Psilotopsida

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Psilotopsida
Psilotum.jpg
Scientific classification edit
Kingdom: Plantae
Division: Pteridophyta
Class: Psilotopsida
D. H. Scott
Orders & families

Psilotopsida is a class of ferns or fern-like plants, considered to be one of the three classes of eusporangiate ferns.[1] It should not be confused with the obsolete class Psilophytopsida. As circumscribed by Smith et al., 2006,[2] Psilotopsida contains two families, Psilotaceae and Ophioglossaceae, placed in orders Psilotales and Ophioglossales, respectively.[3] The affinities of these two groups have long been unclear and a close relationship between them has only recently been confirmed through molecular systematic studies. Some studies show that Psilotopsida is the sister-group to all other ferns (including Marattiaceae and Equisetaceae),[1][4] but others indicate that Equisetaceae is more basal.[5]

Psilotales have rhizoids instead of real roots, and the roots in Ophioglossales are lacking both root branches and root hairs. The gametophytes of both orders are heterotrophic and often subterranean, getting nutrients from mycorrhiza instead of performing photosynthesis, which happens exclusively in the sporophyte.[6]

References[edit]

  1. ^ a b Kathleen M. Pryer; Eric Schuettpelz; Paul G. Wolf; Harald Schneider; Alan R. Smith & Raymond Cranfill (2004). "Phylogeny and evolution of ferns (monilophytes) with a focus on the early leptosporangiate divergences" (PDF). American Journal of Botany. 91 (10): 1582–1598. doi:10.3732/ajb.91.10.1582. PMID 21652310.
  2. ^ Alan R. Smith; Kathleen M. Pryer; Eric Schuettpelz; Petra Korall; Harald Schneider; Paul G. Wolf (2006). "A classification for extant ferns" (PDF). Taxon. 55 (3): 705–731. doi:10.2307/25065646.
  3. ^ Maarten J. M. Christenhusz, Xian-Chun Zhang & Harald Schneider (2011). "A linear sequence of extant families and genera of lycophytes and ferns" (PDF). Phytotaxa. 19: 7–54.
  4. ^ Samuli Lehtonen (2011). "Towards Resolving the Complete Fern Tree of Life" (PDF). PLoS ONE. 6 (10): e24851. doi:10.1371/journal.pone.0024851. PMC 3192703. PMID 22022365.
  5. ^ Hardeep S. Rai & Sean W. Graham (2010). "Utility of a large, multigene plastid data set in inferring higher-order relationships in ferns and relatives (Monilophytes)" (PDF). American Journal of Botany. 97 (9): 1444–1456. doi:10.3732/ajb.0900305. PMID 21616899.
  6. ^ Plant Systematics