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Rediscovery of four narrow endemic Didymocarpus species (Gesneriaceae) from Mizoram, India, with revised species descriptions and lectotypifications

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Here we report the rediscovery of four endemic gesneriads from the state of Mizoram, India, after a span of 86 to 90 years since their last collection. The four species belong to the genus Didymocarpus Wall. and they are: D. adenocarpus , D. lineicapsa , D. parryorum , and D. wengeri . We present revised morphological descriptions, photographs, and designate lectotypes for D. parryorum and D. wengeri . During our study we came across several discrepancies between morphological characters assigned to these four species in the protologue and morphological characters present (or absent) in the type specimens and in plants recollected by us. We list these discrepancies in a section titled ‘amendments to protologue’. Based on the high endemicity and critical conservation status of all the four rediscovered species, we suggest that floristic studies along with large-scale biogeographic studies should be prioritized in the Indo-Burmese region.
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Rediscovery of Didymocarpus and lectotypications 1
Rediscovery of four narrow endemic Didymocarpus
species (Gesneriaceae) from Mizoram, India, with
revised species descriptions and lectotypifications
Naibi Shrungeshwara Prasanna1, Vinita Gowda1
1 Tropical Ecology and Evolution (TrEE) Lab, Department of Biological Sciences, Indian Institute of Science
Education and Research, Bhopal, 462066, India
Corresponding author: Vinita Gowda (gowdav@iiserb.ac.in)
Academic editor: Eric Roalson | Received 1 January 2020| Accepted 6 March 2020| Published 20 May2020
Citation: Prasanna NS, Gowda V (2020) Rediscovery of four narrow endemic Didymocarpus species (Gesneriaceae) from
Mizoram, India, with revised species descriptions and lectotypications. PhytoKeys 148: 1–19. https://doi.org/10.3897/
phytokeys.148.49772
Abstract
Here we report the rediscovery of four endemic gesneriads from the state of Mizoram, India, after a span
of 86 to 90 years since their last collection. e four species belong to the genus Didymocarpus Wall. and
they are: D. adenocarpus, D. lineicapsa, D. parryorum, and D. wengeri. We present revised morphological
descriptions, photographs, and designate lectotypes for D. parryorum and D. wengeri. During our study
we came across several discrepancies between morphological characters assigned to these four species in
the protologue and morphological characters present (or absent) in the type specimens and in plants recol-
lected by us. We list these discrepancies in a section titled ‘amendments to protologue’. Based on the high
endemicity and critical conservation status of all the four rediscovered species, we suggest that oristic
studies along with large-scale biogeographic studies should be prioritized in the Indo-Burmese region.
Keywords
C.E.C. Fischer, gesneriads, Lushai hills, nomenclature, Northeast India, pair-owered cyme, taxonomy
Introduction
e genus Didymocarpus Wall. was recently redened by Weber and Burtt (1998) and it
now consists of approximately 100 species that are distributed in India, Nepal, Bhutan,
southern China, Myanmar, ailand, Vietnam, Laos, Cambodia, Peninsular Malaysia,
PhytoKeys 148: 1–19 (2020)
doi: 10.3897/phytokeys.148.49772
http://phytokeys.pensoft.net
Copyright N.S. Prasanna, V. Gowda. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC
BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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Naibi Shrungeshwara Prasanna & Vinita Gowda / PhytoKeys 148: 1–19 (2020)
2
and Sumatra (Möller 2019). Phylogenetic studies by Palee et al. (2006) suggested the
geographic origin of the genus to be Malay Peninsula, although the northeast region of
India along with southern China accounts for more than half of known Didymocarpus
species (Möller et al. 2017; Möller 2019). India is known to have about 25 species of
Didymocarpus most of which are narrow endemics, restricted to relatively unexplored
areas of Northeast India (Prasanna et al. 2020). Within India, they are mainly distrib-
uted in the Indo-Burmese and Eastern Himalayan region with one species extending
into the Western Himalayas (Möller et al. 2017; Roy 2017).
Mizoram, formerly known as Lushai hills, is a small state in the northeast region of
India and was part of the state of Assam until 1972. It is bordered to the west by Bang-
ladesh and to its east and south by Myanmar, and it is part of the Indo-Burmese biogeo-
graphic region. Two of the earliest colonial-era plant collectors who can be credited with
collecting gesneriads in this region are Mrs Anne Parry (commonly cited as Mrs N.E.
Parry, pers. comm. H. Noltie) and Rev. W.J.L. Wenger. Parry is known to have accompa-
nied her husband, a British ocer, who was appointed as the Superintendent of Lushai
hills, Mizoram (then Assam) from 1924–1928 (Parry 1932). Wenger was a Baptist mis-
sionary who was sent to work at the Baptist church of Lunglei, Mizoram from 1922 to
1933 (Lalzama 1990). During their stay in Mizoram, both Parry and Wenger indepen-
dently made extensive plant collections within the northeast region of India and they
regularly sent their collections to Kew, where C. E. C. Fischer identied and described
these species and published oristic studies (Fischer 1928a–c, 1938). Here we report
rediscoveries of four of these species which were rst collected by either Parry or Wenger
and later described by Fischer. All four gesneriads reported here have not been collected
since either Parry or Wenger collected them in the early 1900s, despite recent revision-
ary, taxonomic, or oristic studies carried out in the Northeast of India (Sinha 2012;
Sinha and Datta 2016; Roy 2017). us, our rediscovery of the four species is clocked
at approximately 86 to 90 years since their last collection. Our observations suggest that
all four species are narrow endemics within the state of Mizoram, India, which was also
noted by earlier botanists like Wenger (Fischer 1928a) in the type description (Fig. 1).
e rediscovery of the four Didymocarpus species is an outcome of our concerted
eort to collect gesneriads from the Northeast of India for our ongoing revision of the
genus using a molecular phylogenetic approach. Although there have been several revi-
sionary studies of Didymocarpus from India (Sinha 2012; Sinha and Datta 2016; Roy
2017), these studies either omitted to list a species (e.g., D. lineicapsa) rediscovered by
us or we found errors in their taxonomic descriptions. We therefore utilized freshly
collected material which allowed us to make an in-depth exploration of morphological
characters that are taxonomically important but may be dicult to study in herbarium
specimens. We have made several amendments to the current taxonomic descriptions
of the four rediscovered species and these are given in a separate section titled ‘amend-
ments to protologue’ (see materials and methods below). Finally, our description and
taxonomic study of D. parryorum C.E.C.Fisch. and D. wengeri C.E.C.Fisch. also re-
sulted in our discovery that Fischer did not assign unambiguous types to both these
taxa. We therefore also assign lectotypes for both these species here.
