Rotala saxatilis W.J.de Wilde & Duyfjes, 2019

Wilde, W. J. J. O. de & Duyfjes, B. E. E., 2019, Three new species of Lythraceae and one new species of Stemonaceae described from Indochina, Blumea 64 (2), pp. 177-182 : 180

Rotala saxatilis W.J.de Wilde & Duyfjes , sp. nov. — Fig. 2

Markedly different from other Rotala species in its yellow flowers. It most resembles Rotala serpyllifolia (Roth) Bremek. , from which it is different in its erect, more-or-less solitary, unbranched 4-angled stem growing from a small woody rhizome, flower-spike rather lax, pedicels distinct, style short, 0.2–0.3 mm long. In R. serpyllifolia , the stem is terete and towards the base more-or-less decumbent,with numerous roots,the flower spike more-or-less peduncled, with densely packed flowers, flowers (sub)sessile, style c. 1 mm long. — Type: Poilane 20144 (holo P P05134370; iso P P05134364, L L.2487636), Laos, Luang Prabang Province,between Dauh Quau and Luong Prabang, 200 m alt., received 27 Aug. 1932.

Etymology. The specific epithet saxatilis refers to the locality, as it was found on rocks.

Perennial herbs, 5 –10 cm tall, possibly gregarious, but not tufted or cushion-forming; stems erect, purplish, 4-angled, solitary, usually unbranched, growing from short, entangled somewhat woody short rhizomes c. 0.5 cm long. Leaves decussate, sessile; lamina with minute cystoliths, (broadly) ovate, 2–5 by 1–3 mm, base obtuse or cuneate, apex obtuse. Inflorescence a rather lax terminal spike, 1–1.5(–2) cm long, not or hardly pedunculate, the lower flowers in bracts approaching the size of upper leaves; bracts leaf-like, smaller than foliage leaves, as long as or longer than the flowers, base obtuse; bracteoles 2, lanceolate, c. 1 mm long. Flowers: pedicel 1.5–3 mm long; c alyx tube somewhat urceolate, c. 2 mm long; calyx lobes 4, triangular, c. 0.8 mm long; calyx appendages absent; petals 4, yellow (according to the field label, see note), persisting in fruit, obovate, 1–1.2 mm long; stamens 4; filaments inserted c. halfway up the calyx tube; anthers c. 0.3 by c. 0.4 mm, included, level or somewhat above the apex of the calyx tube; ovary ovoid, c. 1.2 mm long, style short, 0.2–0.3 mm long. Capsules narrowly ellipsoid, c. 2 by c. 1 mm, opening by 2 valves. Seeds oblong, c. 0.5 mm long.

Distribution — Laos, Luang Prabang Province, between Dauh Quau and Luong Prabang, where known only from the type.

Habitat & Ecology — Growing on rocks along river at 200 m altitude.

Note — The flower colour, recorded as yellow, is remarkable as to date only pink, lilac or white flowers have been observed for Rotala species ( Cook 1979).

Figures

Fig. 2 a–h. Rotala saxatilis W.J.de Wilde & Duyfjes. a. Habit; b. inflorescence; c. detail of stem (note stem quadrangular), leaves with minute cystoliths; d. flower; e. flower with half the calyx removed; f. petal; g. fruit and seed, (note stigma at apex of one valve); h. portion of plant with woody rhizome. — i. Rotala serpyllifolia (Roth) Bremek. Portion of plant with thread-like roots, without a rhizome (a–h: Poilane 20144 (L.2487636); i: Hooker s.n. (L.2487638), (India); all L). — Drawn by Jan van Os.