Dioscoreales
| Dioscoreales Temporal range: Mid Cretaceous – Recent 116–0 Ma | |
|---|---|
 | |
| Dioscorea communis | |
| Scientific classification | |
| Kingdom: | Plantae |
| (unranked): | Angiosperms |
| (unranked): | Monocots |
| Order: | Dioscoreales R.Br.[1] |
| Type species | |
| Dioscorea villosa L. | |
| Families | |
| |
| Synonyms | |
Dioscoreales (yam order) is a botanical name for an order of monocotyledon flowering plants in modern classification systems, such as the Angiosperm Phylogeny Group and the Angiosperm Phylogeny Web. Within the monocots Dioscoreales are grouped in the lilioid monocots where they are in a sister group relationship with the Pandanales. Of necessity the Dioscoreales contain the family Dioscoreaceae which includes the yam (Dioscorea) that is used as an important food source in many regions around the globe. Older systems tended to place all lilioid monocots with reticulate veined leaves (such as Smilacaceae and Stemonaceae together with Dioscoraceae) in Dioscoreales. As currently circumscribed by phylogenetic analysis using combined morphology and molecular methods, Dioscreales contains many reticulate veined vines in Dioscoraceae, it also includes the myco-heterotrophic Burmanniaceae and the autotrophic Nartheciaceae. The order consists of three families, 21 genera and about 1,040 species.
Description
Dioscoreales are vines or herbaceous forest floor plants. They may be achlorophyllous or saprophytic. Synapomorphies include tuberous roots, glandular hairs, seed coat characteristics and the presence of calcium oxalate crystals.[3] Other characteristics of the order include the presence of saponin steroids, annular vascular bundles that are found in both the stem and leaf. The leaves are often unsheathed at the base, have a distinctive petiole and reticulate veined lamina. Alternatively they may be small and scale-like with a sheathed base. The flowers are actinomorphic, and may be bisexual or dioecious. The perianth may be conspicuous or reduced. Fruit is dry capsules or berries.
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.
Taxonomy
Earlier systems
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 eight families Dioscoreaceae, Petermanniaceae, Ripogonaceae, Smilacaceae, Stemonaceae, Taccaceae, Trichopodaceae and Trilliaceae.
Angiosperm Phylogeny Group
Under the Angiosperm Phylogeny Group system of 1998 (APG I), the order was placed in the monocot clade and comprised the five families Burmanniaceae, Dioscoreaceae, Taccaceae, Thismiaceae and Trichopodaceae
In APG II (2003), a number of changes were made to Dioscoreales, as a result of am extensive study by Caddick and colleagues (2000),[3][4] using an analysis of three genes, rbcL, atpB and 18S rDNA, in addition to morphology. These studies resulted in a re-examination of the relationships between most of the genera within the order. Thismiaceae was shown to be a sister group to Burmanniaceae, and so was included in it. The monotypic families Taccaceae and Trichopodaceae were included in Dioscoreaceae, while Nartheciaceae could also be grouped within Dioscoreales. APG III (2009) did not change this, so the order now comprises three families Burmanniaceae, Dioscoreaceae and Nartheciaceae.
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 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.
Distribution and habitat
Species from this order are distributed across all of the continents except Antarctica. They are mainly tropical or subtropical 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.
Ecology
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.
Uses
Many members of Dioscoreaceae produce tuberous starchy roots (yams) which form staple foods in tropical regions. They have also been the source of steroids for the pharmaceutical industry, including the production of oral contraceptives.
References
- ↑ 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.
- ↑ LAPGIII 2009.
- 1 2 Caddick et al 2002a.
- ↑ Caddick et al 2002b.
Bibliography
- Caddick LR, Rudall PJ, Wilkin P, Chase MW. 2000. Yams and their allies: systematics of Dioscoreales. In: WilsonKL, MorrisonDA, eds. Systematics and evolution of monocots. Proceedings of the 2nd International Monocot Symposium. Melbourne: CSIRO, 475–487.
- Caddick, Lizabeth R.; Rudall, Paula J.; Wilkin, Paul; Hedderson, Terry A. J.; Chase, Mark W. (February 2002), "Phylogenetics of Dioscoreales based on combined analyses of morphological and molecular data", Botanical Journal of the Linnean Society 138 (2): 123–144, doi:10.1046/j.1095-8339.2002.138002123.x
- Caddick, Lizabeth R.; Wilkin, Paul; Rudall, Paula J.; Hedderson, Terry A. J.; Chase, Mark W. (February 2002), "Yams Reclassified: A Recircumscription of Dioscoreaceae and Dioscoreales", Taxon 51 (1): 103, doi:10.2307/1554967
- Haston, Elspeth; Richardson, James E.; Stevens, Peter F.; Chase, Mark W.; Harris, David J. (2009). "The Linear Angiosperm Phylogeny Group (LAPG) III: a linear sequence of the families in APG III". Botanical Journal of the Linnean Society 161 (2): 128–131. doi:10.1111/j.1095-8339.2009.01000.x.
External links
- NCBI Taxonomy Browser
- Dioscoreales: Air potatoes and Bat flowers
- Kress WJ. Dioscoreales. Encyclopedia Brittanica 2016
- Science naturalis
- Merckx V. Cretaceous Origins of Myco-Heterotrophic Lineages in Dioscoreales. 2010
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