Didymocarpus adenocarpus C.E.C.Fisch., Bull. Misc. Inform. Kew 1929: 253. 1929.

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 adenocarpus C.E.C.Fisch., Bull. Misc. Inform. Kew 1929: 253. 1929. Fig. 2A-G , Suppl. material 1: Fig. S1A, B

Holotype.

India. 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 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 1/3rd 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.

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 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).

Note.

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 ).

Distribution.

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).

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 florivory 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. 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).

Figures

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.