Didymocarpus lineicapsa (C.E.C.Fisch.) B.L.Burtt, Notes Roy. Bot. Gard. Edinburgh 21(4): 187. 1954.

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

Didymocarpus lineicapsa (C.E.C.Fisch.) B.L.Burtt, Notes Roy. Bot. Gard. Edinburgh 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.

India. Assam (= Mizoram): Lushai Hills, Aijal (= Aizawl), 1225 m, September 1927, Mrs N.E. Parry No.79, K (K000820539!).

Revised description.

Terrestrial or epilithic herbs, to 15 cm tall, 1 to 4 stems arising 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 interspersed globular, yellow pigment glands. Leaves 4-6 pairs, opposite and anisophyllous, decussate, often whorled at the top; petioles up to 2.7 cm long, terete, densely 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. Inflorescence 1 to 4, axillary, spreading from upper leaves forming the whorl, erect, pair-flowered cymes (many-flowered), 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 coloured, 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 rounded; 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, filament inserted at about 1/3rd of the length of the corolla tube; filaments 5-6 mm, glabrous, filament dark purple near the anthers, anthers dorsifixed, coherent by adaxial surfaces, glabrous; staminodes absent. Disc up to 2 mm, tubular, yellowish, glabrous, upper margin undulate, 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.

The protologue by Fischer indicates that D. lineicapsa has bracts at each inflorescence 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 inflorescence. The 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. graciliflorus R.W.MacGregor & W.W.Sm. in its vegetative morphology but differs due to the absence of bracteoles (ovate bracteoles present in D. graciliflorus ) and linear-lanceolate, tripartite calyx lobes (oblong 5-partite lobes in D. graciliflorus ).

Distribution.

The type locality of D. lineicapsa is near Aizawl in northern Mizoram and subsequent collections are known from throughout the state. In our expeditions, we could not locate any populations in its type locality or historical collection 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: VG2018MZ2581, VG2018MZ2584, VG2018MZ2585, VG2018MZ2596).

Habitat.

These plants grow on steep clayey 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. lineicapsa is known from only seven specimens collected from Mizoram, India, and it has not been recollected 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 find 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 populations are located in rapidly degrading, fragmented forests that do not fall under federally protected areas, and therefore we propose the conservation status of this species as vulnerable (VU) following the criteria D2 of IUCN guidelines ( IUCN 2019).

Figures

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.

Figure 3. Didymocarpus lineicapsa (C. E. C. Fisch.) B. L. Burtt A habitat B habit C complete plant with emerging inflorescence. Old stem with dehisced capsules from previous season indicated by arrow D leaf adaxial and abaxial surface E inflorescence F flower (inset - tridentate calyx lobe) G floral dissection from left to right: open floral tube showing fused anthers, gynoecium with disc and ovary. Photographs by NSP.