Isoëtes, also written
Isoetes and commonly known as the
quillworts, is a genus of plants in the class
IsoetopsidaThe Isoetopsida is a class of the Lycopodiophyta. All living plants belong to the genus Selaginella in the Selaginellales or to Isoetes in the order Isoetales. In the past, members of this group have sometimes been placed in the class Isoetopsida, sometimes in the Selaginellopsida or Lycopodiopsida...
and order
IsoetalesIsoetales, also written Isoëtales, is an order of plants in the class Isoetopsida. There are about 140-150 living species, all classified in the genus Isoëtes , with a cosmopolitan distribution but often scarce to rare. Living species are mostly aquatic or semi-aquatic in clear ponds and...
. They are considered "
fern alliesFern allies are a diverse group of seedless vascular plants that are not true ferns. Like ferns, a fern ally disperses by shedding spores to initiate an alternation of generations.-Classification:...
". There are about 140-150 species, with a
cosmopolitan distributionIn biogeography, a taxon is said to have a cosmopolitan distribution if its range extends across all or most of the world in appropriate habitats. For instance, the killer whale has a cosmopolitan distribution, extending over most of the world's oceans. Other examples include humans, the lichen...
but often scarce to rare. Some botanists split the genus, separating two South American species into the genus
Stylites.
Description
Quillworts are mostly aquatic or semi-aquatic in clear ponds and slow-moving streams, though several (e.g.
I. histrix, I. nuttallii) grow on wet ground that dries out in the summer. Quillwort
leavesA leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....
are hollow and quill-like, arising from a central
cormA corm is a short, vertical, swollen underground plant stem that serves as a storage organ used by some plants to survive winter or other adverse conditions such as summer drought and heat ....
. Each leaf is narrow, 2–20 cm long (exceptionally up to 100 cm) and 0.5–3 mm wide; they can be either
evergreenIn botany, an evergreen plant is a plant that has leaves in all seasons. This contrasts with deciduous plants, which completely lose their foliage during the winter or dry season.There are many different kinds of evergreen plants, both trees and shrubs...
, winter
deciduousDeciduous means "falling off at maturity" or "tending to fall off", and is typically used in reference to trees or shrubs that lose their leaves seasonally, and to the shedding of other plant structures such as petals after flowering or fruit when ripe...
, or dry-season deciduous. They broaden to a swollen base up to 5 mm wide where they attach in clusters to a bulb-like, underground
rhizomeIn botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...
characteristic of most quillwort species, though a few (e.g.
I. tegetiformans) form spreading mats. This swollen base also contains male and female sporangia, protected by a thin, transparent covering (
velumVelum may refer to:* Superior medullary velum, part of the nervous system that stretches between parts of the brain* Veil , the veil-like membrane of immature mushrooms extending from the margin of the cap to the stem and torn by growth...
), which is used diagnostically to help identify quillwort species. They are
heterosporousIn biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
. Quillwort species are very difficult to distinguish by general appearance. The best way to identify them is by examining the megaspores under a microscope.
Classification
The genus
Isoëtes is placed in its own family Isoëtaceae. The genus includes about 150 species worldwide.
- Isoetes alpina New Zealand Quillwort
- Isoetes andicola (syn. Stylites andicola)
- Isoetes appalachiana
Isoetes appalachiana, commonly known as the Appalachian quillwort , is an aquatic pteridophyte that is widely distributed in the eastern United States...
Appalachian Quillwort
- Isoetes beestonii (extinct)
- Isoetes bolanderi
Isoetes bolanderi is a species of quillwort, a type of lycopod. Its common name is Bolander's quillwort. This is a "primitive" aquatic plant native to western North America which grows almost entirely underwater in lakes and other water bodies...
Bolander's Quillwort
- Isoetes brochonii Pyreneean Quillwort
- Isoetes durieui Durieu's Quillwort
- Isoetes echinospora Spring Quillwort
- Isoetes eludens
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 , a small temporary pool formed in a hollowed out area of granite rock...
