Isoetes

Isoetes, commonly known as the quillworts, is the only extant genus of plants in the family Isoetaceae, which is in the class of lycopods. There are currently 192 recognized species,[2] with a cosmopolitan distribution 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.[3]

Isoetes
Isoetes lacustris[1]
Scientific classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Lycophytes
Class: Lycopodiopsida
Order: Isoetales
Family: Isoetaceae
Genus: Isoetes
L.
Species

See text

The name of the genus may also be spelled Isoëtes. The diaeresis (two dots over the e) indicates that the o and the e are to be pronounced in two distinct syllables. Including this in print is optional; either spelling (Isoetes or Isoëtes) is correct.[4]

Description
Quillwort megasporangia

Quillworts are mostly aquatic or semi-aquatic in clear ponds and slow-moving streams, though several (e.g. I. butleri, I. histrix and I. nuttallii) grow on wet ground that dries out in the summer. The Quillworts are spore producing plants and highly rely on water dispersion. Quillworts have different ways to spread their spores based on the environment. Quillwort leaves are hollow and quill-like, with a minute ligule at the base of the upper surface.[5]:7 arising from a central corm. Each leaf is narrow, 2–20 centimetres (0.8–8 in) long (exceptionally up to 100 cm or 40 in) and 0.5–3.0 mm (0.02–0.12 in) wide; they can be either evergreen, winter deciduous, or dry-season deciduous. Stomata are absent, yet the leaves have a thick cuticle which prevents CO2 uptake, a task that is performed by their hollow roots instead, which absorbs CO2 from the sediment.[6] Isoetes andicola is unusual in being the only known terrestrial vascular plant that take up all its CO2 through the roots. Only 4% of total biomass, the tips of the leaves, is chlorophyllous.[7] The roots broaden to a swollen base up to 5 mm (0.2 in) wide where they attach in clusters to a bulb-like, underground rhizome 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 (velum), which is used diagnostically to help identify quillwort species. They are heterosporous. Quillwort species are very difficult to distinguish by general appearance. The best way to identify them is by examining their megaspores under a microscope. Moreover, habitat, texture, spore size, and velum provide features that will distinguish Isoëtes taxa.[8] They also possess a vestigial form of secondary growth in the basal portions of its cormlike stem, an indication that they evolved from larger ancestors.[9]

Taxonomy

Compared to other genera, Isoetes is poorly known. Even after studies with cytology, scanning electron microscopy, and chromatography, species are difficult to identify and their phylogeny is disputed. Vegetative characters commonly used to distinguish other genera, such as leaf length, rigidity, color, or shape are variable and depend on habitat. Most classification systems for Isoetes rely on spore characteristics, which make species identification nearly impossible without microscopy.[10]

Species

As of November 2019, Plants of the World Online accepted the following extant species:[11]

