Introduction

Lepidagathis Willd. (Acanthaceae: Acanthoideae: Barlerieae) is distributed mainly in the tropical and subtropical regions of the world (Manzitto-Tripp et al. 2021) with 148 species (POWO 2022). The genus is characterised by having densely secund spikes (sometimes compounded into dense heads) or a many-flowered thyrse with flowers in dense whorls at each node, usually conspicuous bracts and bracteoles which are often similar to calyx lobes in shape and size, unequally 5-lobed calyx lobes (2+2+1 configuration), of which the anterior lobes are often partially fused, posterior lobe broadest and lateral lobes narrowest, corolla distinctly bilabiate (although posterior pair of lobes is fused) with quincuncial aestivation, stamens are included, not exserted beyond the corolla lobes and seeds are covered with long hygroscopic trichomes (Darbyshire et al. 2010; Manzitto-Tripp et al. 2021).

Clarke (1885) documented 24 species and 10 varieties of Lepidagathis in the Flora of British India under two sections, including six taxonomic and nomenclatural novelties. These sections were differentiated by having 2-seeded elongate-conic capsules and ovate-lanceolate seeds with very long spreading mucilaginous hairs (sect. 1) vs 4-seeded oblong capsules and ovate or orbicular seeds with very short elastic hairs when wet (sect. 2) (Clarke 1885). Karthikeyan et al. (2009) reported 23 species and eight varieties of Lepidagathis from the present political boundaries of India. During the last six years, seven novelties, namely L. benojiana Jithin & Jose, L. shrirangii Natekar, Kambale & Chandore, L. ushae Borude, Gosavi & Chandore, L. ananthapuramensis V.S.A.Kumar, P.Biju, Sindhu Arya, Josekutty & Augustine, L. sabui Chandore, Borude, Madhav & S.R.Yadav, L. rajasekharae K.Prasad & A.M.Reddy, and L. mahakassapae S.More, M.Sawant, H.S.Bhosale & Kambale have been described as new species, mostly from the lateritic plateaus of the Western Ghats (Jithin & Jose 2017; Natekar et al. 2019; Borude et al. 2020; Biju et al. 2020; Chandore et al. 2020; Prasad & Reddy 2020; More et al. 2022). Therefore, presently Lepidagathis is represented by 30 species and seven varieties in India, of which 19 species and one variety are endemics.

Materials and Methods

As a part of the on-going study on the ‘Systematics of Lepidagathis Willd. (Acanthaceae) in India’, a thorough review of literature and indexing of herbarium specimens (herbaria visited are indicated with ! and digital images of specimens received are marked with *) housed in four herbaria in India (BSI!, CALI!, MH!, RHT!, SKU! and SUK!), and in international herbaria (B*, BM*, C*, E*, G*, K*, L*, NY*, P*, S* and US*) (herbarium acronyms according to Thiers, continuously updated), were made to collate the information pertaining to the identity and geographical distribution of the species in the country. Subsequently, a number of field explorations have been conducted to different states of India, where the members of this genus are generally known to occur in specific habitats and from where the plant materials were also collected by earlier workers in the past. During one of the explorations, specimens of a morphologically distinct species of Lepidagathis growing in red gravelly soil were collected from different localities in the Tiruppur district (parts of Coimbatore and Erode districts earlier) of Tamil Nadu. The voucher specimens were processed as per the standard method (Forman & Bridson 1989). A critical examination of both fresh and dried specimens under microscopes (LM and SEM), combined with review of relevant literature (Nees 1832, 1847; Clarke 1885; Gamble 1924; Gnanasekaran et al. 2022), revealed that this distinct species has hitherto not been described to science, and that it is morphologically close to another endemic species of Tamil Nadu, L. spinosa Wight ex Nees but it differs consistently from that in a number of characters. Therefore, it is described here as a new species, L. gandhii Gnanasek., A.F.J.King, S.M.Kasim & Arisdason with detailed description, illustrations, colour photographs, micrographs of floral parts taken through light and scanning electron microscopes, taxonomic affinities, distribution map and IUCN conservation status.

