Hydatellaceae
Encyclopedia
Hydatellaceae are small, aquatic flowering plants. The family
includes the genus Trithuria, which has been recently re-defined to include the genus
Hydatella
. The family consists of about a dozen species. These tiny (few cm tall), relatively simple, aquatic plants occur in Australasia and India. The simple leaves are concentrated around a short stem basally. The plants are submerged and emergent aquatic annuals, rooted in the substrate below the water.
The members of this plant family are monoecious or dioecious
and are likely wind-pollinated (anemophilous), water-pollinated (hydrophilous
) or self-pollinating (autogamous). Flower-like reproductive units (which may be pseudanthia
) are composed of small collections of minute stamen- and/or pistil-like structures that may each represent very reduced individual flowers. The non-fleshy fruits are follicles
or achene
s.
The family was for many years assumed to be a close relative of the grasses and sedges
and was even sometimes lumped under the poalean family Centrolepidaceae
. Even as recently as 2003, the APG II system
assigned Hydatellaceae to the grass order Poales
in the commelinid monocots. However, research based on DNA sequences and morphology by Saarela et al. indicates that Hydatellaceae is the living sister group of the water lilies (Nymphaeaceae
and Cabombaceae
) and thus represents one of the most ancient lineages of flowering plants. This realignment is now recognized in the APG III system
of classification; developers of earlier classifications were misled by the apparently reduced vegetative and reproductive morphology of these plants.
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
includes the genus Trithuria, which has been recently re-defined to include the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Hydatella
Hydatella
Trithuria is a genus of minute aquatic herbs in the family Hydatellaceae. Recently the genus Hydatella was subsumed within Trithuria....
. The family consists of about a dozen species. These tiny (few cm tall), relatively simple, aquatic plants occur in Australasia and India. The simple leaves are concentrated around a short stem basally. The plants are submerged and emergent aquatic annuals, rooted in the substrate below the water.
The members of this plant family are monoecious or dioecious
Dioecious
Dioecy is the property of a group of biological organisms that have males and females, but not members that have organs of both sexes at the same time. I.e., those whose individual members can usually produce only one type of gamete; each individual organism is thus distinctly female or male...
and are likely wind-pollinated (anemophilous), water-pollinated (hydrophilous
Hydrophily
Hydrophily is a fairly uncommon form of pollination whereby pollen is distributed by the flow of waters, particularly in rivers and streams. Hydrophilous species fall into two categories: those that distribute their pollen to the surface of water, and those that distribute it beneath the...
) or self-pollinating (autogamous). Flower-like reproductive units (which may be pseudanthia
Pseudanthium
A pseudanthium or flower head is a special type of inflorescence, in which several flowers are grouped together to form a flower-like structure. The real flowers are generally small and greatly reduced, but can sometimes be quite large...
) are composed of small collections of minute stamen- and/or pistil-like structures that may each represent very reduced individual flowers. The non-fleshy fruits are follicles
Follicle (fruit)
In botany, a follicle is a dry unilocular many-seeded fruit formed from one carpel and dehiscing by the ventral suture in order to release seeds, such as in larkspur, magnolia, banksia, peony and milkweed....
or achene
Achene
An achene is a type of simple dry fruit produced by many species of flowering plants. Achenes are monocarpellate and indehiscent...
s.
The family was for many years assumed to be a close relative of the grasses and sedges
Poales
Poales is a large order of flowering plants in the monocotyledons, and includes families of plants such as the grasses, bromeliads, and sedges. Sixteen plant families are currently recognized by botanists to be part of Poales....
and was even sometimes lumped under the poalean family Centrolepidaceae
Centrolepidaceae
Centrolepidaceae is a botanical name for a family of flowering plants. Such a family has been recognized by most taxonomists.The APG II system, of 2003 , also recognises such a family, and assigns it to the order Poales in the clade commelinids in the monocots.The family is now regarded as...
. Even as recently as 2003, the APG II system
APG II system
The APG II system of plant classification is the second, now obsolete, version of a modern, mostly molecular-based, system of plant taxonomy that was published in April 2003 by the Angiosperm Phylogeny Group. It was a revision of the first APG system, published in 1998, and was superseded in 2009...
assigned Hydatellaceae to the grass order Poales
Poales
Poales is a large order of flowering plants in the monocotyledons, and includes families of plants such as the grasses, bromeliads, and sedges. Sixteen plant families are currently recognized by botanists to be part of Poales....
in the commelinid monocots. However, research based on DNA sequences and morphology by Saarela et al. indicates that Hydatellaceae is the living sister group of the water lilies (Nymphaeaceae
Nymphaeaceae
Nymphaeaceae is a family of flowering plants. Members of this family are commonly called water lilies and live in freshwater areas in temperate and tropical climates around the world. The family contains eight genera. There are about 70 species of water lilies around the world. The genus...
and Cabombaceae
Cabombaceae
Cabombaceae is the botanical name of a family of flowering plants. The family has been recognised as distinct by at least some taxonomists and by APG III...
) and thus represents one of the most ancient lineages of flowering plants. This realignment is now recognized in the APG III system
APG III system
The APG III system of flowering plant classification is the third version of a modern, mostly molecular-based, system of plant taxonomy...
of classification; developers of earlier classifications were misled by the apparently reduced vegetative and reproductive morphology of these plants.
External links
- Hydatellaceae in L. Watson and M.J. Dallwitz (1992 onwards). The families of flowering plants: descriptions, illustrations, identification, information retrieval. Version: 27th April 2006. http://delta-intkey.com.
- Hydatellaceae photographs
- Hydatella in western Australia
- Trithuria in western Australia
- NCBI Taxonomy Browser
- links at CSDL
- Original paper recognising the family