Isoetes lacustris
{{Taxobox
color = lightgreen | name = Isoetes lacustris | image = Illustration Isoetes lacustris0.jpg | image_width = 240px | regnum = Plantae | divisio = Lycopodiophyta | classis = Isoetopsida | ordo = Isoetales | familia = Isoetaceae | genus = Isoetes | species = I. lacustris | binomial = Isoetes lacustris | binomial_authority = L.
Isoetes lacustris (Lake Quillwort) is a boreal Quillwort Lycopodiaphyte. It is native on both sides of the northern Atlantic Ocean; in Europe in Poland west to northeastern France, throughout Scandinavia, the west and north of the British Isles, the Faroe Islands and Iceland; in North America in the United States states of Maine, Vermont, New Hampshire and Massachusetts, and in Canada in New Brunswick and Nova Scotia.
The Lake Quillwort has many long, narrow leaves from 8-20 cm long and 0.5-2 mm broad, widening to 5 mm broad at the base. There is a sac that contains the spores at the bottom of each leaf base. It has a very small stem where the leaves attach with the roots. It does not have traditional roots, but instead roots with leaf-like appendages called rhizomorphs. The upper leaves are green and found in sprouting clumps.
It is found on the stony or sandy bottoms of clear, usually slightly acidic ponds, typically in mountain tarns, growing at 5-300 cm depth of water. They are perennial, with typically two flushes of new leaves each year, in spring and autumn.
Reproduction usually takes place during the late summer or early fall. The sacs at the bottom of leaf create two types of spores, female (megaspores, about 0.5 mm diameter) and male (microspores, a few micrometres in diameter). These spores begin the life cycle as a new plant.*Flora Europaea: Isoetes lacustris
*NCRS: USDA Plants Profile and map: Isoetes lacustris
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