Rediscovery of Didymocarpus and lectotypications 3
Figure 1. Map showing distribution records of the four rediscovered species of Didymocarpus Wall.
(Gesneriaceae) in Mizoram, India. Solid symbols indicate historical collection sites and open symbols
indicate extant populations. Hatched area represents southern Mizoram which is referred to as ‘South
Lushai hills’ in the protologues and historical collections.
Materials and methods
Field expeditions were carried out throughout the monsoon season (July to Septem-
ber), when the plants are known to ower, in the years 2017 and 2018. Type localities
of all Didymocarpus species in Mizoram and surrounding areas, including neighbor-
ing states, were visited. Due to logistic and nancial constraints, we were unable to
visit the eld sites in the dry season and therefore the taxonomic descriptions listed
here are based on rainy season forms only, although some species of Didymocarpus
have been known to have morphologically distinct seasonal forms (Weber and Burtt
1998; Nangngam and Maxwell 2013). We carried out extensive metadata collection
Naibi Shrungeshwara Prasanna & Vinita Gowda / PhytoKeys 148: 1–19 (2020)
4
for each species which included scoring of morphological, phenological, reproductive
and ecological characters such as ower opening time, pollinator visitation, and fruit
set. Morphological measurements of ve to six freshly dissected samples of each spe-
cies were taken using both a ruler and a digital calliper. Plant materials used in this
study include herbarium vouchers, spirit samples, and leaf tissues in silica for ongoing
molecular phylogenetic studies. All herbarium vouchers collected by us are deposited
at BHPL and duplicates will be deposited at ASSAM.
For taxonomic and nomenclatural work, we studied relevant Didymocarpus pro-
tologues along with following research materials: Kanjilal et al. 1939; Sinha 2012;
Sinha and Datta 2016; Roy 2017. Herbarium collections including type specimens
were consulted at ARUN, ASSAM, BHPL, CAL, E, K and BM and in online data-
bases (Chinese Virtual Herbarium: http://www.cvh.ac.cn/en; Global Plants: https://
plants.jstor.org/; Kew Herbarium Catalogue: http://apps.kew.org/herbcat/; Muséum
National d’Histoire Naturelle: https://science.mnhn.fr/; Smithsonian Institution:
https://www.si.edu/; e Linnaean Collections: http://linnean-online.org/; see Ap-
pendix 1). We evaluated the conservation status for the four rediscovered species
according to the latest International Union for Conservation of Nature guidelines
(IUCN 2019) using species distribution ranges and size of the populations we en-
countered during eldwork.
In this study, we have modied the terms that describe bracteoles and glands in all
the four species and we provide rationale wherever a dierent term from the protologue
has been used. Within Gesneriaceae, many authors including Fischer (1928a–c, Spare
and Fischer 1929) have used the term ‘bracts’ to indicate modied leaves present in
the inorescence. However, in pair-owered cymes of Didymocarpus, the morphology
of the bracts present at the base of the primary fork may vary from those subtending
the subsequent forks. To bring taxonomic clarity, we nd it necessary to dierentiate
between these two structures and here, we use the term ‘primary bracteoles’ to indicate
the modied leaves subtending the primary forks and ‘secondary bracteoles’ to indicate
all the bract-like structures subtending the subsequent forks within the inorescence.
We have added a new section ‘amendments to protologue’ which is an important
part of the updated taxonomic description for all the four rediscovered species. is
section has been added because we found that the morphological description of all
four rediscovered species of Didymocarpus did not match those given in their respective
protologues. Listing these discrepancies in a separate section allows us to avoid ambi-
guities in the description and therefore avoid future taxonomic confusions. In this sec-
tion, we list all morphological dierences we have noted between the protologue, type
specimen and fresh specimens of the same species. Descriptive discrepancies may have
resulted because Fischer wrote his taxonomic descriptions only from a limited number
of herbarium material shipped to him by Parry and/or Wenger from Northeast India.
us, the quality of the specimens may have resulted in ambiguous or erroneous de-
scriptions (e.g., refer to discrepancy in stem color of D. adenocarpus and indumentum
on corolla in D. lineicapsa).
Rediscovery of Didymocarpus and lectotypications 5
Results
Didymocarpus adenocarpus C.E.C.Fisch., Bull. Misc. Inform. Kew 1929: 253. 1929.
Fig. 2A–G, Suppl. material 1: Fig. S1A, B
Holotype. I. Assam (= Mizoram): Southern Lushai Hills, 4500 ft., Sept. 1928,
Rev. W.J.L. Wenger 239, K (K000820546!).
Revised description. Terrestrial or epilithic herbs, up to 35 cm tall. Stem
16×6mm, terete, light green, sparsely pubescent with 4–10 celled eglandular hairs.
Leaves 2–6 pairs, opposite and anisophyllous, decussate, terminal pair smaller in size,
membranous, exstipulate; petioles 1–8 cm long, pubescent with multicellular eglandu-
lar hairs as on stem; lamina 9–15 × 5–8 cm, oblong to orbicular, lamina separated un-
equally by midrib, base cordate to obliquely cordate, apex acute to acuminate, margin
coarsely crenate-dentate; dorsal surface green, sparsely pubescent with multicellular
eglandular hairs; ventral surface pale green, densely pubescent along veins but sparsely
pubescent otherwise; densely dotted with minute globose, pale-brown glistening pig-
ment glands (in dried specimen); midrib with 6–10 lateral veins on either side, sunken
above, raised below, secondary veins more prominent. Inorescence 1 to 4, peduncu-
late, axillary, pair-owered cymes (many-owered), usually arising only from the axils
of the 1–2 uppermost pairs of leaves, cyme with up to 20 owers; primary bracte-
oles present, 4 × 7 mm, opposite, suborbicular, apex mucronate, glabrous, translucent
white, veins visible when dried; secondary bracteoles (within the cyme) present at each
dichotomous fork, 4 × 6 mm, suborbicular, apex mucronate glabrous, whitish, veins
visible when dried. Inorescence usually hidden below the leaves, pendent; peduncle
3–4 cm long, light green, lower part sparsely pubescent with multicellular eglandular
hairs, upper part glabrous; pedicel ca. 5 mm long, slender, glabrous; Calyx 0.8–1 mm
long, fused, narrowly funnel shaped, with 5–9 short, broadly triangular teeth with a
visible vein running into each, glabrous, whitish, translucent; Corolla 2.8–3.5 cm ×
0.5–0.8 cm, tubular with a slight bend, infundibuliform towards mouth; tube whitish
at base, purple towards lobes; corolla bi-lipped, total 5 lobes, 0.5 × 0.5 cm, subor-
bicular, glabrous, purplish with whitish outer edge, the 3 lower lobes larger than the
2 upper lobes, ventral part of the corolla tube and lobes striated. Stamens 2, inserted
at 1/3rd of the length of the tube from the mouth of the corolla, anthers dorsixed,
coherent by adaxial surfaces; laments 1–1.2 cm, glabrous, whitish; staminodes 2 or 3,
inserted lower than the stamens, tip bifurcated, the third when present below the oth-
ers and much shorter. Disc up to 2 mm long, tubular with undulating upper margin,
glabrous, persistent. Gynoecium 2.1– 2.2 cm, ovary linear, slightly widened upwards,
glabrous, covered with globose yellow glands; stigma peltate, glabrous. Capsule linear,
brown, 3–3.5 cm long, dotted with glistening yellowish glands. Seeds very minute,
pale-reddish-brown, fusiform, acute at both ends.
