On the discovery of a new endemic Cynanchum (Apocynaceae) on
Gunner’s Quoin, Mauritius
Department of Biosciences, University of Mauritius, Réduit, M
Mauritius Herbarium, Mauritius Sugar Industry Research Institute, Réduit, M
Bosser (Apocynaceae), a new Mauritius endemic species was discovered
in 2003 on Gunner’s Quoin Nature Reserve, a highly degraded offshore islet north of Mauritius.
The plant’s basic ecology is described and threats to its persistence are discussed. The species
is Critically Endangered. Recommendations to secure its future are given. The discovery adds
further conservation value to Gunner’s Quoin.
Key words -
Cynanchum scopulosum, islet restoration, invasive species, IUCN conservation status.
The ﬂ ora of Mauritius started to be documented during the late 18
and within two centuries most of its species had been described (B
onwards). However, despite having only about 5% of its original native vegetation left,
new records of native plant species continue to be made. Recent examples include a
new endemic Myrtaceae, Syzygium guehoi Bosser & Florens (B
discovered in 1989, or the orchid Taeniophyllum coxii (Summerh.) Summerh., an
aphylous epiphyte of wide distribution ﬁ rst recorded in Mauritius in 2000 (R
2004). Here we report on the latest such discovery, made in 2003, of a Cynanchum
species (Apocynaceae) endemic to Gunner’s Quoin islet, north of Mauritius.
The Apocynaceae is a large mainly tropical family of some 415 genera
and 4,555 species (S
2001-onwards) of which some 200 belong to the genus
1997). In Mauritius, the Asclepiadoideae is represented by
six native genera and 11 native species (B
The ﬁ rst mention of Cynanchum in Mauritius, of which the species cannot
be ascertained, was made by
was recorded on high mountains on Mauritius, a habitat type today occupied by C.
. Later, B
(1877) mentioned a second species,
Decne (=C. luteiﬂ uens (Jum. & H. Perrier) Desc.)), which appears to be the same as
Bojer’s taxon (B
Later references to Cynanchum in Mauritius are
under Sarcostemma viminale
1988). It is now established
however that Rodrigues has one and Mauritius three endemic species of Cynanchum
2005). No native Cynanchum
is known from Reunion island.
In the Flore de Mascareignes
Flore de Mascareignes Cynanchum
is treated under Asclepiadaceae
Gunner’s Quoin, a 76ha offshore volcanic islet 4
km north of Mauritius,
consists of rock laid down 0.7-0.025M years ago (M
culminates at 162m a.m.s.l. Most of the islet consists of friable volcanic tuft while the
eastern side has an overlying basalt layer. Inferring from C
(2004), the islet
would have been cut off from mainland Mauritius by rising sea level some 10,000 years
(1937) believed that the islet supported a palm savannah in its
pristine condition before being much altered by human activity since the 18
The most recent published botanical surveys previous to our visit revealed an ecosystem
largely overrun by alien plants which made up 48 of the 72 higher plant species (D
1994). Despite its advanced degradation state, where large parts of the islet are dominated
by invasive plants, Gunner’s Quoin still harbours some valuable native relicts like the
largest population of the Mauritius endemic Lomatophyllum tormentorii. The native
vertebrate fauna includes mainly tropic birds (Phaeton rubricauda
vertebrate fauna includes mainly tropic birds (
vertebrate fauna includes mainly tropic birds (
and P. lepturus
Wedge-tailed shearwater (Pufﬁ nus paciﬁ cus
) as well as four species of reptiles. The
eradication of Norway rats (Rattus norvegicus
eradication of Norway rats (
eradication of Norway rats (
), black-naped hare (Lepus nigricollis
), black-naped hare (
), black-naped hare (
and domestic rabbit (Oryctolagus sp.) in the 1990’s (B
2002), greatly enhanced the
conservation value of the islet particularly as a site for eventual reintroduction of reptiles
from Round Island.
The authors found the new Cynanchum species during a four-days biodiversity
survey of the islet in December 2003 under a Government of Mauritius project
commissioned for the creation of the Islets National Park. The survey was carried out
in all different areas safe the inaccessible western cliffs which were examined where
possible with binoculars. Ecological notes, like level of threats posed to the habitat by
alien species, were taken to allow for an assessment of the threat category of the species
using IUCN Criteria (IUCN 2001). Samples were deposited at the Mauritius Herbarium
and duplicates sent to the Herbarium of the Museum National d’Histoire Naturelle,
We found 77 higher plant species including the new Cynanchum of which
a colony of an estimated two dozens intermingled individuals was found. A sample
was deposited at the Mauritius Herbarium (Holotype MAU 23772). Other vouchers
collected on a second visit in 2004 are: MAU 24070, 24071, 24072, 24073 and 24074.
C. scopulosum was growing from the upper scarp downwards on a near vertical
sea facing cliff and its ledges in the south west of the islet between 20-50 m amsl (Fig. 1).
