Global description
Sphenoclea zeylanica is a terrestrial herb, sometimes partially submerged, annual, erect, 7 to 150 cm high. Roots fibrous, white or brown. Stem with round section, hollow, glabrous. Stipules absent. Leaves simple, entire, alternate spiral, stalked, lanceolate to elliptic, glabrous, glaucous beneath, margin entire, apex and base pointed. Flowers bisexual, sessile, grouped in a terminal spike, pentamers, fused petals. The fruit is a dehiscent capsule with two valves.
Cotyledons
Cotyledons are oval elongate to narrowly elliptical, sessile, 5 mm long and 3 mm wide. They are fleshy, with no apparent rib.
First leaves
The first leaves are simple, alternate, oval lanceolate to narrowly elliptic, base attenuated into a slightly marked petiole and with obtuse to rounded tip. They are glaucous green in color.
Growth habit
Annual aquatic herbaceous plant with erect stem, highly branched from the base. The lateral branches are oblique then erect, hence a candlestick shape profile. It can reach 1.50 m high. This is an entirely glabrous plant.
Underground system
Taproot system.
Stem
The erect stem measures between 30 cm and 1.50 m. It is cylindrical in section. It is thick, with smooth and glossy surface. It is hollow, often spongy at the base in its submerged part.
Leaf
The leaves are simple and alternate. They are broad, whole, without stipules. They are arranged spirally. The petiole, slightly marked, measure 0.3 to 3 cm long. The lamina is oblong lanceolate, base narrowly and lengthily decurrent up to the base of the petiole, more or less pointed at the end, the margin is entire. It measures 2.5 to 12.5 cm long and 0.5 to 5 cm wide. The leaf is completely glabrous, pale green in colour.
Inflorescence
Terminal spikelets are green, cylindrical and compact, measure 1.5 to 10 cm long and 5 mm to 1.2 cm in diameter, carried by a peduncle, 1 to 8 cm long.
Flower
The flowers are small, arranged spirally about the axis of the spike and grow by 2 to 3 starting from the base of the inflorescence. The calyx has five rounded ovate nested lobes. The corolla is white, with lobes as long as the calyx, divided near the base. The stamens are attached to the petals. They are subsessile, with suborbicular anthers. The ovary contains 2 loculus that enclosed many ovules. The style carries a very short and bear a shortly bifid stigma.
Fruit
The fruit is a globose dehiscent flattened capsule, 3 to 4 mm in diameter. It opens with a horizontal circular slot which limits a lid on which the sepals of the calyx are placed.
Seed
The seed has an elongated shape, obovoid, rounded at the top. Tiny, it measures 0.5mm long. Its surface is finely reticulated, light brown in colour.
