Lidyanne Yuriko Saleme Aona* & Daniela Zappi**
*Universidade Federal do Recôncavo da Bahia (UFRB), Centro de Ciências Agrárias, Ambientais e Biológicas, Cruz das Almas, Bahia, Brazil.**Royal Botanic Gardens, Kew, United Kingdom.
Herbs: aquatic, emersed, either free-floating, anchored to the bottom or rarely submersed, annual or perennial, reproducing by rhizomes or stolons. Leaves often submerged, simple, alternate or rosulated, young ones often submerged, sessile and linear, mature leaves expanded, emersed and often floating; leaf-blade linear, lanceolate, cordate, kidney-shaped or sagittate. Inflorescences racemose, paniculate or in terminal spikes, flowers rarely solitary, spathe present. Flowers sessile to pedicellate, bisexual, 3-merous, symmetry generally bilateral, with the petals indistinct from the sepals, the tepals glabrous to glandular-pubescent, often with nectar-guides on the upper middle tepal; homo- or heterostylic, the stamens generally 6 (3+3), rarely 3 or 1, attached to the tepals, filaments glabrous or hairy, anthers yellow or bluish, dehiscence by longitudinal slits, rarely poricidal; ovary superior, 3-carpelate, 1-3-locular; ovules 1-many, placentation axillary or parietal, rarely basal, septal nectaries sometimes present. Fruits capsules or achenes, submerged when ripe. Seeds small, with or without a projection or rostrum.
Notes on delimitation
- Molecular data point to the presence of tanniferous cells in the floral tissues as a possible synapomorphy for the Pontederiaceae. The family is included in Order Commelinales together with Commelinaceae, Hanguanaceae, Philydraceae and Haemodoraceae (APG III, 2009; Simpson, 2010; Reveal & Chase, 2011).
- It is closely related to Philydraceae and Haemodoraceae, but both have unifacial leaves, while Pontederiaceae has bifacial leaves. The pollen walls of both Pontederiaceae and Haemodoraceae are non tectate-collumelate (APG III, 2009; Simpson, 2010).
Distribution in the Neotropics
- Eichhornia Kunth: Pantropical, with 7 species in Tropical America.
- Heteranthera J. Agardh: including Zosterella Small, Eurystemon Alexander; Pantropical, 10 species in Tropical and Temperate America, possibly found in the Neotropics as it is used in the aquarium trade.
- Hydrothrix Hook.f.: Ceará, Bahia and Sergipe, Brazil, 1 species.
- Pontederia Kunth: including Reussia Endl.; Pantropical, with 6 species throughout America reaching Canada.
Distinguishing characters (always present)
- All species of Pontederiaceae are aquatic, either obligatory submerged plants with emergent flowers of free -floating or bottom-rooted emergents.
- Within the inflorescences, their flowers are paired or solitary, subtended by opposed spathes (bracts).
- The tepals are very delicate and sometimes deliquescent.
Other important characters
- Tepals usually six, sometimes reduced to four or three.
Key differences from similar families
- In the field, Pontederiaceae always occupy aquatic habitats, while the majority of Commelinaceae, Phylidraceae and Haemodoraceae tend to be terrestrial.
- The Haemodoraceae have perianth segments basally fused while Pontederiaceae have free perianth segments.
Useful tips for generic identification
- The differentiation between the genera of Pontederiaceae is difficult as they lack useful characters. While taxonomic works based on morphology alone (e.g. Cook 1998) accept as many as nine genera, recent molecular evidence suggests that only five of these (Heteranthera, Monochoria, Pontederia, Eichhornia and Hydrothrix) should be recognized (Nees et al., 2011).
- The family is sometimes divided into three tribes: Eichhornieae (trilocular capsules), Pontederiae (1-seeded nutlets), and Heteranthereae (unilocular capsules with numerous seeds).
Amongst the Tropical American genera some useful characters are:
- Eichhornia - often free floating, with hollow petioles, tepals blue, mauve or lilac, expanded, flowers zygomorphic with nectar guides.
- Pontederia - flowers white or pale blue, not strongly zygomorphic, no nectar guides.
- Heteranthera - flowers whitish, yellowish, blue, leaves with expanded limb, sometimes floating.
- Hydrothrix - has filiform leaves that are mostly submerged.
