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Classification of the Phylum Anthocerotophyta Stotl. & Crand.-Stotl.

This generic description of hornworts is based on Renzaglia, Villarreal & Duff (2008), New insights into morphology, anatomy and systematics of hornworts, in Goffinet & Shaw (eds.) Bryophyte Biology 2nd edition, Cambridge University Press. Suprageneric classification has been mostly adopted from Duff, Villarreal, Cargill & Renzaglia (2007) Progress and challenges toward developing a phylogeny and classification of the hornworts, The Bryologist110: 214-243 and Stotler & B. Crandall-Stotler (2005) A Revised Classification of the Anthocerotophyta and a Checklist of the Hornworts of North America, North of Mexico, The Bryologist 108: 16-26.

The site is maintained by JC Villarreal and B. Goffinet. We deeply appreciate the late Dr. Ray Stotler’s comments on nomenclatural clarifications.  The phylogenetic arrangement is followed by the annotated classification.

Please direct any comments, report mistakes, and communicate changes to JC Villarreal A. We would appreciate receiving reprints of publications proposing new phylogenetic relationships or systematic affinities of hornwort genera.


Phylogenetic arrangement of hornwort genera

 

LEIOSPOROCEROTOPSIDA Stotl. & Crand.-Stotl.

LEIOSPOROCEROTALES Hässel

Leiosporocerotaceae Hässel ex Ochyra
Leiosporoceros Hässel

ANTHOCEROTOPSIDA Jancz. ex Stotl. & Crand.-Stotl.

    ANTHOCEROTIDAE Rosenv. corr. Prosk. emend Duff et al.

ANTHOCEROTALES Limpr. in Cohn.

Anthocerotaceae Dumort. corr. Trevis. emend Hässel
Anthoceros L.
Folioceros D.C. Bharadwaj
Sphaerosporoceros Hässel

    NOTOTHYLATIDAE Duff, J.C. Villarreal, Cargill & Renzaglia

NOTOTHYLADALES Hyvönen & Piippo
Notothyladaceae (Milde) Müll. Frib. ex Prosk. emend. Hässel
   Notothylatoideae Grolle
Notothylas Sull. ex A. Gray
   Phaeocerotoideae Hässel
Phaeoceros Prosk.
Paraphymatoceros Hässel
Hattorioceros (J. Haseg.) J. Haseg.
Mesoceros Piippo

   DENDROCEROTIDAE Duff, J.C. Villarreal, Cargill & Renzaglia

DENDROCEROTALES Hässel emend. Duff et al.
Dendrocerotaceae (Milde) Hässel emend Duff et al.
    Dendrocerotoideae R.M. Schust.
Dendroceros Nees
Megaceros Campbell
Nothoceros (R.M. Schust.) J. Haseg.
   Phaeomegacerotoideae Duff, J.C. Villarreal, Cargill & Renzaglia
Phaeomegaceros Duff, J.C. Villarreal, Cargill & Renzaglia
PHYMATOCEROTALES Duff, J.C. Villarreal, Cargill & Renzaglia
Phymatocerotaceae Duff, J.C. Villarreal, Cargill & Renzaglia
Phymatoceros Stotler, Doyle & Crandall-Stotler emend. Duff et al.

Annotation of hornwort classification

LEIOSPOROCEROTOPSIDA Stotl. & Crand.-Stotl., The Bryologist 108: 19. 2005.

LEIOSPOROCEROTALES Hässel J. Hattori Bot. Lab. 64: 82. 1988.

Leiosporocerotaceae Hässel J. Bryol. 14: 255. 1986.

Leiosporoceros Hässel J. Bryol. 14: 255. 1986.

Thalli typically solid, but with schizogenous cavities in older thalli; mucilage clefts absent in Nostoc-infected tissues, present in young uninfected plants. Nostoc colonies in longitudinally oriented strands in mucilage-filled schizogenous canals. Chloroplasts 1 per cell without pyrenoid. Antheridia numerous (to 80 per chamber) with tiered jacket cell arrangement. Capsules with stomata. Massive sporogenous tissue (6–9 layers). Spore tetrads bilateral alterno-opposite. Spores yellow, minute, ovoid, nearly smooth; Y-shaped to monolete mark present. Pseudoelaters usually unicellular, thick-walled. A monotypic class with a single species, Leiosporoceros dussii (Steph.) Hässel.

