Ophioglossaceae

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Ophioglossaceae
Ophioglossum closeup.jpg
Ophioglossum vulgatum
Scientific classification e
Kingdom: Plantae
Division: Pteridophyta
Class: Psilotopsida
Order: Ophioglossales
Family: Ophioglossaceae
C. Agardh
Genera [1]

Ophioglossaceae, the adder's-tongue family, is a family of ferns (though some studies have instead suggested a closer relationship to angiosperms[2]), currently thought to be most closely related to Psilotaceae, the two together comprising the class Ophioglossidae as the sibling group to the rest of the ferns. The Ophioglossaceae is one of two groups of ferns traditionally known as eusporangiate ferns.

Description[edit]

These ferns differ from the other ferns in several respects:

  • they produce only a single leaf at a time
  • instead of the leptosporangia typical of most ferns they produce eusporangia, which are larger, contain more spores, and have thicker walls
  • their sporophylls are divided into two distinct parts, the sporophore which produces sporangia and has a greatly reduced and modified blade, and the trophophore, which is very similar to the trophophylls in size, color, shape, and so forth
  • their gametophytes are subterranean and rely on fungi for their energy (in other words, they are mycoheterotrophic), unlike the terrestrial, photosynthetic gametophytes found in most ferns.

Members of Ophioglossaceae are usually terrestrial (excepting a few epiphytic species of Ophioglossum) and occur in both temperate and tropical areas. The leaves are usually fleshy, and in temperate areas will often turn brownish or reddish during colder months. In addition to having mycoheterotrophic gametophytes, there are a few members of Botrychium that are unique among ferns in having the sporophytes also mycoheterotrophic, producing only small, ephemeral sporophylls that do not photosynthesize.

Adder's tongue (Ophioglossum reticulatum), a member of this family, is notable for having as many as 1260 chromosomes.[3] For comparison, humans have 46 chromosomes, consisting of 23 pairs.

Classification[edit]

In all modern classifications, from the Smith system of 2006 forward, Ophioglossaceae is the single family in order Ophioglossales.[4][5][6] The Smith system of 2006 divides the family into four genera: Botrychium s.l. (including Sceptridium, Botrypus, and Japanobotrychium), Helminthostachys, Mankyua, and Ophioglossum s.l. (including Cheiroglossa and Ophioderma).[4] Christenhusz et al., in 2011, recognized Cheiroglossa as a segregate of Ophioglossum.[5] The Christenhusz and Chase system of 2014 included Cheiroglossa in Ophioglossum again.[7] The PPG I system divides the family into four subfamilies:[6]

References[edit]

  1. ^ Genera Tropicos.org. Missouri Botanical Garden. 15 Jan 2012
  2. ^ [1]
  3. ^ Grubben, Gerardus J. H. Vegetables. PROTA. p. 404. ISBN 978-90-5782-147-9. 
  4. ^ a b Smith, Alan R.; Pryer, Kathleen M.; Schuettpelz, Eric; Korall, Petra; Schneider, Harald; Wolf, Paul G. (August 2006). "A classification for extant ferns" (PDF). Taxon. 55 (3): 705–731. doi:10.2307/25065646. 
  5. ^ a b Christenhusz, Maarten J. M.; Zhang, Xian-Chun; Schneider, Harald (18 February 2011). "A linear sequence of extant families and genera of lycophytes and ferns" (PDF). Phytotaxa. 19: 7–54. 
  6. ^ a b The Pteridophyte Phylogeny Group (November 2016). "A community-derived classification for extant lycophytes and ferns". Journal of Systematics and Evolution. 54 (6): 563–603. doi:10.1111/jse.12229. 
  7. ^ Christenhusz, Maarten J. M.; Chase, Mark W. (13 February 2014). "Trends and concepts in fern classification". Annals of Botany. 113 (4): 571–594. doi:10.1093/aob/mct299. 
  8. ^ Kato, M (1987). "A phylogenetic classification of Ophioglossaceae". The Gardens' Bulletin Singapore. 40: 1–14.