Elodea nuttallii, (Planchon) St John Hydrilla L. C. M. Richard Lagarosiphon Harvey

3. E. nuttallii (Planchon) St John View in CoL , Rhodora 22: 29 (1920).

Leaves up to 15 x 1-8 mm, in whorls of 3(-4) or the lowest opposite, gradually tapered to the acute apex, minutely denticulate. Sepals of female flowers 1-1-8 mm; petals white. Still or slow-moving water. Cultivated in aquaria, and naturalized in N. W. & C. Europe. [Be Br Ge He Ho.] (North America.)

Spreading rapidly, and in some places tending to displace 1.

6. Hydrilla L. C. M. Richard 1

Dioecious; stems elongated. Leaves submerged, verticillate or the lowest opposite, sessile, linear (to ovate), with 2 small, fringed nodal scales. Flowerspollinated at the water-surface. Spathes tubular, axillary, sessile, 1 -flowered. Petals subequalling the sepals. Male flowers breaking free and rising to the surface; stamens 3. Ovary sessile within the spathe, attenuated into a filiform beak; styles 3(- 5), simple, free. Literature: M. J. P. Scanneil & D. A. Webb, Irish Nat. Jour. 18: 327-331 (1976).

1. H. verticillata (L. fil.) Royle View in CoL , III. Bot. Himal. Mount. 376 (1839).

Leaves in whorls of (2-)3-8, up to 20(-40) x 2(-5) mm, conspicuously or minutely denticulate; nodal scales fringed with orange-brown hairs. Sepals of female flowers 1 - 5-3 mm. Petals narrower than the sepals, transparent, with a few red streaks. 2« = 16. From N.E. Germany to N. White Russia; isolated stations in W. Ireland and N. W. England; very local and often impermanent. Br Ge Hb Rs (B, C). (5. & E. Asia, E. Africa, Australia.)

7. Lagarosiphon Harvey 1

Dioecious; stems elongated. Leaves submerged, sessile, linear, with 2 minute nodal scales. Flowers pollinated at the watersurface. Spathes tubular, axillary, sessile, the male manyflowered, the female l(-3)-flowered. Sepals and petals subequal. Male flowers breaking free and rising to the surface; stamens 3; staminodes 3. Ovary sessile within the spathe, attenuated into a long, filiform beak; styles 3, 2-fid, free.

Literature: A. A. Obermeyer, Bothalia 8: 139-146 (1964).

1. L. major (Ridley) Moss View in CoL , Trans. Roy. Soc. S. Afr. 16: 193 (1928).

Leaves up to 30x 3 mm, alternate, densely crowded towards the ends of the branches, patent-recurved, minutely denticulate. Sepals and petals pinkish. Cultivated in aquaria and naturalized in a few ponds, lakes and rivers in W. & C. Europe. [Br Ga He It.] (S. Africa)