WATER PRIMROSE

Ludwigia grandiflora

Willowherb Family [Onagraceae]

month8jul month8july month8aug month8sep month8sept

status
statusZneophyte
flower
flower8yellow
inner
inner8orange
morph
morph8actino
petals
petalsZ5
stem
stem8round
sex
sexZbisexual

20th July 2015, a farm reservoir, way down south. Photo: (CC by 2.0) Geoff Toone
This plant was banned from UK sale in 2014 and is a listed Schedule 9 plant, for it is highly invasive of still freshwaters. Those with garden ponds who have introduced it to their own pond usually end up throwing it out when they find that it completely smothers their pond, excluding light and some oxygen from the water. Sometimes they throw it into other ponds and shallow still waters or slow-flowing streams or rivers nearby where it will similarly spread resulting in the smothering of any other native aquatic plants already happily growing there. It looks like it has a water-depth limit (as most have apart from free-floating plants) and cannot spread further in this pond because the water is too deep away from the sides. It's stems are reddish and only up to 1.5m or sometimes 3m long, and if the water is much deeper it cannot reach down to the waterlogged soil.


20th July 2015, a farm reservoir, way down south. Photo: (CC by 2.0) Geoff Toone
Luckily for anyone north of Watford or so it does not happily grow (as of yet, but with increasing global temperatures that may change). It is a stoloniferous perennial plant.


20th July 2015, a farm reservoir, way down south. Photo: (CC by 2.0) Geoff Toone
The flowers are rather large at between 25 to 50mm across. It is either ascendant or procumbent on water. The fuzzy leaves are those of another highly invasive water plant: Parrot's Feather, which is also listed as a Schedule 9 plant. [Schedule 9 can also apply to other kinds of species, like animals, etc]


20th July 2015, a farm reservoir, way down south. Photo: (CC by 2.0) