Temporal range: Mid Cretaceous – Recent 116–0Ma
Dioscoreales is a botanical name for an order of flowering plants. Of necessity it contains the family Dioscoreaceae which includes the yam that is used as an important food source in many regions around the globe.
In APG II, the family Thismiaceae has been included in family Burmanniaceae and the families Taccaceae and Trichopodaceae have been included in family Dioscoreaceae. Therefore the change is not as large as might appear, and the only plants to have moved across the borders of the order are those belonging to family Nartheciaceae.
The Cronquist system, of 1981, did not recognise such an order, but placed most such plants in order Liliales in subclass Liliidae in class Liliopsida (monocotyledons) of division Magnoliophyta (angiosperms).
Under the Dahlgren system, Dioscoreales was placed in the superorder Lilianae in subclass Liliidae (monocotyledons) of class Magnoliopsida (angiosperms) and comprised the families Dioscoreaceae, Petermanniaceae, Ripogonaceae, Smilacaceae, Stemonaceae, Taccaceae, Trichopodaceae and Trilliaceae.
Ecology and Evolution
The three families included in order Dioscoreales also represent three different ecological groups of plants. Dioscoreaceae contains mainly vines (Dioscorea) and other crawling species (Epipetrum). Nartheciaceae on the other hand is a family composed of herbeceous plants with a rather lily-like appearance (Aletris) while Burmanniaceae is entirely myco-heterotrophic group.
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 Pandanales split up around 121 millions of years ago during Early Cretaceous when the stem group was formed. Then it took 3 to 6 millions of years for the crown group to differentiate in Mid Cretaceous.
Description and Distribution
Species from this order are distributed across all of the continents except Antarctica. They are mainly tropical representatives but however there are members of Dioscoreaceae and Nartheciaceae families found in cooler regions of Europe and North America. Order Dioscoreales contains plants that are able to form an underground organ for reservation of nutritions as many other monocots. An exception is the family Burmanniaceae which is entirely myco-heterotrophic and contains species that lack photosynthetic abilities. All of the species except the genera placed in Nartheciaceae express simultaneous microsporogenesis. Plants in Nartheciaceae show successive microsporogenesis which is one of the traits indicating that the family is sister to all the other members included in the order.
- Angiosperm Phylogeny Group (2009). "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III" (PDF). Botanical Journal of the Linnean Society 161 (2): 105–121. doi:10.1111/j.1095-8339.2009.00996.x. Retrieved 2013-07-06.
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