1. Potamogetonaceae Bercht. & J.Presl

    1. This family is accepted.

[FTEA]

Potamogetonaceae, J.J. Symoens. Flora of Tropical East Africa. 2006

Habit
Aquatic herbs, perennial or rarely annual, glabrous, rooted in the substrate
General
Vegetative shoot system comprising horizontal shoots, mostly stoloniferous, non chlorophyllous (here called rhizomes) and vertical shoots, erect or sometimes ± floating, often densely branched, chlorophyllous (here called stems); tubers or turions sometimes present on the horizontal and/or the erect shoots
Leaves
Leaves alternate or subopposite, rarely ternate, sessile or petiolate, simple, served by 3 traces, parallel-veined or with a single midvein; stipules present throughout or only on young shoots ( Groenlandia ), often forming a tubular sheath around the stem and young inflorescence, either free or adnate to the base of the blade; intravaginal scales 2– several, situated in leaf axils, mostly linear to subulate, rarely ovate, entire and acute; bladeentire, denticulate or serrate
Inflorescences
Inflorescences pedunculate, with 2 opposite flowers ( >i>Groenlandia ) or more than 2 flowers in a dense or interrupted spike ( >i>Potamogeton ); peduncle rigid and mostly slightly elevated above the water level, but sometimes flexuous, the flowers resting then on the water surface, rarely submerged, but often withdrawing the fruits below the surface; bracts abortive or absent
Flowers
Flowers& #2695; (hermaphrodite), small, regular, hypogynous, tetramerous
Perianth
Perianth: a singlewhorl of 4 valvate shortly clawed tepals
Androecium
Stamens 4, opposite the tepals and basally adnate to the claw; anthers sessile, bilocular, extrorse, opening by longitudinal slits
Gynoecium
Gynoecium superior, of (1– 3) 4 (5– 8) carpels, sessile, free or shortly connate at the base, alternating with the stamens; styles usually short; stigma unicellular-papillate and strongly secretory or smooth and dry or weakly secretory; ovule solitary in the carpel and attached to its ventral margin, orthotropous at first, but becoming campylotropous at maturity, pendant and filling the locule, bitegmic, crassinucellate
Fruits
Fruit apocarpous consisting of distinct sessile fruitlets, ± drupaceous, but opening with a dorsal lid, with a rather fleshy parenchymatous mesocarp and a sclerified endocarp, the latter multi-layered ( >i>Potamogeton )or 1-layered ( >i>Groenlandia )
Seeds
Seed without endosperm; embryo unciform or spiral (i.e. coiled more than 1 complete turn), with a large hypocotyl and a single obliquely terminal cotyledon that encloses the plumule
[NTK]

Haigh, A. (2009). Neotropical Potamogetonaceae.

Morphology
Description

Aquatic freshwater or brackish herbs, typically perennial or annual (Zannichellia L.), rooted in the substrate with rhizomes or stolons sometimes; upper stems erect , ± reaching water surface. Leaves alternate , opposite or in pseudo-whorls, simple ; submersed leaves present in all species (although sometimes decayed), these petiolate or sessile , floating leaves present in some species, these nearly always petiolate ; "stipular" sheath always present, distinct from petioles or blades (floating leaves) or occasionally adnate (submersed leaves); distinct ligule usually present when stipular sheath distinct; blade shape similar or dissimilar in floating and submersed leaves of same plant, expanded (in floating leaves and in most petiolate and occasionally sessile submersed leaves) or linear (many submersed sessile leaves), sometimes filiform (Zannichellia), flattened without groove along one side (Potamogeton L.) or semiterete with channel or groove along one side (Stuckenia Börner); cuticle evident on adaxial surface of floating leaves, absent in submersed leaves. Inflorescences terminal or axillary , spikes or of 1 staminate and 1 pistillate flower per axil (Zannichellia, both flowers with short pedicels), the terminal spikes usually emersed or floating on the surface, the axillary spikes usually submersed, rarely with both emersed and submersed spikes on same plant; peduncles sometimes present, then rigid (Potamogeton having considerable supporting tissue) allowing for emersion or non-rigid and never emersed (Stuckenia, this sometimes resulting in spikes lying at water surface); spikes consisting of 1-20+ flower whorls, the flowers mostly 3 per whorl. Flowers actinomorphic , bisexual or unisexual (Zannichellia). Bisexual flowers (Potamogeton, Stuckenia) with 4 clawed tepals; androecium of 4 stamens, the filaments each adnate to tepal claw , the anthers extrorse; gynoecium apocarpous, the ovaries superior , the carpels 4, styles short, stigmas capitate ; placentation marginal , 1 ovule per carpel . Staminate flowers (Zannichellia) located in same leaf axil and directly behind pistillate flowers; androecium of 1 stamen , filament to 3 cm long, anther directly above stigmas. Pistillate flowers (Zannichellia) with perianth fused into a tube; gynoecium apocarpous, ovaries superior , carpels 1-8, surrounded basally by perianth , stigmas funnel-shaped, exserted from perianth tube; placentation apical, 1 pendulous ovule per carpel . Fruits drupelets; seeds 1 per fruit ; embryo coiled or curved.

Distribution
Distribution in the Neotropics

A family of 4-7 genera depending on generic and familiar circumscriptions adopted, and c. 90-95 species (an additional 40-50 putative hybrids of many Potamogeton have been described), occurring in fresh and brackish waters worldwide.  Three genera comprising c. 22 species occur in the Neotropics.

