Scientific name: Hydrilla verticillata (L.f.) Royle
Common name: Esthwaite Waterweed
Description
Habit: Elongated stems to 1m long, branched, rooted in mud, submerged.
Leaves: Submerged, sessile, the lower leaves opposite, the upper leaves in whorls of 3-5, minutely denticulate, 20-40mm long, with 2 minute fringed scales at base with orange-brown hairs; apex acute to acuminate; pale translucent green.
Flowers: Dioecious; spathes tubular, axillary, sessile, 1-flowered; female flowers very rarely produced, axillary, with a long ovarian beak as in Elodea; petals subequalling the sepals, petals transparent, with a few red streaks; sepals of female flowers 1.5-3mm across; ovary sessile within the spathe, attenuated into a filiform beak; styles 3(-5), simple, free; stamens 3. Male flowers unknown in Ireland.
Habitat: Known from two lakes in Ireland- Rusheenduff near Renvyle, Co. Galway and Ballinakill, Co. Galway.
Distribution: Rare.
Native status: Native
Of conservation interest: Yes