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HYDROCHARITACEAE

Vallisneria

Source:

SSA

Description:

Submerged, freshwater, herbaceous, grass-like, glabrous, perennial, +/- stemless aquatics, forming runners, dioecious. Leaves rosulate, radical, linear, up to 2 m or more long, sheathing at the base, with 3-9 parallel veins and faint transverse veinlets, margin denticulate, apex obtuse. Inflorescence axillary; spathe of 2 united bracts. Maleflowers very small, many, shortly pedicelled, maturing consecutively, becoming detached as buds, floating and expanding after reaching surface of water; sepals 3, ovate, convex; petals 3, minute; stamens 1-3, divergent. Female flowers axillary; solitary, tubular, bilobed; peduncle long, reaching surface (if not too deep), spirally contracted after anthesis; sepals 3, ovate or oblong-ovate; petals 3, minute; ovary 1-locular, with 3 parietal placentas bearing many ovules; styles 3, bilobed. Fruit fusiform, breaking irregularly. Seeds many, ellipsoidal, up to 2 mm long. x = 10, 12 (7, 8, 9-1 report each) (polyploidy).

Distribution:

Species 4, tropics and subtropics; 1 in sthn Afr.: Vallisneriaaethiopica Fenzl, N Namibia and Botswana; recently recorded from Lydenburg (Mpumalanga) and Cape Town (Western Cape), probably escapes from aquaria. Plant is totally submerged; male flowers abscise and float on the water surface 'caught' by floating female flowers.

Ottelia

Pers.

Source:

SSA

Description:

Aquatic, rooted, +/- stemless, armed or unarmed annuals, dioecious or monoecious or sometimes flowers bisexual; roots many, simple. Leaves rosulate, sessile or petiolate, sheathing at base, submerged or in some species also with floating blades; lamina of submerged leaves ribbon-like, linear to lanceolate, with floating blade ovate to cordate; nerves 3-11, distinct, connected by cross-veins. Inflorescence pedunculate; spathes saccate, containing many male flowers; female and bisexual flowers usually solitary; spathes firm, with prominent, sometimes muricate, ribs or wings, or occasionally smooth. Flowers: perianth white or yellow, tubular, with 3 outer segments sepaloid, persistent, and 3 inner larger, petaloid, slightly exserted above surface of water at anthesis, ephemeral; pollination entomophilous (or flowers often cleistogamous). Male flowers usually 1-3 exserted at a time, with pedicels lengthening rapidly at anthesis; stamens 6-15; anthers basifixed; pollen globular, tuberculate; gynoecium rudimentary. Female flowers: ovary flask-shaped with 3-6 parietal placentas intruding towards centre; styles 3-15, each divided into 2 stigmatic arms; ovules many, amphitropous; staminodes present or 0. Fruit ripening inside accrescent spathe; lower part of perianth tube forming its beak. Seeds many, small, fusiform, tomentose or glabrous, many released in pulpy mass. x = 11 (10, 12, 17, 26) (aneuploids, high polyploidy).

Distribution:

Species 21, tropics and subtropics, 13 in Africa, 7 in Asia and Australia and 1 in South America; 4 in sthn Afr., restricted to the warmer parts, * Ottelia alismoides (L.) Pers. has spread out of Asia and has naturalised in Africa, Europe and North America. Seeds embedded in pulp (rather like bananas), dispersed by water, fish and perhaps other animals.

Lagarosiphon

Harv.

Source:

SSA

Description:

Submerged (except for flowers during anthesis), dioecious, rooted herbs from a perennial rhizome; stems long, terete, leafy; branches arising from inside a spathe next to a flower; leafy apices compact; internodes elongating later. Leaves alternate, subopposite or whorled, widely spaced below, dense above, linear to linear-lanceolate; margin dentate with unicellular teeth; tissues of lamina differing in each species, with 2 minute axillary scales (intra-vaginal squamulae). Male inflorescence axillary; spathe valves fused, obovate, ovate or lanceolate, compressed or cup-shaped, dentate; axis (rudimentary scape) producing many pedicellate flowers (up to 50 or more) consecutively; buds become detached and rise to surface (because of an enclosed air bubble) where they expand and recurve suddenly to form a bell-shaped, floating flower; perianth 3 + 3, outer segments slightly narrower; stamens 3; filaments ultimately parallel to water surface with anthers at right angles to them; each anther gives rise to 16 pollen grains (4 per pollen sac); pollen grains large; staminodes 3, longer than stamens, papillate, usually coloured above, joined at top (acting as a sail). Female inflorescence axillary; spathe valves fused, narrowly oblong, ovoid or cylindrical, entire or toothed, containing 1-3 flowers; perianth tube exserted laterally near apex of spathe, lengthening (giving off gas bubbles buoying it up) until flower reaches surface of water (ultimate length of flower varies with species); limb 6-lobed; staminodes 3, minute, filiform; ovary with 3 parietal placentas; styles 3, adnate to perianth tube, each divided into 2 long, papillate, often brightly coloured, stigmatic arms; ovules 6-30, orthotropous, funicle short or long, straight or bent. Fruit a capsule protruding from torn spathe (the larger inner spathe valve bursting along midrib), rostrate (persistent perianth base forming a beak) ultimately becoming mucilaginous and disintegrating. Seeds few to many, cylindrical, shortly stipitate, apex acute, closely ribbed or honeycombed, buoyant at first, sinking later. x = 11 (7, 10-1 report each) (polyploidy).

