Dioscoreales

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Dioscoreales
Temporal range: Mid
Ma
Dioscorea communis
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Monocots
Order: Dioscoreales
Mart.[1][2][3]
Type species
Dioscorea villosa
Families
Synonyms
  • Burmanniales Heintze
  • Nartheciales
    Reveal
    & Zomlefer
  • Taccales Dumortier
  • Tamales Dumortier
  • Dioscoreanae Reveal & Doweld
  • Burmanniidae Heintze

The Dioscoreales are an

genera and about 850 species
.

Dioscoreales contains the family Dioscoreaceae, which notably includes the yams (Dioscorea) and several other bulbous and tuberous plants, some of which are heavily cultivated as staple food sources in certain countries.

Certain species are found solely in arid climates (incl. parts of Southern Africa), and have adapted to this harsh environment as caudex-forming, perennial caudiciformes, including Dioscorea elephantipes, the "elephant's foot" or "elephant-foot yam".

Older systems tended to place all lilioid monocots with

autotrophic Nartheciaceae
.

Description

Dioscoreales are

capsule or berry. In the seed, the endotegmen is tanniferous and the embryo short.[6]

All of the species except the genera placed in

microsporogenesis
which is one of the traits indicating that the family is sister to all the other members included in the order.

Taxonomy

Pre-Darwinian

For the early history from

dicotyledons, leading some authors to place the order as intermediate between the monocotyledons and the dicotyledons.[9]

D. polystachya
) in Hooker's A General System of Botany 1873

While Lindley did not use the term "Dioscoreales", he placed the family Dioscoraceae together with four other families in what he referred to as an Alliance (the equivalent of the modern Order) called Dictyogens. He reflected the uncertainty as to the place of this Alliance by placing it as a class of its own between Endogens (monocots) and Exogens (dicots)

Hook.f.) for his use of the term "Dioscorales" in 1873[12] with a single family, Dioscoreae.[13] However, in his more definitive work, the Genera plantara (1883), he simply placed Dioscoraceae in the Epigynae "Series".[14]

Post-Darwinian

Although

Magnoliophyta=angiosperms) recognised Dioscoreales as a distinct order, but demonstrated wide variations in its composition.[5][9]

monogeneric Taccaceae, then in its own order, Taccales. Similar considerations were discussed with respect to two Asparagales families, Smilacaceae and Petermanniaceae.[20]

In Dahlgren's third and final version (1985)

Trichopodaceae and Trilliaceae. Thismiaceae has either been treated as a separate family closely related to Burmanniaceae or as a tribe (Thismieae) within a more broadly defined Burmanniaceae, forming a separate order, Burmanniales, in the Dahlgren system.[23] The related Nartheciaceae were treated as tribe Narthecieae within the Melanthiaceae in a third order, the Melanthiales, by Dahlgren.[22] Dahlgren considered the Dioscoreales to most strongly resemble the ancestral monocotyledons, and hence sharing "dicotyledonous" characteristics, making it the most central monocotyledon order.[9] Of these seven families, Bouman considered Dioscoreaceae, Trichopodaceae, Stemonaceae and Taccaceae to represent the "core" families of the order. However, that study also indicated both a clear delineation of the order from other orders particularly Asparagales, and a lack of homogeneity within the order.[9]

Molecular phylogenetics and the Angiosperm Phylogeny Group

The increasing availability of

suffixes of the superorders from "-iflorae" to "-anae".[a]
This demonstrated that the Lilianae comprised three lineages corresponding to Dahlgren's orders Dioscoreales, Liliales, and Asparagaless.

Under the

monocot clade and comprised the five families Burmanniaceae, Dioscoreaceae, Taccaceae, Thismiaceae
and Trichopodaceae.

In

monotypic families Taccaceae and Trichopodaceae were included in Dioscoreaceae, while Nartheciaceae could also be grouped within Dioscoreales. APG III (2009)[29]
did not change this, so the order now comprises three families Burmanniaceae, Dioscoreaceae and Nartheciaceae.

