The World Flora Online

SELECTED REFERENCES

Haynes, R. R. 1978. The Potamogetonaceae in the Southeastern United States. J. Arnold Arbor. 59: 170--191.

Herbs, annual or rarely perennial, not rhizomatous, caulescent; turions absent [present]. Leaves alternate to subopposite, submersed, sessile; sheath not persisting longer than blade, not leaving circular scar when shed, not ligulate, not auriculate; blade linear; intravaginal squamules scales, 2. Inflorescences terminal, capitate spikes, with subtending spathe, pedunculate; peduncle following fertilization often elongating, often spiraling. Flowers bisexual; subtending bracts absent; perianth absent; stamens 2, in 1 series; anthers distinct, dehiscing longitudinally; pollen arcuate; pistils 4--16, distinct, stipitate; ovules parietal, campylotropous. Fruits drupaceous. Seeds 1; embryo straight.

Herbes aquatiques, submergées ou parfois flottantes, généralement des eaux marines ou des eaux saumâtres, annuelles ou rarement pérennes, glabres ; tige s’enracinant aux nœuds, à ramifications monopodiales distiques dans les parties végétatives, sympodiales au niveau de l’inflorescence, à écailles étroites entourant la base des ramifications. Stipules absentes. Squamules intravaginales présentes à l’aisselle des feuilles. Feuilles alternes, opposées ou verticillées, à base engainante à bords libres ; limbe linéaire ou filiforme, à bords entiers ou denticulés vers le sommet, à une nervure. Inflorescences terminales (mais semblant axillaires en raison des ramifications sympodiales), à fleurs solitaires ou en épi court, souvent 2-flores, d’abord incluses dans les gaines de 2 feuilles terminales subopposées, puis exsertes, sur un pédoncule qui s’allonge souvent nettement en fruit et, en tant que telle, formant une structure ombelliforme ; bractées absentes. Fleurs bisexuées, actinomorphes, petites, vertes ; périanthe absent ou réduit à 2 tépales minuscules ; étamines 2, opposées, à anthère sessile, à déhiscence longitudinale, à 2 thèques bisporangées, connectif large ; gynécée avec (2–)4 à 16 ovaires libres, supères, sessiles mais portés sur des stipes rapidement allongés après la fécondation, à 1 loge et 1 ovule, à placentation apicale ; style absent, stigmate pelté à omboné. Fruits drupacés, indéhiscents, asymétriques, rostrés ; exocarpe présentant 2 fenêtres latérales parenchymateuses sous le rostre. Graines exalbuminées, à testa membraneux et sans phytomélanine.

Famille cosmopolite dans des eaux maritimes et saumâtres, avec un seul genre et une dizaine d’espèces, dont une au Gabon.

Herbes'aquatiques submergées; rhizomes grêles, rampants, lacuneux, portant des racines adventives simples; tiges ± grêles; lacuneuses, à ramification monopodiale distique dans les parties végétatives, sympodiale au niveau de l'inflorescence; écailles étroites entourant la base des ramifications.'Feuilles'distiques, alternes, simples, à base engainante assez longue et soudée aux stipules, accompagnées de 2 petites squamules axillaires, ovales; limbe linéaire-filiforme, lacuneux, ± denticulé dans la région apicale. Inflorescences : épis terminaux courts, le plus souvent 2-flores, d'abord inclus dans les gaines spathiformes de 2 bractées subopposées, puis exserts; pédoncule grêle, lacuneux, initialement court mais allongé et parfois enroulé après la floraison.'Fleurs'bisexuées, à périanthe réduit à 2 tépales minuscules; étamines 2, opposées, à anthère subsessile, grande, à 2 thèques bisporangiées, extrorses, à déhiscence longitudinale, séparées par un connectif large; grains de pollen oblongs, coudés, ± renflés en leur milieu du côté convexe ainsi qu'aux extrémités, à exine mince, formant un fin réseau, discontinue sur les dilatations; carpelles (2-)4(-16), libres, d'abord sessiles, portés après la fécondation sur des podogynes; stigmates sessiles, peltés, en forme de bouclier, parfois déprimés; ovules solitaires, pendant du sommet de la loge, subatropes, bitégumentés.'Fruits'drupacés, pyriformes, souvent obliques, à endocarpe rostré, scléreux, présentant sous le rostre 2 fenêtres latérales parenchymateuses.'Graines à tégument double, exalbuminées; embryon à radicule latérale; hypocotyle hypertrophié latéralement et rempli de substances de réserve; cotylédon petit, cylindrique, ± incurvé, adossé à l'hypocotyle.\n\t\t\tFamille unigénérique, comportant 7 espèces, subcosmopolite, absente seulement des régions arctiques. Pour la Flore : 1 espèce.