Distribution:

Species 9, tropical Africa and Madagascar, 8 occur in Africa south of the Sahara, 1 is endemic to Madagascar; 5 in sthn Afr., Lagarosiphon major (Ridl.) V.A.Wager has naturalised in Europe and New Zealand.

Halophila

Thouars

Source:

SSA

Description:

Marine perennials, monoecious or dioecious, with a much-branched creeping rhizome; rhizomes bearing at nodes an abbreviated shoot and a pair of leaves, each surrounded by a basal scale; roots simple, 1 or rarely 2 from a node, densely covered with long root hairs. Leaves in pairs, petiolate, linear, lanceolate, oblong or ovate, entire or serrulate, glabrous or pubescent; midrib distinct, with a prominent lateral marginal nerve connected to midrib by many oblique secondary nerves. Flowers unisexual, usually solitary in axil of a secondary shoot, rarely 1 or 2 male and a female flower together in a spathe; spathe of 2 free, membranous bracts. Male flowers shortly pedicelled, with 3 perianth segments; stamens 3, anthers sessile, 2-4-celled, extrorse; pollen adhering to form threads; pollination hydrophilous. Female flower sessile; ovary ovoid, beaked, bearing 3 reduced perianth segments near apex; styles 2-6, linear. Fruit ovoid, rostrate, thin-walled. Seeds few to many, small, globose. x = 9.

Distribution:

Species 9, tropical to warm seas of the world; 1 in sthn Afr.: Halophila ovalis (R.Br.) Hook.f., coastal waters of KwaZulu-Natal as far south as Knysna (Western Cape).

Egeria

Planch.

Source:

SSA

Description:

Permanently submerged, attached, much-branched, densely leafy, dioecious perennials. Leaves in whorls of 3 or more, sessile, linear to widely lanceolate, 1-nerved, margins without fibre cells, serrulate, apex acute, terminating in a single spine. Inflorescence in axil of foliage leaves; spathe sessile or subsessile, of 2 united bracts. Flowers unisexual, arising from spathes situated in upper leaf axils; each flower with a thread-like hypanthium; sepals 3; petals 3, large, 2-3 times longer than sepals and alternating with them. Male flowers 2 or 4, held above water surface on rigid pedicels; sepals ovate, spreading, green; petals obovate to suborbicular, white; stamens 9 or rarely more; filaments club-shaped, orange, glandular, much longer than anthers, central 3 erect and opposite sepals, outer 6 in 2 whorls of 3 and upcurved; anthers unequal, each theca dehiscing longitudinally into two equal valves; staminodes 0; pollen liberated in monads; pistillodium 3-lobed, green. Female flowers solitary, similar to male flowers; stamens replaced by 3 linear, yellow to orange staminodes, elongated hypanthium bearing flower above water surface; ovary of 3 carpels; enclosed in base of hypanthium, placentas parietal; ovules several; styles 3, flattened, variously bifid or trifid. Fruit ellipsoidal, irregularly dehiscent. Seeds long, spindle-shaped. x = 12, 23 (1 report each, polyploidy).

Distribution:

Species 2, both from subtropical and temperate South America; *Egeria densa Planch. has been introduced into KwaZulu-Natal, probably during Medley Wood's time when a submerged aquatic was needed as an 'oxygen plant' for the fish introduced to combat malaria-carrying mosquito larvae; also recorded from the Baakens River in Port Elizabeth (Eastern Cape), a sewerage pond in Bloemfontein (Free State) and a dam in Stellenbosch (Western Cape). This potentially serious weed, is a popular aquarium or outdoor pond plant and is sold at various nurseries and aquarium shops. It is often confused with some of the species of Lagarosiphon, but it is more robust and the leaves are in definite whorls.

Thalassia

Banks ex K.D.Koenig

Description:

Submerged, dioecious marine perennial herbs; roots unbranched; horizontal scale-bearing rhizomatous axes (long shoots) buried in substrate giving rise, at regular intervals, to erect, contracted, leaf-bearing axes (short shoots). Leaves distichous, 2

Distribution:

Species 2, coasts of Caribbean and Indo-Pacific Ocean; sthn trop. Afr. 1: Thalassia hemprichii (Solms) Aschers., Mozambique.

Source:

SSTA

Hydrilla

Rich.

Description:

Submerged, freshwater annual or perennial herbs, gynodioecious; roots unbranched; stems horizontal and stoloniferous below, erect and spreading above; bulbil-like turions (hibernacula) developing underground terminally on stolons, or axillary on erect stems or their branches. Leaves opposite and scale-like towards base of stem or branch, otherwise linear to ovate and in whorls of 3

Distribution:

Monotypic: Hydrilla verticillata (L.f.) Royle, Old World, naturalised in America and a serious pest in U.S.A.; sthn trop Afr.: Zambia, Mozambique, probably introduced.

Source:

SSTA

Blyxa

Noronha ex Thouars

Description:

Submerged, freshwater, annual or perennial herbs, dioecious or bisexual; roots unbranched; stems corm-like and shortly erect, shortly rhizomatous or stoloniferous. Leaves radical or cauline and spirally arranged, sessile, linear to narrowly lanceolate, not differentiated into stipule, petiole and blade, flaccid, translucent, margin usually minutely toothed, midrib usually prominent. Inflorescence: spathe solitary in leaf axil, pedunculate or rarely sessile, 2-lobed at apex, containing 1 or 2(

Distribution:

Species 9, tropical Old World but naturalised in N America and Europe; sthn trop. Afr. 3: Angola, Zambia, Mozambique.

Source:

SSTA

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HYDROCHARITACEAE