Download 647. RONDELETIA BUXIFOLIA Plant in Peril, 32 Rubiaceae

647. RONDELETIA BUXIFOLIA
Rubiaceae
Plant in Peril, 32
Colin Clubbe, Martin Hamilton and Marcella Corcoran
Summary. Rondeletia buxifolia Vahl (Rubiaceae) a critically endangered shrub,
restricted to the Caribbean Island of Montserrat, is described and illustrated.
Its distribution and conservation status are reviewed.
Rondeletia buxifolia Vahl is a small multi-stemmed shrub, restricted
to the Caribbean island of Montserrat, a UK Overseas Territory
(UKOT). The earliest botanical collections in Montserrat were made
by John Ryan in the late 18th century. He lived and worked on the
island for many years as a physician and a plantation owner. During
this time, Ryan sent many herbarium specimens to the Copenhagen
Herbarium in his home country of Denmark. These included the type
specimens of R. buxifolia and another Montserrat endemic, the small
tree Xylosma serrata Urb. (Salicaceae). Based on Ryan’s collections,
M. H. Vahl published R. buxifolia as a new species in 1798.
Rondeletia L. is a neotropical genus of small trees and shrubs in
the family Rubiaceae. A few species, such as Rondeletia odorata Jacq.
and Rondeletia amoena Hemsl. have been brought into cultivation for
their colourful flowers and their scented inflorescence. Two hundred and sixty-four species of Rondeletia have been described and
are distributed from Mexico to Tropical America and across the
Caribbean (Govaerts et al., 2008). One hundred and thirty species
have a Caribbean distribution with a centre of diversity in Cuba
where 65 species are endemic. Of the Caribbean species, 135 are single island endemics and the smaller islands of Montserrat, Anguilla,
St Vincent and Martinique each support a single species. Seventeen
species of Rondeletia are listed on the global red list of threatened
species (IUCN, 2008).
From the late 18th century, Montserrat was little visited by botanists
and there are relatively few records of Rondeletia buxifolia, most notably
by J.S. Beard in 1944, and by G.R. Proctor in 1959. Richard Howard
produced the first extensive checklist of the flora of Montserrat for his
Flora of the Lesser Antilles (Howard, 1974–1989). This remains the most
Curtis’s Botanical Magazine 2009 vol. 26 (1&2): pp. 131–141
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important and comprehensive botanical inventory of Montserrat
and the other islands in the Lesser Antilles. Howard’s collections
of R. buxifolia in 1979 represent the last known herbarium specimen
vouchers of this species collected before the current Kew programme
in Montserrat.
In 1995, the Soufrière Hills volcano in the south of the island
rumbled to life for the first time in more than 400 years. For two
years it released gas and ash and there was increased seismic activity
and lava dome growth. A major set of explosions in 1997 and
dome collapse unleashed a series of pyroclastic flows that buried
the capital city of Plymouth and many surrounding villages. Among
the losses were the island’s agriculture station and botanic garden
together with large areas of natural forest. Today, nearly half the
island is an exclusion zone and life is re-establishing itself in the north
creating inevitable pressure on the remaining forested areas and their
constituent plant and animal species.
In 2005 the UK government’s Darwin Initiative funded a collaborative project to undertake a biodiversity assessment of Montserrat’s
Centre Hills and to develop a management plan to help guide
future conservation activities (www.malhe.gov.ms/centrehills/). This
project enabled Kew’s UK Overseas Territories Programme to work
with the Montserrat government and the Montserrat National Trust
to undertake the first comprehensive botanical assessment of the
Centre Hills, and the first major piece of botanical fieldwork in
Montserrat since Howard’s pioneering work in the seventies. Over
the last three years a series of botanical expeditions has resulted in
a good understanding of the plants of Montserrat, their key habitats
and how the volcanic eruptions have impacted on them. This has
enabled the production of a new vegetation map for Montserrat, a
species checklist and candidate red list, with a clearer understanding
of the distribution of Montserrat’s most important species for conservation, including Rondeletia buxifolia (Hamilton et al., 2008). The first
steps were also taken in indentifying the key threats these species face
and the conservation action required for their long-term survival.
