Flower:

Flowers are not produced, reproduction is by spores.

Leaves and stems:

Leaves are all basal, narrowly grass-like, erect to spreading, pliant, bright green but paler towards the base, 2 to 6 inches long (rarely to 16 inches), about 1 mm wide, gradually tapering from the base to a blunt or pointed tip, and arise from a nearly round rootstock.

The leaf base is abruptly expanded and white to brownish. Plants are commonly completely submersed but in shallow water may be emersed or become stranded on land when water recedes.

Fruit:

Spores are produced starting in early summer, in a nearly round sac (sporangium) on the inner face of the leaf base. Translucent tissue (velum) covers at least a portion of the tip end but usually not more than half of the sac.

Two types of spores are produced: megaspores (female) are visible to the naked eye, white at maturity, .25 to .55 mm diameter with numerous protrusions on the surface giving a spiny appearance; microspores (male) are gray to light brown and less than 1/10th the size of megaspores.

Notes:

Spiny-spore Quillwort, formerly Isoetes tenella, is the most common of the 3 Isoetes species in Minnesota, found in soft water lakes, ponds and slow moving rivers and streams, most often in less than 2 feet of water but sometimes deeper. It is usually completely submersed but near shorelines it can be emersed or become stranded on land when water levels drop.

Spiny-spore Quillwort, as its common name suggests, is best recognized by the spiny texture on its megaspores, but also by pliant leaves that have a long, gradual taper all the way to the tip. Most similar is Lake Quillwort (Isoetes lacustris), which is also found in the northeast quadrant of Minnesota, but has stiffer leaves that are more parallel-sided with a shorter taper at the tip end, and its megaspores are larger, .55 to .8 mm diameter, with irregular ridges across the surface. A good hand lens or microscope is recommended. The third species, Prairie Quillwort (Isoetes melanopoda), is only found in rainwater and seepage pools in quartzite rock outcrops in the southwestern corner of Minnesota.

The Quillworts resemble some other aquatic species with basal clumps of linear leaves, such as Water Lobelia (Lobelia dortmana), Pipewort (Eriocaulon aquaticum), American Shoreweed (Littorella americana) and others, all of which are flowering plants that lack any sporangium at the leaf base.