Hydrocharitaceae

By: Sajita Dhakal & Jovita Yesilyurt

Taxon Description 

Annual or perennial, submerged aquatic herbs. Roots adventitious. Leaves submerged, rarely floating or partly emerged, basal or spirally whorled, linear, lanceolate, elliptic or ovate. Stipules generally absent, but present in Hydrilla, sessile or petiolate. Petioles mostly sheathing, venations more or less parallel, straight or curved, connected by perpendicular or ascending cross-veins. Spathe sessile or peduncled, often ribbed or winged, apex mostly bifid. Flowers actinomorphic, usually unisexual, rarely bisexual, usually arising from two united bracts forming a spathe. Perianth segments ­­­­free. Sepals 3, often green, mostly valvate. Petals mostly coloured, imbricate. Stamens 2 or many; anthers basifixed, 2–4 celled; filaments more or less slender, sometimes absent. Ovary inferior, linear lanceolate or ovate, 1-loculed consisting of 2–9 fused carpels, apex often narrowed into a long, filiform beak, ovules parietal; styles 2–9 often more or less split into 2 crests. Fruit linear, lanceolate or ovate, opening irregularly from top by decay of pericarp. Seeds fusiform, elliptic-ovate or globose.

Taxon Statistics

Worldwide ca. 16 genera and 148 species (Bernardini & Lucchese, 2018). Six genera and 10 species in Nepal.

Key to Genera

1a Plants annual, submerged. Leaves sessile ……………………….………….…………….……..…………….……..…………….……..……………….…….. 3.  Najas

b Plants perennial, rarely annual. Leaves petiolate, rarely sessile …………….…………….……..…………….……..…………….……..…….………….…….…. 2

2a Leaves basal. Stems short ………………………………………………….…..….…………….……..…………….………..…………….……..………….….…….…………… 3

b Leaves cauline. Stems elongated ………………………….…………..…….…………….……..…………….……..…………….……..…………….………….…………….… 4

3a Leaves linear, sessile …………………………………………………………….…………….……..…………….……………..…………….……..…………….…….……………. 5

b Leaves with extended lanceolate to suborbicular blades, petiolate …………………….……..…………….……..………………..……..………… 5. Ottelia

4a Leaves in whorls along a stem, distinct midvein …………..…………….……..…………….……..…………….……..…………….…….…..…………. 2. Hydrilla

b Leaves alternate, lacking distinct midvein …………………..…….….……..…………….……..…………….……..…………….……….…..……. 4. Nechamandra

5a Flowers bisexual, peduncle of female flower shorter. …………….….……..…………….……..…………….……..………….….…….………….……… 1. Blyxa

b Flowers unisexual, peduncle of female flower longer. …………..…………….……..…………….……..…………….……..…….……………..…. 6. Vallisneria