Isoetes, commonly known as the quillworts, is a genus of lycopod. It is the only living genus in the family Isoetaceae and order Isoetales. There are currently 192 recognized species, with a cosmopolitan distribution mostly in aquatic habitats but with the individual species often scarce to rare. Some botanists split the genus, separating two South American species into the genus Stylites, although molecular data place these species among other species of Isoetes, so that Stylites does not warrant taxonomic recognition. Species virtually identical to modern quillworts have existed since the Jurassic epoch, though the timing of the origin of modern Isoetes is subject to considerable uncertainty.
Isoetes louisianensis, the Louisiana quillwort, is a small, grass-like aquatic plant of the family Isoetaceae. It is "one of the rarest quillworts in North America." It occurs in only five locations in St. Tammany and Washington Parishes of Louisiana, as well as some spots in southern Mississippi and south-central Alabama. It is federally listed as an endangered species, partly due to its highly restricted range.
Isoetes lacustris, the lake quillwort or Merlin's grass, is a boreal quillwort native on both sides of the northern Atlantic Ocean. Synonyms include Isoetes hieroglyphica.
Isoetes histrix, the land quillwort, is an aquatic pteridophyte native to the Mediterranean region, northwestern Africa, and the coasts of western Europe northwest to Cornwall. It occurs mainly in temporarily wet habitats, otherwise called vernal pools.
Isoetes engelmannii is a species of aquatic plant in the family Isoetaceae. It is referred to by the common names Engelmann's quillwort or Appalachian quillwort, and is the most widely distributed species of its genus in eastern North America. Its range extends from Ontario in the north, south to Florida and west Arkansas and Missouri. It can be found from April to October in temporary pools, bogs, marshes, stream edges, swamps and along wet roadsides.
Isoetes melanospora, commonly known as black-spored quillwort or black-spored Merlin's grass, is a rare and endangered aquatic lycophyte endemic to the U.S. states of Georgia and South Carolina.
Isoetes howellii, or Howell's quillwort, is a species of quillwort, a type of lycophyte. It is an aquatic plant native to North America.
Isoetes nuttallii, or Nuttall's quillwort, is a species of quillwort, a type of lycopod. It is native to shallow waters and other wet habitats of western North America from British Columbia to California. It produces up to 60 pointed, cylindrical, green to gray-green leaves, each 7 to 17 centimeters long. The velum completely covers the spherical sporangia, which are 5 millimeters long and 1.5 millimeters wide. The ligule is small and triangular. The megaspores are 400 to 500 micrometers in diameter. The microspores, which are spiny and covered in tubercles, are 28 to 31 micrometers long.
Isoetes eludens is an aquatic plant in the genus commonly known as quillwort that is native to the Kamiesberg Mountains in Namaqualand, South Africa. So far it is known to grow only in a single !gau (gnamma), a small temporary pool formed in a hollowed out area of granite rock. It has likely been growing in that region for millions of years, but was only discovered in 2007 and described in 2009. The specific epithet eludens refers to the fact that it eluded discovery, in spite of several searches in recent years in the area for new quillwort species.
Isoetes maritima, the maritime quillwort, is a quillwort in the Isoetaceae family. It is native to Alaska, British Columbia, and Washington state. It bears eight to fifteen dark green, erect, rigid leaves that are each two to five centimeters long and 1.5 millimeters wide. The oval sporangia are small and inconspicuous, measuring at four millimeters long. The velum covers a third to a half of the sporangia. The white microspores are kidney-shaped and 30-36 micrometers long. The white megaspores are spherical and 490-670 micrometers in diameter. It is similar to I. echinospora, but with blunt spines and crests on the megaspores. I. echinospora has sharp, thin spines, though most of the other species in the genus have no megasporal spines. The epithet "maritima" and the common name "maritime quillwort", meaning "of the sea or ocean", are misnomers. Because it was first discovered by Macoun near tidal flats in British Columbia, it was treated as a coastal species. Since that time, however, it has been found in fresh-water lakes and streams.