Amendments to protologue. Upon examining fresh specimens (Fig. 2 and Suppl.
material 1: Fig. S1A, B), we noted that the stem color is light green (brown in proto-
Naibi Shrungeshwara Prasanna & Vinita Gowda / PhytoKeys 148: 1–19 (2020)
6
Figure 2. Didymocarpus adenocarpus C.E.C.Fisch. A habitat B habit C complete plant with inores-
cence D pair-owered cyme E ower, side view F glands on abaxial surface of leaves G oral dissection
(from left to right): primary bracteole, secondary bracteole, sepal, gynoecium, open oral tube showing
fused anthers, gynoecium surrounded by persistent calyx. Photographs by NSP.
Rediscovery of Didymocarpus and lectotypications 7
logue), corolla tube is whitish at base, purple towards lobes (white tinged with pink in
protologue), and bracteoles are translucent white (reddish brown in protologue). Leaf
apex is acute to acuminate (acute or abruptly acutely cuspidate in protologue) and in-
orescence is typical pair-owered cyme (central 1-ower and trichotomous branching
in protologue). We found stigma to be glabrous (pubescent in protologue).
Note. D. adenocarpus is similar to D. purpureobracteatus W.W.Sm. but diers from
it in having slightly cordate leaves (rounded or oblique in D. purpureobracteatus),
sparsely pubescent peduncle (glabrous in D. purpureobracteatus), and glabrous pistil
(sparsely puberulent in D. purpureobracteatus).
Distribution. Historically, D. adenocarpus is known from southern Mizoram.
However, in this study we located one extant population at Reiek Tlang in Mamit dis-
trict of northern Mizoram (specimen numbers: VG2018MZ2589, VG2018MZ2590,
VG2018MZ2592).
Habitat. Grows on moist loamy banks in partially shaded areas of tropical wet
evergreen forests.
Phenology. Flowering in August to September, fruiting in September to December.
Ecology. We observed that D. adenocarpus has a tubular calyx which can retain and
immerse the buds in water (see Suppl. material 1: Fig. S1B). In other gesneriads such as
Aeschynanthus and Chrysothemis, a similar character was referred to as watery calyces, and
was suggested as a mechanism to reduce orivory by insects (Carlson and Harms 2007).
Conservation status and preliminary IUCN assessment. D. adenocarpus is
known from only four specimens collected from southern Mizoram, India. To the best
of our knowledge there have been no further collections of D. adenocarpus until this
study, which brings the time until its current rediscovery up to 87 years. We surveyed
multiple potential locations in Mizoram and we could not locate any population in
southern Mizoram. e extant population is limited to an area of about 15 km2 in
Reiek Tlang hills, Mamit district, which is in northern Mizoram. Although it is a
community protected forest, with limited anthropogenic disturbance, the population
has only 300 mature individuals. erefore, based on the criterion C2a(i) of IUCN
guidelines (IUCN 2019), we propose that the species should be considered as endan-
gered (EN).
Didymocarpus lineicapsa (C.E.C.Fisch.) B.L.Burtt, Notes Roy. Bot. Gard. Edin-
burgh 21(4): 187. 1954.
Fig. 3, Suppl. material 1: Fig. S1D
Basionym. Trisepalum lineicapsa C.E.C.Fisch., Bull. Misc. Inform. Kew 1928 (7): 276
(1928).
Holotype. I. Assam (= Mizoram): Lushai Hills, Aijal (= Aizawl), 1225 m,
September 1927, Mrs N.E. Parry No.79, K (K000820539!).
Naibi Shrungeshwara Prasanna & Vinita Gowda / PhytoKeys 148: 1–19 (2020)
8
Revised description. Terrestrial or epilithic herbs, to 15 cm tall, 1 to 4 stems aris-
ing from the same rhizome. Stems 3 to 15 cm long, 2–4 mm wide at base, erect, dark
green, terete, densely tomentose with 3 to 4 celled eglandular hairs and sparsely inter-
spersed globular, yellow pigment glands. Leaves 4–6 pairs, opposite and anisophyl-
lous, decussate, often whorled at the top; petioles up to 2.7 cm long, terete, densely
Figure 3. Didymocarpus lineicapsa (C.E.C.Fisch.) B.L.Burtt A habitat B habit C complete plant with
emerging inorescence. Old stem with dehisced capsules from previous season indicated by arrow D leaf
adaxial and abaxial surface E inorescence F ower (inset - tridentate calyx lobe) G oral dissection from
left to right: open oral tube showing fused anthers, gynoecium with disc and ovary. Photographs by NSP.
