Reissantia sessiliflora N. V. Page, Srivastav & Rao, 2017

Page, Navendu V., Srivastav, Mansa & Rao, Ramachandra G., 2017, A new species of Reissantia (Celastraceae) from coastal Karnataka, India, Phytotaxa 297 (2), pp. 209-215 : 209-214

Reissantia sessiliflora N. V. Page, Srivastav & Rao , sp. nov. ( Figs. 1 , 2 & 3 )

Reissantia sessiliflora is morphologically most closely related to R. indica but can be distinguished from the latter by sessile flowers, entire leaf margin with coriaceous texture and larger size, terete to subterete stem and inflorescence branches and laciniate calyx margin ( Almeida, 1996; Matthew, 1999).

Type: — INDIA. Karnataka: Honnavar, Uttara Kannada district, 14° 12’ 23.22”N, 74° 27’ 13.61”E, 50 m, 13 January 2016 (with flowers), Page 105 (holotype JCB!, isotype FRLH!).

Scandent shrub, glabrous at all stages. Stem with white reticulation, branchlets decussate, terete, coiled and robust, axillary buds black, circular, 2–3 in a row. Petiole up to 2 cm; leaf blade ovate-elliptical, 8–19 × 4–13 cm, base cuneate, margin entire, apex acuminate, adaxial surface glabrous, dark green, abaxial becoming glaucous, coriaceous, entire (in vivo); no stipules seen, secondary nerves 5–7 pairs, tertiary nerves irregularly branched, inconspicuous. Inflorescence a dichasial cyme of small, compactly-arranged flowers, 3–4 cm long and 5 cm wide, axillary, branching 4 times or more up to 6, accessory branches present; peduncle terete, slender up to 2 cm long, branches opposite to subopposite. Bracts present singly at the base of each flower and inflorescence branches, subulate-lanceolate to ovatelanceolate, 1–1.5 × 0.5–0.8 mm, acuminate, sessile, light green with maroon tinge on margins, turning maroon with maturity, submembranous, glabrous, incised. Flowers greenish-yellow or rust-coloured, sessile, 1.5–3 mm in diameter at anthesis. Sepals 5, pandurate to deltoid, 0.6 × 0.5 mm, apex apiculate-obtuse to rounded, light green to maroon, sub-membranous, glabrous, laciniate, aestivation quinquincially imbricate; petals 5, sometimes 6 or 7, oblong-oval to subulate-lanceolate, 1 × 0.4–0.5 mm, apex obtuse, thin carnose to sub-membranous, glabrous, erose, more so towards apex, curved inwards on sides, aestivation quinquincially imbricate; stamens 3, suberect, flattened, slightly longer than the style, filament 0.25–0.3 × 0.13 mm, white, uniform in width throughout, inserted at the base of ovary, anther lobes extrose, 0.2 × 0.4 mm, light green, rectangular-globose; gynoecium flask-shaped, 0.6 mm long, light-green, style 0.25 mm long, stigma obscure, ovary superior, trilocular, 0.4 mm in diameter; disk 0.5 mm in diameter, 0.03– 0.04 mm thick, extrastaminal, annular, fleshy, inconspicuous; ovules 2 per locule. Fruits 3-fascicled capsule, usually several per inflorescence; capsules sessile, attached separately to the receptacle, divergent, flattened, striated, obovateelliptical, 4.9 × 10–10.5 cm, base acute, apex obliquely emarginated, one half of the capsule slightly shorter than the other, green, turning yellowish to brown on maturity, pericarp chartaceous, entire, dehiscing along a median suture; seeds 2, occupying less than half of the capsule cavity when mature, oval, 4 × 2.5 cm, white when young, flattened with a conspicuous basal membranous wing, wing elliptical, falcate, 2.7 × 0.65 cm, apex obliquely ellipsoid, funicle conspicuous.

Phenology:—The flowering season of this species extends from December to March while fruiting from March to May.

Etymology:—The specific epithet refers to the sessile nature of the flowers which is the main diagnostic character of this species.

Distribution:— Reissantia sessiliflora is currently known from coastal parts of Uttar Kannada district of Karnataka. It is found in association with Pterospermum diversifolium Blume (1825:88) , Diospyros candolleana Thwaites (1860:181) , Calamus thwaitesii Beccari (1892:441) and Premna serratifolia Blanco (1845:342) . So far, we have been able to locate only a few populations, growing sparsely in coastal sea facing-lateritic scrub and nearby fringes of semi-evergreen and moist deciduous forest. Reissantia sessiliflora is one of the few species that is peculiar and endemic to these highly fragmented and scattered coastal vegetation patches. These coastal habitats and forests are not part of the existing protected area network and are under tremendous pressure from anthropogenic activities. Moreover, the extent of occurrence of this species is estimated to be less than 100 sq km and therefore likely to qualify for the Critically Endangered category.

Interrelationships and critical notes:—Comparison of Reissantia sessiliflora with its morphologically closely related species R. indica has been provided in Table 1 and Fig. 3 . When compared to other genera, R. sessiliflora most closely resembles Pristimera Miers (1872:360) but the number of ovules per locule is 2 in former while 2–8 in latter ( Smith, 1940). It also resembles Arnicratea N. Hallé (1984:12) to some extent but can be distinguished from the latter by 2 ovules per locule, dichasial cyme type of inflorescence, glabrous and sessile flowers and 1 mm long petals as opposed to usually 6 (4–7) ovules per locule, paniculate or thyrsiform inflorescence, papillate and pedicellate flowers and 2.5–3.5 mm long petals of Arnicratea .

We have observed two populations of Reissantia sessiliflora growing in two different habitats which exhibit variation in morphological features. The coastal population has oblong-ovate petals, an average petal number of 5, more closed flowers with greater reddish tinge, larger average leaf size and many flowered, dense inflorescence as opposed to the subulate-lanceolate petals, petal numbers going up to 6-7 in most cases, more open flowers with lesser reddish tinge, smaller average leaf size and few flowered, lax inflorescence of the population found in the forest.

Additional specimens examined: — INDIA. Karnataka: Uttara Kannada, Shirali, 14° 3’ 44.89”N, 74° 34’ 2.39”E,

50 m, 13 January 2016 (with flowers), Page106 (JCB!).

Figures

FIGURE 1. Reissantia sessiliflora A. Flowering twig. B. Leaf. C. Inflorescence. D. Flower. E. Longitudinal section of flower. F.Subulatelanceolate petal. G. Oblong-oval petal. H. Sepal. J. Pistil. K. Stamen. All from Page 105. Illustration by Mansa Srivastav.

FIGURE 2. Reissantia sessiliflora A. Stem showing reticulation. B. Flowering twigs. C. Inflorescence showing sessile flowers. D. Fruit. E. Torn capsule showing seeds.

FIGURE 3. Morphological comparison between Reissantia sessiliflora (A–D) and Reissantia indica (E–H). A, E Flowering twig. B, F. Adaxial surface of leaf. C, G. Inflorescence D, H. Flowers.