ANTHOCEROTOPSIDA Jancz. ex Stotl. & Crand.-Stotl., The Bryologist 108: 19, 24. 2005.

Differing from Leiosporocerotopsida by cyanobacteria in discrete globose colonies and presence of ventral clefts in young and adult plants. Spores mostly in tetrahedral tetrads, except some species that have decussate tetrads, ornamented, not smooth.

   ANTHOCEROTIDAE Rosenv. corr. Prosk. emend Duff et al., Taxon 7: 214. 1958.*

ANTHOCEROTALES Limpr. in Cohn., Krypt.-Fl. Schlesien 1: 239, 345. 1877.

Anthocerotaceae Dumort. corr. Trevis. emend Hässel, J. Hattori Bot. Lab. 64: 79. 1988.

Thallus with mucilage-containing schizogenous cavities. Pyrenoid present or absent. Antheridia numerous (to 60) per chamber with a tiered jacket cell arrangement. Capsules with stomata (except Folioceros incurvus (Steph.) D. C. Bharadwaj. Spores smoky gray to dark brown to blackish with or without a defined trilete mark; ornamentation spinose, punctate, baculate, jagged, mamillate or lamellate.

Anthoceros L. emend. Prosk., Bull. Torrey Bot. Club 78: 346. 1951.

Thalli and involucres with mucilage-containing schizogenous cavities. Chloroplasts 1 (–4) per cell with pyrenoid (A. punctatus L. ) or starch-free area (A. fusiformis Aust.). Antheridia numerous (to 45) per chamber with tiered jacket cell arrangement. Capsules with stomata. Spores smoky gray, dark brown to blackish with a defined trilete mark; ornamentation spinose, punctate, baculate, or lamellate, sometimes with proximal foramens or depressions (A. punctatus group). Pseudoelaters thin-walled.

Folioceros D.C. Bharadwaj, Geophytology 1: 9. 1971.

Thalli and involucres with mucilage-containing schizogenous cavities. Chloroplasts 1 (–2) per cell with a pyrenoid [ F. fuciformis (Mont.) D.C. Bharadwaj ] or absent [ F. assamicus D.C. Bharadwaj). Antheridia numerous (to 60) per chamber with tiered jacket cell arrangement. Capsules with stomata, except F. incurvus. Spores smoky gray, brown to blackish without a defined trilete mark; distal and proximal ornamentation spinose, reticulate, mamillose, or lamellate. Pseudoelaters elongated strongly, thick-walled.

Sphaerosporoceros Hässel, J. Hattori Bot. Lab. 64: 79. 1988.

Thalli and involucres with mucilage-containing schizogenous cavities. Chloroplasts 1 per cell with a pyrenoid. Capsules with stomata. Spores dark brown to blackish with a reduced defined trilete mark; ornamentation connate-cristate with ridges to short blunt-spines. Pseudoelaters quadrate–subglobose to cylindrical cells, thin-walled with faint thickenings.

   NOTOTHYLATIDAE Duff, J.C. Villarreal, Cargill & Renzaglia, The Bryologist 110: 240. 2007.

Thallus solid [except one unconfirmed report of N. orbicularis (Schwein.) Sull.]. Pyrenoid present or absent. Antheridia (1–)2–4(−8) per chamber. Stomata present or absent, suture elaborate, rudimentary or absent. Spores yellow to blackish, often with equatorial girdle. The type species of both genera have conspicuous pyrenoids, but otherPhaeoceros [e.g., P. pearsonii** (M. Howe) Prosk.] in that clade and several Notothylas (e.g., N. nepalensis Singh) lack pyrenoids.

NOTOTHYLADALES Hyvönen & Piippo, J. Hattori Bot. Lab. 74: 117. 1993 “Notothylales.”

