Hydrocharitaceae

Vallisneria P.Micheli ex L.

First published in Sp. Pl.: 1015 (1753)
This genus is accepted
The native range of this genus is Old World, N. & Central America, Caribbean.

Descriptions

J. R. Timberlake, E. S. Martins (2009). Flora Zambesiaca, Vol 12 (part 2). Royal Botanic Gardens, Kew

Morphology General Habit
Perennial, freshwater, submerged herbs (except for flowers at anthesis), dioecious
Morphology Roots
Roots unbranched, vertical stem axis mostly short and bearing stolons, rarely erect and elongate
Morphology Leaves
Leaves basal or distinctly alternate on elongate stem (V. caulescens), sessile, first erect and submerged, but floating when reaching the water surface, linear, strap-shaped, apex obtuse; margins entire or bearing minute unicellular teeth, more dense near apex; main veins 3–5(9), longitudinal, parallel, connected by cross-veins, only midrib reaching the apex, the other longitudinal nerves gradually joining together near apex
Morphology Reproductive morphology Inflorescences
Inflorescences in leaf-axils, pedunculate; spathes comprising 2 united bract
sex Male
Male flowers very minute, pedicellate, abscising as buds and rising to the water surface where they open and float freely, slightly irregular; sepals 3, ovate-oblong to broadly ovate, reflexed at anthesis; petal 1, rudimentary; stamens (1)2–3, usually 2 fertile, free or with united filaments, and 1 staminode 1–4-sporangiate Male spathes shortly pedunculate, ovoid, 2- lobed at apex, containing many flower buds
sex Female
Female flowers sessile, regular; sepals (2)3, oblong or oblong-ovate; petals (2)3, rudimentary, translucent; staminodes (2)3, rudimentary, sometimes absent; ovary linear, 1-locular, placentation laminar-diffuse, ovules numerous (c.150), oblong, orthotropous, crassinucellar, embedded in a viscous pulp Female spathes tubular with bifid apex, 1-flowered, on a long coiled peduncle bringing flower up to surface at anthesis, contracting helicoidally after fertilization
Morphology Reproductive morphology Flowers Gynoecium Style
Styles (2)3, short or highly reduced; stigma (2)3, linear, 2-lobed or bifid, papillate on adaxial face
Morphology Reproductive morphology Fruits
Fruit a linear capsule, often very long, opening by decay of the pericarp
Morphology Reproductive morphology Seeds
Seeds numerous, oblong to fusiform; testa membranous, areolate or striate.
Distribution
A genus of 3 to 10 species, probably c.6, widely distributed throughout warmer regions of the world. Only 1 species in Africa and the Flora Zambesiaca area.
[FZ]

Hydrocharitaceae, David Simpson. Flora of Tropical East Africa. 1989

Morphology General Habit
Dioecious, submerged, freshwater, perennial herbs
Morphology Roots
Roots simple
Morphology Stem
Stems elongate, shortly stoloniferous or very shortly erect
Morphology Leaves
Leaves sessile, spirally arranged, radical, linear, obtuse, sheathing at the base, patent or erect, opaque or somewhat translucent, with 3–5 longitudinal veins; margins green, entire to coarsely serrate Nodal scales not seen
Morphology Leaves Stipules
Stipules 0
Morphology Reproductive morphology Flowers
Flowers unisexual Female flowers: sepals 3, ovate to oblong-ovate, obtuse, erect; petals 3, minute, linear, rudimentary; staminodes 3, linear, rudimentary or absent; ovary elongate, narrowly cylindric, 1-locular, placentation parietal; ovules numerous, orthotropous; perianth-tube absent; styles 3, reduced; stigmas 3, linear, deeply 2-lobed, papillose on adaxial surface Male flowers shortly pedicellate, breaking free and floating before anthesis; sepals 3, oblong to ovate, cucullate, reflexed at anthesis; petal 1, minute, linear, rudimentary, erect or reflexed; stamens 1–3, erect, or divergent, the filaments sometimes united; staminode 1, linear, rudimentary
Morphology Reproductive morphology Inflorescences
Male spathe solitary in leaf-axil, shortly pedunculate, ovoid, shortly 2-lobed at the apex, translucent, with numerous flowers Female spathe solitary in leaf-axil, long-pedunculate (the peduncle spirally contracting after fertilisation), cylindric, 2-lobed at apex, translucent, 1-flowered
sex Male
Male spathe solitary in leaf-axil, shortly pedunculate, ovoid, shortly 2-lobed at the apex, translucent, with numerous flowers Male flowers shortly pedicellate, breaking free and floating before anthesis; sepals 3, oblong to ovate, cucullate, reflexed at anthesis; petal 1, minute, linear, rudimentary, erect or reflexed; stamens 1–3, erect, or divergent, the filaments sometimes united; staminode 1, linear, rudimentary
sex Female
Female flowers: sepals 3, ovate to oblong-ovate, obtuse, erect; petals 3, minute, linear, rudimentary; staminodes 3, linear, rudimentary or absent; ovary elongate, narrowly cylindric, 1-locular, placentation parietal; ovules numerous, orthotropous; perianth-tube absent; styles 3, reduced; stigmas 3, linear, deeply 2-lobed, papillose on adaxial surface Female spathe solitary in leaf-axil, long-pedunculate (the peduncle spirally contracting after fertilisation), cylindric, 2-lobed at apex, translucent, 1-flowered
Morphology Reproductive morphology Fruits
Fruit elongate, narrowly cylindric, opening by decay of the pericarp
Morphology Reproductive morphology Seeds
Seeds narrowly ellipsoid to oblong, striate.
[FTEA]

Sources

  • Flora Zambesiaca

    • Flora Zambesiaca
    • http://creativecommons.org/licenses/by-nc-sa/3.0

  • Flora of Tropical East Africa

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

  • Herbarium Catalogue Specimens

    • 'The Herbarium Catalogue, Royal Botanic Gardens, Kew. Published on the Internet http://www.kew.org/herbcat [accessed on Day Month Year]'. Please enter the date on which you consulted the system.

  • Kew Backbone Distributions

    • The International Plant Names Index and World Checklist of Vascular Plants 2026. Published on the Internet at http://www.ipni.org and https://powo.science.kew.org/
    • © Copyright 2023 World Checklist of Vascular Plants. http://creativecommons.org/licenses/by/3.0

  • Kew Names and Taxonomic Backbone

    • The International Plant Names Index and World Checklist of Vascular Plants 2026. Published on the Internet at http://www.ipni.org and https://powo.science.kew.org/
    • © Copyright 2023 International Plant Names Index and World Checklist of Vascular Plants. http://creativecommons.org/licenses/by/3.0