Lepidagathis decumbens N. Dhatchan. & S. Soosairaj, 2022

Dhatchanamoorthy, Narayanasamy, Karthikeyan, Chinnasamy, Raja, Prakasam, Soosairaj, Sebastian & Balachandran, Natesan, 2022, Lepidagathis decumbens N. Dhatchan. & S. Soosairaj, sp. nov. (Acanthaceae), a new species from Tamil Nadu, India, Adansonia (3) 44 (24), pp. 321-329 : 322-326

Lepidagathis decumbens N. Dhatchan. & S. Soosairaj , sp. nov.

( Fig. 1 ; Table 1 ).

Lepidagathis decumbens sp. nov. resembles L. diffusa C.B. Clarke , but differs in having erect and decumbent habit, short internodes, long unilateral spikes, multicelled glandular hairs, sericeous floral parts and ovate-suborbicular seeds ( Table 1 ).

TYPE MATERIAL. — India. Tamil Nadu, Dharmapuri district, Thippampatti village , 12°14’53.304”N, 78°16’31.980”E, alt. c. 358 m, 25.X.2013, N. Dhatchanamoorthy 1295 (holo-, HIFP! • iso-, RHT!) .

ETYMOLOGY. — The species epithet “ decumbens ” describes the erect and geniculate habit of the plant.

DISTRIBUTION. — Lepidagathis decumbens sp. nov. is endemic to Dharmapuri district of Tamil Nadu, South India.

PHENOLOGY. — Flowering and fruiting from October to January. ECOLOGY. — Dry, red, barren and gravel mixed soils at an elevation of 300-400 m a.s.l. Associated with Andrographis serpyllifolia (Vahl) Wight , Aristida hystrix L.f., Corbichonia decumbens (Forssk.) Exell , Cyanotis tuberosa (Roxb.) Schult. & Schult.f. , Indigofera cordifolia Roth , I. linnaei Ali , Mollugo stricta L. Oldenlandia umbellata L., Oropetium thomaeum (L.f.) Trin., Senna italica Mill. and Tribulus subramanyamii P.Singh, G.S.Giri &V.Singh.

CONSERVATION STATUS. — This species occurs in an area of only about one hectare which lies between the segments of Eastern Ghats. The population has about 50 mature individuals, there is a possibility that the species may occur in nearby areas with similar ecological niches. However, these habitats are yet to be explored. The species is currently categorized as ‘Data Deficient’ following IUCN (2020) criteria and categories.

ADDITIONAL SPECIMEN EXAMINED. — India. Tamil Nadu, Dharmapuri district, Thippampatti village , 12°14’53.304”N, 78°16’31.980”E, 30.XI.2015, N. Dhatchanamoorthy, P. Raja & S. Soosairaj 2125 (SJC) .

DESCRIPTION

Erect-decumbent herb, perennial, with woody rootstock; branches up to 30 cm long, stem terete, young branches purplish, scabrid-glabrescent; internodes up to 1 cm long. Leaves opposite, linear-oblong to lanceolate, 0.8-2.5 × 0.3-0.5 cm, sessile, attenuate at base, entire at margins, apex curved and spiny; lateral nerves 3-5, prominent at abaxial surface, indistinct on adaxial surface, scabrous hairy on both sides, leaf scars prominent. Inflorescence axillary, spike unilateral, 3-6 × 1-1.5 cm. Bracts lanceolate, 1.2 × 0.3 cm, truncate at base, acute-acuminate at apex, spiny, outer surface glandular sericeous, inner surface sericeous, margin with long hispid hairs in lower 2/3, scabridulous at apex, midnerve prominent. Bracteoles lanceolate, 10 × 2.8 mm, acute-acuminate, glandular sericeous, midnerve prominent, laterals actinodromus, spiny at apex. Calyx 5 lobed, 8.5-9 mm long, minutely mucronate-spiny at apex, outer surface glandular sericeous, inner surface sericeous; posterior sepal broader, lanceolate, 8.5 × 3.5 mm, acute-acuminate; anterior sepals 2, connate up to middle, lanceolate, 8.5 × 1.5 mm; lateral sepals 2, linear, 8.5 × 1.2 mm, smaller than the others. Corolla white, c. 1.4 cm long, 1 cm across, hispid on outer surface except at base; sparsely hispid inside, purple with yellow spots along the ribs, lobes 5, glabrous inside, upper 2 lobes connate, obtuse, emarginate, lower 3 lobes, median broader than the lateral, obtuse, emarginate, margins sinuate, lateral lobes obtuse. Stamens 4, didynamous, dorsifixed, filament 2-3.5 mm long, sparsely glandular; anthers ovoid-oblong, c. 2 mm long, bearded, pollen 3-colporate, 41.81-48.85 × 28.22-32.26 µm, exine thin, c. 3.52 µm, reticulate. Disk annular; ovary ovoid, c. 1.2 × 1 mm, glabrous; 2-locular; ovules 2 in each cell; style slender, 6 mm long, hispidglandular at base; stigma slightly bifid, glabrous. Capsules shorter than calyx, ovate-oblong, c. 6 × 4 mm, glabrous. Seeds 2, ovoid-suborbicular, c. 3.5 × 3 mm, densely short mucilaginous hairy.

