapids in Seli R., N of Yara village, 9°16'
9.0"N; 11°34'50.6"W, 300 m a.s.l., fl., fr., 6 April 2016,
van der Burgt 1992 (holotype K; isotypes BM, BR, FBC,
G, MO, P, SL, WAG, Z).
http://www.ipni.org/urn:lsid:ipni.org:names:77161646-1
Rheophytic, probably perennial herb; forming mounds
20 – 50 cm diam., composed of numerous sprawling or
suberect stems radiating from a central holdfast
(thallus) when exposed in dry season by low water.
Stems 10 – 30 cm long, fleshy-rubbery, brown outside,
green inside, drying black, irregularly cylindrical 0.5 –
1 cm diam., each with one or two main branches
which in the distal parts branch repeatedly; rarely with
naked filiform extension shoots 3 – 7 cm long, c. 2 –
3 mm diam. Shoots and leaves dimorphic, thickly
covering upper parts of the stem surface. Vegetative
KEW BULLETIN (2017) 72: 31
Page 3 of 7 31
Fig. 1. Ledermanniella yiben at its only known locality in the Seli (Rokel) river within the proposed Yiben reservoir, 6 April 2016. A,
B dried plants on flat bedrock in the river bed; C several individual plants; D part of a half-submerged plant in flower and fruit.
PHOTOS: XANDER VAN DER BURGT.
shoots infrequent, erect (Fig. 2A & B), most numerous
towards the apex of the main stems, 5 – 10 (– 30) mm
long, (3 –) 5 (– 7) leaves per shoot, each leaf sheathing
that above, arranged distichously, 3 – 7 mm long,
erect, narrowly ribbon-shaped and shallowly
canaliculated (channelled), tapering towards the acute
apex, base sheathing, but lacking stipule lobes,
elongated and not cupular. Fertile shoots sessile, erect,
sometimes intermixed with sterile shoots, but usually
in dense crustose masses completely covering large
sections of the stem up to 10 or 15 cm long; each with
a single terminal spathellum subtended by 2 – 3 pairs
of inconspicuous approximately opposite and decussate cupuliform (shallowly concave), suborbicular
leaves 1 mm long, best observed in the developing
shoots (Fig. 2G). Spathellum (with inverted flower bud)
Table 1. Diagnostic characters separating Ledermanniella jaegeri and L. yiben.
Character
Stamen length
Cupuliform leaves
Elongate leaves: insertion
Elongate leaves: shape
Styles
Spathellum shape
Pollen
Ledermanniella jaegeri
Ledermanniella yiben
Shorter than ovary
Absent
Spirally inserted on short shoots
which terminate in a spathellum
Terete (filiform)
Longer than ovary
Subtending spathellum
Distichous on short shoots which
are sterile: spathellae absent
Dorsiventrally flattened (ribbon-like)
and slightly channelled.
Ellipsoid, 0.3 – 0.4 mm long, united
at base
Ellipsoid-cylindrical
Monads
Filiform, 0.2 – 0.3 mm long,
not united at base
Subobovoid
Dyads
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31 Page 4 of 7
KEW BULLETIN (2017) 72: 31
Fig. 2. Ledermanniella yiben. A habit, mid region of main axis of plant showing lateral vegetative short shoots; B detail of
vegetative short shoot, showing distichous, slightly channelled leaves; C main axis, distal region, showing dense mass of fertile
shoots (right) and numerous branches (left); D apex of main axis showing branches and vegetative short shoot; E stem branch with
mass of fertile shoots terminating in flowers at anthesis; F detail from C showing multiple fertile shoots; G cluster of immature
fertile shoots; H – M spathellum with flowers showing stages from spathellum rupture to post-anthesis; N detail of gynoecium; P
transverse section of ovary; Q variation in stigma size, shape and orientation. All from van der Burgt 1992. DRAWN BY ANDREW BROWN.
© The Author(s), 2017. This article is an open access publication
KEW BULLETIN (2017) 72: 31
elliptic-cylindrical 1.4 – 2.4 (– 3.2) × 0.7 – 1.2 mm,
apex rounded, very rarely with a mucro, base
contracted, rarely with a short stipe, opening at the apex
by three more or less equal triangular lobes or sometimes irregularly, each c. 0.4 × 0.4 mm; pedicel erect,
angular-terete, white, 6.0 – 6.8 mm long, 0.2 – 0.3 mm
diam. Tepals two, patent, cylindric, 0.3 – 0.5 × 0.02 mm
long, inserted opposite filament at base of gynophore.
Androecium exceeding ovary, with a single stamen,
filament 1.8 – 2.5 mm long, about as long as ovary;
anther 4-celled, drying black, suboblong, c. 1 × 0.6 mm.
Pollen white, in monads. Gynophore 0.2 – 0.3 mm long.
