Didymocarpus wengeri C.E.C.Fisch., Bull. Misc. Inform. Kew. 1928(2): 74. 1928.
Prasanna, Naibi Shrungeshwara & Gowda, Vinita, 2020, Rediscovery of four narrow endemic Didymocarpus species (Gesneriaceae) from Mizoram, India, with revised species descriptions and lectotypifications, PhytoKeys 148, pp. 1-19: 1
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|Didymocarpus wengeri C.E.C.Fisch., Bull. Misc. Inform. Kew. 1928(2): 74. 1928.|
Didymocarpus wengeri C.E.C.Fisch., Bull. Misc. Inform. Kew. 1928(2): 74. 1928. Fig. 5View Figure 5, Suppl. material 1: Fig. S1F
(designated here). India, Assam (= Mizoram): South Lushai Hills, 2500 ft, comm. September 1927, Rev. W. J. L. Wenger 1, K (K000820530!).
There are only four historical collections of D. wengeri , two of which are specimens collected by Wenger, and the third by Parry. There is a fourth specimen at CAL, collected from southern Mizoram, which does not have the collectors’ 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 Fischer’s 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 specific collection date or number. We could not locate any specimen collected 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. There is a specimen collected by Wenger (Wenger 1) at Kew (K000820530), without a collection date but with a note " comm. Sept 1927", presumably written by Fischer. The 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.
Terrestrial or epilithic herbs, 7 cm tall, total height including inflorescence 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, density 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 multicellular hairs; dorsal surface dark green, villous with eglandular hairs, ventral surface, densely villose along veins but sparsely villose otherwise; lower lamina covered with cruciform, dark brown pigment glands (in dried specimen), dense along the (midrib) and veins; midrib with 5-8 lateral veins on either side, basal 3-5 veins palmate, sunken above, raised below. Inflorescence 1 to 5, pedunculate, axillary, pair-flowered cymes usually arising only from the axils of the 1-2 uppermost pairs of leaves, cyme with 6-16 flowers; 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 primary 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; filaments 3-4 mm long, glabrous, filament yellowish, anthers oblong, dorsifixed, coherent by adaxial surfaces, pubescent; staminodes absent. Disc up to 1.5 mm, tubular with undulating upper margin, greenish yellow, glabrous, persistent. Gynoecium 10-12 mm, ovary greenish yellow, linear, indistinct from stipe, glabrous; style ca. 4 mm glabrous; stigma yellow, capitate. Capsule 1.5-2.5 cm long, linear, glabrous, dehiscence longitudinal. Seeds data deficient.
Amendments to protologue.
The 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 HView Figure 5).
This species is similar to D. margaritae W.W.Sm., but differs from it in having cruciform brownish glands on abaxial surface of the leaves (glands absent in D. margaritae ) and has yellow colored corolla lobes (orange corolla lobes in D. margaritae ). Peduncle with glandular hairs in D. wengeri , whereas peduncle of D. margaritae is glabrous.
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 district of southern Mizoram (specimen numbers: VG2018MZ2556, VG2018MZ2557, VG2018MZ2558). This locality corresponds to where Parry had collected specimens in 1928. In addition, we found a second population in the Lawngtlai district of southern Mizoram (specimen numbers: VG2018MZ2568, VG2018MZ2569, VG2018MZ2570).
Growing on steep clay banks along the roads in partially shaded, tropical wet evergreen forests.
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 Lawngtlai district. Only one population each has been located in these two districts and they are separated by a distance of 135 km. This rediscovery is after a span of 87 years and a total of 52 individuals were found during the flowering season of 2018. In the protologue, 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 first 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).
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