Rediscovery of Didymocarpus and lectotypications 9
tomentose as on stem, sparsely covered with globular, yellow pigment glands; lamina
3–10 cm × 1.5–3.5 cm, lanceolate to narrowly elliptic, lamina separated unequally
by midrib, base oblique, apex acute; margin dentate, often entire towards the base,
dorsal surface dark green, densely strigose with short eglandular hairs, ventral surface
light green, strigose with yellow-glandular (colour as observed in dried specimen) and
eglandular hairs, hairs more dense along the veins; midrib with 8–10 secondary veins
on each side, sunken above, raised below. Inorescence 1 to 4, axillary, spreading from
upper leaves forming the whorl, erect, pair-owered cymes (many-owered), usually
arising only from the axils of the 1–2 uppermost pairs of leaves; peduncle 1.5–6 cm
long, up to 5 mm thickness (slender), sparsely covered with multicellular glandular
and eglandular hairs; pedicel up to 2 cm long, pale pink, covered with multicellular
glandular and eglandular hairs; bracteoles absent. Calyx 5–6.5 mm long, maroon col-
oured, tripartite; two segments up to 0.5 mm wide, linear-lanceolate, tip acute, free to
base, held ventrally along the lower side of the corolla tube; third segment tridentate,
up to 1.2 mm wide, held dorsal to the corolla tube, central tooth wider than the two
lateral teeth; dorsal surface glandular-pubescent; ventral surface glabrous. Calyx not
persistent. Corolla 1.5–1.8 cm long, ca.2.2 mm wide, tubular, light purple at base but
dark purple towards throat and lobes. Corolla tube usually held perpendicular to the
pedicel; corolla tube glabrous at base but with multicellular glandular hairs below the
lobes, hairs sometimes present also on lower part of the lobes, corolla tube glabrous on
the inside; corolla bi-lipped, total 5 lobes; upper lobes 2, 1.6 × 3.1 mm, apices round-
ed; lower lobes 3, 6.5–7.5 × 3.5–4.5 mm, spreading at right angles to the upper lobes,
middle lobe apex rounded, lateral lobes apices obtuse. Stamens 2, lament inserted
at about 1/3rd of the length of the corolla tube; laments 5–6 mm, glabrous, lament
dark purple near the anthers, anthers dorsixed, coherent by adaxial surfaces, glabrous;
staminodes absent. Disc up to 2 mm, tubular, yellowish, glabrous, upper margin un-
dulate, persistent. Gynoecium 10–11 mm, ovary white, linear, indistinct from stipe,
glabrous; style ca. 2 mm glabrous; stigma dark purple, capitate. Capsule 1.5–2.5 cm
long, linear/straight, glabrous, longitudinal dehiscence. Seeds data not available.
Amendments to protologue. e protologue by Fischer indicates that D. linei-
capsa has bracts at each inorescence fork (“bracteae ad furcas”). However, we observed
that the holotype and other subsequent collections by Parry, Wenger as well as our
own collections (Fig. 3), do not have any bracts or bracteoles within the inorescence.
e protologue also mentions that D. lineicapsa has a glabrous corolla tube, however
all specimens including the type specimen have been found to be sparsely covered with
multicellular, glandular hairs towards the lobes.
Note. D. lineicapsa is similar to D. graciliorus R.W.MacGregor & W.W.Sm. in
its vegetative morphology but diers due to the absence of bracteoles (ovate bracteoles
present in D. graciliorus) and linear-lanceolate, tripartite calyx lobes (oblong 5-partite
lobes in D. graciliorus).
Distribution. e type locality of D. lineicapsa is near Aizawl in northern Mizo-
ram and subsequent collections are known from throughout the state. In our expedi-
tions, we could not locate any populations in its type locality or historical collection
Naibi Shrungeshwara Prasanna & Vinita Gowda / PhytoKeys 148: 1–19 (2020)
10
sites. However, we found three scattered populations in Mamit district of northern
Mizoram which is at least 40 km away from its type locality (specimen numbers: VG-
2018MZ2581, VG2018MZ2584, VG2018MZ2585, VG2018MZ2596).
Habitat. ese plants grow on steep clayey banks along the roads in partially shad-
ed, tropical wet evergreen forests.
Phenology. Flowering in August to September, fruiting in October to January.
Conservation status and preliminary IUCN assessment. D. lineicapsa is known
from only seven specimens collected from Mizoram, India, and it has not been recol-
lected for the past 89 years. We carried out collection expeditions in the years 2017
and 2018 to the type location (Aizawl, Mizoram) as well as other historical collection
sites (Fig. 1). All of the historical locations have undergone dramatic urbanization in
the last eight decades and we could not nd any population of D. lineicapsa in any of
these sites. Instead, we found only three disjunct populations of D. lineicapsa with a
total of less than 1000 individuals, in Mamit district, Mizoram. All the extant popula-
tions are located in rapidly degrading, fragmented forests that do not fall under feder-
ally protected areas, and therefore we propose the conservation status of this species as
vulnerable (VU) following the criteria D2 of IUCN guidelines (IUCN 2019).
Didymocarpus parryorum C.E.C.Fisch., Bull. Misc. Inform. Kew. 1928(4):
142.1928.
Fig. 4, Suppl. material 1: Fig. S1C, E
Lectotype (designated here). I. Assam (= Mizoram), Lunglei district, Lushai hills
at Sairep, 5000 ft., July 1926, Mrs N.E. Parry 7, K (K000820535!).
Lectotypication. e protologue by Fischer indicates the specimen that was stud-
ied for the description of the species as “I. Assam, South Lushai Hills at Sairep,
1700 m. July, Mrs N E.Parry 7”. During our study we located ve dierent sheets at
Kew herbarium having the same collection number and locality as quoted above. Hill-
iard and Burtt (1995) noted that Parrys numbers do not refer to individual collections,
but instead they refer to unique species that she had recognized in the eld. Weber et
al. (2000) recognized three of these specimens as type material, but failed to designate
a lectotype. One of these specimens, with a barcode number K000820535, has the
collector’s original label which mentions ‘July 1926’ as the collection date. e author’s
note on the label matches the note that Fischer has quoted in the protologue: “grows on
rocky clis, leaves pale-green, silvered when dry, calyx light yellow, corolla orange red”.
Since this is the only specimen where the collection number, month, and the author’s
note matches the protologue, we designate K000820535 as the lectotype here.
Revised description. Terrestrial or epilithic herbs, up to 20 cm tall, total height in-
cluding inorescence ca. 25 cm. Rhizome 1–2 × 0.5–1.0 cm. Stem 3–10 × 3.5–8 mm,
erect, dark brown to light green, terete, pubescent with eglandular hairs, interspersed
Rediscovery of Didymocarpus and lectotypications 11
Figure 4. Didymocarpus parryorum C.E.C. Fisch. A habitat B habit C complete plant with inorescence
D inorescence E oral dissection from left to right: primary bracteoles (above), secondary bracteoles (be-
low), corolla tube, calyx with gynoecium, open oral tube with anther (fusion of anther lost in dissection
of ower) F mature fruit G glands on the lower surface of leaves. Photographs by NSP.
