Aponogeton rigidifolius Bruggen (1962: 91)

Manawaduge, Chapa G. & Yakandawala, Deepthi, 2018, Morphometrics and taxonomic update to the Sri Lankan Aponogetonaceae, Phytotaxa 365 (3), pp. 201-224 : 214-215

4. Aponogeton rigidifolius Bruggen (1962: 91)

Type:— H. W. E. van Bruggen s.n., cult. ( WAG).

Rhizome creeping, cylindrical, up to 0.8 cm Ø and 14 cm long. Leaves arise along the rhizome or rarely as a tuft. Submerged leaves lamina 19–59 × 2–5 cm; linear and slightly curved, apex narrowly acute and base cuneate, margin slightly undulate or flat, Protrude midrib with 4–8 parallel veins. Petioles up to 56 cm long, bluntly triangular. Immature leaves are purple to maroon, turn to dark green with maturity. Floating leaves absent. Peduncle up to 93 cm, widening towards the inflorescence. Spathe up to 3 mm, caducous. Inflorescence with 1 spike up to 18 cm long, white, densely or laxly flowered, florets turned towards all directions. Tepals 2, obovate, 1.5–2.6 × 1.1–1.4 mm, white, persistent, 1-nerved. Stamens 6, 1.8–2.3 mm, filaments slightly widening towards the base, white, anthers light purple. Ovaries 3, white, 1.5–2.6 × 0.9–1.1 mm, ovules 2. Infructescence up to 43 cm, dense. Folicals up to 15 × 7 mm, elongated, triangular, with rough coat and a short, terminal, curved beak. Seeds with a simple testa, relatively thick and transparent. Embryo up to 12 × 4 mm, plumule attached near the base of the embryo and in a very wide groove.

Phenology:— Flowering throughout the year. But flowering intensity increases just after the rainy season.

Distribution:— Lowland wet zone Kalutara, Ratnapura and Galle Districts of Sri Lanka.

Ecology:— In slow or fast running streams and rivers in rapids, or along the banks.

Uses:— Rhizomes and inflorescence are eaten. Tubers are extracted for medicinal purposes.

Notes:— In genaral, A. rigidifolius has a distinct secondary venation pattern where, they form nearly a 450 angle with primary veins while in other Sri Lankan Aponogeton species, it is nearly a right angle. This character can be used to easily differentiate A. ridgidifolius from A. dassanayakei and A. kannangarae .

Specimens examined:— SRI LANKA. Galle District : Kottawa, 28 Jul. 2014, Manawaduge & Yakandawala 506, 507 ( PDA!) ; Kanneliya , 28 Jul. 2014, Manawaduge & Yakandawala 107 ( PDA!) ; Sinharaja , 07 Feb. 2015, Manawaduge & Yakandawala 114 ( PDA!) ; Wanduramba , 15 Feb. 2015, Manawaduge & Yakandawala 315, 316 ( PDA!) ; Kanneliya Forest , along stream near forestry bungalow, 18 Feb. 1977, Bremer 835 ( PDA!, US) ; Kanneliya Forest Reserve , Aug. 1975, Jayasuriya 2264 ( K, PDA!) ; Kanneweliya Forest Reserve , 5 miles S. of Hiniduma, 4 Feb. 1979, Nicolson 4253 ( PDA!, US) ; Kanneliya , 1 July 1975, Waas 1338 ( PDA!) ; rivulet near schoolhouse, Hiniduma , 5 Oct. 1974, Kostermans 25702 ( K, L, PDA!) ; KDN BR, Kanneliya : 4 km from entrance, Nannikitaela stream, 11 Aug. 2008, Jayasuriya and Abayawardana 9847 ( PDA!) ; Kalutara District : Hallawakellae Forest, Welipenna, 28 Jan. 1972, Balakrishnan NBK 1161 ( PDA!) ; Delwitiya Dola-Morapitiya , 28 Feb. 1977, Waas 2089 ( K, L, PDA!, US) ; Yagirala Forest Reserve , 2 Jun. 1990, Jayasuriya & Balasubramanium 5188( PDA!) ; Ratnapura District : Nawalakanda , W. of Kalawana, Keppetiyamukalana, 25 Feb 1978, Jayasuriya 2486 ( PDA!) ; Kanneliya Forest Reserve , Kanneli-ela near Circuit Bungalow, 26 Nov. 1986, Jayasuriya 3710 ( PDA!) ; Periphery of Sinharaja Forest Kudawa-Pitakele trail, along Pitakele Ganga, 12 Nov. 1988, Jayasuriya & Balasubramanium 4285 ( PDA!) .