The World Flora Online

Perennes o algunas anuales, rizomatosas, totalmente sumergidas o con algunas hojas flotantes, la infl. aveces emergente; tallos alargados. Hojas sumergidas sésiles o pecioladas, lineares o liguladas a elípticas (enCR), los márgenes enteros o (a veces) serrulados, las estípulas libres (en CR), o adnatas a la base de la láminacon los ápices libres; hojas flotantes pecioladas, elípticas u oblongo-elípticas (en CR). Fls. en 3–15 verticilos(en CR); perianto de 4 tépalos (en CR); estambres 4. Frs. drupitas, sésiles.

1. Potamogeton L.

Por A. Novelo R. y A. Lot H.

Generalmente perennes; tallos ramificados, los erectos ocasionalmente con glándulas en los nudos, las puntas de los tallos frecuentemente modificadas en hibernáculos. Hojas sumergidas sésiles, pecioladas o con la base envolviendo al tallo, las flotantes generalmente pecioladas, alternas y a veces en la parte superior subopuestas; estípulas tubulares, libres o connatas a la base de las láminas, con o sin lígula; láminas homo- o heteromorfas, de las sumergidas generalmente lineares, lanceoladas a ampliamente ovadas, membranáceas, el margen entero a serrulado, de las flotantes ovadas a lanceoladas, coriáceas, el ápice agudo, redondeado a mucronulato. Inflorescencia con 2-30 flores, capitada o cilíndrica, compacta o moniliforme. Flores con un perianto de 4 tépalos libres; estambres 4; pistilos 4, sésiles o subsésiles. Aquenio dorsalmente redondeado o crestado. Más de 100 spp. Cosmopolita.

Bibliografía: Fernald, M.L. Mem. Amer. Acad. Arts n.s., 17: 1-183 (1932). Haynes, R.R. Rhodora 76: 564-649 (1974); Sida 11: 173-188 (1985). Ogden, E.C. Rhodora 45: 57-105, 119-163, 171-214 (1943). St. John, H. Rhodora 18: 121-138 (1916).

A near cosmopolitan genus of ca. 95 species; 17 species are known from the Neotropics and temperate South America. González (1989) lists an additional species, Potamogetón natans, but we are not including it here since the species is included in numerous treatments of the genus for North America.

Herbs propagated by seeds, turions, or rhizomes; stems terete or compressed, the nodes occasionally with oil glands. Leaves submersed or both submersed and floating, alternate to subopposite; submersed leaves pellucid, sessile or petiolate, linear to orbicular, noncaniculate, flattened, subulate to obtuse at apex, acute to perfoliate at base, the margins entire or serrate, rarely crimped, the veins 1-35; floating leaves coriaceous, mostly petiolate, rarely subsessile, elliptic to ovate, acute to obtuse at apex, cuneate to rounded or cordate at base, the margins entire, the veins 1-51; basal sheaths tubular, sheathing stem and young inflorescences, connate or convolute, either free from or adnate to base of submersed leaves for less than 1/2 the length of basal sheaths, free from base of floating leaves. Turions present or absent, with extremely shortened internodes, divided into inner and outer leaves, the inner leaves few to numerous, rolled into a fusiform structure, unmodified, or shortened and oriented at 90° angles with respect to outer leaves, the outer leaves 1-5 per side, mostly similar to vegetative leaves or occasionally corrugated near the base. Inflorescence a capitate or cylindrical spike or panicle of spikes with 1-20 whorls of flowers, compact or moniliform, with 2-4 flowers in each whorl, submersed or held above surface of water; peduncle stiff, if long enough, projecting the inflorescence above water surface. Flowers with perianth of 4, free, rounded, short-clawed segments; androecium of 4 stamens, filaments adnate to the perianth claw; anthers 2-locular; gynoecium of 1 or 4 carpels. Fruits abaxially rounded or keeled, beaked; embryo coiled 1 or more times. Chromosomes: x = 13 or 14.