Fruits long-stipitate with spirally twisted stalks, indehiscent Seeds pendulous, without endosperm Carpels 4 or more, free, stigmas peltate or umbonate Ovule solitary, pendulous Flowers hermaphrodite, small, in terminal spikes at first enclosed by the sheathing base of the leaves, at length much elongated; bracts and perianth absent Leaves opposite or alternate, linear or setaceous, sheathing at the base Stamens 2; filaments short, broad; anthers extrorse, loculi reniform and separated by the connective Aquatic herbs of saline marshes Seeds pendulous, without endosperm Carpels 4 or more, free, stigmas peltate or umbonate Ovule solitary, pendulous Flowers hermaphrodite, small, in terminal spikes at first enclosed by the sheathing base of the leaves, at length much elongated; bracts and perianth absent Leaves opposite or alternate, linear or setaceous, sheathing at the base Stamens 2; filaments short, broad; anthers extrorse, loculi reniform and separated by the connective Aquatic herbs of saline marshes

Fls perfect, very small and inconspicuous, borne in very short, mostly 2-fld, terminal spikes, each spike initially concealed in the sheath of the uppermost vegetative lf; peduncle eventually much elongate and commonly becoming spirally twisted; tep wanting; stamens 2, opposite; anthers subsessile, extrorse, the pollen-sacs well separated on the expanded connective, which has a tiny abaxial appendage near the tip; pollen isobilateral; pistils (2–)4(–8), each with an expanded, ventro-apical stigma, becoming elevated on a slender stipe in fr, so that the several pistils of a fl form an umbelliform cluster; ovule solitary, pendulous, ventral-apical; fr an ovoid, commonly asymmetrical drupelet; endosperm wanting; embryo with an obliquely terminal cotyledon and a lateral plumule; glabrous, submersed aquatic herbs, rooted in the substrate; shoot-tip very compact and congested, but branched just beneath the terminal infl, the stem elongating and again terminating in an infl, etc.; typically 4 lvs between successive infls; lvs alternate or opposite, linear or setaceous, with a single midvein, expanded below into a well developed, distally open sheath. A single genus and sp.

Plants perennial or annual, in saline, brackish, or extremely hard water, totally submerged. Rhizomes slender, usually branched. Stems terete, elongated or not. Leaves alternate, sessile, narrowly linear, entire or minutely denticulate toward apex; stipules adnate to leaf base and sheathing stems; sheaths shortly auriculate, ligule absent. Inflorescences of few-flowered spikes, pedunculate; spikes enclosed by involucral leaves at first; peduncles short at first but elongated in fruit. Flowers hermaphroditic, small, ebracteate. Perianth absent. Stamens 2; anthers sessile, extrorse, opening by longitudinal slits. Carpels 4 or more, free, 1-ovuled, sessile in flower but usually becoming narrowly stipitate in fruit; stigma sessile, peltate or umbonate. Fruit drupaceous, asymmetric, indehiscent. Seeds without endosperm.

Ovaries 2-8, but usually 4, free, superior, sessile at first, becoming long-stipitate in fruit; ovule solitary, pendulous, campylotropous, crassinucellar; stigma sessile, peltate, ventroapical Fruits ovoid-pyriform, often asymmetric, beaked drupes Perianth absent Stamens 2, opposite each other; filaments very short and broad; anthers 2-thecous, extrorse, the 2 relatively large pollen-sacs divergent and well separated; pollen-grains luniform and of a unique type, buoyant Inflorescence usually a 2-flowered terminal spike with the flowers inserted at unequal heights and on opposite sides of the rachis, when young concealed in the sheath of the uppermost vegetative leaf, and just exserted above the water at anthesis; peduncle short or long, sometimes spirally coiled Flowers bisexual, actinomorphic, protandrous, very small and inconspicuous Leaves alternate or opposite; blade simple, linear or setaceous, with a single midvein; sheath wide, distally open Seeds hard, without endosperm Submerged monoecious glabrous aquatic herbs of alkaline or brackish water, sometimes in sea-water Stem slender, erect, branching freely, monopodial below, sympodial above Rhizome thin, matted, perennial, rooted in the substrate Fruits ovoid-pyriform, often asymmetric, beaked drupes Perianth absent Stamens 2, opposite each other; filaments very short and broad; anthers 2-thecous, extrorse, the 2 relatively large pollen-sacs divergent and well separated; pollen-grains luniform and of a unique type, buoyant Inflorescence usually a 2-flowered terminal spike with the flowers inserted at unequal heights and on opposite sides of the rachis, when young concealed in the sheath of the uppermost vegetative leaf, and just exserted above the water at anthesis; peduncle short or long, sometimes spirally coiled Flowers bisexual, actinomorphic, protandrous, very small and inconspicuous Leaves alternate or opposite; blade simple, linear or setaceous, with a single midvein; sheath wide, distally open Seeds hard, without endosperm Submerged monoecious glabrous aquatic herbs of alkaline or brackish water, sometimes in sea-water Stem slender, erect, branching freely, monopodial below, sympodial above Rhizome thin, matted, perennial, rooted in the substrate