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Gardens’ Bulletin Singapore 68(1): 1–63. 2016
doi: 10.3850/S2382581216000016
A revision of Aeschynanthus (Gesneriaceae)
in Singapore and Peninsular Malaysia
D.J. Middleton
Herbarium, Singapore Botanic Gardens, National Parks Board,
1 Cluny Road, Singapore 259569
david_middleton@nparks.gov.sg
ABSTRACT. The genus Aeschynanthus Jack is revised for Singapore and Peninsular Malaysia.
Four species for Singapore and fourteen species for Peninsular Malaysia are recognised, keys
to the species are given, all names are typied, and detailed descriptions of all species are
provided. Conservation assessments are provided for all species. Eleven names are lectotypied
here and one epitype is designated.
Keywords. Conservation assessments, Didymocarpoideae, identication key, lectotypications
Introduction
Aeschynanthus Jack is a large and variable genus with around 160 species from Sri
Lanka and India through southern China and Southeast Asia to New Guinea and
the Solomon Islands (Weber, 2004; Middleton, 2007). The last complete account of
the genus was by Clarke (1883) who included 64 species. More recently, regional
revisions have been published for China (Wang et al., 1998), Thailand (Middleton,
2007), Cambodia, Laos and Vietnam (Middleton, 2009), and India (Bhattacharyya &
Goel, 2015). Checklists have been published for Singapore (Turner, 1993; Chong et
al., 2009), Peninsular Malaysia (Turner, 1997), Myanmar (Kress et al., 2003), Sulawesi
(Mendum & Atkins, 2003), and Sumatra (Tjitrosoedirdjo et al., 2009). Several of these
checklists are now rather out-of-date due to the discovery of new species and/or due to
the synonymisation of names.
A general background to research on Aeschynanthus was given in Middleton
(2007). For Singapore and Peninsular Malaysia the last comprehensive treatment
was by Ridley (1923), in which 14 species of Aeschynanthus for the Malay Peninsula
were recognised. The checklists for Singapore (Turner, 1993; Chong et al., 2009) both
included four native species; the checklist for Peninsular Malaysia (Turner, 1997)
included 17 species (one with two varieties).
In preparation for a revision of Gesneriaceae for the Flora of Peninsular
Malaysia the genus has been revised for Peninsular Malaysia and for neighbouring
Singapore. Fourteen species are recognised. All fourteen species are in Peninsular
Malaysia and four of these are also in Singapore. One of the species in Singapore
is presumed extinct there and the other three are considered Critically Endangered
(Chong et al., 2009; Williams, 2014).
Gard. Bull. Singapore 68(1) 2016
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An infrageneric classication is not followed in this paper pending a more
thorough investigation of the genus using molecular sequence data to compare the
morphological characters. A preliminary study by Denduangboripant et al. (2001)
found that a phylogeny based on ITS data did not reveal monophyletic clades that
corresponded to the existing sections.
All provisional IUCN Conservation Assessments given here, calculated using
the methodology of IUCN (2012), are for the species throughout their range rather
than only for Peninsular Malaysia and/or Singapore. Additional comments are given
under each species when the local situation differs from the global.
Morphological Characters
A more detailed discussion of morphological characters is given in Middleton (2007)
and references given therein. Here is a brief discussion of the range of characters found
in the species in Singapore and Peninsular Malaysia.
All species are epiphytes or occasionally lithophytes. Species such as
Aeschynanthus speciosus Hook., A fulgens Wall. ex R.Br. and A. rhododendron Ridl.
are large with robust stems that arch or hang due to their own weight. Others such as
Aeschynanthus albidus (Blume) Steud., A. angustifolius (Blume) Steud., A. fecundus
P.Woods, A. longicaulis Wall. ex R.Br., A. longiorus (Blume) A.DC., A. obconicus
C.B.Clarke in A.DC. & C.DC. and A. wallichii R.Br. are generally more delicate
and are more pendulous, although usually not loosely hanging (as, for example, is
found in A. gracilis Parish ex C.B.Clarke from Thailand to NE India). Aeschynanthus
dischidiodes (Ridl.) D.J.Middleton has often been reported as growing from ants’ nests
in trees. Aeschynanthus pulcher (Blume) G.Don, A. radicans Jack and probably A.
volubilis Jack either have the habit of the more delicate species previously mentioned,
sometimes with long pendent stems, or creep over tree trunks and branches or rocks,
rooting at the nodes. The erect habit of species such as Aeschynanthus andersonii
C.B.Clarke and A. humilis Hemsl. from Thailand is not found in Singapore or
Peninsular Malaysia.
The leaves of most species are opposite but are always in whorls of three or
more in Aeschynanthus speciosus and A. angustifolius. In Aeschynanthus angustifolius
the leaf blades are extraordinarily variable in shape (see discussion under that species).