Naibi Shrungeshwara Prasanna & Vinita Gowda / PhytoKeys 148: 1–19 (2020)
12
with yellowish cruciform pigment glands (in dried specimen). Leaves 1 – 4 pairs, op-
posite, anisophyllous, decussate, arrangement tufted in close pairs, terminal pair is
reduced, exstipulate; petioles 4–9 cm long, light brown to light green, pubescent as on
stem, interspersed with yellowish cruciform pigment glands (in dried specimen); lam-
ina 6–12 × 5–10 cm, orbicular to ovate, base cordate to obliquely cordate, apex acute
to subobtuse, margins crenate to serrate, dorsal surface dark green, pubescent with eg-
landular hairs, ventral surface light green, veins pubescent and intervals sparsely pilose,
hairs eglandular, abaxial surface is covered with yellow to brownish cruciform pigment
glands (in dry specimen); midrib with 6–8 secondary veins in either side, basal 3–4
pairs palmate, sunken above, raised below. Inorescence 1–4, pedunculate, erect, axil-
lary, pair-owered dichasial cymes, arising from the axils of the 1–2 uppermost pairs of
leaves, cyme with 12–16 owers; primary bracteoles present, 8 × 4 mm, greenish-yel-
low, opposite, ovate, apex subacute, glabrous, abaxial surface covered with small cru-
ciform pigment glands, secondary bracteoles yellow, present at the base of each cyme
unit, 6 × 3 mm, thick, veins visible in dried specimens; orange owers contrast against
yellow calyces; peduncle 10–25 cm long, up to 2 mm wide, brownish at the base, light
green towards apex, pubescent with eglandular hairs, sparsely covered with minute
cruciform pigment glands as on bracteoles; pedicel 4–12 mm long, greenish-yellow,
glabrous, pigment glands absent. Calyx up to 1 cm long, bright yellow, linear lanceo-
late, apex acute, lobes 5, free to base, conspicuously veined, glabrous, thick, persistent.
Corolla 1.3–2.2 cm long, ca. 1.5 mm wide, tubular, tip infundibuliform, glabrous,
corolla tube dorsally orange while ventral section of the corolla tube with a light yellow
stripe running along the length of the tube, corolla lobes bilabiate, orange, glabrous,
orbicular, upper lobes 2, 1.5 × 2 mm; lower lobes 3, 4 × 3 mm, spreading at right an-
gles to the upper lobes, central lobe wider than the 2 lateral lobes. Stamens 2, oblong,
glabrous, inserted near the throat of the corolla tube, anthers dorsixed, coherent by
adaxial surfaces; laments 4–5 mm long, yellowish orange, glabrous; staminodes 2, 2
mm long, linear. Disc up to 1.2 mm, tubular with undulating upper margin, yellowish,
glabrous, persistent. Gynoecium ca. 2 cm, ovary greenish yellow, linear, glabrous; style
ca. 0.5 cm, glabrous; stigma capitate, green. Capsules 17–24 mm, linear, glabrous,
orthocarpic. Seeds minute, ellipsoid, glabrous, muricate.
Amendments to protologue. Upon examining the historical specimens and our
fresh collections (Fig. 4) we believe that the indumentum on the stem is better de-
scribed as pubescent rather than as strigose. Similarly, we describe corolla lobe shape as
orbicular and not suborbicular (as mentioned in the protologue).
Note. Diers from D. tristis Craib in having larger, bright yellow colored bracte-
oles and sepals respectively (maroon bracteoles and sepals in D. tristis). In addition, D.
parryorum has orbicular to ovate leaves (oblong to lanceolate in D. tristis) and smaller
corolla (1.3–2.2 cm in D. parryorum, 2–2.4 cm in D. tristis).
Distribution and vernacular name. Historically, D. parryorum is known from
only two districts (Lunglei and Lawngtlai) of southern Mizoram. We could locate the
species only from the type locality (Sairep village in Lunglei district, specimen num-
bers: VG2018MZ2522, VG2018MZ2528, VG2018MZ2529, VG2018MZ2546). In
Sairep, the plant is known as ‘Chhakzhau’ in local Mizo language.
Rediscovery of Didymocarpus and lectotypications 13
Habitat. is plant is generally found growing on moist loamy banks in partially
shaded tropical wet evergreen forests.
Phenology. Flowering in July to September, fruiting in August to December.
Conservation status and preliminary IUCN assessment. Didymocarpus parryo-
rum is historically known from only two localities in southern Mizoram, India: Lun-
glei and Lawngtlai districts. It has not been collected for the past 90 years, until this
study in 2018, when we found it growing in its type locality. e extant population
is restricted to a small patch of less than 10 km2 in a rapidly degrading forest and it
has about 500 mature individuals. A village road passes through the plant’s habitat,
further threatening its population. erefore we propose that the species should be
considered as critically endangered (CR) as per the B2ab criteria of IUCN guidelines
(IUCN 2019).
Didymocarpus wengeri C.E.C.Fisch., Bull. Misc. Inform. Kew. 1928(2): 74. 1928.
Fig. 5, Suppl. material 1: Fig. S1F
Lectotype (designated here). I, Assam (= Mizoram): South Lushai Hills, 2500 ft,
comm. September 1927, Rev. W. J. L. Wenger 1, K (K000820530!).
Lectotypication. ere are only four historical collections of D. wengeri, two
of which are specimens collected by Wenger, and the third by Parry. ere is a fourth
specimen at CAL, collected from southern Mizoram, which does not have the collec-
tors’ details, but there is a possibility that it may be from Wenger or Parry’s collection, as
the specimen was received from Kew herbaria and the script matches Fischers writing.
In the protologue, Fischer indicated the specimen he studied for the description of the
species as “Assam, South Lushai Hills, 2400 ft., Rev. W.J.L. Wenger’’, but he did not
mention any specic collection date or number. We could not locate any specimen col-
lected by Wenger at South Lushai hills at 2400 feet elevation in any herbaria (ARUN,
ASSAM, CAL, E, K and BM), where Wenger’s specimens are known to exist. ere is
a specimen collected by Wenger (Wenger 1) at Kew (K000820530), without a collec-
tion date but with a note “comm. Sept 1927”, presumably written by Fischer. e label
clearly mentions that the specimen was collected at ‘2500 ft.’ In their study, Weber et
al. (2000) considered K000820530 as a type but they did not designate the status of the
type: “Type: INDIA, Mizoram (previously Assam), South Lushai Hills, 2500 ft., IX.