Ovary light green-brown, elliptic-oblong, 1.4 – 1.6 × 0.8
mm, not laterally compressed, apex and base rounded,
side with 6 main longitudinal ribs, commissural ribs 2,
each paired and reduced, not as prominent as the main
ribs and with a central longitudinal groove. Stigmas 2,
diverging by c. 90 degrees, united at the base, elliptic, 0.3 –
0.4 × 0.1 mm, (Fig. 2E, J – N) widest towards base, tapering
gradually to the acute apex, surface densely covered in
minute acute papillate projections. Fruit dehiscing by a
single valve. Seeds ellipsoid, pale brown, c. 0.6 × 0.4 mm.
Figs 1, 2.
RECOGNITION. Similar to Ledermanniella jaegeri, differing
in that cupuliform, approximately opposite and decussate leaves subtend the spathellae (not filiform
spirally inserted leaves) and in the presence of sterile
shoots with distichously arranged, tapering, ribbonlike leaves (absent in L. jaegeri), also in the stamen
being longer than the ovary and monad pollen (not
shorter than ovary and dyads).
DISTRIBUTION. Sierra Leone. Only known from the river
bed of the Seli River in Koinadugu District, where it
occurs in the proposed Yiben Reservoir area, to be
permanently submerged when the construction of the
proposed hydroelectric reservoir is implemented.
SPECIMEN EXAMINED. SIERRA LEONE. Koinadugu Distr.,
proposed Yiben Reservoir area, large rapids in Seli R.,
N of Yara village, 9°16'29.0"N; 11°34'50.6"W, 300 m
a.s.l., fl., fr., 6 April 2016, van der Burgt 1992 (holotype
K; isotypes BM, BR, FBC, G, MO, P, SL, WAG, Z).
HABITAT & ECOLOGY. Growing in a colony on bare,
gneissic rocks forming the base of a river bed at a
single set of rapids, submerged for most of the year,
exposed and flowering only at end of dry season.
Growing with no other vascular plant species.
CONSERVATION STATUS. Ledermanniella yiben is here
assessed as Critically Endangered, using the Categories
and Criteria of IUCN (2012), since a single global
location is known on current evidence, containing, so
far as is known, the entire world population of the
species, which will be destroyed by permanent submergence under the waters of the reservoir of the proposed
Yiben Hydroelectric Project if construction is realised.
The area occupied by the species on the ground has
been estimated by the second author as 0.25 Hectare
Page 5 of 7 31
(c. 50 m × 50 m). The area of occupancy (AOO) can be
calculated using the preferred IUCN cell size for riverine
species of 1 km2. The second and third authors have
spent weeks surveying plants in the Yiben area but only
found this species in an area of the Seli (Rokel) river bed
about 50 m wide, and about as long, corresponding to a
single rapid on the river. L. yiben was absent at rapids up
and down the river from this location. The authors have
also searched other fast flowing river systems in Sierra
Leone for rheophytic species over the last seven
years, yet have never before encountered this species. Many species of Podostemaceae in Africa are
only known from a single waterfall or set of rapids
(Cheek & Haba 2016; Cheek et al. 2015; Cheek &
Ameka 2016; Cusset 1983, 1984).
It is hoped that searching further upriver (which
has not been exhaustive) from the type and only
known locality of Ledermanniella yiben might discover
additional locations for the species but this is by no
means a certainty. Such searches are now underway
(March 2017) and attempts will be made at the same
time to establish the species at other, secure sites in
order to avoid its extinction. Establishing the species at
another location will be a challenge. Translocation of
species of Podostemaceae in Africa is not yet known to
have been achieved successfully, yet it is not known
that it has ever been attempted before.
ETYMOLOGY. Ledermanniella yiben is named for the
proposed Yiben hydroelectric dam in Sierra Leone;
the construction of which is likely to result in the
extinction of the new species.
Discussion
The homology of cupuliform leaves in African
Podostemaceae
In the first couplet of her key to the species of
Ledermanniella subg. Ledermanniella, Cusset (1984)
divides those species with “Leaves with sheath very
enlarged, cupuliform, membranous” (that is, L. aloides
(Engl.) C. Cusset, L. thalloidea (Engl.) C. Cusset and
L. batangensis (Engl.) C. Cusset) from those without,
including those with leaf sheaths which are oblong,
such as L. sanagensis C. Cusset. In fact, intermediates
occur, such as the elliptic leaf sheaths of L. lunda
Cheek. L. aloides itself often has laterally compressed
leaf sheaths which are then not truly cupuliform. In
L. thalloidea and L. batangensis the leaf-sheath origin of
the cupuliform structure is especially clear since a
filiform leaf-blade arises peltately from near the apex
of the dorsal surface of the cupuliform structure. The
presence of a pair of short triangular stipules on each
side of the apex of the cupuliform structure in
L. batangensis (Cusset 1987) further confirms the
homology, since these stipules are typical of those that
appear sporadically on the margins of leaf sheaths in
© The Author(s), 2017. This article is an open access publication
31 Page 6 of 7
other African Podostemaceae, such as in Saxicolella
marginalis (G. Taylor) Cheek.
