Quillwort, a genus of cryptogamic plants so called from having some resemblance to a bunch of quills; they are mostly aquatics, and being evergreens, Linnaeus called the genus isoŽtes (Gr. , equal, and , year); this is placed by some botanists in the family of club mosses (lycopodiaceoe), while others give it the rank of an order. The external appear ance of the plants is that of a tuft of linear leaves, attached by their enlarged bases to a very short rootstock, from the lower part of which roots are produced. The organs of reproduction are curiously concealed; the sporangia or spore cases are orbicular or ovoid, plano-convex, and sessile in the axils of the leaves, the bases of which are hollowed out to receive and partly cover the sporangia, which are united to them by the back. The spores are of two kinds, those in the cases of the outer leaves being very much larger than those near the centre of the cluster. The large spores (macrospores) are from 20 to 200 in a spore case, and are divided into two hemispheres by a line, one of the halves being marked by three radiating lines; the minute spores of the inner leaves (microspores) are so small that it is estimated that each case contains over a million; they are obliquely oblong and triangular.
Ten or a dozen species are found in the whole country, one of which, I. lacustris, occurs also in northern Europe and Asia, and is found along our northern border from New England to Lake Superior; it has 10 to 25 leaves, 2 to 6 in. long; the largest species, I. Engelmannii, has from 50 to 200 leaves, often 25 in. long. These singular plants are not rare, but they escape general notice from their resemblance to submerged grasses.
Quillwort (IsoŽtes lacustris). A small plant of natural size; magnified bases of two leaves, showing macrospores and microspores; and macrospores greatly magnified.