1927. Wenger (K)”. We suggest that the ‘2400 ft.’ in Fischer’s protologue possibly is a
typographical error, which has also been suggested by Weber et al. (2000), wherein the
elevation has been cited as ‘2500 ft.’ by them and not as ‘2400 ft.’, as featured in the
protologue. Given these observations, we designate K000820530 as the lectotype here.
Revised description. Terrestrial or epilithic herbs, 7 cm tall, total height including
inorescence ca. 10 cm. Stem 5–60 × 3 mm, subacaulascent to 6 cm, terete, light green
to dark maroon, villose with 4–10 celled glandular hairs (rarely eglandular), densely
covered with cruciform pigment glands. Leaves 1–4 pairs, opposite and anisophyllous,
decussate, terminal pair smaller in size, arrangement tufted in close pairs, exstipulate;
petioles 2–5 cm long, villose with 4–10 celled eglandular hairs, glands cruciform, den-
Naibi Shrungeshwara Prasanna & Vinita Gowda / PhytoKeys 148: 1–19 (2020)
14
sity and structure similar to the ones on stem; lamina 1.8–6 × 1.5–6 cm, orbicular,
base cordate and often unequal, apex sub-obtuse, margin crenate to serrate with mul-
ticellular hairs; dorsal surface dark green, villous with eglandular hairs, ventral surface,
Figure 5. Didymocarpus wengeri C.E.C. Fisch. A habitat B habit C plant with inorescence D leaf adaxial
and abaxial surface E glands on the lower surface of leaves F owers (lateral view) G owers (frontal view)
H oral dissection from left to right: opened oral tube, calyx with gynoecium. Photographs by NSP.
Rediscovery of Didymocarpus and lectotypications 15
densely villose along veins but sparsely villose otherwise; lower lamina covered with
cruciform, dark brown pigment glands (in dried specimen), dense along the (mid-
rib) and veins; midrib with 5–8 lateral veins on either side, basal 3–5 veins palmate,
sunken above, raised below. Inorescence 1 to 5, pedunculate, axillary, pair-owered
cymes usually arising only from the axils of the 1–2 uppermost pairs of leaves, cyme
with 6–16 owers; primary bracteoles present, 2 × 1 mm, opposite, lanceolate, reddish
brown, sometimes with eglandular hairs, below densely covered with cruciform glands;
secondary bracteoles (within the cyme) present at each dichotomous fork, 1–2 mm
in diam., orbicular, reddish brown, sparsely covered with eglandular hairs, hirsute on
upper surface, glandular hairs on lower surface; peduncle 5–15 cm long, dark maroon,
primary axis is sparsely covered with both glandular and eglandular hairs, secondary
axis with glandular hairs, cruciform pigment glands present near the base of the prima-
ry axis and at the fork; pedicel 2–10 mm long, glandular hairs present. Calyx 5 lobes,
1.5–3.5 mm long, free to base, linear lanceolate, glabrous, dark brown to maroon,
persistent. Corolla 0.8–2.2 cm long, ca. 2–3 mm wide, tubular, tip infundibuliform,
orange-red at the base and yellow ventrally from throat to mouth, yellow extending
into the lower lobes, corolla bi-lipped, total 5 lobes, yellow, upper 2 lobes fused with
2 × 2 mm, orbicular; lower lobes 3, 7 × 4 mm, orbicular, spreading at right angles to
the upper lobes, middle/central lobe wider than the 2 lateral lobes, glabrous. Stamens
2, inserted near the throat of the corolla tube; laments 3–4 mm long, glabrous, la-
ment yellowish, anthers oblong, dorsixed, coherent by adaxial surfaces, pubescent;
staminodes absent. Disc up to 1.5 mm, tubular with undulating upper margin, green-
ish yellow, glabrous, persistent. Gynoecium 10–12 mm, ovary greenish yellow, linear,
indistinct from stipe, glabrous; style ca. 4 mm glabrous; stigma yellow, capitate. Cap-
sule 1.5–2.5 cm long, linear, glabrous, dehiscence longitudinal. Seeds data decient.
Amendments to protologue. e protologue mentions that disc is absent at the
base of the ovary. Fresh specimens show the presence of small tubular disc at the base
of the ovary (Fig. 5 H).
Note. is species is similar to D. margaritae W.W.Sm., but diers from it in having
cruciform brownish glands on abaxial surface of the leaves (glands absent in D. margari-
tae) and has yellow colored corolla lobes (orange corolla lobes in D. margaritae). Pedun-
cle with glandular hairs in D. wengeri, whereas peduncle of D. margaritae is glabrous.
Distribution. All collections of D. wengeri, including the type specimen, are from
southern Mizoram. In our study, we located a population from Tuipang in the Saiha dis-
trict of southern Mizoram (specimen numbers: VG2018MZ2556, VG2018MZ2557,
VG2018MZ2558). is locality corresponds to where Parry had collected specimens in
1928. In addition, we found a second population in the Lawngtlai district of southern Mi-
zoram (specimen numbers: VG2018MZ2568, VG2018MZ2569, VG2018MZ2570).
Habitat. Growing on steep clay banks along the roads in partially shaded, tropical
wet evergreen forests.
Phenology. Flowering in August to September, fruiting in October to January.
Conservation status and preliminary IUCN assessment. D. wengeri is currently
known from only two locations in southern Mizoram, India: Saiha district and Lawngt-
lai district. Only one population each has been located in these two districts and they
Naibi Shrungeshwara Prasanna & Vinita Gowda / PhytoKeys 148: 1–19 (2020)
16
are separated by a distance of 135 km. is rediscovery is after a span of 87 years and
a total of 52 individuals were found during the owering season of 2018. In the pro-
tologue, Fischer has quoted Wenger’s (collector) note as “apparently scarce, at least in
these hills, for I have only found one small patch on a steep clayey bank”, indicating that
these plants were very rare even when they were rst collected. Considering the small,
fragmented population and rapidly degrading habitat, the species should be considered
as critically endangered (CR) as per C2a(i) of the IUCN guidelines (IUCN 2019).
