Manual de Plantas de Costa Rica

 

 

HYDROCHARITACEAE

• By Garrett E. Crow

 

 

Novelo R., A. and A. Lot H. 1994. Hydrocharitaceae. Pp. 10-12 in Davidse, G., Sousa, M. and Chater, A. (eds.). Flora Mesoamericana 6: 1-543. Universidad Nacional Autónoma de México: México, D. F.

Thorne, R. F. 1992. Classification and geography of the flowering plants. Bot. Rev. 58: 225-348.

 

17 genera and ca. 74 species; chiefly tropical to warm temperate, extending into cold temperate regions of the Old and New Worlds; fresh or saline waters, 3 genera marine; 5 gen. and 5 spp. reported for CR.

Annual or perennial aquatic herbs, freshwater and marine; mostly submersed, some floating or stranded on mud. Plants monecious or dioecious. Stems elongate with leaves cauline, or stem very short, leaves in a basal rosette, rhizomatous (forming new rosettes). Leaves variable, simple, petiolate or sessile, basal or cauline, then alternate, opposite or whorled, margins entire or sometimes toothed, some sheathing at base (Najas); stipules present in petiolate leaves, forming a sheath, with 2-several small scales in leaf axils. Flowers solitary, axillary, terminal or borne on a scape or in a cyme, then subtended by 2 sheathing bracts, or 1 forming a tubular spathe; bisexual or, more often, unisexual (the male flowers sometimes abscising and floating to surface.). Perianth present, or absent (Najas). Sepals 3 or fewer, or absent. Petals 3 or fewer, inconspicuous to showy, or absent. Staminate flowers with stamens 1-12 (sometimes more, often the inner whorl staminodial). Pistillate flowers with ovary inferior or superior (Najas), carpels usually 3-5, or 1 (Najas), styles often divided. Fruit a berry or capsule (often dehiscing irregularly), seeds numerous, or an achene (Najas).

Vallisneria spirilis, an attractive submersed fresh water plant with long ribbon-like leaves in a basal rosette, is sometimes grown in artificial garden pools such as at the cathedral ruins in Cartago. It is also a popular aquarium plant. There is potential for this plant to escape from cultivation.

Recent studies have strongly suggested that Najas has close affinities with genera of the Hydrocharitaceae and Thorne's (1992) classification of the flowering plants formally places Najas in the Hydrocharitaceae (subfam. Hydrocharitoideae) rather than treating it in a family by itself.

Aquatic plants are poorly collected and the taxa of the Hydrocharitaceae are probably more widely distributed than indicated by specimens.

1. Leaves differentiated into distinct blade and petiole.

2. Plants free floating or stranded on mud, leaf blades floating on surface, or when growing dense, then ascending; stipules present; freshwater habitats...Limnobium

2. Plants totally submerged; stipules absent; marine sites...Halophila

1. Leaves not differentiated into blade and petiole.

3. Leaves borne on elongate ascending stem, opposite or in whorls of 3-8; freshwater habitats.

4. Leaves with distinct basal sheath; fruit 1-seeded, seed (seen through transparent fruit wall) with surface pitted...Najas

4. Leaves lacking basal sheath; seed coat not pitted.

5. Leaves spinulose along central nerve on lower surface, margins conspicuously spinulose-serrate (easily seen with naked eye); petals inconspicuous, narrower than the sepals...Hydrilla

5. Leaves not spinulose along central nerve, margins appearing entire or only slightly serrulate (magnification needed); petals showy, at least twice as wide as the sepals...Egeria

3. Leaves ribbon-like, up to 70 cm long, borne in clusters of 2-6 on short shoots arising from rhizomatous shoot buried in substrate (almost appearing as lines of basal rosettes); marine sites...Thalassia

Cook, C. D. K. and K. Urmi-König. 1984. A revision of the genus Egeria. Aquatic Bot. 19: 73-96.

2 spp., subtropical and temperate S. Am., naturalized widely in warm regions throughout the world, spreading readily by vegetative means, usually represented by only male plants; only 1 sp. reported for CR.

Egeria densa Planch., Ann. Sci. Nat. Bot. ser. 3, 11: 80. 1849. [Elodea densa (Planch.) Caspary].

Perennial, submersed aquatic herbs, freshwater. Plants dioecious. Stems ascending, often to the surface. Leaves sessile, cauline, opposite or in whorls of 3 on lower portion of stem, in whorls of 4-8 on upper stem, linear to narrowly lanceolate, 5-35 mm long; margins appearing entire to only slightly serrulate (ours) to spinulose-serrulate. Staminate flowers 2-5, subtended by 2 bracts. Pedicels ca. 6 cm long, with flower exserted above water surface. Sepals 3, green, ovate. Petals 3, white, large and showy, broadly obovate to nearly orbicular. Stamens 9 in 3 whorls, rarely more, staminodes absent. Pistillate flowers solitary, subtended by 2 bracts. Floral tube 2-6 cm long, flowers exserted above water surface. Sepals and petals as in male flowers. Staminodes present, 3, yellow to orange. Pistil with 3 carpels, styles 3. Fruit somewhat dehiscent.