Herbs, perennial or annual, in fresh or brackish water, totally submerged or with floating leaves. Stems terete to compressed, rarely strongly compressed. Leaves alternate, occasionally opposite, mono- or dimorphic; stipules membranous, free or partially adnate to leaf base (sheaths); submerged leaves sessile or petiolate, linear or with thin blades lanceolate; margins entire, denticulate, or serrulate; floating leaves petiolate, with leathery blades lanceolate to ovate or broadly elliptic-oblong. Inflorescence a pedunculate spike, terminal or axillary, surrounded by sheath in bud, emergent, floating or submerged at anthesis. Perianth 4-merous, free, bractlike and shortly clawed, each inserted opposite a stamen. Stamens 4, united with perianth at base; anthers sessile, 2-celled, extrorse, dehiscence longitudinal. Carpels (1-)4(or 5), free; stigmas sessile or on short styles, expanded, capitate or peltate; ovule solitary, attached to adaxial side of carpel. Fruit drupaceous with fleshy exocarp and bony endocarp. Embryo curved or spiral, rarely erect; endosperm absent.

POTAMOGETON L.

Hierbas anuales o perennes, sumergidas, creciendo en aguas dulces o salobres, reproduciéndose por semillas, turiones o rizomas; tallos de largos diversos, dependiendo en la profundidad del agua donde crecen, ramificados o no, teretes o comprimidos, con raíces en los nudos, los nudos ocasionalmente con glándulas de aceite. Hojas sumergidas o sumergidas y flotantes, alternas o subopuestas; hojas sumergidas sésiles o pecioladas, lineares a orbiculares, subuladas a obtusas en el ápice, agudas a perfoliadas en la base, pelúcidas, los márgenes enteros a serrados, raramente encrespados, con 1–35 nervios; hojas flotantes mayormente pecioladas o raramente subsésiles, elípticas a ovadas, agudas a obtusas en el ápice, cuneadas a redondeadas o cordadas en la base, coriáceas, los márgenes enteros, con 1–51 nervios; estípulas connadas o convolutas, libres o adnadas a la base de las hojas sumergidas, libres de la base en las hojas flotantes; turiones presentes o ausentes, con entrenudos extremadamente acortados, divididos entre las hojas internas y externas; turiones internos pocos a numerosos, enrollados formando una estructura fusiforme, acortados y orientados perpendicularmente hacia las hojas exteriores, o no modificados; turiones externos 1–5 por lado, mayormente similares a las hojas vegetativas, raramente corrugados cerca de la base. Inflorescencias axilares o terminales, a capitadas o espigas cilíndricas o panículas de espigas con 1–20 verticilos de flores cada una, éstos compactos o monoliformes, con 2–4 flores por verticilo, sumergidos o por encima de la superficie del agua; perianto de 4 segmentos cortamente unguiculados, libres y redondeados; androceo de 4 segmentos, los filamentos adnados al perianto unguiculado, las anteras 2-loculares, extrorsas, el tapete ameboide, el polen esférico a fusiforme, adornado; gineceo de 4 carpelos, los óvulos ortótropos o campilótropos, micrópilo formado por el integumento interno. Fruto dorsalmente redondeado o aquillado, rostrado; embrión en espiral.

Un género de distribución casi cosmopolita con unas 100 especies; 1 especie se encuentra en Nicaragua y otra se espera encontrar.

M.L. Fernald. The linear-leaved North American species of Potamogeton, section Axillares. Mem. Amer. Acad. Arts, n.s. 17: 1–183. 1932; E.C. Ogden. The broad-leaved species of Potamogeton of North America north of Mexico. Rhodora 45: 57–105, 119–163, 171–214. 1943; R.R. Haynes. A revision of North American Potamogeton subsection Pusilli (Potamogetonaceae). Rhodora 76: 564–649. 1974.

A genus of perhaps 100 species, widespread throughout both hemispheres, especially in temperate and subtemperate regions.

