Common name : Willow primrose
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Diagnostic characters
Biology
Ecology and distribution
Nuisance
Weed control
Botany
Uses/Remark
References
Ludwigia octovalvis is an erect, well branched and robust annual or perennial plant. It may be woody at the base and shrubby with the stems red-brown sometimes reaching 4m tall. The leaves are alternate, narrowly lanceolate. The flowers are yellow and the fruits are thing-walled, 4-nagled and cylindrical of 3 to 5cm long, terminated by persistent calyx lobes. Its color may vary from green to pale reddish brown or purplish.
L. octovalvis reproduces by seed and may also occupy new areas by sending out runners and rhizomes. In Philippines is a very prolific seed producer (more than 375.000 seeds/plant).
L. octovalvis is a weed on many Pacific islands, in South and Central Asia, Australia, over much of Africa, and in the warm areas of the Americas. It frequents a very wide range of humid, wet places and is found in marshes, fresh water lakes and streams, ditchs banks of all kinds, along railroads, and on gravelly riverbeds and sandy or silty flood banks. It is found in paddy rice over much of the world and grows in damp, occasionally flooded grassland. It is found at sea level, up to 1000 m in the Celebes and in Indonesia, and up to 1400 m in New Guinea.
L. octovalvis is one of the most widespread weeds of the world.
Habit
is an erect , stout, well-branched, robust plant of damp or flooded areas, may be woody at the base and shrubby at times, to 4 m, annual or perennial, with long stiff hairs sometimes appressed and oriented in one direction.
Roots
Taproots.
Stem
May be red-brown and lignified at base.
Leaves
The leaves are alternate, light green, may turn red upon aging, narrowly lanceolate to ovate, up to 15cm long, 4 to 40mm wide, densely pubescent both sides, attenuate at base and apex, 12 to 22 veins each side of midrib. The leaves have a short petiole.
Inflorescence
The flowers are solitary in axils of the leaves. Petals 4, pale to bright yellow, 1 to 2cm long and 4 to 17mm wide, broadly ovate and may be emarginate at apex. Sepals 4, 8 to 15mm long. Stamens 8, filaments 1 to 4mm long; anthers 1 to 4mm long, white, hairy, sunken nectary surrounding base of each epipetalous and shorther stamen. Style 1.5 to 3.5mm long with stigma subglobulose and shallowly 4-lobed.
Fruit
Thing-walled, 4 angled, narrowly cylindrical, 8-ribbed capsule, 3 to 5cm long, 2 to 8mm in diameter, pubescent, irregularly locullicidal, terminated by persistent calyx lobes, color may vary from green to pale or reddish brown or purplish; pedicel up to 1cm.
Seeds
Brown, rounded, beaked, in several indistinct rows in each locule, free, each with inflated raphe equal in size to body of seed, 0.6 to 0.75mm in size.
L. octovalvis differs from L. adscendens by its more erect habit and larger, lanceolate leaves that are somewhat acute. This species is formerly well known as Jussiaea suffruticosa.
- Holm L., Doll J., Holm E., Pancho J., Herberger J. 1997. World weeds. Natural Histories and Distribution. John Wiley & Sons. New York.
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