Although further research on the deeper relationships within Dioscoreales continues,

APG IV (2016) authors felt it was still premature to propose a restructuring of the order. Specifically these issues involve conflicting information as to the relationship between Thismia and Burmanniaceae,[32] and hence whether Thismiaceae should be subsumed in the latter, or reinstated.[1]

Phylogeny

monophyletic and is placed as a sister order to Pandanales, as shown in Cladogram I.[32][1]

Cladogram I: The phylogenetic composition of the monocots.[1]
monocots

Evolution

The data for the evolution of the order is collected from molecular analyses since there are no such fossils found. It is estimated that Dioscoreales and its sister clade

stem group was formed. Then it took 3 to 6 million years for the crown group to differentiate in Mid Cretaceous
.

Subdivision

The three families of Dioscreales constitutes about 22 genera and about 849 species[33] making it one of the smaller monocot orders.[31] Of these, the largest group is Dioscorea (yams) with about 450 species. By contrast the second largest genus is Burmannia with about 60 species, and most have only one or two.[31]

Some authors,[23] preferring the original APG (1998)families, continue to treat Thismiaceae separately from Burmanniaceae and Taccaceae from Dioscoreaceae.[31] But in the 2015 study of Hertwerk and colleagues, seven genera representing all three families were examined with an eight gene dataset. Dioscoreales was monophyletic and three subclades were represented corresponding to the APG families. Dioscoreaceae and Burmanniaceae were in a sister group relationship.[32]

Cladogram II: Relationship of Dioscoreales families[32] (number of genera)[33]
Dioscoreales

Etymology

Named after the

Dioscorides.[9]

Distribution and habitat

Species from this order are distributed across all of the continents except

photosynthetic
abilities.

Ecology

Narthecium ossifragum - bog asphodel

The three families included in order Dioscoreales also represent three different ecological groups of plants.

myco-heterotrophic
group.

Uses

Many members of

contraceptives
.

Notes

  1. ^ For a detailed discussion on this nomenclature, see Lilianae

References

  1. ^ a b c d APG IV 2016.
  2. ^ Tropicos 2015, Dioscoreales Mart.
  3. ^ a b Martius 1835, Ordo 42. Dioscore R. Br. p. 9
  4. ^ LAPGIII 2009.
  5. ^ a b c d Caddick et al 2002a.
  6. ^ Stevens 2016, Dioscoreales
  7. ^ Lindley 1853.
  8. ^ Caddick et al 2000.
  9. ^ a b c d e f g Bouman 1995.
  10. ^ Lindley 1853, Dictyogens p. 211
  11. ^ Brands 2015, Dioscoreales (Order)
  12. ^ Le Maout & Decaisne 1873, Cohort VI. Dioscorales p. 1018
  13. ^ Le Maout & Decaisne 1873, XV Dioscoreae p. 794
  14. ^ Bentham & Hooker 1862–1883, vol. 3 part 2 Ordo Dioscoreaceae p. 741
  15. ^ Stuessy 2009, Natural classification p. 47
  16. ^ Eichler 1886, Dioscoreaceae p. 35
  17. ^ Engler 1903, Dioscoreaceae p. 99
  18. ^ Wettstein 1924, Dioscoreaceae p. 880
  19. ^ Hutchinson 1959.
  20. ^ a b Dahlgren & Clifford 1982.
  21. ^ Huber 1969.
  22. ^ a b Dahlgren, Clifford & Yeo 1985.
  23. ^ a b c Merckx & Smets 2014.
  24. ^ Chase et al 1993.
  25. ^ Thorne 1992.
  26. ^ APG I 1998.
  27. ^ APG II 2003.
  28. ^ Caddick et al 2002b.
  29. ^ APG III 2009.
  30. ^ a b Merckx et al 2009.
  31. ^ a b c d Merckx et al 2010.
  32. ^ a b c d Hertweck et al 2015.
  33. ^ a b Christenhusz & Byng 2016.

Bibliography

Articles and chapters

Books and symposia

Databases

APG

External links
Wikispecies has information related to Dioscoreales.
Wikimedia Commons has media related to Dioscoreales.

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