Much of Montserrat’s 63 km2 is very rugged comprising three
distinct volcanic ranges: the oldest geologically is the Silver Hills (to
450 m) in the north, the Centre Hills (to 740 m) and the youngest
and currently active volcanic region of the Soufrière Hills (to 900 m)
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Plate 647 Rondeletia buxifolia (large flowers and leaves × 5) christabel king
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The northern flanks of the Centre Hills, dominated by Katy Hill (740m). The lower elevation forests in the foreground show typical habitat for Rondeletia
buxifolia. Patches of encroaching agriculture are also evident. Photograph: Colin Clubbe.
in the south. The vegetation of Montserrat is largely determined by
the amount of rainfall, which is in turn closely linked to elevation.
Secondary vegetation now covers most of the island due to historical
clearance for agriculture, timber and charcoal. Hamilton et al. (2008)
identified three major forest types for their vegetation map largely
based on a broad moisture gradient and containing a characteristic
set of species: Dry Forest types, Mesic Forest types and Wet Forest
types. Two further habitats of much more restricted distribution and
fewer characteristic species were also identified: Littoral Forest and
Elfin Woodland.
Inland, at lower altitudes and where rainfall is limited Rondeletia
buxifolia grows in the dry scrub or thickets of the Silver Hills. It occurs
in stands of Dry Forest (seasonally deciduous sub-tropical woodland)
with low rainfall, usually along lower valleys and hill ridges and
alongside seasonal stream beds. Mesic Forest begins to appear as
more moisture becomes available, usually at moderate elevations and
further up along stream beds and is a preferred habitat for R. buxifolia.
(Hamilton et al., 2008). R. buxifolia does not occur in Wet Forest types.
When growing in the shade and shelter of other species, R. buxifolia has
an elongated and spindly habit, with soft lush green leaves; however, it
will eventually fall over, reaching the ground and producing new roots
on the stem thus creating a new plant. The opposite is true for the
individuals growing in full sun, which produce a sturdy compact shrub
with thicker stems and leaves able to withstand the harsh environment
of sun and wind. Individuals growing in full sun flower earlier and
much more profusely, with flowering declining as shade increases
indicating a preference for forest edge habitats. An analysis by Jones
(2008) showed sexual reproduction, as indicated by fruit presence, to
be predominantly positively influenced by increasing light levels.
A recent study has shown that Rondeletia buxifolia is more widespread
within the Silver Hills than was originally realised and has provided
a better understanding of its distribution outside the Centre Hills
(Jones, 2008). Jones (2008) also calculated a total extent of occurrence
(sensu IUCN, 2001) of R. buxifolia to be 16.6 km2 . The only forest
area in Montserrat currently under legal protection is the Centre
Hills Forest Reserve which comprises an area of approximately 1110
ha occupying the central areas of the Centre Hills range above an
elevation of approx 200 m. Although an important protected area
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© The Board of Trustees of the Royal Botanic Gardens, Kew 2009.
Legend:
Rondeletia buxifolia points
Contours
Forest Reserve boundary
Volcanic deposits
Scale: 1 cm = 1.4 Km
Map of Montserrat, showing recorded locations of Rondeletia buxifolia. Drawn by M.A. Hamilton.
for many Montserrat species and for watershed protection, ∼ 90%
of the population of R. buxifolia is located outside the Forest Reserve
and afforded no real protection. However, a new Conservation
and Environmental Management Bill is being drafted which will
offer species level protection to Montserrat’s key species, including
R. buxifolia. The Bill is due to be enacted in 2009.
© The Board of Trustees of the Royal Botanic Gardens, Kew 2009.
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There is great concern for the long-term survival of Rondeletia
buxifolia, due to a decline in suitable habitat attributable to:
• Volcanic eruptions which threaten the Dry and Mesic Forest
habitats. Apart from pyroclastic flows which destroy everything
in their path, volcanic ash and acid rain defoliate the vegetation,
leading to a decline in the number of individuals.
• Pressure from residential infrastructure and tourism development resulting in direct loss, degradation and fragmentation of
suitable habitat.