Taxonomic Treatment

Lepidagathis gandhii Gnanasek., A.F.J.King, S.M.Kasim & Arisdason sp. nov. Type: India, Tamil Nadu, Tiruppur Distr., Manjappur near Pongalur, 10°58'12.0"N, 77°23'36.0"E, alt. 320 m, 7 Jan. 2022, G. Gnanasekaran & A. F. J. King 12860 (holotype CAL!; isotypes MH!, Madras Christian College Herbarium, Chennai!).

http://www.ipni.org/urn:lsid:ipni.org:names:77313903-1

Perennial undershrub with woody rootstock, erect, up to 60 cm high. Stems well-branched, 4-angled, ash-coloured when old, green to purplish when young; internodal distance 5 – 30 mm long, pubescent when young, becoming retrorsely hairy only on angles at maturity. Leaves sessile, isophyllous, opposite-decussate, oblong to oblanceolate, 15 – 30 × 4 – 8 mm, obtuse or truncate at base, undulate with minute retrorsely ciliolate margins, acute with spinose process at apex, pubescent when young, becoming glabrate at maturity; midvein broad at base, lateral veins 3 – 5 pairs, conspicuous on lower surface. Inflorescence a spike, compactly ovoid due to adpressed/converged fertile bracts, alternately arranged in the axils of leaves with scale-like sterile bracts at the base, 8 – 15 mm long, up to 9-flowered. Bracts: sterile bracts 4, arranged in two pairs, opposite-decussate, heteromorphic, lanceolate to oblong, 3.5 – 7.5 × 1 – 2.7 mm, truncate at base, pilose at margins, cuspidate or acuminate with spinose process at apex; fertile bract 1 per flower, lance-ovate to narrowly elliptic, 8.5 – 11 × 1.5 – 2.5 mm, densely pilose at margins, acuminate with spinose process at apex, sericeous throughout. Bracteoles 2 per flower, oblong, 9.5 – 11 × 1.5 – 2.5 mm, densely pilose at margins, acuminate or caudate with spinose process at apex, sericeous on upper surface, glabrous on lower surface. Calyx 5-lobed, heteromorphic, densely pilose at margins, acuminate with spinose process at apices, sericeous on lower surface, glabrous on upper surface; anticous lobes 2, connate at base (more than half of their total lengths, i.e., 4.2 – 6.3 mm long), almost equal, overlapping; lobes oblong to narrowly elliptic, 8.5 – 10.4 × 2.3 – 3.3 mm; posticous lobe, lance-ovate, 8.5 – 11.2 × 1.5 – 3.4 mm; lateral lobes 2, equal, linear, 6.8 – 9.8 × 0.8 – 1.5 mm. Corolla bilabiate, 12 – 16 mm long, white (yellowish at anthesis) with many purplish-brown markings on expanded portion of tube inside and yellow dots or patches on the palate; tube 8.8 – 10.5 mm long, cylindric below, 4.4 – 6 mm long, glabrous inside, abruptly expanded above, 4.3 – 4.7 mm long, retrorsely hirsute just above the cylindrical tube to throat on either side of lower lip inside, densely sericeous throughout outside; upper lip arcuate, 1.8 – 3.6 × 4 – 4.7 mm, entire at margins, minutely 2-lobed (0.3 – 0.5 mm long) at apex, each lobe 3-veined; lower lip 3-lobed, 4.5 – 6.2 mm long including lobes; middle lobe broader than the lateral lobes, suborbicular, 2.7 – 2.9 × 2.5 – 4.5 mm, crenulate, 3-veined; lateral lobes 1.7 – 3.1 × 2.5 – 3.4 mm, 3-veined. Stamens 4, didynamous, adnate at the base of expanded tube; filaments white with purple stripes, glabrous; anticous (longer) filaments 4 – 4.5 mm long; posticous (shorter) filaments 2.9 – 3.5 mm long; anthers bithecous, oblong, divergent, 1 – 1.7 mm long, white to yellowish, sparsely hairy at base of the slit, scabrous at the connectives, longitudinally dehiscing. Ovary subglobose, 1 – 1.3 × 0.8 – 1 mm, glabrous, 2-loculed; ovules 2 in each locule; nectary disk cupulate; style 8 – 8.7 mm long, bristled-hairy; stigma simple. Capsules ovoid, 5.6 – 6.6 × 2.9 – 3.2 mm, glabrous, yellowish-brown; seeds 1 or 2, fertile, ovoid to widely ovoid, 2.6 – 3.2 × 1.8 – 2.5 mm, flat, densely clothed with hygroscopic white hairs on both surfaces (longer than seeds). Figs 1, 2 & 3.

Fig. 1.
figure 1

Lepidagathis gandhii. A habit; B portion of stem showing the indumentum; C leaf upper surface; D leaf lower surface; E corolla split open. drawn by s. madhura.