  • Isoetes abyssinica Chiov.
  • Isoetes acadiensis Kott
  • Isoetes aemulans J.P.Roux
  • Isoetes aequinoctialis Welw. ex A.Br.
  • Isoetes alcalophila S.Halloy
  • Isoetes alpina Kirk – New Zealand quillwort
  • Isoetes alstonii C.F.Reed & Verdc.
  • Isoetes × altonharvillii Musselman
  • Isoetes amazonica A.Br.
  • Isoetes anatolica Prada & Rolleri
  • Isoetes andicola (Amstutz) L.D.Gómez
  • Isoetes andina Spruce ex Hook.
  • Isoetes appalachiana D.F.Brunt. & D.M.Britton – Appalachian quillwort
  • Isoetes araucaniana Macluf & Hickey
  • Isoetes asiatica (Makino) Makino
  • Isoetes attenuata C.R.Marsden & Chinnock
  • Isoetes australis S.Williams – Australian quillwort
  • Isoetes azorica Durieu
  • Isoetes baculata Hickey & H.P.Fuchs
  • Isoetes biafrana Alston
  • Isoetes bischlerae H.P.Fuchs
  • Isoetes bolanderi Engelm. – Bolander's quillwort
  • Isoetes boliviensis U.Weber
  • Isoetes boomii Luebke – Boom's quillwort; southeast US
  • Isoetes boryana Durieu
  • Isoetes boyacensis H.P.Fuchs
  • Isoetes bradei Herter
  • Isoetes brasiliensis H.P.Fuchs
  • Isoetes brevicula E.R.L.Johnson
  • Isoetes × brittonii D.F.Brunt. & W.C.Taylor
  • Isoetes × bruntonii Knepper & Musselman
  • Isoetes butleri Engelm. – Butler's quillwort
  • Isoetes cangae J.B.S.Pereira, Salino & Stützel
  • Isoetes capensis
  • Isoetes × carltaylorii Musselman
  • Isoetes caroli E.R.L.Johnson – Brazil
  • Isoetes caroliniana (A.A.Eaton) Luebke is regarded by Plants of the World Online as a synonym of Isoetes valida, but other sources treat it as a valid species[12]
  • Isoetes chubutiana Hickey, Macluf & W.C.Taylor
  • Isoetes coreana Y.H.Chung & H.K.Choi is a synonym of Isoetes sinensis var. coreana
  • Isoetes coromandelina L.f.
  • Isoetes creussensis Lazare & S.Riba
  • Isoetes cristata C.R.Marsden & Chinnock
  • Isoetes cubana Engelm.
  • Isoetes delilei (Bory) Rothm.
  • Isoetes dispora Hickey
  • Isoetes dixitii Shende
  • Isoetes × dodgei A.A.Eaton
  • Isoetes drummondii A.Braun – Drummond's quillwort
  • Isoetes durieui Bory – Durieu's quillwort
  • Isoetes × eatonii R.Dodge – Eaton's quillwort
  • Isoetes echinospora Durieu
  • Isoetes × echtuckerii D.F.Brunt. & D.M.Britton
  • Isoetes ecuadoriensis Aspl.
  • Isoetes ekmanii U.Weber
  • Isoetes elatior A.Braun
  • Isoetes eludens J.P.Roux, Hopper & Rhian J.Sm. – elusive quillwort
  • Isoetes engelmannii A.Braun – Engelmann's quillwort
  • Isoetes escondidensis S.Halloy
  • Isoetes eshbaughii Hickey & H.P.Fuchs
  • Isoetes × fairbrothersii J.D.Montgom. & W.C.Taylor
  • Isoetes flaccida Shuttlew. – southern quillwort
  • Isoetes fluitans M.I.Romero
  • Isoetes × foveolata A.A.Eaton
  • Isoetes fuliginosa R.L.Small & Hickey
  • Isoetes fuscomarginata H.P.Fuchs
  • Isoetes gardneriana Kunze
  • Isoetes georgiana Luebke – Georgia quillwort; southeast US
  • Isoetes giessii Launert
  • Isoetes gigantea U.Weber
  • Isoetes × gopalkrishnae S.K.Singh, P.K.Shukla & N.K.Dubey
  • Isoetes graniticola D.F.Brunt.
  • Isoetes gunnii A.Braun
  • Isoetes gymnocarpa (Gennari) A.Braun
  • Isoetes habbemensis Alston
  • Isoetes hallasanensis H.K.Choi, Ch.Kim & J.Jung – Korea
  • Isoetes × harveyi A.A.Eaton (syn. Isoetes × heterospora Eaton)
  • Isoetes haussknechtii Troìa & Greuter
  • Isoetes hawaiiensis W.C.Taylor & W.H.Wagner
  • Isoetes heldreichii Wettst.
  • Isoetes hemivelata R.L.Small & Hickey
  • Isoetes × herb-wagneri W.C.Taylor
  • Isoetes herzogii U.Weber
  • Isoetes hewitsonii Hickey
  • Isoetes × hickeyi W.C.Taylor & Luebke
  • Isoetes hieronymi U.Weber
  • Isoetes histrix Bory – land quillwort; Channel Islands
  • Isoetes hopei J.R.Croft
  • Isoetes howellii Engelm. – Howell's quillwort
  • Isoetes humilior A.Braun
  • Isoetes hyemalis D.F.Brunt. is a synonym of Isoetes riparia var. amesii
  • Isoetes hypsophila Hand.-Mazz.
  • Isoetes inflata E.R.L.Johnson
  • Isoetes jaegeri Pitot
  • Isoetes jamaicensis Hickey
  • Isoetes japonica A.Braun – Japan
  • Isoetes × jeffreyi D.M.Britton & D.F.Brunt.
  • Isoetes jejuensis H.K.Choi, Ch.Kim & J.Jung
  • Isoetes junciformis D.F.Brunt. & D.M.Britton – rush quillwort; southeast US
  • Isoetes karstenii A.Braun
  • Isoetes killipii C.V.Morton
  • Isoetes kirkii A.Braun
  • Isoetes labri-draconis N.R.Crouch
  • Isoetes lacustris L. – lake quillwort
  • Isoetes laosiensis C.Kim & H.K.Choi
  • Isoetes lechleri Mett.
  • Isoetes libanotica Musselman, Bolin & R.D.Bray