Elusive Quillwort
- Isoetes engelmannii
Isoetes engelmannii, commonly known as Engelmann's quillwort or Appalachian quillwort , is an aquatic pteridophyte and is the most widely distributed species of its genus in eastern North America...
Engelmann's Quillwort
- Isoetes flaccida Southern Quillwort
- Isoetes gemmifera (syn. Stylites gemmifera)
- Isoetes histrix
Isoetes histrix 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....
Land Quillwort
- Isoetes howellii
Isoetes howellii is a species of quillwort, a type of lycopod. Its common name is Howell's quillwort. This is a "primitive" aquatic plant native to western North America which grows in wet habitat such as vernal pools. It produces pointed, cylindrical, bright green leaves approaching 30 centimeters...
Howell's Quillwort
- Isoetes ivones
- Isoetes lacustris
Isoetes lacustris is a boreal quillwort native on both sides of the northern Atlantic Ocean. In Europe, it is distributed from Poland west to northeastern France, throughout Scandinavia, the west and north of the British Isles, the Faroe Islands and Iceland...
Lake Quillwort
- Isoetes louisianensis Louisiana Quillwort
- Isoetes melanospora
Isoetes melanospora, commonly known as black-spored quillwort or black-spored Merlin's grass, is a rare and endangered aquatic pteridophyte endemic to the U.S. States of Georgia and South Carolina. It grows exclusively in shallow, temporary pools on granite outcrops, often with only 2 cm of soil...
Black-spored Quillwort
- Isoetes nuttallii
Isoetes nuttallii is a species of quillwort, a type of lycopod. Its common name is Nuttall's quillwort. This is a "primitive" plant native to western North America from British Columbia to California which grows in wet habitat such as seasonal streams. It produces pointed, cylindrical, green to...
Nuttall's Quillwort
- Isoetes setacea
- Isoetes taiwanensis
Isoetes taiwanensis is a species of plant in the Isoetaceae family. It is endemic to Taiwan. Its natural habitat is swamps. It is threatened by habitat loss.-Source:* China Plant Specialist Group 2004. . Downloaded on 22 August 2007....
- Isoetes tegetiformans
Isoetes tegetiformans, commonly known as mat-forming quillwort or mat-forming Merlin's grass, is an aquatic pteridophyte endemic to the U.S. State of Georgia. It grows exclusively in shallow, temporary pools on granite outcrops, often with only 2 cm of soil. Only 7 populations are known to exist,...
Mat-forming Quillwort
- Isoetes tenella Spiny Spore Quillwort
- Isoetes tenuissima French Quillwort
- Isoetes valida
Isoetes valida, commonly known as the strong quillwort or true quillwort, is an aquatic pteridophyte native to eastern North America. It is found primarily in the Appalachian Mountains from Pennsylvania south to Alabama and Georgia...
Strong Quillwort
- Isoetes velata
Many species, such as the Louisiana Quillwort and the Mat-forming Quillwort, are
Endangered speciesAn endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...
. Several species of
Isoetes are commonly called
Merlin's grass, especially
I. lacustrisIsoetes lacustris is a boreal quillwort native on both sides of the northern Atlantic Ocean. In Europe, it is distributed from Poland west to northeastern France, throughout Scandinavia, the west and north of the British Isles, the Faroe Islands and Iceland...
, but also the endagered species
I. tegetiformans and
I. virginica.
Evolution
Fossilised specimens of
Isoetes beestonii have been found in rocks dating to the early
TriassicThe Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
. Quillworts are considered by some to be the last remnant of the
fossilFossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
tree
LepidodendronLepidodendron is an extinct genus of primitive, vascular, arborescent plant related to the Lycopsids . It was part of the coal forest flora. They sometimes reached heights of over , and the trunks were often over in diameter, and thrived during the Carboniferous period...
with which they share some unusual features including the development of both wood and bark, a modified shoot system acting as roots, bipolar growth, and an upright stance.
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