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Fig. 2.
figure 2

Lepidagathis gandhii. A habitat; B habit; C, D flowering twigs; E leaves upper and lower surface; F micrograph showing leaf margin; G sterile bracts. photos:a – d g. gnanasekaran; e &g a. f. j. king; f w. arisdason.

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Fig. 3.
figure 3

Lepidagathis gandhii. A fertile bract; B bracteoles; C, D calyx upper and lower surface; E, F flower close-up; G corolla split open; H carpel; J capsule; K micrograph of seed; L seed (dry); M seed with hygroscopic hairs (wet). photos: a – d, g – j, l & m a. f. j. king; e & f g. gnanasekaran; k w. arisdason.

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recognition. Lepidagathis gandhii is morphologically similar to L. spinosa but differs in having the following characters: (i) habit erect undershrub (vs prostrate to rarely decumbent herb); (ii) stem pubescent (vs glabrous); (iii) leaves oblong to oblanceolate, 15 – 30 mm long, obtuse or truncate at base, minutely ciliolate margins, pubescent when young but becoming glabrate at maturity (vs oblance-ovate to obovate, 9 – 22 mm long, attenuate at base, minutely serrulate at margins, glabrous throughout); (iv) inflorescence a compactly ovoid spike due to the adpressed/converged fertile bracts, 8 – 15 mm long (vs broadly ovoid spike due to spreading/diverged fertile bracts, 14 – 20 mm long); (v) sterile bracts 2 pairs, 3.5 – 7.5 × 1.1 – 2.7 mm (vs 2 – 5 pairs, 10 – 18.5 × 3.3 – 4.5 mm); (vi) fertile bracts lance-ovate to narrowly elliptic, 8.5 – 11 mm long, acuminate with short spinose process at apex, sericeous (vs oblong, rarely lance-ovate, 11 – 18.5 mm long, caudate with long spinose process at apex, glabrous); (vii) bracteoles 9.5 – 11 mm long, densely pilose at margins (vs 14 – 19 mm long, minutely ciliolate at margins); (viii) calyx lobes acuminate with spinose process at apices; anticous lobes are fused to more than half of their total lengths (4.2 – 6.3 mm long); posticous lobe lance-ovate (vs caudate with spinose process at apices; anticous lobes are fused to less than a quarter of their total lengths (1.3 – 2.1 mm long); posticous lobe elliptic to broadly elliptic); and (ix) upper lip of corolla with many purplish-brown markings up to the expanded portion of tube inside (vs with many purplish-brown markings throughout inside including lips). Fig. 4.

Fig. 4.
figure 4

Lepidagathis spinosa. A leaf; B micrograph showing leaf margin; C, D flower close-up; E sterile bracts; F calyx. photos: a, c & d g. gnanasekaran; b w. arisdason; e & f a. f. j. king.

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distribution. India: Tamil Nadu (Tiruppur Distr.). Map 1.

Map 1.
figure 5

Lepidagathis gandhii. A geographical distribution map; B distribution polygon showing Extent of Occurrence (EOO).

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specimens examined . india. Tamil Nadu: Tiruppur Distr., Manjappur near Pongalur, 10°58'12.0"N, 77°23'36.0"E, alt. 320 m, 7 Jan. 2022, G. Gnanasekaran & A. F. J. King 12860 (holotype CAL!; isotypes MH!, Madras Christian College Herbarium, Chennai!); Tiruppur Distr., Goundampalayam near Palladam, 11°00'30.0"N, 77°18'06.4"E, alt. 351 m, 20 Oct. 2019, G. Gnanasekaran 12735 (Madras Christian College Herbarium, Chennai); 10 Sept. 2021, A. F. J. King & W. Arisdason 12802, 12803 (Madras Christian College Herbarium, Chennai); 25 Nov. 2021, A. F. J. King 12824, 12825 (Madras Christian College Herbarium, Chennai); 7 Jan. 2022, G. Gnanasekaran & A. F. J. King 12858, 12859 (Madras Christian College Herbarium, Chennai); Goundamputhur on Palladam to Dharapuram Road, 10°57'36.2"N, 77°25'45.5"E, alt. 310 m, 7 Jan. 2022, G. Gnanasekaran & A. F. J. King 12862 (Madras Christian College Herbarium, Chennai); Nilali Kanchipuram on Dharapuram Road, 10°55'34.6"N, 77°26'45.6"E, alt. 320 m, 7 Jan. 2022, G. Gnanasekaran & A. F. J. King 12863 (Madras Christian College Herbarium, Chennai); Manjappur near Pongalur, 10°58'12.0"N, 77°23'36.0"E, alt. 320 m, 7 Jan. 2022, G. Gnanasekaran & A. F. J. King 12861 (Madras Christian College Herbarium, Chennai).

