14. Spirodela Schleid., Linnaea 13: 391 (1839).
By: Himanchal T. Magar & Mohan Siwakoti
Taxon Description
Aquatic herbs, fronds free-floating. Roots (–5) 7–21, surrounded by a tubular sheath at base, enclosed by a rounded to pointed cap at apex. Few individuals attached together forming a cluster, daughter fronds connected to mother frond by a thin white stripe, upper surface of fronds glossy green, flat, lower surface red, slightly gibbous, usually with an asymmetric outline, base having 2 lateral pouches from which daughter fronds and flowers arise, veins 7–16 (–21), splitting from the node to the apex, adaxially visible. Pigment cells visible as brown dots in dried fronds. Flowers unisexual, usually 1, occasionally 2, surrounded by a minute, sac-like, membranous scale with a narrow apicular opening. Sepals and petals absent. Stamens 2. Style 1. Seeds 1–3, longitudinally ribbed.
Taxon Statistics
Worldwide four species. Three species are restricted to Central and South America. One species in Nepal.
1. Spirodela polyrhiza (L.) Schleiden, Linnaea. 13:392 (1839).
Lemna polyrhiza L. Sp. Pl.: 970 (1753); Lenticula polyrrhiza (L.) Lam.
Perennial aquatic herbs, forming a mat on water surface, 5–7 cm. Roots few to many up to 21, with few perforating scales, 0.5–3 cm. Wintering underwater buds (turions) sometime present, usually devoid of roots, orbicular or reniform, 1–2 mm, brown. Fronds free-floating, forming a small group of 2–3 individuals. Leaves orbicular, flat, rarely gibbous, 1–1.5 X 1–1.5 mm, usually green, sometimes red, dark red underside, base rounded, apex rounded, veins 7–16(–21); inconspicuous papillae on the upper surface along the length of the veins.
Distribution: Nepal, W Himalaya, Assam-Burma, S Asia, E Asia, C Asia and SW Asia; Europe, N America, S America, Australasia.
Altitudinal range: 65–1300 m.
Ecology: Aquatic, floating on Ponds, lakesides, rice fields, pools, ditches.
Flowering: June–September. Fruiting: June–September.
Spirodela polyrhiza undergoes vegetative growth in spring and summer, forming new fronds, while rarely flowering. In fall and winter, it enters a dormant phase, represented by turions, as a response to nutrition starvation and freezing temperatures.