Plants annual or perennial, propagated from seeds, winter buds, or rhizomes, submersed in fresh or rarely brackish water. Stems variable in length according to water depth, branched or unbranched, terete or compressed, rooting at the nodes. Leaves all submersed and/or floating, alternate or subopposite; submersed leaves pellucid, sessile or petiolate, linear to orbicular, apically subulate to ob- tuse, basally cuneate to rounded or cordate, the margins entire, the nerves 1-35; floating leaves coriaceous, mostly petiolate, rarely subsessile, elliptic to ovate, acute to obtuse at apex, cuneate to rounded or cordate at base, the margins en- tire, the nerves 3-51; stipules tubular, sheathing the stem and young inflores- cences, connate or convolute, either free or adnate to the base of submersed leaves, free from the base of floating leaves. Winter buds present or absent, with extremely shortened internodes, divided into inner and outer leaves; inner leaves few to numerous, unmodified or shortened and oriented at 90? with respect to outer leaves, rolled into a fusiform structure; outer leaves 1-5 per side, mostly similar to vegetative leaves, rarely corrugated near the base. Inflorescence a capitate or cylindric spike with 1-20 whorls of flowers, compact or moniliform, with 2-4 flowers in each whorl, mostly buoyed above surface of water at an- thesis. Flowers bisporangiate; perianth of 4 distinct, rounded, short-clawed, greenish segments; stamens 4, the filaments adnate to the perianth claw, the anthers bithecate, extrorse, pollen spherical, monoaperturate; gynoecium of 4 distinct, unilocular, uniovulate carpels, the placentation parietal, the ovule campylotropus. Fruit drupe-like, dorsally rounded or keeled; embryo coiled.

Characters of the family. 100, cosmop. The plants normally produce lvs (or phyllodia) on the submersed part of the stem. If the stem reaches the surface, some spp. also produce floating lvs of different shape and texture. In some spp. the midrib is paralleled by one or more rows of colorless, translucent lacunar cells, forming lacunar strips or bands that are usually easily observed by transmitted light. Lf-measurements are taken from the principal lvs of the main axis, not from those of short, lateral branches. In some spp. the sides of the achenes are depressed at the center, and the achenes are said to be pitted.

Herbes'aquatiques ou rampant occasionnellement sur la vase, vivaces, sempervirentes en conditions favorables, persistant sous forme de rhizomes et de turions écailleux pendant la saison défavorable dans les régions à saisons marquées, rarement annuelles; rhizomes ordinairement ramifiés, sympodiaux, portant des ligules écailleuses, parfois absents; tiges grêles, dressées, ramifiées, cylindriques ou ± comprimées.'Feuilles'alternes mais ordinairement opposées immédiatement sous les inflorescences, souvent hétéromorphes, toutes submergées ou les inférieures seules submergées et les supérieures flottant à la surface de l'eau; stipules ± longuement soudées entre elles en une ligule libre ou adnée à la base du limbe, parfois fermée en une gaine tubulaire; pétiole présent ou absent; limbe elliptique, oblong, lancéolé, linéaire ou filiforme, à bord le plus souvent entier, parfois denticulé. Inflorescences axillaires, simples, en épis ovoïdes à cylindriques, denses ou lâches, parfois interrompus, émergeant ordinairement à l'anthèse.'Fleurs'actinomorphes, bisexuées, protogynes; périgone à 4 tépales libres, valvaires, obovales à suborbiculaires, onguiculés; étamines 4, opposées aux tépales, à connectif adné à leur onglet; grains de pollen ellipsoïdaux-sphéroïdaux, inaperturés ou 1-colpés, à exine mince, réticulée; carpelles (1-)4, ovoïdes, à bec surmonté du stigmate, ou à surface stigmatique s'étendant sur la suture ventrale.'Fruits'drupacés, subsessiles, ovoïdes, surmontés d'un bec ± long; exocarpe tendre; endocarpe dur.'Graines exalbuminées, à tégument membraneux.\n\t\t\t\tGenre cosmopolite comprenant environ 100 espèces. Pour la Flore : 5 espèces.