  • Isoetes lithophila N.Pfeiff.
  • Isoetes longissima Bory
  • Isoetes louisianensis Thieret – Louisiana quillwort
  • Isoetes luetzelburgii U.Weber
  • Isoetes macrospora
  • Isoetes malinverniana Ces. & De Not.
  • Isoetes × marensis D.M.Britton & D.F.Brunt.
  • Isoetes maritima Underw. – maritime quillwort
  • Isoetes martii A.Braun
  • Isoetes mattaponica Musselman & W.C.Taylor
  • Isoetes maxima Hickey, Macluf & Link-Pérez
  • Isoetes melanopoda J.Gay & Durieu – black-footed quillwort
  • Isoetes melanospora Engelm. – black-spored quillwort
  • Isoetes melanotheca Alston
  • Isoetes mexicana Underw. (syn. Isoetes montezumae A.A.Eaton)
  • Isoetes × michinokuana M.Takamiya, Mits.Watan. & K.Ono
  • Isoetes microvela D.F.Brunt.
  • Isoetes minima A.A.Eaton
  • Isoetes mississippiensis S.W.Leonard, W.C.Taylor, Musselman & R.D.Bray
  • Isoetes mongerensis E.R.L.Johnson – Monger quillwort
  • Isoetes montana U.Weber
  • Isoetes mourabaptistae J.B.S.Pereira, P.G.Windisch, Lorscheitt. & Labiak
  • Isoetes muelleri A.Braun – Mueller's quillwort
  • Isoetes naipiana P.G.Windisch, Lorscheitt. & Nervo
  • Isoetes nana J.B.S.Pereira
  • Isoetes neoguineensis
  • Isoetes nigritiana A.Br.
  • Isoetes nigroreticulata Verdc.
  • Isoetes × novae-angliae D.F.Brunt. & D.M.Britton
  • Isoetes novogranadensis H.P.Fuchs
  • Isoetes nuttallii A.Braun – Nuttall's quillwort
  • Isoetes occidentalis L.F.Hend.
  • Isoetes olympica A.Br.
  • Isoetes orcuttii A.A.Eaton - Orcutt's quillwort
  • Isoetes organensis U.Weber
  • Isoetes orientalis Hong Liu & Q.F.Wang
  • Isoetes ovata N.Pfeiff.
  • Isoetes pallida Hickey
  • Isoetes palmeri H.P.Fuchs
  • Isoetes panamensis Maxon & C.V.Morton
  • Isoetes × paratunica D.F.Brunt., Mochalova & A.A.Bobrov
  • Isoetes parvula Hickey
  • Isoetes pedersenii H.P.Fuchs ex E.I.Meza & Macluf
  • Isoetes perralderiana Durieu & Letourn. ex Milde
  • Isoetes perrieriana Iversen
  • Isoetes philippinensis Merr. & L.M.Perry
  • Isoetes phrygia Hausskn.
  • Isoetes piedmontana (N.Pfeiff.) C.F.Reed – Piedmont quillwort
  • Isoetes pitotii Alston
  • Isoetes precocia R.L.Small & Hickey
  • Isoetes pringlei Underw.
  • Isoetes prototypus D.M.Britton & Goltz
  • Isoetes pseudojaponica M.Takamiya, Mits.Watan. & K.Ono
  • Isoetes × pseudotruncata D.M.Britton & D.F.Brunt.
  • Isoetes pusilla C.R.Marsden & Chinnock
  • Isoetes quiririensis J.B.S.Pereira & Labiak
  • Isoetes ramboi Herter
  • Isoetes riparia Engelm. ex A.Braun
  • Isoetes sabatina Troìa & Azzella
  • Isoetes saccharata Engelm.
  • Isoetes sahyadrii Mahab.
  • Isoetes saracochensis Hickey
  • Isoetes savatieri Franch.
  • Isoetes schweinfurthii A.Br.
  • Isoetes sehnemii H.P.Fuchs
  • Isoetes septentrionalis D.F.Brunt.
  • Isoetes serracarajensis J.B.S.Pereira, Salino & Stützel
  • Isoetes setacea Lam.
  • Isoetes sinensis T.C.Palmer – China
  • Isoetes smithii H.P.Fuchs
  • Isoetes spannagelii H.P.Fuchs
  • Isoetes spinulospora C.Jermy & Schelpe
  • Isoetes stellenbossiensis A.V.Duthie
  • Isoetes stephanseniae A.V.Duthie
  • Isoetes stevensii J.R.Croft
  • Isoetes storkii T.C.Palmer
  • Isoetes taiwanensis De Vol – Taiwan
  • Isoetes tamaulipana Mora-Olivo, A.Mend. & Mart.-Aval. – Tamaulipas, México
  • Isoetes tegetiformans Rury – mat-forming quillwort
  • Isoetes tenella Léman ex Desv. – spiny-spore quillwort
  • Isoetes tennesseensis Luebke & Budke – Tennessee quillwort; southeast US
  • Isoetes tenuifolia Jermy
  • Isoetes tenuissima Boreau – French quillwort
  • Isoetes texana Singhurst, Rushing & W.C.Holmes
  • Isoetes todaroana Troìa & Raimondo
  • Isoetes toximontana Musselman & J.P.Roux - green-spored quillwort; South Africa
  • Isoetes transvaalensis C.Jermy & Schelpe
  • Isoetes triangula U.Weber
  • Isoetes tripus A.Braun
  • Isoetes truncata Clute
  • Isoetes tuckermanii A.Braun ex Engelm.
  • Isoetes tuerckheimii Brause
  • Isoetes udupiensis P.K.Shukla, G.K.Srivast., S.K.Shukla & P.K.Rajagopal
  • Isoetes ulei U.Weber
  • Isoetes valida Clute – Carolina or strong quillwort
  • Isoetes vanensis M.Keskin & G.Zare
  • Isoetes vermiculata Hickey
  • Isoetes virginica N.Pfeiff. is a synonym of Isoetes melanopoda subsp. melanopoda
  • Isoetes viridimontana M.A.Rosenthal & W.C.Taylor – Green Mountain quillwort
  • Isoetes weberi Herter
  • Isoetes welwitschii A.Br. ex Kuhn
  • Isoetes wormaldii Sim
  • Isoetes yunguiensis Q.F.Wang & W.C.Taylor

