Rotala protracta 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 protracta W.J.de Wilde & Duyfjes , sp. nov.

Distinct from the most similar species, Rotala cordata Koehne in its (4–)5-merous flowers,vs flowers 4-merous,stamens long-protruding from the perianth, vs stamens level with the tips of the calyx lobes. — Type: Schmid 981 (holo P P05103028 ; iso P P05103027 ), Vietnam, Dac Lac Prov., Ban Brieng , Nov. 1949 .

Etymology. The specific epithet protracta (Latin, protractus = drawn out, lengthened) refers to the protruding stamens.

Amphibious or terrestrial annual herb, erect or at base decumbent and rooting, 20–30 cm long, stem broadly 4-winged. Leaves decussate, sessile; lamina (narrowly) ovate-elliptic or elliptic or oblong, c. 1 by c. 0.5 cm, base narrowly cordate, apex more-or-less obtuse. Flowers solitary in leaf axils, towards apex of branches forming spikes, with the bracts about twice as long as the flowers, bract apex subacute. Flowers (4–)5-merous, sessile, bracteoles scarious, minute; calyx campanulate, tube c. 1.5 mm long, lobes c. 0.3 mm long, calyx appendages absent; petals rose-purple, persistent, 1–1.5 mm long, obtuse; stamens (4–)5, inserted near the base of the calyx (but filaments about halfway adherent to the calyx tube when young), filaments long, c. 4 mm long, c. twice the length of the calyx, carrying the anthers far outside the flower; ovary about half as long as the calyx tube, style as long as ovary. Capsule globose, as long as calyx tube, opening by 3 valves. Seeds c. 0.5 mm long.

Distribution — Cambodia, Laos and Vietnam.

Habitat & Ecology — Moist places; on basalt bedrock; 100– 500 m altitude; flowering and fruiting in October and November.

Specimens studied. CAMBODIA, Kompong Cham Prov., Chup near Kompong Cham, Evrard 720, Nov. 1921 ( P05134365 , P05134366 , P05134367 ) . – LAOS, Prov. Champassak, Poilane 16051, Bassac, near Kuang si, 100 m, 20 Oct. 1928 ( P05134533 ) ; Thorel s.n., Expédition du Mékong, Sedone, 1866–1868 ( P05134537 ) . – VIETNAM, Cân Tho prov., Vu Van Cuong 1028, 1966 ( P05134526 ) ; Daclac Prov., Ban Brieng, Schmid 981, 450– 500 m, Nov. 1949, type ( P05103027 , P05103028 ) .

Note — Rotala protracta deceptively resembles R. cordata in general appearance, both species share conspicuously 4-winged branches, and most specimens assigned to R. protracta were formerly determined as R. cordata . Cook (1979) apparently did not examine Indochinese specimens of R. cordata in P.