Spikes cylindrical or subglobose, 3- to many-flowered, dense or lax, sometimes interrupted, mostly borne above the water and wind-pollinated, but sometimes submerged and water-pollinated Leaves alternate, but mostly subopposite toward the inflorescence apex (involucral leaves), sessile or petiolate, 1- to many-nerved, all submerged and with filiform, grass-like or ± expanded blade, or dimorphic, the submerged ones thin and ± translucent, sometimes reduced to phyllodes, the floating ones ± coriaceous, opaque, petiolate,and usually broader; stipulesalways present,although sometimes fugacious, forming a sheath, connate or convolute around the stem; blade or petiole sometimes attached near the top of the sheath which projects beyond the joint as a ventralligule, sometimes attached farther down the sheath or arising from the node Rhizome present or absent, if present well differentiated from the stem, filiform, slender or robust, terete or ± compressed; stems terete or compressed, ± densely branched; turions present or absent Embryo unciform or spiral; cotyledon curved in the seed. Fruitlets with soft mesocarp and multi-layered sclerified endocarp, with or without a distinct beak Tepals rounded at the apex Leaves alternate, but mostly subopposite toward the inflorescence apex (involucral leaves), sessile or petiolate, 1- to many-nerved, all submerged and with filiform, grass-like or ± expanded blade, or dimorphic, the submerged ones thin and ± translucent, sometimes reduced to phyllodes, the floating ones ± coriaceous, opaque, petiolate,and usually broader; stipulesalways present,although sometimes fugacious, forming a sheath, connate or convolute around the stem; blade or petiole sometimes attached near the top of the sheath which projects beyond the joint as a ventralligule, sometimes attached farther down the sheath or arising from the node Rhizome present or absent, if present well differentiated from the stem, filiform, slender or robust, terete or ± compressed; stems terete or compressed, ± densely branched; turions present or absent Embryo unciform or spiral; cotyledon curved in the seed. Fruitlets with soft mesocarp and multi-layered sclerified endocarp, with or without a distinct beak Tepals rounded at the apex

SELECTED REFERENCES

Fernald, M. L. 1932. The linear-leaved North American species of Potamogeton section Axillaries. Mem. Amer. Acad. Arts, n. s. 17: 1--183. Haynes, R. R. 1975. A revision of North American Potamogeton subsection Pusilli (Potamogetonaceae). Rhodora 76: 564--649. Haynes, R. R. 1985. A revision of the clasping-leaved Potamogeton (Potamogetonaceae). Sida 11: 173--188. Ogden, E. C. 1943. The broad-leaved species of Potamogeton of North America north of Mexico. Rhodora. 45: 57--105, 119--163, 171--214. Preston, C. D. 1995. Pondweeds of Great Britain and Ireland. Botanical Society of the British Isles, London. Handbook No. 8. Reznicek, A. A. and R. S. W. Bobbette. 1976. The taxonomy of Potamogeton subsection Hybridi in North America. Rhodora. 78: 650--673.

Herbs: rhizomes present or absent; tubers absent; turions present or absent. Stems terete or compressed, nodes occasionally with oil glands; turions with extremely shortened internodes, divided into outer and inner leaves; outer leaves 1--5 per side, similar to vegetative leaves or occasionally corrugate near base; inner leaves 1--10, rolled into fusiform structure, unmodified, or shortened and oriented at 90° angles to outer leaves. Leaves submersed or both submersed and floating, alternate to nearly opposite; stipules connate or not, if not, then convolute,  tubular, sheathing stem and young inflorescences. Submersed leaves sessile or petiolate; stipules either free from or adnate to base of leaf blade for less than ½ length of stipule, if adnate, then extending past adnation as free ligule; blade translucent, linear to orbiculate, not channeled, flattened, base acute to perfoliate, margins entire or serrate, rarely crispate, apex subulate to obtuse; veins 1--35. Floating leaves petiolate, rarely nearly sessile; stipules free from base of leaf blade; blade elliptic to ovate, leathery, base cuneate to rounded or cordate, margins entire, apex acute to obtuse; veins 1--51. Inflorescences spikes or panicles of spikes, submersed or emersed, capitate or cylindric; peduncles stiff, if long enough then projecting inflorescence above surface of water. Flowers: pistils 1 or 4. Fruits abaxially rounded or keeled, flattened to turgid, beaked; embryo coiled 1 or more times. x = 13 or 14.