The sizes of plant genera vary widely from those containing a single species to genera containing thousands of species, and this disparity became clear early in the history of plant classification. The largest genus in Carl Linnaeus' seminal Species Plantarum was Euphorbia, with 56 species; Linnaeus believed that no genus should contain more than 100 species.
Part of the disparity in genus sizes is attributable to historical factors. According to a hypothesis published by Max Walters in 1961, the size of plant genera is related to the age, not of the taxon itself, but of the concept of the taxon in the minds of taxonomists. Plants which grew in Europe, where most of the early taxonomy was based, were therefore divided into relatively small genera, while those from the tropics were grouped into much larger and more heterogeneous genera. Likewise, plants which shared common medicinal properties, such as the many species of Euphorbia, were united into a single genus, while plants of diverse uses, such as the grasses, were split into many genera. Where there were many classical names for groups of plants, such as in Apiaceae / Umbelliferae or Brassicaceae / Cruciferae, small genera were defined, whereas groups not subdivided by classical authors remained as larger genera, such as Carex. A number of biological factors also influence the number of species. For instance, the occurrence of apomixis allows the recognition of large numbers of agamospecies, and such taxa have helped to bolster genera such as Ranunculus and Potentilla.
The introduction of infrageneric taxa (such as the subgenus, section and series) in the 19th century by botanists including Augustin Pyrame de Candolle allowed the retention of large genera that would otherwise have become unwieldy. E. J. H. Corner believed that studying large genera might enable greater insights into evolutionary biology, and he concentrated his efforts on large tropical genera such as Ficus.
A total of 57 genera of flowering plants contain at least 500 species, according to a 2004 analysis by the botanical taxonomist David Frodin. The actual numbers of species are imprecisely known, as many of the genera have not been the subject of recent monographs. For instance, estimates of the number of species in the orchid genus Pleurothallis range from 1,120 to 2,500. Genera from other groups of vascular plants, but which have similarly large numbers of species, include Selaginella, Asplenium and Cyathea.
|1||Astragalus||3,270||Fabaceae||List of Astragalus species|
|2||Bulbophyllum||2,032||Orchidaceae||List of Bulbophyllum species|
|3||Psychotria||1,951||Rubiaceae||List of Psychotria species|
|4||Euphorbia||1,836||Euphorbiaceae||List of Euphorbia species|
|5||Carex||1,795||Cyperaceae||List of Carex species|
|6||Begonia||1,484||Begoniaceae||List of Begonia species|
|7||Dendrobium||1,371||Orchidaceae||List of Dendrobium species|
|8||Acacia||c. 1,353||Fabaceae||List of Acacia species|
|9||Solanum||c. 1,250||Solanaceae||List of Solanum species|
|10||Senecio||c. 1,250||Asteraceae||List of Senecio species|
|11||Croton||1,223||Euphorbiaceae||List of Croton species|
|12||Pleurothallis||1,120+||Orchidaceae||List of Pleurothallis species|
|13||Eugenia||1,113||Myrtaceae||List of Eugenia species|
|14||Piper||1,055||Piperaceae||List of Piper species|
|15||Ardisia||1,046||Primulaceae||List of Ardisia species|
|16||Syzygium||1,041||Myrtaceae||List of Syzygium species|
|17||Rhododendron||c. 1,000||Ericaceae||List of Rhododendron species|
|18||Miconia||1,000||Melastomataceae||List of Miconia species|
|19||Peperomia||1,000||Piperaceae||List of Peperomia species|
|20||Salvia||945||Lamiaceae||List of Salvia species|
|21||Erica||860||Ericaceae||List of Erica species|
|22||Impatiens||850||Balsaminaceae||List of Impatiens species|
|23||Cyperus||839||Cyperaceae||List of Cyperus species|
|24||Phyllanthus||833||Phyllanthaceae||List of Phyllanthus species|
|25||Allium||815||Amaryllidaceae||List of Allium species|
|26||Epidendrum||800||Orchidaceae||List of Epidendrum species|
|27||Vernonia||800–1,000||Asteraceae||List of Vernonia species|
|28||Lepanthes||c. 800||Orchidaceae||List of Lepanthes species|
|29||Anthurium||789||Araceae||List of Anthurium species|
|30||Diospyros||767||Ebenaceae||List of Diospyros species|
|33||Justicia||c. 700||Acanthaceae||List of Justicia species|
|39||Eucalyptus||681||Myrtaceae||List of Eucalyptus species|
|41||Galium||661||Rubiaceae||List of Galium species|
|47||Ranunculus||600||Ranunculaceae||List of Ranunculus species|
|48||Habenaria||600||Orchidaceae||List of Habenaria species|
|49||Schefflera||584||Araliaceae||List of Schefflera species|
|50||Ixora||561||Rubiaceae||List of Ixora species|
|51||Berberis||556||Berberidaceae||List of Berberis species|
|52||Quercus||531||Fagaceae||List of Quercus species|
|53||Pandanus||c. 520||Pandanaceae||List of Pandanus species|
|54||Panicum||500+||Poaceae||List of Panicum species|
|57||Potentilla||500||Rosaceae||List of Potentilla species|
A genus (, pl. genera ) is a taxonomic rank used in the biological classification of living and fossil organisms, as well as viruses, in biology. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclature, the genus name forms the first part of the binomial species name for each species within the genus.
E.g. Panthera leo (lion) and Panthera onca (jaguar) are two species within the genus Panthera. Panthera is a genus within the family Felidae.The composition of a genus is determined by a taxonomist. The standards for genus classification are not strictly codified, so different authorities often produce different classifications for genera. There are some general practices used, however, including the idea that a newly defined genus should fulfill these three criteria to be descriptively useful:
monophyly – all descendants of an ancestral taxon are grouped together (i.e. phylogenetic analysis should clearly demonstrate both monophyly and validity as a separate lineage).
reasonable compactness – a genus should not be expanded needlessly; and
distinctness – with respect to evolutionarily relevant criteria, i.e. ecology, morphology, or biogeography; DNA sequences are a consequence rather than a condition of diverging evolutionary lineages except in cases where they directly inhibit gene flow (e.g. postzygotic barriers).Moreover, genera should be composed of phylogenetic units of the same kind as other (analogous) genera.Lepanthes
Lepanthes (from Greek "scaled-flower") is a large genus of orchids with about 800–1000 species, distributed in the Antilles and from Mexico through Bolivia (with very few species in Brazil). The genus is abbreviated in horticultural trade as Lths. Almost all the species in the genus are small and live in cloud forests. Babyboot orchid is a common name.List of Astragalus species
This is a list of Astragalus species, including infraspecific taxa. They are listed according to subgenera (for Old World species) or informal groups called phalanxes (for North American species). Subgenera and phalanxes are further subdivided into sections. Phylogenetic analyses have determined that many of these subgenera, phalanxes, and sections are not monophyletic.Psychotria
Psychotria is a genus of flowering plants in the family Rubiaceae. It contains 1,582 species and is therefore one of the largest genera of flowering plants. The genus has a pantropical distribution and members of the genus are small understorey trees in tropical forests. Some species are endangered or facing extinction due to deforestation, especially species of central Africa and the Pacific.
Many species, including Psychotria viridis, produce the psychedelic chemical dimethyltryptamine (DMT).