The species is a rather procumbent liana with branches reaching one cm in diameter. It
has markedly constricted nodes and a silvery green tinge that distinguishes it vegetatively
from all other Mauritian Cynanchum. Its branching stems reach several metres long and
creeps over exposed rocks and low cliff vegetation. Towards their extremities, the stems
are usually erect sometimes reaching one meter high. The colony spans a maximum
of about 40 m laterally and 30 m vertically and varies from dense monospeciﬁ c areas
towards its core to more diffused growth towards the edges where it grows together
with several other native species including Tylophora coriacea (Apocynaceae),
(Asphodelaceae), Scaevola taccada
more rarely with Latania loddigesi (Arecaceae) and Dicliptera falcata (Acanthaceae).
There is, however, a number of invasive alien plants that appear to be encroaching on the
Cynanchum’s habitat, including the ﬁ re prone grass Heteropogon contortus and other
aggressive weeds like Flacourtia indica (Salicaceae) and Opuntia vulgaris (Cactaceae)
that have already developed into dense stands or thickets elsewhere on the islet.
The ﬂ ora of Gunner’s Quoin was thoroughly surveyed at least three times
1994, MWF 2003) since its description in the 1930’s
1937). It thus appears surprising that the new Cynanchum
covering a patch of several dozen metres across was discovered only in December 2003.
However, while some surveys genuinely missed the plant (V
MWF 2003), others appeared to have located but misidentiﬁ ed it. Thus Bullock et al.
(1983) recorded an alien tree weed, Euphorbia tirucalli (Euphorbiaceae) where we
discovered C. scopulosum.
Another survey by B
(1994) mentioned a clump
of E. tirucalli where we later found the Cynanchum colony. In fact, C. scopulosum
superﬁ cially resembles E. tirucalli from a distance. Infertile herbarium samples of the
two species can also be very similar. We found no E. tirucalli on the islet.
Distribution of Cynanchum scopulosum
on Gunner’s Quoin Islet Nature Reserve,
north of Mauritius.
It is fortunate that there was no attempt to eradicate the misidentiﬁ ed Cynanchum
during restoration of the islet like was successfully done with rats, hares and rabbits
2002). But it is worrying that a plant found on nearby Serpent Island in 2003
and identiﬁ ed as a weed by the expedition members, which comprised no experienced
botanist, has been destroyed and that no sample was kept (T
There exists also the unfortunate habit on Mauritius to weed Cynanchum spp. from
areas managed for conservation because it is a toxic plant. Weeding of Cynanchum has
been reported from Ile aux Aigrettes Nature Reserve (A. K
pers. comm. 2004),
Perrier Nature Reserve and Mondrain Private Reserve (G. D’ A
, pers. comm.
2004). Cynanchum seems now eradicated from the latter two sites.
is known only from Gunner’s Quoin. A second expedition there
in August 2004, revealed a tiny second clump of two plants on a ridge 100m from the
ﬁ rst colony bringing the total area occupied by the species to less than 0.1ha in two
separate places (Fig. 1). The species thus has one of the most restricted range for an
endemic plant on Mauritius.
This fact alone exposes it to a high threat of extinction in the wild. The colony
may thus easily be destroyed by ﬁ re, the more so that much of the islet is today invaded
by ﬁ re prone Heteropogon contortus, and also receive illegal visitors regularly lighting
camp ﬁ res. Indeed, devastation by ﬁ re has been recorded in the past (D
probably explains partly at least both why the islet is so poor in native plants and why
the Cynanchum itself has such a restricted and marginal distribution.
Fig. 2. Cynanchum scopulosum on Gunner’s Quion - young plant and ﬂ owers.
Destruction of the colony by a landslide appears likely as this is a common
feature on the island as indicated by numerous rock fall scars on the sea facing cliffs.
The site where Cynanchum grows is also gradually being invaded by alien plants. Thus,
the species should be regarded as Critically Endangered (CR B1ab(iii) + 2ab(iii); D).
Given these risks, we recommend that the plant be propagated to several
locations of suitable ecology on the islet itself, including well inland. Also the proximity
and similar climate and geology of Round and Flat Islands, and their ongoing restoration
programmes make them ideal sites to receive translocated C. scopulosum. Establishing
these populations would greatly reduce the plant’s extinction risks in the wild. It is quite
conceivable that C. scopulosum might have once grown on these two islets given the
plant’s efﬁ ciently wind-dispersed seeds and the fact that many native species are known
not to have survived the human-induced ecological devastation of both islets.
Extinction risks will also be minimised by maintaining the plant in ex-situ
facilities. C. scopulosum is easy to propagate. All 12 cuttings taken rooted without
rooting hormones within 5-6 weeks. These are being grown in the arboreta of the
National Parks and Conservation Service and of the Mauritius Herbarium (MSIRI).
Propagation by seeds, although advisable, seems less easy for the moment due to the
currently rather rare expeditions to the islet and since the plants appear to set very few
fruits at a time.
We are grateful to Mr Yousouf Mungroo and Mr Kevin Ruhomaun of the
National Parks and Conservation Service, for having organised the trip to the islet. C.B.
thanks J-C. Autrey for reviewing the draft.
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