Many species, such as the Louisiana quillwort and the mat-forming quillwort, are endangered species. Several species of Isoetes are commonly called Merlin's grass, especially I. lacustris, but also the endangered species I. tegetiformans.

Evolution

Fossilised specimens of I. beestonii have been found in rocks dating to the latest Permian.[13][14] Quillworts are considered to be the closest extant relatives of the fossil tree Lepidodendron, 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.

 
 

† Lepidodendrales

 
 
 

† Pleuromeia

 
 
 

† Nathorstiana

 
 

Isoetes

 
 
 
 
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References
  1. Illustration from Otto Wilhelm Thomé, Flora von Deutschland, Österreich und der Schweiz, 1885, Gera, Germany
  2. Troia, Angelo; Pereira, Jovani B.; Kim, Changkyun; Taylor, W. Carl (2016). "The genus Isoetes (Isoetaceae): a provisional checklist of the accepted and unresolved taxa". Phytotaxa. 277 (2): 101. doi:10.11646/phytotaxa.277.2.1. ISSN 1179-3163.
  3. Larsén, Eva; Rydin, Catarina (2016). "Disentangling the Phylogeny ofIsoetes(Isoetales), Using Nuclear and Plastid Data". International Journal of Plant Sciences. 177 (2): 157–174. doi:10.1086/684179. ISSN 1058-5893.
  4. International Code of Nomenclature for algae, fungi, and plants (Melbourne Code) see section 60.6: "The diaeresis, indicating that a vowel is to be pronounced separately from the preceding vowel (as in Cephaëlis, Isoëtes), is a phonetic device that is not considered to alter the spelling; as such, its use is optional."
  5. Stace, C. A. (2010). New Flora of the British Isles (3rd ed.). Cambridge, U.K.: Cambridge University Press. ISBN 9780521707725.
  6. Ecology of High Altitude Waters].
  7. Tropical Alpine Environments: Plant Form and Function
  8. Isoëtes Linnaeus, Sp. Pl. 2: 1100. 1753; Gen. Pl. ed. 5, 486, 1754.
  9. The Formation of Wood in Forest Trees: The Second Symposium Held under the Auspices of the Maria Moors Cabot Foundation for Botanical Research
  10. Cody, William; Britton, Donald (1989). Ferns and Fern Allies of Canada. Agriculture Canada.
  11. "Isoetes L.". Plants of the World Online. Royal Botanic Gardens, Kew. Retrieved 2019-11-18.
  12. Hassler, Michael & Schmitt, Bernd (November 2019). "Isoetes caroliniana". Checklist of Ferns and Lycophytes of the World. 8.11. Retrieved 2019-11-18.
  13. Retallack, G. J. (1997). "Earliest Triassic Origin of Isoetes and Quillwort Evolutionary Radiation". Journal of Paleontology. 71 (3): 500–521. doi:10.1017/s0022336000039524. JSTOR 1306630.
  14. Retallack, Gregory J. (2013). "Permian and Triassic greenhouse crises". Gondwana Research. 24: 90–103. doi:10.1016/j.gr.2012.03.003.
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