Lagunas. Known only from Alajuela at Laguneta de Centro universitario San Ramón [Lot & Novelo 1225, MO, MEXU], sterile; probably occurring more widely. Native of South America; introduced widely in warmer waters of the world.

A noxious weed in many places, spreading vegetatively. Introduced populations are typically represented only by male plants.

Ca. 10 spp., widely distributed in tropical to warm marine waters throughout the world; only 1 sp. reported for CR.

Halophila baillonii Asch., a marine plant of shallow bays and reefs, with 4-6 leaves per stem and globose, rather than ellipsoid fruits, has been collected on the Pacific slope of Panama and might be expected in CR.

Halophila decipiens Ostenf., Bot. Tidsskr. 24: 260. 1902.

Perennial or annual submersed aquatic herbs, marine. Plants monoecious or dioecious. Rhizomes stoloniferous, creeping, bearing subopposite scales; erect stems bearing foliage leaves. Leaves distichous, sessile or more typically petiolate, linear-lanceolate to ovate, margins entire or serrulate. Flowers solitary, subtended by 2 membranous bracts. Staminate flowers pedicellate. Perianth 3. Stamens 3. Pistillate flowers sessile. Perianth 3 very reduced segments, or absent. Ovary superior, styles typically 3-5. Fruit indehiscent; seeds several.

Marine; shallow bays and reefs. Limón, reported only from Cahuita [Lot & Novelo 1257, MO, MEXU], sterile. Mexico to Venezuela.

Cook, C. D. K. and R. Lüönd. 1982. A revision of the genus Hydrilla. Aquatic Bot. 13: 485-504.

 

1 sp.; widely distributed in Old World, naturalized in warmer regions of New World; 1 sp. in CR.

Hydrilla verticillata (L. f.) Royle. Ill. Bot. Himal. Mts. 1: 376. 1839.

Perennial sumbersed aquatic herbs, sometimes annual in areas with pronounced dry season. Plants dioecious. Stems submersed, ascending to near the surface. Leaves sessile, cauline, opposite or in whorls of 3 on lower portion of stem, in whorls of 4-12 on upper stem, linear to narrowly lanceolate, typically 5-20 mm long. Staminate flowers axillary, solitary, abscising while in bud, opening at water surface. Sepals 3, ovate, reflexed, forming a floating flower. Petals 3, linear, reflexed. Stamens 3, anthers dehiscing explosively; staminodes absent. Female flowers axillary, solitary, nearly sessile, with long hypanthium growing to surface of water. Perianth 3 sepals and 3 petals, spreading, allowing flower to float on surface. Staminodes 3, vestigial. Ovary inferior, 3-carpellate, styles 3. Fruit enlongate, indehiscent; seeds few.

Lagunas and reservoirs. Known from Tortuguero, Valle Central and Valle Coto Brus [Crow 7575, CR, MO, NHA], sterile; probably occurring widely in Costa Rica. Distributed widely in the Old World, naturalized in warmer regions of New World, extending into eastern North America to Virginia.

This species is a noxious weed, readily spreading vegetatively.

Cook, C. D. K. and K. Urmi-König. 1983. A revision of the genus Limnobium including Hydromystria. Aquatic Bot. 17: 1-27.

Lowden, R. M. 1992. Floral variation and taxonomy of Limnobium L. C. Richard (Hydrocharitaceae). Rhodora 94: 111-134.

 

2 spp., tropical America, extending into eastern U.S.; only 1 sp. in CR.

Limnobium laevigatum (Humb. & Bonpl. ex Willd.) Heine, Adansonia 8: 315. 1968. [Salvinia laevigatum Humb. & Bonpl. ex Willd., Sp. Pl. 5: 537. 1810; Limnobium spongia ssp. laevigatum (Humb. & Bonpl. ex Willd.) Lowden; Hydromystria laevigata (Humb. & Bonpl. ex Willd.) Hunz.]

