''Wolffia'' is a genus of aquatic plants with a

cosmopolitan distribution In biogeography, cosmopolitan distribution is the term for the range of a taxon that extends across all or most of the world in appropriate habitats. Such a taxon, usually a species, is said to exhibit cosmopolitanism or cosmopolitism. The ext ...

. They include the smallest

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...

s on Earth. Commonly called watermeal or duckweed, these

aquatic plant Aquatic plants are plants that have adapted to living in aquatic environments (saltwater or freshwater). They are also referred to as hydrophytes or macrophytes to distinguish them from algae and other microphytes. A macrophyte is a plant that ...

s resemble specks of

cornmeal Cornmeal is a meal (coarse flour) or a cell membrane ground from dried corn. It is a common staple food, and is ground to coarse, medium, and fine consistencies, but not as fine as wheat flour can be.Herbst, Sharon, ''Food Lover's Companion'', ...

floating on the water. Individuals often float together in pairs or form floating mats with related plants, such as ''

Lemna ''Lemna'' is a genus of free-floating aquatic plants referred to by the common name "Lemnoideae, duckweed". They are morphologically divergent members of the arum family Araceae. These rapidly growing plants have found uses as a Model organism, m ...

'' and ''

Spirodela ''Spirodela'' is a genus of aquatic plants, one of several genera containing plants commonly called duckweed. ''Spirodela'' species are members of the Araceae under the APG II system. They were formerly members of the Lemnaceae. ''Spirodela' ...

'' species.

Description

''Wolffia'' are free-floating aquatic plants with

frond A frond is a large, divided leaf. In both common usage and botanical nomenclature, the leaves of ferns are referred to as fronds and some botanists restrict the term to this group. Other botanists allow the term frond to also apply to the lar ...

s that are nearly spherical to cylindrical in shape and lack airspaces or veins. They do not have roots. Their rarely seen flowers originate from a cavity on the upper surface of the frond, and each flower has one stamen and one pistil. Although ''Wolffia'' can reproduce by seed, they usually use

vegetative reproduction Vegetative reproduction (also known as vegetative propagation, vegetative multiplication or cloning) is any form of asexual reproduction occurring in plants in which a new plant grows from a fragment or cutting of the parent plant or spec ...

. A mother frond has a terminal conical cavity from which it produces daughter fronds.

Physiology

The growth rate of ''Wolffia'' varies within and among species. The rates of

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...

and

respiration Respiration may refer to: Biology * Cellular respiration, the process in which nutrients are converted into useful energy in a cell ** Anaerobic respiration, cellular respiration without oxygen ** Maintenance respiration, the amount of cellul ...

also vary proportionately to growth rate. The fastest growth rate (in fact, the fastest growth rate of any

) is shown by a clone of ''Wolffia microscopica'', with a

doubling time The doubling time is the time it takes for a population to double in size/value. It is applied to population growth, inflation, resource extraction, consumption of goods, compound interest, the volume of malignant tumours, and many other things th ...

of 29.3 hours.

As food

''Wolffia'' are a potential high-protein human food source. One species, ''W. microscopica'', is over 20%

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

by dry weight and has high content of

essential amino acid An essential amino acid, or indispensable amino acid, is an amino acid that cannot be synthesized from scratch by the organism fast enough to supply its demand, and must therefore come from the diet. Of the 21 amino acids common to all life form ...

s. They have historically been collected from the water and eaten as a vegetable in Asia.

Species

, eleven species are accepted on

Kew Kew () is a district in the London Borough of Richmond upon Thames. Its population at the 2011 census was 11,436. Kew is the location of the Royal Botanic Gardens ("Kew Gardens"), now a World Heritage Site, which includes Kew Palace. Kew is a ...

Plants of the World Online Plants of the World Online (POWO) is an online database published by the Royal Botanic Gardens, Kew. It was launched in March 2017 with the ultimate aim being "to enable users to access information on all the world's known seed-bearing plants by ...

: *''

Wolffia angusta ''Wolffia angusta'' is a species of flowering plant in the family Araceae. It has been listed by the Guinness Book of World Records as the smallest flowering plant on record, measuring in length and in width. However, more recently ''Wolffia ...

'' *''

Wolffia arrhiza ''Wolffia arrhiza'' is a species of flowering plant known by the common names spotless watermeal and rootless duckweed, belonging to the Araceae, a family rich in water-loving species, such as ''Arum'' and '' Pistia''. It is the smallest vascul ...

'' *'' Wolffia australiana'' *''

Wolffia borealis ''Wolffia borealis'' is a species of flowering plant known by the common name northern watermeal. It is native to North America including sections of Canada and the United States. It grows in mats on the surface of calm water bodies, such as pon ...

'' *''

Wolffia brasiliensis ''Wolffia brasiliensis'' is a species of flowering plant known by the common name Brazilian watermeal. It is native to North and South America, where it grows in mats on the surface of calm water bodies, such as ponds. It is a very tiny plant wit ...

'' *''

Wolffia columbiana ''Wolffia columbiana'', the Columbian watermeal,USDA PLANTS Profile for ''Wolffia columbia ...

'' *''

Wolffia cylindracea ''Wolffia'' is a genus of aquatic plants with a cosmopolitan distribution. They include the smallest flowering plants on Earth. Commonly called watermeal or duckweed, these aquatic plants resemble specks of cornmeal floating on the water. Ind ...

'' *''

Wolffia elongata ''Wolffia'' is a genus of aquatic plants with a cosmopolitan distribution. They include the smallest flowering plants on Earth. Commonly called watermeal or duckweed, these aquatic plants resemble specks of cornmeal floating on the water. Ind ...

'' *''

Wolffia globosa ''Wolffia globosa'' is a species of flowering plant known by the common names Asian watermeal and duckweed. It is native to Asia and is found in parts of the Americas and Africa, where it is an introduced species. It grows in mats on the surface ...

'' *''

Wolffia microscopica ''Wolffia'' is a genus of aquatic plants with a cosmopolitan distribution. They include the smallest flowering plants on Earth. Commonly called watermeal or duckweed, these aquatic plants resemble specks of cornmeal floating on the water. Ind ...

'' *''

Wolffia neglecta ''Wolffia'' is a genus of aquatic plants with a cosmopolitan distribution. They include the smallest flowering plants on Earth. Commonly called watermeal or duckweed, these aquatic plants resemble specks of cornmeal floating on the water. Ind ...

References

External links

The Duckweed Genome Project
from Rutgers University * *Landolt, E. (1986) Biosystematic investigations in the family of duckweeds (Lemnaceae). Vol. 2. The family of Lemnaceae - A monographic study. Part 1 of the monograph: Morphology; karyology; ecology; geographic distribution; systematic position; nomenclature; descriptions. Veröff. Geobot. Inst., Stiftung Rübel, ETH, Zurich. {{Taxonbar, from=Q163015 Lemnoideae Araceae genera Freshwater plants