Exacum laxiflorum (Gamble) Geethakumary, Deepu, Kissling & Pandurangan, 2022

Geethakumary, M. P., Deepu, S., Kissling, J. & Pandurangan, A. G., 2022, Revisiting the taxonomy of Exacum courtallense (Gentianaceae) and recognizing E. courtallense var. laxiflorum at the species rank, Phytotaxa 559 (2), pp. 185-192 : 190

Exacum laxiflorum (Gamble) Geethakumary, Deepu, Kissling & Pandurangan , comb. et stat. nov.

Exacum courtallense var. laxiflorum Gamble (1923: 873) .

Type :— INDIA. Travancore, 1873, Beddome s.n. (lectotype MH [barcode MH00002366 ], designated by Henry & Swaminathan (1983: 458); isolectotype K [barcode K000759944 ]) .

Exacum courtallense var. boneccordense M. Mohanan in M. Mohanan & A.N. Henry (1994: 305, as “ boneccordensis ”).

Type:— INDIA. Kerala, Thiruvananthapuram district , Bonacaud, s. d., M. Mohanan 63225 (holotype CAL n.v.; isotype MH n.v.) .

Herbs, 15–152 cm tall. Stems much branched, terete at the base, sharply 4-angular above, young branches 4-lineolate, internodes 10–95 mm. Leaves opposite, subsessile, narrowly elliptic to lanceolate, 15–88 × 5–20 mm, chartaceous, glabrous, green, base attenuate, petiolate, apex long acuminate, 3–veined (midvein with one secondary vein on each side), tips recurved, veins diverging from the base of the lamina reaching to the apex prominent. Inflorescence terminal or axillary dichasial lax cymes, rarely solitary from terminal axis; peduncles 15–55 mm long; pedicels 6–25 mm long, enlarging in fruit (10–30 mm), bent towards one side. Calyx 5-lobed; tube campanulate, 2–3 mm long; lobes 5–7 mm long acuminate at apex, winged; wings 2–3 mm broad, wings narrowing at the apex, abruptly narrowing to base, accrescent in fruit, with prominent veins. Corolla tube 3-4 mm long, green; lobes 5, broadly obovate-oblong, 8–11 × 5–12 mm, subacute at apex, long persistent in fruit with prominent nerves but eventually deciduous, blue towards purplish. Stamens 5, 6.5–9.5 mm long; filaments ca. 4 mm long, attached at distal portion of the corolla tube; anthers bottle-shaped with long narrow neck, 5–5.5 mm long, slightly curved with the convex back face, base cordate, opening by apical pores that later widen to slits to the base, without papilla. Ovary ellipsoid, ca. 4mm long; style 9–10 mm long, curved, persistent; stigma capitate. Capsule ovoid, 6–9 × 3–4 mm, dehiscing septicidally, 2-valved; style persistent. Seeds many, irregularly rhomboid, angular, with shallowly sunken sides ( Fig. 2 ).

Note:—We searched for the type specimens of Exacum courtallense var. boneccordense in both CAL and MH, and we were unable to locate them. However, for this study, specimens collected from the type locality matching the drawing in the protologue were used for logical conclusions.

Phenology:—Flowering and fruiting were observed from July to December.

Chromosome number:—2n=68 ( Mallikarjuna et al. 1987)

Distribution and Habitat:—Occurs in the evergreen and semi-evergreen forests of the Southern Western Ghats in Kerala and Tamil Nadu. This species has a wider distribution than E. courtallense and is recorded from many districts in Kerala.

Conservation status: —Based on the information from field surveys and herbarium data, the species is known from 13 subpopulations. Some of these subpopulations are under stress due to a decline in the quality of habitat. The species is annual, and it is observed to have undergone a reduction of over 50% over a period of 10 years due to a decline in area of occupancy (AOO) and quality of habitat, as evident by the fact that some subpopulations seen in the past are currently not present. Some subpopulations occur along the trek paths and wall cuttings along the roads, which are subjected to annual clearing, posing a threat to these subpopulations. Based on the available population information, the AOO of the species is not expected to be greater than 500 km 2. Given the species has a low AOO, suffered population decline over the past, and the continuing threat due to the decline in habitat quality, the species is assessed as Endangered [EN A2ac; B2b(ii, iv, v)].

Specimens examined:— INDIA. Kerala, Ernakulam District, Bhoothathankettu , 22September2012, Geethakumary 70936 ( TBGT) . Idukki District, Kulamavu , 7 July 1984, C.N. Mohanan 82012 ( MH) ; Thiruvananthapuram District, Travancore hills, 26 December 1821, R. H. Beddome s.n. ( MH) ; Travancore , 1873, R. H. Beddome s.n. ( MH) ; Neyyar Dam , K. Rajappan, s.n. ( UCT) ; Forest near Bonaccord , 500 m, 1 October 1973, J. Joseph 44484 ( MH) ; Bonaccord , 600 m, 22 March 1978, M. Mohanan 54736 ( MH) ; ibid., + 575 m, 3 August 1978, M. Mohanan 58523 ( MH) ; ibid., 700 m, 18 May 1991, N. Mohanan 10818 ( TBGT) ; ibid., 30 October 1992, E S Santhoshkumar & M. A. Jabbar 14727 ( TBGT) ; ibid., ± 600 m, Geethakumary 53681 ( TBGT) ; ibid., 11 December 2014, Geethakumary 80885 ( TBGT) ; ibid., + 700m, 11 December 2014, Geethakumary 80885 ( TBGT) ; ibid., 12 August 2011, Geethakumary 67929 ( TBGT) ; ibid., 16 November 2011, Geethakumary 69883 ( TBGT) ; Athirumala , 11 December 2014, Geethakumary 80887 ( TBGT) ; ibid., 1100 m, 12 October 1988, N. Mohanan 4215 ( CALI, TBGT) ; Meenmutty , 500 m, 6 November 1990, N. Mohanan 10147 ( TBGT) ; Chemunji , 900 m, 5 February 1991, N. Mohanan 10325 ( TBGT) ; Karamanayar , 700 m, 30 July 1991, N. Mohanan 10704 ( TBGT) ; Near Karamana River , 660 m, 26 September 1995, C.S. K. & S. A. K. 24359 ( TBGT) ; near Karamanayar , s.d., Geethakumary 63693 ( TBGT) ; Agasthiyamala MPCA, 27 April 1994, N. Mohanan & T. Shaju 2055 ( TBGT) ; Cement cana, 800 m, 14 August 2001, NWFP team 46630 ( TBGT) ; Way to Koviltherimala , 16 November 2011, Geethakumary 69884 ( TBGT) ; ibid., Geethakumary 69886 ( TBGT) ; Chemunji , 16 November 2011, Geethakumary 69888 ( TBGT) . TAMILNADU: Kanyakumari District, Way to Muthukuzhivayal , ± 1000 m, 31 August 1976, A.N. Henry 48174 ( MH) ; Thovazha hill, s.d., Narayana Iyer s.n. ( TBGT) ; Tirunelveli District, Mahendragiri , 18 September 1916, s.coll. 13249 ( MH) .

Figures

FIGURE 2. Exacum laxiflorum (Gamble) Geethakumary, Deepu, Kissling & Pandurangan A. Habit; B. Flower; C. Calyx; D. Petal; E. Stamen; F. Pistil; G. Mature fruit split open; H. Seeds.