Key to the Neotropical genera of Pontederiaceae
1a. Stamens 6 ... 41b. Stamens 1-3 … 2
3a. Perigonium shortly tubular, fused only at base; anthers heteromorphic, with appendages on the filament of the largest stamen … 4. Monochoria (naturalised)3b. Perigonium long tubular; all anthers similar in size and shape, without appendages … 1. Eichhornia
4a. Leaves alternate, distichous to spiralled, leaf-blade linear to rounded; stamens 3 or 1 stamen and 2 staminodes … 2. Heteranthera4b. Leaves verticillate; limb needle-like; stamen 1, staminodes absent … 3. Hydrothrix
Notable genera and distinguishing features
- Eichhornia, commonly found as free -floating in watercourses throughout the topics, has leaves with inflated petioles.
- Most genera cited here are native from the Neotropics (Eichhornia, Pontederia, Heteranthera and Hydrothrix).
- Species of Pontederia are widely cultivated as ornamental and Eichhornia is considered an invasive of water-courses.
- Monochoria is naturalised in North America, with 1 species.
Amaral, M.C.E. 2014. Pontederiaceae. In: Lista de Espécies da Flora do Brasil. Jardim Botânico do Rio de Janeiro. (http://floradobrasil.jbrj.gov.br/jabot/floradobrasil/FB197)
APG III. 2009. An update of the Angiosperm Phylogenetic Group classification for the orders and families of flowering plants: APG III. Botanical Journal of the Linnean Society 161: 105-121.
Cook, C.D.K. 1998. Pontederiaceae. In: Kubitzki, K. (ed.) The Families and Genera of Vascular plants, vol. IV, pp. 395-403. Springer-Verlag. Berlin.
Faria, A.D. & Amaral, M.C.E. 2005. Pontederiaceae. In: Wanderley, M. G. L., Shepherd, G. J. & Giulietti, A. M. (Eds.). Flora Fanerogâmica do Estado de São Paulo. Vol. 4, pp: 325-330. São Carlos, Editora RiMA.
Ness, R.W.; Graham, S.W. & Barrett, S.C.H. 2011. Reconcilling gene and genome duplication events: Using multiple nuclear gene families to infer the phylogeny of the aquatic plant family Pontederiaceae. Molecular Biology and Evolution 28(11): 3009-3018
Reveal, J.L. & Chase, M.W. 2011. APG III: Bibliographical Information and Synonymy of Magnoliidae. Phytotaxa 19: 71-134.
Simpson, M.G. 2010. Plant Systematics. 2 ed. Oxford: Elsevier. 740p.
Spencer, C.H. Barrett 2004. Pontederiaceae. In: Smith, N., Mori, S.A., Henderson, A., Stevenson, D.W. & Heald, S.V. (eds.). Flowering Plants of the Neotropics, pp. 474-476. Princeton University Press, Princeton.
Sousa, D.J.L. 2014. Taxonomia e morfologia das Pontederiaceae do estado da Bahia. Dissertação de Mestrado. Universidade Estadual de Feira de Santana, Feira de Santana.
How to cite
Lidyanne Yuriko Saleme Aona & Daniela Zappi (2014). Neotropical Melanthiaceae. In: Milliken, W., Klitgård, B. & Baracat, A. (2009 onwards), Neotropikey - Interactive key and information resources for flowering plants of the Neotropics. http://www.kew.org/science/tropamerica/neotropikey/families/Pontederiaceae.htm
Click images to enlarge
Aquatic roots of Eichhornia azurea in Bolivia © B.B. Klitgaard, RBG, Kew
Flowers of Eichhornia azurea in Bolivia © B.B. Klitgaard, RBG, Kew
Flowers of Eichhornia crassipes in Brazil (MT) © D.Sasaki, Programa Flora Cristalino
Floating leaves and flowers of Eichhornia diversifolia in Brazil (MT) © D.Sasaki, Programa Flora Cristalino
Inflorescence of Pontederia cordata in Brazil (MG) © W.Milliken, RBG, Kew
Detail of inflorescence of Pontederia cordata in Brazil (MG) © W.Milliken, RBG, Kew
Flowers of Pontederia subovata in Brazil (MT) © W.Milliken, RBG, Kew