India. Assam (= Mizoram): Southern Lushai Hills, 4500 ft., Sept. 1928, Rev. W.J.L. Wenger 239, K (K000820546!).

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 eglandular hairs as on stem; lamina 9–15 × 5–8 cm, oblong to orbicular, lamina separated unequally 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 pigment glands (in dried specimen); midrib with 6–10 lateral veins on either side, sunken above, raised below, secondary veins more prominent. Inflorescence 1 to 4, pedunculate, axillary, pair-flowered cymes (many-flowered), usually arising only from the axils of the 1–2 uppermost pairs of leaves, cyme with up to 20 flowers; primary bracteoles 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. Inflorescence 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, suborbicular, 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 1/3^rd of the length of the tube from the mouth of the corolla, anthers dorsifixed, coherent by adaxial surfaces; filaments 1–1.2 cm, glabrous, whitish; staminodes 2 or 3, inserted lower than the stamens, tip bifurcated, the third when present below the others 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.

Upon examining fresh specimens (Fig. 2 and Suppl. material 1: Fig. S1A, B), we noted that the stem color is light green (brown in protologue), 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 inflorescence is typical pair-flowered cyme (central 1-flower and trichotomous branching in protologue). We found stigma to be glabrous (pubescent in protologue).

Figure 2. 

Didymocarpus adenocarpus C.E.C.Fisch. A habitat B habit C complete plant with inflorescence D pair-flowered cyme E flower, side view F glands on abaxial surface of leaves G floral dissection (from left to right): primary bracteole, secondary bracteole, sepal, gynoecium, open floral tube showing fused anthers, gynoecium surrounded by persistent calyx. Photographs by NSP.

D. adenocarpus is similar to D. purpureobracteatus W.W.Sm. but differs 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).

Historically, D. adenocarpus is known from southern Mizoram. However, in this study we located one extant population at Reiek Tlang in Mamit district of northern Mizoram (specimen numbers: VG2018MZ2589, VG2018MZ2590, VG2018MZ2592).

Grows on moist loamy banks in partially shaded areas of tropical wet evergreen forests.

Flowering in August to September, fruiting in September to December.

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 florivory by insects (Carlson and Harms 2007).

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. The 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. Therefore, based on the criterion C2a(i) of IUCN guidelines (IUCN 2019), we propose that the species should be considered as endangered (EN).

Trisepalum lineicapsa C.E.C.Fisch., Bull. Misc. Inform. Kew 1928 (7): 276 (1928).

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

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.

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 1/3^rd 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.

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.

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).

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).

These plants grow on steep clayey banks along the roads in partially shaded, tropical wet evergreen forests.

Flowering in August to September, fruiting in October to January.

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).

(designated here). India. Assam (= Mizoram), Lunglei district, Lushai hills at Sairep, 5000 ft., July 1926, Mrs N.E. Parry 7, K (K000820535!).

The protologue by Fischer indicates the specimen that was studied for the description of the species as “India. Assam, South Lushai Hills at Sairep, 1700 m. July, Mrs N E.Parry 7”. During our study we located five different sheets at Kew herbarium having the same collection number and locality as quoted above. Hilliard and Burtt (1995) noted that Parry’s numbers do not refer to individual collections, but instead they refer to unique species that she had recognized in the field. 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. The author’s note on the label matches the note that Fischer has quoted in the protologue: “grows on rocky cliffs, 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.

Terrestrial or epilithic herbs, up to 20 cm tall, total height including inflorescence 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 with yellowish cruciform pigment glands (in dried specimen). Leaves 1 – 4 pairs, opposite, 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); lamina 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 eglandular 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. Inflorescence 1–4, pedunculate, erect, axillary, pair-flowered dichasial cymes, arising from the axils of the 1–2 uppermost pairs of leaves, cyme with 12–16 flowers; primary bracteoles present, 8 × 4 mm, greenish-yellow, opposite, ovate, apex subacute, glabrous, abaxial surface covered with small cruciform pigment glands, secondary bracteoles yellow, present at the base of each cyme unit, 6 × 3 mm, thick, veins visible in dried specimens; orange flowers 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 lanceolate, 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 angles 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 dorsifixed, coherent by adaxial surfaces; filaments 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.

Figure 4. 

Didymocarpus parryorum C.E.C. Fisch. A habitat B habit C complete plant with inflorescence D inflorescence E floral dissection from left to right: primary bracteoles (above), secondary bracteoles (below), corolla tube, calyx with gynoecium, open floral tube with anther (fusion of anther lost in dissection of flower) F mature fruit G glands on the lower surface of leaves. Photographs by NSP.

Upon examining the historical specimens and our fresh collections (Fig. 4) we believe that the indumentum on the stem is better described as pubescent rather than as strigose. Similarly, we describe corolla lobe shape as orbicular and not suborbicular (as mentioned in the protologue).

Differs from D. tristis Craib in having larger, bright yellow colored bracteoles 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).

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 numbers: VG2018MZ2522, VG2018MZ2528, VG2018MZ2529, VG2018MZ2546). In Sairep, the plant is known as ‘Chhakzhau’ in local Mizo language.

This plant is generally found growing on moist loamy banks in partially shaded tropical wet evergreen forests.

Flowering in July to September, fruiting in August to December.

Didymocarpus parryorum is historically known from only two localities in southern Mizoram, India: Lunglei 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. The 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. Therefore we propose that the species should be considered as critically endangered (CR) as per the B2ab criteria of IUCN guidelines (IUCN 2019).

(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.

Figure 5. 

Didymocarpus wengeri C.E.C. Fisch. A habitat B habit C plant with inflorescence D leaf adaxial and abaxial surface E glands on the lower surface of leaves F flowers (lateral view) G flowers (frontal view) H floral dissection from left to right: opened floral tube, calyx with gynoecium. Photographs by NSP.

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 H).

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.

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).