Discussion
Northeast India, and the state of Mizoram in particular, has been oristically underex-
plored, and our study highlights the need for more careful and extensive biodiversity
studies in this region. e rediscovery of three species close to their type localities and
the collection of one away from its type locality (D. adenocarpus) suggests that con-
servation of the narrow endemics is critical and understanding their biology should
be prioritized. e geographic placement of Mizoram (between Bangladesh and My-
anmar) also indicates that cross-border biogeographic studies should be carried out to
understand the dispersal and evolution of plants in this region.
Acknowledgements
We would like to thank the Ministry of Human Resource Development (MHRD) and
the Science and Engineering Research Board (SERB) for research funds to VG.; IISER
Bhopal for Infrastructure support and fellowship to NSP; Sibbald Trust (RBGE) and
Nellie D. Sleeth Scholarship Endowment Fund (NDSSEF) of Gesneriad Society, USA,
for grants to NSP towards eldwork and herbarium consultation. We thank the State
Forest Department of Mizoram for research permit; ABD, ARUN, ASSAM, BHPL,
BM, BSHC, C, CAL, E, K, M, P, and TCD for herbarium consultation; and Henry J.
Noltie (RBGE) for sharing genealogy of Parry. Finally, we gratefully acknowledge the
critical comments by John L. Clark (the Lawrenceville School) and the reviewer, which
helped us to improve the manuscript.
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18
Appendix 1
List of Didymocarpus specimens examined
Didymocarpus adenocarpus C.E.C.Fisch.: INDIA, Mizoram. S. Lushai hills, Sep-
tember 1928, Rev. W.J.L. Wenger 239, K (K000820546); S. Lushai hills, September
1931, Rev. W.J.L. Wenger 347, K (K000820547); S.Lushai hills, September 1931,
Rev. W.J.L. Wenger 347, E (E00627876); Sairep, September 1927, Mrs N.E. Parry,
No.251, K; Reiek Tlang, 25 August 2018, Prasanna N.S., VG2018MZ2589, BHPL;
Reiek Tlang, 25 August 2018, Prasanna N.S., VG2018MZ2590, BHPL; Reiek Tlang,
25 August 2018, Prasanna N.S., VG2018MZ2592, BHPL.
Didymocarpus purpureobracteatus W.W.Sm.: CHINA, Yunnan. S. of Red Riv-
er, without date, Henry 9746A, US (US00056528); San Teo Chen, without date, A.
Henry 9189, NYBG (NY00063234).
Didymocarpus lineicapsa (C.E.C.Fisch.) B.L.Burtt: INDIA. Mizoram: S.
Lushai, August 1928, Rev. W.J.L. Wenger, No.238, E (E00627917); Aizawl, September
1927, Mrs N.E. Parry, No.79, K (K000820539); Aizawl, March 1928, Mrs N.E. Par-
ry, No.79, K (K000820540); Aizawl, 1928, Mrs N.E. Parry, No.79. K (K000820541);
S. Lushai, August 1928, Rev. W.J.L. Wenger, No.238 K; Hmuifang, August 1927, Mrs
N.E. Parry, No.262, K; Hmuifang, August 1927, Mrs N.E. Parry, No.259, K; Mamit,
Reiek Village, August 2018, Prasanna N.S., VG2018MZ2581, BHPL; Mamit, Reiek
Tlang, August 2018, Prasanna N.S., VG2018MZ2584, BHPL; Mamit, Reiek Tlang,
August 2018, Prasanna N.S., VG2018MZ2585, BHPL; Mamit, Luanpawl to Dawpui
road, August 2018, Prasanna N.S.,VG2018MZ2496, BHPL.
Didymocarpus graciliorus R.W.MacGregor & W.W.Sm.: MYANMAR. S.
Shan States: Keng Tung, August 1909, MacGregor, R.W., No.714, K, (K000820542).
Didymocarpus parryorum C.E.C.Fisch.: INDIA. Mizoram. Lunglei, Sairep, July
1926, Mrs N.E. Parry No.7, K (K000820535); Sairep, 1928, Mrs N.E. Parry No.7,
K, (K000820536); Sairep, December 1927, Mrs N.E. Parry No.7, K, (K000820537);
Phongpui, March 1927, Mrs N.E. Parry No.NA (2 sheets) K; N.Vanlaphai,’comm
January 1928, Mrs N.E. Parry CAL (CAL0000019176); Sairep, August 2018,
Prasanna N.S., VG2018MZ2522, BHPL; Sairep, August 2018, Prasanna N.S.,
VG2018MZ2528, BHPL; Sairep, August 2018, Prasanna N.S., VG2018MZ2529,
BHPL; Sairep, August 2018, Prasanna N.S., VG2018MZ2546, BHPL.
Didymocarpus tristis Craib: THAILAND, Chanthaburi, Khao Khitchakut, 27
Aug 2012, Middleton et al, 5673, E.
Didymocarpus wengeri C.E.C.Fisch.: INDIA. Mizoram. S. Lushai, August
1931, Rev. W.J.L. Wenger (collectors number not mentioned), E, (E00627988);
South Lushai hills, (without date, comm. September 1927), Rev. W.J.L. Wenger,
1, K, (K000820530); Lushai hills, Tuipang, January 1928, Mrs N.E. Parry, 452, K,
(K000820531); S. Lushai, without collectors name, and date, CAL (CAL0000019172);
Saiha, August 2018, Prasanna N.S., VG2018MZ2556, BHPL; Saiha, August 2018,
Prasanna N.S., VG2018MZ2557, BHPL; Saiha, August 2018, Prasanna N.S., VG-
Rediscovery of Didymocarpus and lectotypications 19
2018MZ2558, BHPL; Lawngtlai, August 2018, Prasanna N.S., VG2018MZ2568,
BHPL; Lawngtlai, August 2018, Prasanna N.S., VG2018MZ2569, BHPL; Lawngtlai,
August 2018, Prasanna N.S., VG2018MZ2570, BHPL.
Didymocarpus margaritae W.W.Sm.: CHINA, Yunnan. Szemoa. Henry, A.,
#12380b, US, (US00056517).