• Alien invasive plant species including Psidium guajava L. and
Cryptostegia madagascariensis Bojer ex Decne. These species
compete aggressively with native vegetation and are spreading
rapidly, causing serious damage to habitats and species. A
recent study used prediction mapping of the spread of these two
species and showed a near complete overlap with the habitat
requirements of R. buxifolia which could result in the virtual
elimination of this species from Montserrat should the spread of
these invasive species remain unchecked (Stow, 2008).
• Pressure from feral livestock poses a major threat to the
R. buxifolia, in particular the goats roaming in the Silver Hills,
which chew plants to the ground, severely limiting regeneration.
The effect that rats have on seedling regeneration is currently
unknown, but is under investigation.
• Climate change has the potential to change the climatic envelope
of R. buxifolia with as yet unknown effects.
Based on knowledge of the distribution of Rondeletia buxifolia and
the threats that the species is facing Hamilton et al. (2008) suggested
a candidate red list status of critically endangered. Data provided by
Jones (2008) has confirmed this assessment and enabled R. buxifolia to
be formally assessed as Critically Endangered B1ab(iii, v) based on
the IUCN red list criteria (IUCN, 2001).
Conservation Measures. An integrated conservation strategy is
being developed for R. buxifolia involving both ex situ and in situ
conservation measures, plus raising awareness about the status and
importance of this species. The UK government’s Overseas Territories Environment Programme (OTEP) have recently funded a
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project to enable species action plans to be developed in a participatory way with local stakeholders in Montserrat for the most important
species of plants, amphibians, reptiles and mammals. These follow
the successfully completed action plant for the critically endangered
Montserrat oriole (Hilton et al., 2005). The workshop to develop a
species action plan for Montserrat’s endemic plants was held in 2008
and a draft action plan is in circulation for comment. Recommended
conservation actions build on those currently under way.
In 2006 seed of Rondeletia buxifolia was collected for long-term
seed banking at Kew’s Millennium Seed Bank (MSB). The seed was
collected from within the Centre Hills Forest Reserve and sent to the
MSB for banking. This collecting was undertaken as part of a broader
conservation strategies training workshop to help build conservation
capacity in Montserrat, and seeds of other critical species have been
collected for the MSB since then. A portion of the seed lot of
R. buxifolia was sent to Kew to be used to develop a horticulture
protocol. The UKOT Programme is engaged in developing full
horticulture protocols for UKOT’s threatened species, and training
local counterparts is part of their core activity (Hamilton et al., 2007;
Corcoran et al., 2008). This is also contributing directly to meeting
the targets of the Global Strategy for Plant Conservation (GSPC,
2002). The horticulture protocol has been completed and sent to the
Montserrat National Trust (Corcoran et al., 2008). Kew has been
helping the Montserrat National Trust to establish a new botanic
garden at its headquarters in the north of the island in a project
also funded by OTEP. The Trust’s original offices in Plymouth were
destroyed by the 1997 volcanic eruptions as was the island’s original
botanic garden. A new nursery has been completed and several of
Montserrat’s threatened and culturally important plant species are
in cultivation there. Observations on the growth form of R. buxifolia
in the wild suggested that it would make a good hedging plant
and a trial hedge has been planted out at the Montserrat Botanic
Garden. Early indications from this trial are very positive and a
plan is being developed to supply plants for the Montserrat general
public to encourage wider use of this species in landscaping. This
would have several benefits. An endemic species being used in a
sustainable way would be a flagship for conservation awareness. It
could replace non-native species of Ficus currently widely used for
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F
E
A
C
D
B
Rondeletia buxifolia. A, leaf (largest), × 1; B, growing point with buds and two leaves, × 2; C,
node with buds, × 4; D, l.s. flower, × 4; E, style, × 8; F, t.s. ovary, × 10. Drawn by Christabel
King from living material at Kew.
hedging which has detrimental impacts on the soil and provide an
unfriendly environment for local biodiversity. In the short-term the
outlook for R. buxifolia is quite positive. Its future has been secured
ex situ by long-term seed banking in the MSB, and by cultivation in
Montserrat and at Kew. However, its future in situ remains precarious,
as habitat is lost and individuals destroyed as the infrastructural
demands of a re-establishing nation in the north of the island clash
with the centre of diversity for this critically endangered species.
