Exacum courtallense Arnott (1839: 175)

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 : 186-187

Exacum courtallense Arnott (1839: 175) .

Type:― INDIA. Tamil Nadu: Tirunelveli District, Courtallum hills, August 1835, Wight 1835. 553 (lectotype E [barcode E00001507, image], designated by Klackenberg (1985: 66); isolectotypes E [barcode E00001508, image], NY [barcode NY00297601, image]) .

Perennial herbs, to 30 cm tall; low, bushy, dichotomously branched from the base (older plants occasionally diffuse). Stem terete at the base, sharply 4-angular at medio-distal portion; young branches 4-lineolate; internodes 4–45 mm long. Leaves opposite, sessile, orbicular (when young) to lanceolate, 10–45 × 7–23 mm, succulent, glabrous, green, base cuneate, stem-clasping, margin scarious, apex acute to obtuse, (1–)3–5 veined, secondary veins diverging from base of the lamina, abaxially prominent. Inflorescence terminal, 5-flowered cyme, rarely solitary from terminal axis; peduncles 15–20 mm long; pedicels 8–15 mm long, slightly enlarging in fruit (10–20 mm), straight. Calyx 5-lobed; tube about half the length of the calyx, campanulate, 3–4 mm long; lobes 6–7 mm long, overlapping at the base in fruit, tapering to a long point at the apex, winged; wings ca. 2 mm broad, rounded or in fruit subcordate at the base, accrescent in fruit with prominent veins. Corolla tube ca. 6 mm long, green; lobes 5, obovate, 11–13 × 6–7 mm, obtuse to acute at apex, long persistent in fruit but eventually deciduous, blue to deep blue. Stamens 5, 8–9 mm long; filaments ca. 3 mm, as long as the anther, attached at the distal portion of the corolla throat; anthers bottle-shaped with a long narrow neck, ca. 6 mm long, base cordate, opening by apical pores that later widen to slits to the base, without papilla. Ovary oblong, ca. 5 mm long; style 10–12 mm long, curved; stigma capitate. Capsule oblong-ovate, ca. 7 × 3 mm, dehiscing septicidally, 2-valved; fruiting pedicel straight; style persistent. Seeds many, irregularly rhomboid, angular, with shallowly sunken sides ( Fig. 1 ).

Phenology:—Flowering and fruiting were observed from September to February.

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

Distribution and Habitat:—Occurs in the rocky outcrops, mostly in high altitude grasslands in the southern Western Ghats of Kerala and Tamil Nadu.

Specimens examined:— INDIA. Tamil Nadu, Tirunelveli District, Courtallum hills, 1836, Wight 1836.552 ( MH) . Kerala, Thiruvananthapuram District, Ponmudi , ± 793 m, 7 December 2014, Geethakumary 83197 ( TBGT) ; ibid., 18 October 2015, Geethakumary 84385 ( TBGT) ; ibid., 12 January 2015, Geethakumary 84743 ( TBGT) ; ibid., 7 December 2015, Deepu Sivadas 78878 ( TBGT) ; ibid., 10 January 2016, Geethakumary 84794 ( TBGT) .

Note:—The specimen NY00297601 is likely to be the material studied by Arnott as this material reached NY from Arnott’s collection.

Figures

FIGURE 1. Exacum courtallense Arnott. A. Habit; B. Flower split open; C. Calyx; D–E. Petal; F–H. Stamen; I. Pistil; J. Fruit; K. Young fruiting calyx; L. Dry fruiting calyx.