Notothyladaceae (Milde) Müll. Frib. ex Prosk., Phytomorphology 10: 10. 1960.

   Notothylatoideae Grolle J. Bryol. 7: 215. 1972.

Notothylas Sull. ex A. Gray, Amer. J. Sci. Arts, II, 1: 74. 1846.

Thalli solid. Chloroplasts 1 (–3) per cell with a pyrenoid (N. orbicularis) or absent (N. nepalensis). Antheridia 2–4(–6) per chamber usually with non-tiered jacket cell arrangement. Sporophytes short, lying horizontally in the thallus, mostly or totally enclosed within the involucre. Stomata absent. Suture elaborate, rudimentary, or absent. Columella present (N. dissectaSteph.) or absent [ N. javanica (Sande Lac) Gottsche]. Spores yellow to blackish with an equatorial girdle; ornamentation finely vermiculate, granulose to tuberculate, sometimes with dimples in proximal face (N. depressipora J. Haseg.). Pseudoelaters absent to sub- quadrate–elongated with or without annular thickenings.

   Phaeocerotoideae Hässel J. Hattori Bot. Lab. 64: 81. 1988.

Phaeoceros Prosk., Bull. Torrey Bot. Club 78: 346. 1951.

Thalli solid. Marginal or short ventral tubers present or absent. Chloroplasts 1 (–2) per cell with pyrenoid present [ P. laevis (L.) Prosk.] or absent (P. pearsoni). Antheridia (1–) 2–6 (–8) per chamber with non-tiered jacket cell arrangement. Stomata present. Spores yellow to brownish when completely mature, with equatorial girdle; ornamentation spinose (P. laevis–carolinianus group) to distally covered by rounded protuberances [ P. himalayensis (Kash.) Prosk. ex Bapna & Vyas]. Pseudoelaters thin-walled.

Paraphymatoceros Hässel, Phytologia 88: 208. 2006.

Thalli solid. Apical flattened and disk-shaped tubers. Chloroplasts 1 (–2) per cell, without pyrenoid. Antheridia 2–5 per chamber with non-tiered jacket cell arrangement. Stomata present. Spores yellow to blackish-brownish when completely mature, with equatorial girdle; ornamentation of rounded protuberances in distal face. Pseudoelaters mostly unicellular [ P. hallii (Aust.) Prosk.], 4-celled in the other taxa (disintegrating in P. diadematus Hässel).

Hattorioceros (J. Haseg.) J. Haseg., J. Hattori Bot. Lab. 76: 32. 1994.

Thalli solid. Chloroplast and antheridium morphology unknown. Stomata present. Spores yellow to brownish. Spores small (usually less than 20 mm) without a triradiate mark, variable in shape, mostly ovoidal; ornamentation surface deeply canaliculate–striate. Pseudoelaters unevenly thick-walled.

Mesoceros Piippo, Acta Bot. Fenn. 148: 30. 1993.***

Thalli solid. Chloroplast morphology unknown. Antheridia 2–3 per chamber with a non-tiered jacket cell arrangement. Spores dark brown; ornamentation papillate to connate with reticulate ridges. Pseudoelaters thin-walled with faint thickenings.

   DENDROCEROTIDAE Duff, J.C. Villarreal, Cargill & Renzaglia, The Bryologist 110: 239. 2007.

Thallus solid except in Dendroceros subgenus Apoceros and with a single antheridium per cavity except Phymatoceros bulbiculosus (Brot.) Stotler et al. and Phaeomegaceros hirticalyx (Steph.) Duff et al. ; chloroplast without pyrenoid except Phymatoceros bulbiculosus and some Nothoceros or a modified pyrenoid as in Dendroceros.

DENDROCEROTALES Hässel emend. Duff et al., J. Hattori Bot. Lab. 64: 82. 1988.

Dendrocerotaceae (Milde) Hässel emend Duff et al., The Bryologist 110: 239. 2007.

   Dendrocerotoideae R.M. Schust., Phytologia 63: 195, 200. 1987.