Rondeletia buxifolia Vahl, Eclogae Americanae ii. 11, t. 12 (1798). Type:
habitat in Montserrat. Ryan (C).
Description. A lax or dense shrub 1–3 m tall, with slender arching
branches. Stipules subannular, 1 mm long, strigillose. Leaf petioles 1–2 mm long;
blades cuneate-obovate to spathulate, 1.3–3.5 × 0.7–1.7 cm, base cuneate, apex
rounded or retuse, glabrous or appressed pubescent on the veins at the leaf base.
Inflorescence axillary, 1- to 3-flowered, pedicels to 2 mm; calyx lobes 4, linear
or oblanceolate, 1.5–3 mm long, acute; corolla salveri form, tube 6–7 mm,
cream or buff to yellowish, retrorsely pubescent outside, lobes 4, 1.5–2 mm
long. Capsules sub-globose, 4 mm in diameter, tomentulous; seeds 1 mm long,
angulate, reticulate, winged (adapted from Howard, 1989 p.456).
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© The Board of Trustees of the Royal Botanic Gardens, Kew 2009.
Distribution. Caribbean: restricted to Montserrat.
Habitat. Restricted to an area of 16.6 km2 in the north of the island in
Dry Forest (seasonally deciduous sub-tropical woodland), Dry Scrub, and Mesic
Forest at low elevations.
Conservation status. Critically Endangered B1ab(iii, v).
REFERENCES
Corcoran, M.R., Robbins, S.K., Hamilton, M.A. & Clubbe, C. (2008). Report
on the Status of Rondeletia buxifolia Vahl., Including a Germination and Cultivation
Protocol. Internal Report, Royal Botanic Gardens, Kew.
Govaerts, R., Ruhsam, M., Andersson, L., Robbrecht, E., Bridson, D.,
Davis, A., Schanzer, I. & Sonké, B. (2008). World Checklist of Rubiaceae. The
Board of Trustees of the Royal Botanic Gardens, Kew. Published on the
Internet; www.kew.org/wcsp/rubiaceae/. Downloaded on 10 November
2008.
GSPC (2002). Global Strategy for Plant Conservation. Published by the Secretariat of
the Convention on Biological Diversity. Available at: www.cbd.int/gspc/.
Hamilton, M.A., Clubbe, C., Robbins, S.K. & Bárrios, S. (2008). Plants and
habitats of the Centre Hills and Montserrat. In: Young, R.P. (ed.), A Biodiversity
Assessment of the Centre Hills, Montserrat. Durrell Conservation Monographs, Vol. 1,
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(2007). Report on the status of Acacia anegadensis Britton Including a Germination
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Clubbe, C. & Ivie, M. (eds.) (2005). Species Action Plan for the Montserrat oriole,
Icterus oberi, 2005–2009. Department of Agriculture, Montserrat.
Howard, R.A. (1974–1989). Flora of the Lesser Antilles: Leeward and Windward
Islands. 6 volumes. Arnold Arboretum, Harvard University, Jamaica Plain,
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and Windward Islands. vol. 6 Dicotyledoneae (Part. 3). Arnold Arboretum,
Harvard University, Jamaica Plain, USA. p. 456–457.
IUCN (2001). IUCN Red List Categories version 3.1. IUCN Species
Survival Commission, IUCN. Gland and Cambridge. Available at:
www.iucnredlist.org/static/categories_criteria.
IUCN (2008). 2008 IUCN Red List of Threatened Species. www.iucnredlist.org.
Downloaded on 10 November 2008.
Jones, M. (2008). Distribution and Conservation of Montserrat’s Endemic Flora.
Unpublished MSc thesis Imperial College, London.
Stow, S. (2008). Non-Native Plant Distribution in Montserrat: Conservation and Ecological
Aspects. Unpublished MSc thesis Imperial College, London.
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