TAXONOMIC NOTES

The distinguished characters between the species were compared ( Table 1 ) with their images ( Fig. 2 ). Lepidagathis diffusa is a prostrate herb, with up to 3 cm long internodes, leaf nerves prominent on both surfaces, spike dense, ovoid-oblong at upper axils, and the seeds are oblong with long mucilaginous hairs whereas the new species is erect-decumbent herb, with up to 1 cm short internodes, leaves linear-oblong and nerves indistinct on adaxial surface, spike oblong (unilateral) up to 6 cm long at leaf scar axils, floral parts glandular sericeous, and the seeds are ovoid-suborbicular with short mucilaginous hairs ( Fig. 1 ).

Anatomically, leaves of Lepidagathis diffusa have simple and non-glandular hairs, cystoliths on both surfaces, anisocytic and diacytic types of stomata. The cross section (CS) of stem shows vascular bundles (VB) surrounded by 2 layers of sclerenchyma cells, uniseriate medullary rays, absence of intra-xylary phloem and presence of acicular crystals at pith. Anatomy of L. decumbens leaves shows simple and four lobed glandular foliage hairs, cystoliths occur only on abaxial surface, epidermal peel has only diacytic type of stomata. The CS of stem shows VB surrounded by 3 layers of sclerenchyma cells, uni- and biseriate medullary rays, presence of intra-xylary phloem, and absence of acicular crystals ( Fig. 3 ; Table 2) at pith. The SEM images of seeds from the two species clearly represented the difference in size and shape, particularly the base of seeds and the length of hydrophilic hairs ( Fig. 4 ). In all, clear differences in morphology, anatomy, reproductive features and SEM images are strongly evidenced to confirm this Lapidagathis was new and named as L. decumbens .

Figures

FIG. 1. — Lepidagathis decumbens N. Dhatchan. & S. Soosairaj, sp. nov. (drawing by P. Raja): A, flowering branch; B, inflorescence; C, bract; D, bracteole; E, flower; F, posterior sepal; G, lateral sepal; H, anterior sepals; I, corolla split open; J, stamen; K, pistil; L, capsule; M, seed. Scale bars: A, B, 1 cm; C, D, F-H, 5 mm; E, I, K, L, 2 mm; J, 1 mm; M, 3 mm.

FIG. 2. — A-D, Lepidagathis diffusa C.B.Clarke;E-H, L. decumbens N. Dhatchan.& S. Soosairaj,sp.nov.:A, E, habit;B, F, inflorescence;C, G, flower;D, H, seed.

FIG. 3. — Anatomical comparisons: A-C, Lepidagathis diffusa C.B.Clarke: A, CS of midrib; B, stomata; C, CS of stem; D-F, L. decumbens N. Dhatchan. & S. Soosairaj, sp. nov.: D, CS of midrib; E, four lobed glandular hair; F, CS of stem. Abbreviations: ADE, adaxial epidermis; ABE, abaxial epidermis; Co, cortex; E, epidermis; MS, mesophyll; Pa, parenchyma; Pi, pith; St, stomata; Tri, trichome; VB, vascular bundle; Xy, xylem. Scale bars: A, C, F, 175 µm; D, 28 µm.

FIG. 4. — SEM images of seeds of: A, Lepidagathis diffusaC.B.Clarke with long hydrophilic hairs; B, L. decumbens N. Dhatchan. & S. Soosairaj, sp. nov. with short hairs. Scale bars: A, 1 mm; B, 300 µm.