Supplementary material 1
Figure S1
Authors: Naibi Shrungeshwara Prasanna, Vinita Gowda
Data type: Multimedia
Explanation note: A Underside of D. adenocarpus C.E.C.Fisch. plant showing inores-
cence hidden under leaves B Watery calyx of D. adenocarpus C.E.C.Fisch. C Lateral
view of D. parryorum C.E.C.Fisch. ower showing color stripe along the oral tube
D Tridentate calyx lobe of D. lineicapsa (C.E.C.Fisch.) B.L.Burtt E Inorescence
of D. parryorum C.E.C.Fisch. F Inorescence of D. wengeri C.E.C.Fisch. Photo-
graphs by NSP.
Copyright notice: is dataset is made available under the Open Database License
(http://opendatacommons.org/licenses/odbl/1.0/). e Open Database License
(ODbL) is a license agreement intended to allow users to freely share, modify, and
use this Dataset while maintaining this same freedom for others, provided that the
original source and author(s) are credited.
Link: https://doi.org/10.3897/phytokeys.148.49772.suppl1
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Until recently the genus Didymocarpus Wall. (Gesneriaceae) was used in an unwarrantably wide sense and included more than 180 species. It has now been remodelled and restricted to around 70 species. Of these, 18 species and one variety are known to occur in Thailand. To clarify the relationships among Thai species of Didymocarpus we sequenced the internal transcribed spacers (ITS) of nuclear ribosomal DNA (nrDNA) from a sample of 23 taxa, including 15 from Thailand, four from China, three from Malaysia and one from Bhutan. Seventeen morphological characters were coded for all 23 taxa and optimized onto a retention index (RI) reweighted maximum parsimony (MP) tree. The phylogenetic analyses suggested that Didymocarpus taxa formed a strongly supported monophyletic clade, with several supported subclades. The combination of molecular phylogeny and optimization of morphological characters suggests the presence of three distinct groups: the first, corresponding to Didymocarpus sect. Elati Ridl., includes plants with tall stems, yellow or white flowers and one-celled conoid or two-celled headed pigment glands; the other two groups, which represent Didymocarpus sect. Didymocarpus, both contain plants with dwarfed stems and violet or purple flowers, but are distinguished by the presence of both four-celled conoid or onecelled globose glands in one, and the absence in the other. Optimization of geographical locality onto the phylogeny led us to propose the hypothesis that, based on this sample, the geographical origin of Didymocarpus is the Malay Peninsula, and the ancestral corolla colour is white/yellow. Subsequent dispersal northward through southern and northern Thailand to China and Bhutan was accompanied by the evolution of a purple/violet corolla colour.
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Zusammenfassung Als Grundlage für eine zukünftige Revision von Didymocarpus WALL, (im emendierten Umfang von WEBER & BURTT 1998) wird eine Liste der Sektionen und der relevanten Arten (einschließlich infraspezi-fischer Taxa, nomina nuda und illegitimer Namen) präsentiert. Die Information zu den einzelnen Arten umfaßt das Zitat der Originalpublikation, die Typen, Verbreitung (soweit bekannt), Hinweise auf Abbildungen und neuere Literatur und ggf. Anmerkungen. Die von CLARKE (1874) beschriebenen Arten D. andersonii, D. aurantiacus, D. hookeri und D. mortomi werden lektotypifiziert. D. macrocalyx KRAENZL. wird zu D. primulifolius D.DON gestellt. Arten mit unklarer Position (aber möglicherweise Didymocarpus) und zu exkludierende Arten sind durch einen bzw. zwei Sterne gekennzeichnet. Alle bisher der Gattung Didymocarpus zugeordneten Artnamen werden (unter Angabe der gegenwärtigen Stellung) in einem Appendix zusammengefaßt (genauere Angaben und Typen bei VITEK & al. 2000). Abstract Basic taxonomic information is supplied that will be useful for a future revision of Didymocarpus WALL. (in the emended sense of WEBER & BURTT 1998). The paper includes a list of sectional, specific and infras-pecific names (including nomina nuda and illegitimate names) relevant for Didymocarpus in its present definition, with reference to the original description, type, distribution (provisional, according to available records), illustrations, and recent literature. Notes are given where appropriate. Lectotypes are proposed for D. andersonii, D. aurantiacus, D. hookeri, and D. mortomi described by CLARKE (1974). One species, D. macrocalyx KRAENZL., is reduced to D. primulifolius D.DON. Species of uncertain position (but possibly Didymocarpus) and species to be excluded are earmarked by one and two asterisks, respectively. All spe-cific epithets ever used in Didymocarpus are summarized in the appendix, with indication of the current position of the species (for detailed references and types see VITEK & al. 2000).
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Protective floral structures may evolve in response to the negative effects of floral herbivores. For example, water calyces--liquid-filled, cup-like structures resulting from the fusion of sepals--may reduce floral herbivory by submerging buds during their development. Our observations of a water-calyx plant, Chrysothemis friedrichsthaliana (Gesneriaceae), revealed that buds were frequently attacked by ovipositing moths (Alucitidae), whose larvae consumed anthers and stigmas before corollas opened. Almost 25% of per-plant flower production was destroyed by alucitid larvae over two seasons, far exceeding the losses to all other floral herbivores combined. Experimental manipulation of water levels in calyces showed that a liquid barrier over buds halved per-flower alucitid egg deposition and subsequent herbivory, relative to buds in calyces without water. Thus, C. friedrichsthaliana's water calyx helps protect buds from a highly detrimental floral herbivore. Our findings support claims that sepal morphology is largely influenced by selection to reduce floral herbivory, and that these pressures can result in novel morphological adaptations.
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Didymocarpus rodgeri (incl. var. siamensis) is reduced to a synonym of D. aureoglandulosus (SE India, Burma and Thailand); D. subalternans var. curvicapsa (Nepal–Sikkim) is raised to specific rank, and a new species, D. triplotrichus (Darjeeling distr. and Sikkim), is described. Lysionotus himalayensis is redetermined and reduced to synonymy under L. serratus; as a result L. atropurpureus, which name it had recently superseded, is reinstated. Aeschynanthus kingii and A. levipes are both transferred to Lysionotus, while L. wardii and L. gracilipes are reduced to synonymy under L. pubescens. Notes and new records are provided for L. confertus and L. serratus var. pterocaulis.
The flora of Lushai hills.
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Fischer CEC (1938) The flora of Lushai hills. Records of Botanical Survey of India 12(2): 75-161.
Didymocarpus (Gesneriaceae) in Thailand.
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Weber A, Burtt BL (1998) ("1997") Remodelling of Didymocarpus and associated genera (Gesneriaceae). Beiträge zur Biologie der Pflanzen 70: 293-363.