  • Potamogeton: about 80 species worldwide, with ca. 17 species of these occurring in the Neotropics.
  • Stuckenia: about four species subcosmopolitan, three species occur in the Neotropics.
  • Zannichellia: about five species near cosmopolitan, with two species in the Neotropics.
Diagnostic
Distinguishing characters (always present)
  • Aquatic herbs.
  • Leaves simple (submersed or floating).
  • Fruits drupes.
Other important characters
  • Inflorescences usually spikes, terminal or axillary.
  • Stipular sheath usually present.
General Description
Status
  • Native: some species are endemic.
Notes on delimitation
  • Potamogetonaceae is placed in the Alismatales, most closely related to Zosteraceae.
  • Zannichellia is rather weakly embedded in the Potamogetonaceae but placed here in APG II.
General notes
  • Fruits provide the most important features in separating species of this family; consequently one should always collect fruiting specimens.
  • Some species are important foods for waterfowl and are also grown in aquaria.
  • Environmentally some species are very important in substrate stabilization and in removing particles from the water column.
Literature
Important literature

Haynes, R.R., 2004. Potamogetonaceae. Pp. 476-477. In: Smith, N., Mori, S.A., Henderson, A., Stevenson, D.W. & Heald, S.V. (eds.). Flowering Plants of the Neotropics. New York Botanical Garden, Princeton University Press, Princeton.

Haynes, R.R., 2004. Zannichelliaceae. Pp. 493-494. In: Smith, N., Mori, S.A., Henderson, A., Stevenson, D.W. & Heald, S.V. (eds.). Flowering Plants of the Neotropics. New York Botanical Garden, Princeton University Press, Princeton.

Haynes, R.R., Les, D.H. & Holm-Nielsen L.B., 1998. Potamogetonaceae. In: K. Kubitzki (ed.), The families and genera of vascular plants 4: 408-415. Springer Verlag, Berlin, Heidelberg, New York.

Haynes, R.R., Les, D.H. & Holm-Nielsen L.B., 1998. Zannichelliaceae. In: K. Kubitzki (ed.), The families and genera of vascular plants 4: 470-474. Springer Verlag, Berlin.Stevens, P. F. (2008). Angiosperm Phylogeny Website. Version 9 onwards. http://www.mobot.org/MOBOT/research/APweb/.

[FWTA]

Potamogetonaceae, F.N. Hepper. Flora of West Tropical Africa 3:1. 1968

Habit
Aquatic herbs of fresh, water
Leaves
Leaves alternate or opposite, those immersed thin, those above water often leathery, sheathing at the base, sheath free or partially adnate to the petiole
Flowers
Flowers hermaphrodite, small, arranged in pedunculate axillary spikes; peduncle surrounded by a sheath at the base; bracts absent
Perianth
Perianth of 4 free rounded shortly clawed valvate segments
Androecium
Stamens 4, inserted in the claws of the segments; anthers extrorse, 2-locular, sessile
Gynoecium
Carpels 4, free, 1-locular; stigmas sessile or on short styles; ovule solitary, on the adaxial angle
Fruits
Fruits free, 1-seeded, indehiscent
Seeds
Seeds without endosperm
[FTEA]

Zannichelliaceae, H. J. Beentje, M.Sc., Ph.D., F.L.S.. Flora of Tropical East Africa. 2000

Habit
Submerged aquatics of fresh or brackish water, monoecious; rhizomes with unbranched roots; stems branched
Leaves
Leaves spirally arranged or distichous, sometimes appearing whorled or subopposite; sheath amplexicaul; blade linear, 1(–3)-veined
Flowers
Flowers small, terminal in complex sympodial inflorescences; petals absent or scale-like and basally connate; anthers 1 (or several with thecae united), with 1 or more longitudinal slits; ovaries 1–5(–8), surrounded by a perianth-like structure, each with short style; ovules 1 per ovary, apical and pendulous
Fruits
Fruit a dense group of achenes or drupelets, the wall 2-layered, the inner wall persisting; endosperm absent
[FWTA]

Zannichelliaceae, F.N. Hepper. Flora of West Tropical Africa 3:1. 1968

Habit
Submerged aquatic herbs in fresh, brackish, or salt water; rhizome creeping, slender
Leaves
Leaves alternate or opposite, or crowded at the nodes, linear, sheathing at the base, sheaths mostly ligulate at the apex; flowering leaves sometimes reduced to sheaths
Flowers
Flowers minute, monoecious or dioecious, axillary, solitary or in cymes
Perianth
Perianth of 3 small free scales, or absent
Androecium
Stamens 3, 2 or 1; anthers 2-1-locular, opening lengthwise; pollen globose or thread-like
Gynoecium
Ovule solitary, pendulous Carpels 1-9, free; style simple or 2-4-lobed
Fruits
Fruits sessile or stipitate, indehiscent
Seeds
Seed pendulous, without endosperm

Images

Potamogetonaceae Bercht. & J.Presl appears in other Kew resources:

First published in Prir. Rostlin Aneb. Rostl. 1(Sig. 7*-13): 1, 3. 1823 (as "Potamogetinae") (1823)

Accepted by

  • APG IV (2016) http://dx.doi.org/10.1111/boj.12385

Sources

Flora of Tropical East Africa
Flora of Tropical East Africa
http://creativecommons.org/licenses/by-nc-sa/3.0

Flora of West Tropical Africa
Flora of West Tropical Africa
http://creativecommons.org/licenses/by-nc-sa/3.0

Kew Names and Taxonomic Backbone
The International Plant Names Index and World Checklist of Selected Plant Families 2018. Published on the Internet at http://www.ipni.org and http://apps.kew.org/wcsp/
© Copyright 2017 International Plant Names Index and World Checklist of Selected Plant Families. http://creativecommons.org/licenses/by/3.0

Neotropikey
Milliken, W., Klitgard, B. and Baracat, A. (2009 onwards), Neotropikey - Interactive key and information resources for flowering plants of the Neotropics.
http://creativecommons.org/licenses/by/3.0