The cupuliform structures of Ledermanniella yiben
lack filiform blades, but occasionally a small peltate
protuberance can be found on their dorsal surface
which may indicate a vestigial leaf-blade. This same
condition occurs in Macropodiella pellucida (Engl.) C.
Cusset, in which the cupuliform structures (leaf-bases),
as in L. yiben, also occur in short shoots and which also
subtend a terminal spathellum.
It is difficult not to conclude that these last two
species have a sister relationship despite their current
placement in different genera. This generic placement is based on a single floral character, the
presence of laterally flattened ovary or not, which
further research may show to be labile. Vegetative and
architectural characters may be as important or
sometimes a better indicator of evolutionary relationships of species than floral characters hitherto exclusively used in defining the genera of African
Podostemaceae (Cusset 1973, 1974, 1978, 1983, 1984,
1987). Genera such as Macropodiella may be artificial as
currently defined (Cheek & Ameka 2016) as is
Ledermanniella (Thiv. et al. 2009).
We have seen that cupuliform leaves of leaf sheath
origin occur in African Podostemaceae and that they
may be a modification of the widespread leaf type that
occurs in the group, in which the leaf is long and
slender, ribbon-like or terete, with a dilated, sheathing
base attaching it to the stem. That these cupuliform
leaves always occur on short shoots and subtend
spathellae suggests that their function is to protect
t h e de v e l o pi ng s p at h e l l u m r at h e r t h an t o
photosynthesise. Essentially, they function as bracts.
Dyad and monad lineages of Ledermanniella
Thiv et al. (2009) and Koi et al. (2012) showed that
Ledermanniella is divided into Ledermanniella-Monad and
Ledermanniella-Dyad lineages based on molecular phylogenetic evidence. L. yiben has monad pollen. Attempts to
find morphological synapomorphies that support the
monad lineage have not yet been successful.
Recent botanical novelties in Sierra Leone
Ledermanniella yiben is among a host of new species that
have been brought to light and published from Sierra
Leone in recent years, following decades of relative
inactivity in plant species discovery in that country and its
neighbours. This has mostly been driven by increased
industrial activity and associated Environmental Impact
Assessment work, but also greater ease of accessibility
following reduced conflict. Examples of such newly
discovered species in Sierra Leone are: Dactyladenia
globosa Jongkind (2012), Pseudovigna sulaensis R. Clark
& Burgt (Clark et al. 2012), Xysmalobium samouritourei
Goyder (2009), Stylochaeton pilosus Bogner (2011),
© The Author(s), 2017. This article is an open access publication
KEW BULLETIN (2017) 72: 31
Isoglossa dispersa I. Darbysh. & L. J. Pearce (Darbyshire
et al. 2011), Gilbertiodendron tonkolili Burgt & Estrella
(Estrella et al. 2012), Eriocaulon cryptocephalum S. M.
Phillips & Mesterházy and E. tingilomum S. M. Phillips &
Mesterházy (2015), E. sulanum S. M. Phillips & Burgt and
E. petraeum S. M. Phillips & Burgt (Phillips et al. 2012),
Napoleonaea alata Jongkind (Prance & Jongkind 2015)
and Psychotria samoritourei Cheek (Cheek & Williams
2016). Just over the border in Ivory Coast examples
include Macropodiella cussetiana Cheek (Cheek & Ameka
2016), and in Guinea Striga magnibracteata Eb. Fisch. & I.
Darbysh. (Fischer et al. 2011) and Gymnosiphon
samoritoureanus Cheek (Cheek & van der Burgt 2010).
Even a new rheophytic genus, Karima Cheek &
Riina has recently been discovered in Sierra Leone
(Cheek et al. 2016).
Acknowledgements
The authors thank ERM for co-ordinating the field
studies and for financing the work that resulted in this
discovery. Mrs K. M. B. Garnett, Director of the
Conservation and Wildlife Management Unit of the
Ministry of Agriculture, Forestry and Food Security
kindly provided permission to perform botanical
research in Sierra Leone. Two anonymous reviewers
made helpful comments on an earlier version of this
manuscript. Janis Shillito typed the manuscript.
Open Access This article is distributed under the
terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/
licenses/by/4.0/), which permits unrestricted use,
distribution, and reproduction in any medium, provided you give appropriate credit to the original
author(s) and the source, provide a link to the
Creative Commons license, and indicate if changes
were made.
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