Halophila Thouars

J. R. Timberlake, E. S. Martins (2009). Flora Zambesiaca, Vol 12 (part 2). Royal Botanic Gardens, Kew

Morphology General Habit

Perennial or annual marine herbs, totally submerged including the flowers, monoecious or dioecious

Morphology Roots

Roots unbranched, arising at creeping stem nodes, covered with long fine hairs and sand-binding

Morphology Stem

Stems elongate, dimorphic, creeping stem with 2 scales at each node, one embracing the creeping stem, the other a short erect stem bearing foliage leaf

Morphology Leaves

Foliage leaf in opposite rows or in pseudo-whorls, sessile or petiolate, ovate, elliptic, oblong or linear, entire or serrulate; midrib distinct, mostly connected by oblique secondary nerves (“cross-veins”) to two longitudinal (intramarginal) nerves running along or very near margins and reaching it near the top

Morphology Reproductive morphology Flowers

Flowers unisexual, male and female spathes similar, solitary in leaf axils, sessile, comprising 2 free bract, one embracing the other, bract elliptic, obovate to suborbicular, membranous, acute, rounded to emarginate or indented, keeled, with entire or minutely serrate keel and margins; spathes 1(2)-flowered, rarely with 1 of each sex; 2 scales in axil of each bract

sex Male

Male flowers pedicellate, remaining attached; tepals 3, imbricate, elliptic or ovate, hooded; stamens 3, alternating with tepals, anther sessile, erect, oblong, linear, 2- or 4- sporangiate

sex Female

Female flowers sessile; tepals 3, reduced to lobes at apex of hypanthium; staminodes absent; ovary of 3–5 carpels, ellipsoid or ovoid, beaked, unilocular, ovules few to many, anatropous, styles 3–5, stigma filiform, entire, papillate on adaxial surface

Morphology Reproductive morphology Fruits

Fruit ovoid or globose, beaked, with membranous pericarp, opening by dehiscence or decay

Morphology Reproductive morphology Seeds

Seeds few to numerous, globose or subglobose; testa tuberculate, reticulate or smooth

Morphology Reproductive morphology Seeds Embryo

Embryo consisting of a large hypocotyl and a coiled cotyledon, the plumula lying in a depression of hypocotyl sheathed by expanded base of cotyledon.

Distribution

About 11–16 species found in tropical and subtropical seas, extending into some warm-temperate waters. Three species in the Flora Zambesiaca area.

M. Thulin et al. Flora of Somalia, Vol. 1-4 [updated 2008] https://plants.jstor.org/collection/FLOS

Morphology General Habit

Monoecious or dioecious annuals or perennials with creeping rhizomes; rhizome bearing at each node a subopposite pair of scales with a lateral shoot and 1–few unbranched root(s) covered with sand-binding, fine hairs

Morphology Leaves

Leaves in pairs, in pseudo-whorls or distichously arranged, sessile or long-petiolate, usually with a distinct blade, linear to ovate; veins conspicuous, including a thickened midrib and a pair of longitudinal veins usually connected by cross-veins

Morphology Reproductive morphology Inflorescences

Inflorescences sessile, usually of a solitary unisexual flower or with 2 flowers of different sex; spathe of 2 sessile imbricate keeled bracts

Morphology Reproductive morphology Flowers

Female flower usually sessile, with 3 minute tepals at top of hypanthium; ovary of 3–5 carpels; styles 2–6, undivided Male flower pedicellate; tepals 3, imbricate; stamens 3; anthers sessile, linear-oblong, 2–4-celled, latrorsely or extrorsely dehiscent; pollen grains ellipsoid, united in moniliform chains

Morphology Reproductive morphology Fruits

Fruit fleshy, thin-walled, beaked, opening by decay of pericarp; seeds several, globose.

Distribution

Genus of about 10 species, widely distributed in all tropical seas and extending also into warm temperate waters.

Note

All species reported from the East African coast belong to section Halophila, with very short erect lateral shoots bearing one pair of petiolate leaves at each node, and with leaf blade with ascending lateral veins. H. decipiens Ostenfeld and H. minor (Zoll.) den Hartog, found respectively in Tanzania and Kenya, have not yet been found in Somalia.

Hydrocharitaceae, David Simpson. Flora of Tropical East Africa. 1989

Morphology General Habit

Monoecious or dioecious, submerged, marine perennials

Morphology Stem

Stems elongate, rhizomatous or shortly erect, the latter produced from nodes at regular intervals along the rhizome

Morphology Roots

Roots 1(–3) at each node where the erect stems produced, simple, sand binding, covered with fine hairs

Morphology Leaves

Leaves in pairs, whorls or distichously arranged on the erect stems, sessile or petiolate; blade linear to ovate, acute, obtuse or rounded, cuneate or rounded at the base, opaque or somewhat translucent, usually glabrous, rarely sparsely pubescent, with 3 longitudinal veins, often connected by ascending cross-veins; margins green, entire or serrulate Nodal scales 0

Morphology Leaves Stipules

Stipules 2, obtuse to suborbicular or transversely elliptic, membranous, subtending each pair or whorl of leaves

Morphology Reproductive morphology Flowers

Flowers unisexual Male flowers pedicellate, remaining attached to the plant; tepals 3, ovate, cucullate; stamens 3, anthers sessile, linear-oblong, erect, 2–4-thecous, latrorsely or extrorsely dehiscent Female flowers with tepals 3, reduced to lobes at the apex of perianth-tube; staminodes 0; ovary of 3–5 carpels, ellipsoid or ovoid, 1-locular, placentation parietal; ovules few to many; perianth-tube narrowly cylindric; styles 3–5; stigmas 3–5, filiform, entire

Morphology Reproductive morphology Inflorescences

Male and ♀ spathes similar, solitary in leaf-axils, sessile, 1–2-flowered, rarely with 1 flower of each sex in the same spathe, composed of 2 free, overlapping bracts, the bracts elliptic to sub-orbicular, acuminate, obtuse, often keeled, translucent, the margins entire or serrulate

sex Male

Male flowers pedicellate, remaining attached to the plant; tepals 3, ovate, cucullate; stamens 3, anthers sessile, linear-oblong, erect, 2–4-thecous, latrorsely or extrorsely dehiscent

sex Female

Female flowers with tepals 3, reduced to lobes at the apex of perianth-tube; staminodes 0; ovary of 3–5 carpels, ellipsoid or ovoid, 1-locular, placentation parietal; ovules few to many; perianth-tube narrowly cylindric; styles 3–5; stigmas 3–5, filiform, entire

Morphology Reproductive morphology Fruits

Fruit ovoid to globose, membranous, opening by decay of pericarp

Morphology Reproductive morphology Seeds

Seeds subglobose to globose, tuberculate, reticulate or smooth.