There are over 80 genera of flowering plants estimated to contain at least 500 described species. The largest of these is currently the legume genus Astragalus (milk-vetches), with over 3,000 species.

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.

Largest genera , there are a total of 86 genera of flowering plants with at least 500 species. It is clear that there are other genera with over 500 species, as the work of taxonomists continues. Currently, the number of species included in many genera is very different (e.g. see Psychotria), so their ranking is subject to changes. The actual number of species is also imprecisely known because of different approaches of taxonomists, and 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 some other groups of vascular plants (like pteridophytes), which have similarly large numbers of species, include Selaginella, Asplenium and Cyathea.

+ Genera of flowering plants with at least 500 species in 2023Rank Genus Species Family Species list1 Astragalus 3,239 Fabaceae List of Astragalus species2 Taraxacum 2,387 Asteraceae List of Taraxacum species3 Hieracium 2,349 Asteraceae List of Hieracium species4 Carex 2,328 Cyperaceae List of Carex species5 Bulbophyllum 2,190 Orchidaceae List of Bulbophyllum species6 Piper 2,169 Piperaceae List of Piper species7 Euphorbia 2,157 Euphorbiaceae List of Euphorbia species8 Begonia 2,144 Begoniaceae List of Begonia species9 Miconia 1,939 Melastomataceae List of Miconia species10 Epidendrum 1,872 Orchidaceae List of Epidendrum species11 Rubus 1,732 Rosaceae List of Rubus species12 Senecio 1,681 Asteraceae List of Senecio species13 Psychotria 1,650 Rubiaceae List of Psychotria species14 Dendrobium 1,647 Orchidaceae List of Dendrobium species15 Ranunculus 1,616 Ranunculaceae List of Ranunculus species16 Peperomia 1,384 Piperaceae List of Peperomia species17 Anthurium 1,346 Araceae List of Anthurium species18 Stelis 1,338 Orchidaceae List of Stelis species19 Eugenia 1,284 Myrtaceae List of Eugenia species20 Solanum 1,238 Solanaceae List of Solanum species21 Syzygium 1,236 Myrtaceae List of Syzygium species22 Acacia 1,234 Fabaceae List of Acacia species23 Rhododendron 1,195 Ericaceae List of Rhododendron species24 Lepanthes 1,189 Orchidaceae List of Lepanthes species25 Croton 1,178 Euphorbiaceae List of Croton species26 Salvia 1,049 Lamiaceae List of Salvia species27 Phyllanthus 1,025 Phyllanthaceae List of Phyllanthus species28 Impatiens 1,002 Balsaminaceae List of Impatiens species29 Justicia 983 Acanthaceae List of Justicia species30 Allium 970 Amaryllidaceae List of Allium species31 Cyperus 961 Cyperaceae List of Cyperus species32 Habenaria 908 Orchidaceae List of Habenaria species33 Ficus 876 Moraceae List of Ficus species34 Eucalyptus 865 Myrtaceae List of Eucalyptus species35 Erica 853 Ericaceae List of Erica species36 Myrcia 820 Myrtaceae List of Myrcia species37 Centaurea 793 Asteraceae List of Centaurea species38 Diospyros 787 Ebenaceae List of Diospyros species39 Indigofera 787 Fabaceae List of Indigofera species40 Vaccinium 785 Ericaceae List of Vaccinium species41 Crotalaria 760 Fabaceae List of Crotalaria species42 Cyrtandra 749 Gesneriaceae List of Cyrtandra species43 Alchemilla 734 Rosaceae List of Alchemilla species44 Viola 727 Violaceae List of Viola species45 Verbascum 724 Scrophulariaceae List of Verbascum species46 Vernonia 723 Asteraceae List of Vernonia species47 Ardisia 721 Primulaceae List of Ardisia species48 Pedicularis 711 Orobanchaceae List of Pedicularis species49 Cousinia 709 Asteraceae List of Cousinia species50 Mimosa 689 Fabaceae List of Mimosa species51 Palicourea 689 Rubiaceae 52 Festuca 686 Poaceae List of Festuca species53 Tillandsia 678 Bromeliaceae List of Tillandsia species54 Galium 678 Rubiaceae List of Galium species55 Polygala 673 Polygalaceae List of Polygala species56 Maxillaria 658 Orchidaceae List of Maxillaria species57 Masdevallia 656 Orchidaceae List of Masdevallia species58 Oxytropis 654 Fabaceae List of Oxytropis species59 Elatostema 652 Urticaceae 60 Lupinus 650 Fabaceae List of Lupinus species61 Dioscorea 649 Dioscoreaceae 62 Salix 629 Salicaceae List of Salix species63 Berberis 628 Berberidaceae64 Quercus 627 Fagaceae List of Quercus species65 Aloe 623 Asphodelaceae List of Aloe species66 Ipomoea 621 Convolvulaceae List of Ipomoea species67 Poa 617 Poaceae List of Poa species68 Pilea 613 Urticaceae List of Pilea species69 Pandanus 605 Pandanaceae List of Pandanus species70 Ilex 596 Aquifoliaceae List of Ilex species71 Coelogyne 595 Orchidaceae List of Coelogyne species72 Helichrysum 580 Asteraceae List of Helichrysum species73 Philodendron 569 Araceae List of Philodendron species74 Ixora 566 Rubiaceae List of Ixora species75 Passiflora 561 Passifloraceae List of Passiflora species76 Saxifraga 561 Saxifragaceae List of Saxifraga species77 Oxalis 557 Oxalidaceae List of Oxalis species78 Pleurothallis 556 Orchidaceae List of Pleurothallis species79 Primula 553 Primulaceae List of Primula species80 Ocotea 545 Lauraceae List of Ocotea species81 Corydalis 528 Papaveraceae List of Corydalis species82 Aristolochia 524 Aristolochiaceae List of Aristolochia species83 Artemisia 523 Asteraceae List of Artemisia species84 Hypericum 517 Hypericaceae List of Hypericum species85 Potentilla 505 Rosaceae List of Potentilla species86 Delphinium 503 Ranunculaceae List of Delphinium species

References