Isoetes echinospora, also known as spiny quillwort, spiny-spored quillwort or spring quillwort is a species of quillwort in the Isoetaceae family, and is the most abundant species in Canada. It can be found in shallow aquatic environments from Labrador and Newfoundland to Alaska, and south to Pennsylvania, Wisconsin, Michigan, Colorado, and California. In Germany it is found in only two locations: the Feldsee and Lake Titisee, both in the High Black Forest.
Isoetes riparia, the shore quillwort, is a species of plant in the family Isoetaceae. It can be found in rivers, creeks, and tidal mud flats in southern Quebec and southeastern Ontario, south to eastern New York. It has 5 to 35 long, erect bright green to yellow-green leaves, which are 6 to 35 centimeters long. The velum covers one fourth of the sporangium, which can be 7 millimeters long and 4 millimeters wide. The elongated ligule can grow to be 3 millimeters long. The spherical megaspores are 430 to 680 micrometers in diameter with closely set ridges. The kidney-shaped microspores are 24-35 micrometers long, and usually have spine-tipped tubercules. The megaspores can sometimes come to resemble that of either I. echinospora, if the megaspores become eroded and bear projections that could resemble spines, or I. macrospora, if the broken ridges take a certain shape.
Isoetes acadiensis, the Acadian quillwort is a species of quillwort in the Isoetaceae family described by Kott in 1981. It can be found along the shores of lakes, ponds, and rivers in Newfoundland, Nova Scotia, and New Brunswick, as well as in the American states Maine, Massachusetts, and New Hampshire. It has a similar distribution to that of I. tuckermanii. It bears 9 to 35 mostly recurved leaves, each 5–21 cm long. The leaves are usually dark green, though can occasionally be tinged with red. The sporangium can be up to five millimeters long and 3 millimeters in length, covered one sixth to one third by the velum. The spherical megaspores are 400-570 micrometers in diameter, and bear smooth ridges. The kidney shaped microspores are 25 to 30 micrometers long. It was originally believed to be a member of Isoetes hieroglyphica because of their similar megaspore structure.
Isoetes tuckermanii, or Tuckerman's quillwort, is a tetraploid species of plant in the family Isoetaceae. It can be found in shallow water in Newfoundland, Nova Scotia, New Brunswick, and south through the New England states to Maryland. It bears 10 to 45 long bright green to yellow green leaves that are 4 to 25 centimeters long, usually erect, but sometimes recurved. The velum covers one fourth or less of the sporangium, which is usually unspotted, 5 millimeters long, and 3 millimeters wide. The white spherical megaspores are 400 to 650 micrometers in diameter, and bear rough-crested ridges that form a hexagonal honeycomb shape. The kidney shaped microspores are 24 to 33 micrometers long, bearing tubercles. It is very similar to I. macrospora, only reliably distinguishable by cytology or through careful megaspore measurement.
Isoetes occidentalis, the western quillwort, is a species of quillwort in the family Isoetaceae. It can be found in aquatic habitats of coastal Alaska and British Columbia south to California and Colorado. It is frequently found on Vancouver Island and around the Fraser Valley region. It bears 10 to 30 or more rigid, dark green leaves, each 5 to 20 centimeters long. The velum covers one fourth to one third of the orbicular sporangium, which is 5 to 6 millimeters in diameter. The ligule is shaped like a shortened triangle. The white megaspores are 500 to 700 micrometers in diameter and bear sharp ridges and crests. The microspores are 36 to 43 micrometers long. Though the leaves seem to bear resemblance to those of I. lacustris, especially the occasionally occurring reddish base, I. occidentalis is a hexaploid and I. lacustris is a decaploid.
Isoetes brevicula is a quillwort species native to Western Australia. It is a cormous, perennial, herb or, to 1 cm (0.39 in) high, stock 3-lobed; leaves 4–8 mm (0.16–0.31 in) long; mature megaspores greyish white when dry. Submerged in rock pools on granitic outcrops.
Isoetes melanopoda is a species of nonflowering vascular plant belonging to the quillworts in the family Isoetaceae. Its common names include: black-footed quillwort, midland quillwort, and prairie quillwort.
Isoetes capensis, the cape quillwort, is a species of quillwort from South Africa.
Isoetes stellenbossiensis, the Stellenbosch quillwort or Cape Flats quillwort, is a species of plant from South Africa.
