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(Last Modified On 5/9/2013)
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(Last Modified On 5/9/2013)
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Genus
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Hydrilla Rich.
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PlaceOfPublication
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Mem. Cl. Sci. Math. Inst. Natl. France 12(2): 9, 61, 73, t. 2 (upper part). 1814.
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Synonym
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Hydrospondylus Hassk., Flora 25, Beibl. 2: 33. 1842.
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Description
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Perennial, submerged fresh-water herbs, with an erect main axis,- rooting basally, the roots unbranched, smooth, the stem slender, unbranched or slightly to moderately branched. Leaves not differentiated into blade and petiole, linear or lanceolate, rarely elliptic, translucent, green, with many tannin cells, acute apically, the margin serrate, with 1 medium nerve, at most 4 cm long, the lower alternate or in whorls of 3, usually reduced in size, the middle and upper in whorls of 3-8; squamulae intravaginales 2, minute, fringed. Inflorescences axillary, sessile or subsessile, 1-flowered; spathe of 2 connate bracts. Flowers unisexual, the plants dioecious; staminate spathe subsessile, globose, dorso-ventrally flat- tened, with subulate appendages and a minute central knob; staminate flower freely-floating, pedicellate, the sepals 3, ovate to oblong-elliptic, strongly convex, reflexed, the petals 3, linear to spatulate, narrower than the sepals, spreading to reflexed, the stamens 3, the anthers erect, 4-thecate, latrorsely dehiscent; carpellate spathe sessile, tubular, bifid, membranous; carpellate flower sessile, with a long hypanthium, the sepals 3, oblong to obovate, convex, the petals 3, spatulate, narrower than the sepals, the ovary linear, unilocular with 3 parietal placentas, the ovules several, ortho- to anatropous, the styles 3, filiform to subulate, entire. Fruits linear, cylindrical; seeds cylindrical, glabrous, 2-6 in a row.
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Habit
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herbs
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Distribution
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A monotypic Old World genus, introduced into Panama. The habit of Hydrilla is similar to that of Elodea. In fact, there is not a single vegetative character which gives an absolute distinction between the two genera.
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