habitat. This species grows on dry lands with red gravelly soil usually in association with grasses at elevations ranging from 300 – 350 m.

conservation status. The species is evaluated provisionally here as ‘Critically Endangered’ [CR B1b(i,iii,v)c(i) + 2b(ii,iii,v)c(ii)] following the IUCN Red List Categories and Criteria version 15.1 (IUCN Standards and Petitions Committee 2022). The species has been collected so far from four severely fragmented locations in the Tiruppur District (parts of Coimbatore and Erode districts earlier) of Tamil Nadu. The species distribution polygons have been prepared to calculate the Extent of Occurrence (EOO) and Area of Occupancy (AOO) for the species using Google Earth Pro (Version 7.3) and GeoCAT tool (Bachman et al. 2011) available at http://geocat.kew.org/. The result of this analysis shows that the EOO and AOO for this species are 21.2 km2 and 16 km2 respectively. AOO was calculated using the standard 2 × 2 km grid cell size as recommended by the IUCN Standards and Petitions Committee (2022). Besides, it is noted that all these four locations are situated in fast-growing residential areas or along the national highways, which is causing severe decline of mature individuals. Therefore, this species requires a special conservation initiative before it becomes extinct in the wild. In addition, an intensive exploration in the adjoining regions is essential to study the natural EOO, AOO and threat factors.

phenology. Flowering September – January; fruiting December – February.

etymology. The new species is named in honour of Dr Kanchi N. Gandhi, Senior Nomenclatural Registrar, Harvard University Herbaria, Cambridge, USA, for continuously imparting his knowledge on botanical nomenclature to the whole botanical fraternity.

notes. The new species is morphologically close to a group of species predominantly found on the dry barren wastelands in the state of Tamil Nadu, namely L. barberi Gamble, L. pungens Nees and L. spinosa. A taxonomic key to differentiate these four species is given below for precise identification:

  • 1. Leaf margins undulate or entire.......................................................................................................................................2

  • 1. Leaf margins with 3 – 6 pairs of spinose teeth.........................................................................................................3

  • 2. Erect undershrub, up to 60 cm high; stem not rooting at basal nodes; leaves oblong to oblanceolate, truncate or obtuse at base, glabrous, pubescent when young; spikes compactly ovoid due to adpressed/converged fertile bracts, axillary, 8 – 15 mm long; sterile bracts 2 pairs, 3.5 – 7.5 mm long; calyx lobes acuminate with spinose process at apices, anticous lobes fused for more than half of their length (4.2 – 6.3 mm long).......................................................................................................................L. gandhii

  • 2. Prostrate to rarely decumbent herb, spreading up to 80 cm in diam.; stem rooting at basal nodes; leaves oblance-ovate to obovate, attenuate at base, glabrous; spikes broadly ovoid due to spreading/diverged fertile bracts, terminal or axillary, 14 – 20 mm long; sterile bracts 2 – 5 pairs, 10 – 18.5 mm long; calyx lobes caudate with spinose process at apices, anticous lobes fused for less than a quarter of their total length (1.3 – 2.1 mm long)..................................................................................................................................L. spinosa

  • 3. Erect (rarely decumbent at maturity) undershrub, up to 50 cm high; stem not rooting at basal nodes; leaves oblong to narrowly elliptic with ciliate margins, glabrous; spikes compactly ovoid due to adpressed/converged fertile bracts, short, 8 – 16 mm long; fertile bract 9.5 – 10.5 mm long; anticous and posticous calyx lobes lanceolate to lance-ovate, acuminate with spinose process at apices; corolla 10 – 14 mm long; capsules ovoid in face view, 4 – 5 mm long.....................................................................................L. barberi

  • 3. Prostrate to straggling undershrub, spreading up to 1.5 m in diam.; stem rooting at basal nodes; leaves elliptic with minutely ciliolate margins, puberulous; spikes broadly ovoid due to spreading/diverged fertile bracts, long, 10 – 22 mm long; fertile bract 10.2 – 15.5 mm long; anticous and posticous calyx lobes broadly elliptic, caudate with spinose process at apices; corolla 13.5 – 17 mm long; capsules lance-ovoid in face view, 5.5 – 5.8 mm long..........................................................................................................L. pungens