In the other species the leaves are generally ovate to elliptic and not particularly
variable in shape and size. In most species the margins are entire but they are distinctly
toothed in Aeschynanthus dischidioides, sometimes slightly so in A. angustifolius, and
strongly undulate in A. speciosus. All species are shortly petiolate and the blades are
mostly coriaceous, more rarely thinner and softer.
The structure of the inorescence is discussed in Middleton (2007) and references
therein. In Singapore and Peninsular Malaysia all species either lack a peduncle or the
peduncle is so short as to appear absent. The owers are, therefore, either axillary and
solitary, axillary and appearing fasciculate, or subterminal and clustered. In all species
in Singapore and Peninsular Malaysia the bracts are fairly small, simple and linear.
The calyx consists of ve lobes free to the base (Aeschynanthus angustifolius,
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Aeschynanthus in Singapore and Peninsular Malaysia
A. dischidiodes, A. fecundus, A. longicaulis, A. longiorus and A. speciosus), or a very
short tube with ve long lobes (A. albidus), or of a narrow or somewhat widening tube
that is around half or more of the length of the calyx with either obvious or obscure
lobes at margin (A. fulgens, A. pulcher, A. radicans, A. rhododendron and A. volubilis),
or of an open cup-shaped calyx with obscure lobes at the margin (A. obconicus and A.
wallichii). The colour of the calyx can either be quite xed within a species (it always
appears to be red in A. obconicus for example) or very variable within a species (dark
purple or red to green in A. pulcher for example). The calyx shape and size is very
variable in a number of species.
The corolla is zygomorphic, tubular, and weakly to quite strongly curved. The
limb is 2-lipped with the upper lip 2-lobed and the lower lip 3-lobed. Visitation by
animals has not been observed in most species but pollination is assumed to be by
birds for most, possibly all, species (see Middleton (2007) for further discussion). The
corolla is red, orange, yellow or green, or a combination of these colours, in the species
in Singapore and Peninsular Malaysia. Flower colour is highly diagnostic for most
species although is often very subjectively recorded on herbarium specimen labels
when it is described at all.
All Aeschynanthus species are strongly protandrous with the stamens withering
as the style elongates and the stigma enlarges. There are four stamens in two pairs with
the anthers of each pair fused at their tips. In Singapore and Peninsular Malaysia no
species have all four anthers fused together as is found in Aeschynanthus chiritoides
C.B.Clarke from Vietnam to NE India. The gynoecium consists of the stipe, the
ovary, the style and the stigma. The stipe is short in all species but rather longer in
Aeschynanthus rhododendron. The dimensions given in the descriptions below reect
the measurements made on specimens to hand. It should be borne in mind though that
the absolute and relative lengths of the parts of the gynoecium are enormously variable
depending on the age of the ower.
The fruit is a long and narrow capsule in all species. Dehiscence is loculicidal.
The basal portion of the capsule, the stipe of the unfertilised gynoecium, lacks seeds
and is generally short except in Aeschynanthus rhododendron where it forms an
obvious narrow stalk.
The seeds have been the principal source of characters for earlier infrageneric
classications of Aeschynanthus (see Middleton (2007) and references cited therein).
The seeds of Aeschynanthus species consist of the seed grain, one apical appendage
and one or more hilar appendages. Seeds with two hilar appendages are not found
anywhere in Malesia (Mendum et al., 2001). The apical appendage points towards the
base of the capsule. In Singapore and Peninsular Malaysia there is one hilar appendage
in Aeschynanthus angustifolius, A. fulgens, A. longiorus, A. obconicus, A. pulcher,
A. radicans, A. rhododendron, A. speciosus, A. volubilis and A. wallichii and three or
more hilar appendages in A. albidus, A. dischidioides, A. fecundus and A. longicaulis.
Of those with only one hilar appendage, the appendage is long and liform in all
species except Aeschynanthus rhododendron where it is short and stout. In a number
of species there is a curious cluster of inated cells, termed bubble cells, at the hilar
end of the seed. These are found in A. obconicus, A. pulcher, A. radicans, A. volubilis
and A. wallichii.
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Materials studied
Herbarium material was studied from the following herbaria: A, AAU, BISH, BKF,
BM, C, CGE, E, FI, G, G-DC, K, KEP, KLU, K-W, L, LAE, M, MEL, MICH, NY, P,
PSU, SING, SINU, TI, U, UKMB, US (herbarium codes from Thiers (continuously
updated)). All specimens cited have been seen unless otherwise indicated with nv. A
single standardised name is given for those collectors whose name appears in more
than one form, including when abbreviated to initials, on different collections.
The dimensions given in the descriptions are for dried material for vegetative
characters and rehydrated or fresh material for oral characters. Dimensions given
closely resemble those given in Middleton (2007) for some of the taxa due to the
paucity of material collected since and because Malaysian material was used in the
Thai descriptions when the Thai material was insufcient (as it was for several taxa).