Dendroceros Nees in Gottsche, Lindenb. & Nees, Syn. Hepat. 579. 1846.

Thalli solid (subg. Dendroceros) or with mucilage- containing schizogenous cavities (subg. Apoceros), involucres solid in both subgenera. Thalli with a conspicuous midrib and perforated wings. Nostoc present as bulging globose colonies in the ventral and dorsal side of the thallus. Band or pit-field-like thickenings present in the thallus cell walls. Chloroplasts 1 per cell with a conspicuous pyrenoid with spherical inclusions. Antheridia typically 1 per chamber with a non-tiered jacket cell arrangement. Stomata absent. Spores multicellular owing to endosporic germination, colorless to pale yellow, appearing green in live spores owing to large chloroplasts and thin exine; ornamentation papillose to shortly tuberculate. Pseudoelaters with helical thickenings.

Megaceros Campbell, Ann. Bot. (London) 21: 484. 1907.

Thalli solid. Band or pit-field-like thickenings present in the thallus cell walls. Chloroplasts 1–8 (–12) per cell without pyrenoid. Antheridia typically1 (–2) per chamber with non-tiered jacket cell arrangement. Stomata absent. Spores colorless to pale yellow, appearing green in live spores due to large chloroplasts and thin exine; ornamentation mamillose and/or tuberculate in distal face, lowly papillate in proximal face. Pseudoelaters with helical thickenings.

Nothoceros (R.M. Schust.) J. Haseg., J. Hattori Bot. Lab. 76: 32. 1994, “Notoceros.”****

Thalli solid, in rosette or pinnately branched with thin (less than 1 mm) branches resembling Riccardia[e.g. one phenotype of Megaceros aenigmaticus R.M Schust.] or with a conspicuous midrib and imperforated wings (e.g. Nothoceros superbus J.C. Villarreal et al.). Band or pit-field-like thickenings present in the thallus cell walls. Chloroplasts 1–2 (–8) per cell. Pyrenoid absent [ N. endiviaefolius(Mont.) J. Haseg.] or present [ M. vincentianus (Lehm. & Lindenb.) Campbell]. Antheridia typically1 (–2) per chamber with a non-tiered jacket cell arrangement. Stomata absent. Spores colorless to pale yellow, appearing green in live spores owing to large chloroplasts and thin exine; ornamentation mammillose and/or tuberculate, similar to that of Megaceros. Pseudoelaters with helical thickenings.

   Phaeomegacerotoideae Duff, J.C. Villarreal, Cargill & Renzaglia, The Bryologist 110: 241. 2007.

Phaeomegaceros Duff, J.C. Villarreal, Cargill & Renzaglia, The Bryologist 110: 241. 2007.

Thalli solid. Band or pit-field-like thickenings present in the thallus cell walls. Chloroplasts 1–2 per cell without a pyrenoid. Antheridia typically 1 (–8, in Javanese P. hirticalyx) per chamber with a non-tiered jacket cell arrangement. Stomata present. Spores yellow to brownish when completely mature, with equatorial girdle; ornamentation finely vermiculate with distal dimples. Pseudoelaters thin-walled to unevenly thick-walled.

PHYMATOCEROTALES Duff, J.C. Villarreal, Cargill & Renzaglia, The Bryologist 110: 240. 2007.

Phymatocerotaceae Duff, J.C. Villarreal, Cargill & Renzaglia, The Bryologist 110: 240. 2007.

Phymatoceros Stotler, Doyle & Crandall-Stotler emend Duff et al., The Bryologist 110: 240. 2007.

Thalli solid. Long-stalked ventral tubers. Chloroplasts 1 (–2) per cell with a pyrenoid (P. bulbiculosus) or absent [ P. phymatodes (M. Howe) Duff et al.] Antheridia 1–3 (–4) per chamber with non-tiered jacket cell arrangement . Stomata present. Spores yellow to brownish when completely mature, with equatorial girdle; ornamentation finely vermiculate with a distal protuberance, distal spore ornamentation obscured by late spore wall deposition. Pseudoelaters thin-walled.