Haloragaceae

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Haloragaceae (the watermilfoil family) is a eudicot flowering plant family in the order Saxifragales, based on the phylogenetic APG system. In the Cronquist system, it was included in the order Haloragales.

Description

The Haloragaceae (alternate spelling Halorrhagidaceae) are very diverse in habit, including both small trees and submerged aquatics. Most members of the Haloragaceae are herbaceous, and most of those in turn are perennials, though some species are annuals. In contrast however, members of the genus Haloragodendron are woody. Most species of Myriophyllum are monoecious while most other taxa have hermaphrodite flowers. The flowers are usually small and inconspicuous, but some genera can have more "showy" conspicuous flowers (Haloragodendron, Glischrocaryon). Flowers are usually radially symmetrical, and unusual for core eudicots, merosity is (2-3)-4 parted. Petals are usually keeled or hooded when present. In Myriophyllum, female flowers usually lack a perianth. They have (2-)4-8 stamens and an inferior ovary of (2-)4 carpels. In Myriophyllum, the fruit is a schizocarp of 1-seeded 'nutlets'. Other genera can have nuts or drupes that can be winged or inflated.Template:SfnTemplate:Sfn The genus Gunnera, formerly included here, are now in the separate family Gunneraceae.

Taxonomy

Phylogeny

Molecular phylogenetic studies, in particular, the APG system, placed the Haloragaceae within the core eudicot order, Saxifragales.Template:Sfn Earlier versions of the APG had allowed either the broader circumscription (Haloragaceae s.l.) or a narrower Haloragaceae s.s..Template:Sfn Template:Cladogram

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Subdivision

History

Historically, the Haloragaceae included many disparate genera, since segregated. A major circumscription was carried out by Schindler in 1905, dividing the "Halorrhagaceae" into two subfamilies (Halorrhagoideae and Gunneroideae) and the former into two tribes (Halorrhageae and Myriophylleae), with a total of seven genera. He removed some of the disparate genera and merged Gonocarpus and Meionectes into Haloragis.Template:Sfn This classification long remained the standard till Shaw (1966) removed Gunnera (into its own family Gunneraceae, within the order Gunnerales), the sole genus in Gunneroideae, leaving six genera.Template:Sfn This situation remained until the monograph of Orchard (1975). Orchard restored Gonocarpus and split Haloragodendron from Haloragis, leaving 8 genera.Template:SfnTemplate:Sfn
List of genera, habitat, distribution (Number of species)

Molecular era

A molecular study resolved the infrafamilial relationships among the genera, resulting in some taxonomic revision, including redistribution of species. In addition, Meionectes was reinstated, separating two species from Haloragis and creating a new monotypic genus, Trihaloragis by segregating Gonocarpus hexandrus. Consequently, the number of genera is increased to ten, with the addition of:Template:Sfn

  • Meionectes R.Br. (2)
  • Trihaloragis Moody & Les (1)

Glischrocaryon-Haloragodendron is resolved as the basal node, sister to the remaining family. While monophyly of this group is well supported, monophyly of the two separate genera is less well supported, and suggests some paraphyly. Thus the generic limits remain unresolved.Template:Sfn

A subsequent, more detailed study of Myriophyllum demonstrated that the monotypic genus Meziella was embedded within it, leading to its submersion within the former as Myriophyllum subgenus Meziella, thereby reducing the number of genera within the family to 9.Template:Sfn

Species

As of 2014, the family has 138 species, distributed among the nine genera as follows:Template:Sfn Template:Div col

  • Glischrocaryon (4)
  • Gonocarpus (36)
  • Haloragis (24)
  • Haloragodendron (6)
  • Laurembergia (4)
  • Myriophyllum (60)
  • Proserpinaca (2)
  • Meionectes (2)
  • Trihaloragis (1)

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Distribution and habitat

The distribution of the family is nearly worldwide.Template:Sfn The center of species diversity is in Australia where all genera are found excepting Proserpinaca and Laurembergia. Habitats vary from arid desert regions to freshwater lakes. The terrestrial genera (Glischrocaryon, Gonocarpus, Haloragis, Haloragodendron, Trihaloragis) are primarily limited to the southern hemisphere. Meionectes, Meziella, Myriophyllum and Proserpinaca are aquatic, while Laurembergia are semiaquatic. Glischrocaryon, Haloragodendron, Meionectes and Trihaloragis are Australian endemics, where about 70% of all species are found.Template:SfnTemplate:Sfn For detailed maps of the distribution of each genus, see Template:Harvtxt Figure 1.

References

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Books and theses

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