The vegetation types given in the Habitat and Ecology sections below follow
notes on the specimens and observations in the eld using the vegetation classication
of Saw (2010).
Aeschynanthus Jack
Trans. Linn. Soc. London 14: 42 (1823); C.B.Clarke in A.DC. & C.DC., Monogr. Phan.
5(1): 18 (1883); Ridley, Fl. Malay Penins. 2: 496 (1923); Wang, Fl. Reipubl. Popularis
Sin. 69: 498 (1990); Middleton, Edinburgh J. Botany 64: 368 (2007); Middleton,
Edinburgh J. Botany 66: 393 (2009). – TYPE: Aeschynanthus volubilis Jack.
Trichosporum D.Don, Edinburgh Philos. J. 7: 82 (1822), nom. rej; Blume, Bijdr.
Fl. Ned. Ind. (1826). – TYPE: Trichosporum parviorum D.Don (= Aeschynanthus
parviorus (D.Don) Spreng.), lectotype designated by Middleton (2007).
Rheitrophyllum Hassk., Flora 25 (2): beibl. 56 (1842). – TYPE: Rheitrophyllum
subverticillatum Hassk. (= Aeschynanthus angustifolius (Blume) Steud.).
Oxychlamys Schltr., Bot. Jahrb. Syst. 58: 286 (1923). – TYPE: Oxychlamys pullei
Schltr. (= Aeschynanthus oxychlamys Mendum)
Euthamnus Schltr., Bot. Jahrb. Syst. 58: 284 (1923). – TYPE: Euthamnus papuanus
Schltr. (= Aeschynanthus papuanus (Schltr.) B.L.Burtt)
Micraeschynanthus Ridl., Fl. Malay Penin. 5: 324 (1925). – TYPE: Micraeschynanthus
dischidioides Ridl. (= Aeschynanthus dischidioides (Ridl.) D.J.Middleton)
Epiphytic herbs or subshrubs with erect, arching or pendulous stems, these sometimes
rooting along their lengths when in contact with a suitable substrate. Leaves opposite or
verticillate, pedicellate; blades coriaceous to distinctly eshy, more rarely herbaceous,
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Aeschynanthus in Singapore and Peninsular Malaysia
simple, margins entire to weakly crenate or weakly dentate, sometimes somewhat
undulate, venation pinnate but more often than not obscure. Inorescence an axillary
few-owered cyme, or owers solitary in the axils of leaves, or a pseudoterminal
cluster. Flowers strongly protandrous. Calyx of 5 sepals, these free or variously fused
into a tube for part or most of length, when fused the whole tubular or cup-shaped.
Corolla zygomorphic, tubular, widening towards lobes, curved to various degrees,
sometimes distinctly inated at the base, glabrous to variously pubescent outside and
inside; with 5 lobes, these consisting of a 2-lobed upper lip, 2 lateral lobes and a lower
lobe; very variable in colour but most frequently red, orange, yellow or green (or
combination of these) and then often with other darker or lighter patterning. Stamens
4, in 2 pairs, attached to the inside of the corolla tube and occupying the space in
the upper curve of the owers, included or exserted from corolla tube when mature;
vestigial staminode present; anthers of each pair attached by their apices (occasionally
all 4 attached together outside this region). Disk present, annular to dentate. Pistil
developing as laments wither and reex downwards and also occupying the space in
the upper curve of the corolla tube, consisting of a sterile stipe at the base, the fertile
ovary section, the style and the peltate stigma; ovules many, anatropous. Fruit a long
narrow capsule which opens loculicidally by two valves. Seeds many, tiny, with short
to long appendages at both ends.
About 160 species from India and southern China through Southeast Asia and Malesia
to the Solomon Islands. Fourteen species in Peninsular Malaysia, four species in
Singapore (of which one is considered to be nationally extinct).
Key to Aeschynanthus species recorded from Singapore
1a. Corolla predominantly green or yellowish, inside with coarse multicellular hairs;
seeds with many hairs at one end ..................................................... 1. A. albidus
1b. Corolla red, inside without coarse multicellular hairs; seeds with only 1 hair at
each end ............................................................................................................. 2
2a. Calyx < 7 mm long, in a wide and shallow cup or saucer, much wider at apex than
at base .......................................................................................... 14. A. wallichii
2b. Calyx > 10 mm long, tube mostly parallel to corolla tube, apex not much wider
than base ............................................................................................................ 3
3a. Ovary, stipe and style densely pubescent; leaves pubescent beneath .....................
...................................................................................................... 10. A. radicans
3b. Ovary with sessile glands, only stipe and style pubescent; leaves usually glabrous,
more rarely sparsely pubescent beneath ........................................... 9. A. pulcher