Perennial aquatic herbs, free-floating, emergent, or stranded on mud. Plants monoecious. Stems short, bearing rosettes of petiolate leaves, strongly stoloniferous, forming new rosettes. Floating leaves spreading, blades nearly round, with thick layer of aerenchymous tissue on under side; emergent leaves ascending (when plants growing densely) nearly round to sometimes elliptical. Males flowers borne in a few-flowered cyme, one open at a time, pedicellate, subtended by 2 sheathing bracts. Sepals 3, reflexed. Petals 3, white. Stamens variable, 3-10, usually 6, united in a staminal column, staminodes usually absent, sometimes 1(-3). Pistillate flowers solitary. Sepals 3. Petals usually absent. Staminodes present, opposite sepals, poorly developed. Ovary inferior, 3-9-carpellate, styles bifid nearly to base. Fruit an elliptic berry-like capsule, with irregular dehiscence, seeds numerous.

Lagunas. Gulfo de Nicoya coastal plain [Crow & Rivera 6205, CR, F, MO, NHA], July, Aug., Sept., Oct., Nov.; probably more widely occurring in lowlands along Pacific slope of Costa Rica. Mexico and Central America (Pacific slope) to Paraguay and Argentina; Antilles.

Haynes, R. R. 1979. Revision of North and Central American Najas (Najadaceae). Sida 8: 34-56.

Lowden, R. M. 1986. Taxonomy of the genus Najas L. (Najadaceae) in the Neotropics. Aquat. Bot. 24: 147-184.

 

Ca. 40 spp., nearly cosmopolitan; 2 spp. reported for CR.

Annual (rarely perennial) aquatic herbs, freshwater or sometimes saline. Plants monoecious (CR) or dioecious. Stems submersed, rooted ascending, often fragmenting freely and then free-floating. Leaves subopposite or appearing whorled, linear to linear-lanceolate, sheathing at base, sheath rounded (CR) or truncate at summit; margins usually serrulate. Flowers very small, axillary, solitary or in small clusters. Staminate flower enclosed in membranous sheath. Perianth absent. Stamens 1. Pistillate flower solitary, axillary, 1 ovary superior, stigmas 2-3. Fruit an achene, seeds pitted (CR) or smooth.

1. Leaf margins minutely serrulate, appearing entire, 18-100 teeth per side; seed coat pitted, with areolae squarish or wider than long...N. guadalupensis

1. Leaf margins conspicuously serrulate, 15-25 teeth per side; seed coat pitted, areolae longer than broad, sometimes inconspicuous...N. arguta

Najas arguta H.B.K., Nov. Gen. et Sp. Pl. 1: 371. 1815.

Stems much branched, with dense tufts of leaves at apices. Leaves linear to linear-lanceolate, subopposite to appearing whorled, margins conspicuously serrulate, with 15-25 teeth per side. Seeds 1.3-2.5(-2.8) mm long, surface pitted, areolae longer than broad, sometimes inconspicuous.

Lakes and lagunas. Valle Tempisque [Crow & Rivera 5971, CR, MO, NHA], fl/fr Sept., Oct. Lowlands, Costa Rica and Panama to Ecuador and Brazil.

This species readily fragments and short stems of dense tufts of leaves occur free-floating in the water.

Najas guadalupensis (Sprengel) Magnus, Beitr. Gatt. Najas viii. 1870. [Caulinia guadalupensis Sprengel, Syst. Veg. 1: 20. 1824.]

Stems submersed, little branched. Leaves linear to linear-lanceolate, subopposite, margins appearing entire, with many small unicellular teeth; leaf sheath rounded at summit. Seeds (0.8-)1-2.5(-3) mm long, surface pitted, areoles squarish, wider than long.

Lakes, lagunas, quiet streams and ditches. Guanacaste lowlands, La Cruz, Santa Rosa, Valle Tempisque, Cordillera Central, Talamanca, Limon [Crow & Rivera 6064, CR, MO, NHA], fl/fr Sept., Oct., Nov., Feb. Widely distributed, s. Canada to Bolivia.

Var. guadalupensis in CR; may be deserving of only forma rank (Lowden, 1986).

2 spp., marine, tropical waters of the New World and Indo-Pacific Ocean; 1 sp. reported for CR.

Thalassia testudinum Banks & Solander ex König, Ann. Bot. 2: 96. 1805.

Perennial submersed aquatic herbs. Dioecious. Stems of short shoots borne along rhizomatous shoot buried in substrate. Leaves ribbon-like, up to 70 cm long, borne in clusters of 2-6, appearing as basal rosettes.

Flowers 1-4, on submerged inflorescences, sessile or nearly so, subtended by 2 united, bracts, forming a spathe. Perianth of 1 whorl of 3 segments. Staminate flowers with 3-13 stamens. Pistillate flowers with elongate ovary, inferior, with a hypanthium; styles 6-8, bifid. Fruit a fleshy, globose capsule, with irregular dehiscence.

Marine; shallow bays and reefs. Limón, reported only from Cahuita [Lot & Novelo 1255, MO, MEXU], sterile. Florida; Caribbean coast of Mexico to Venezuela; Antilles.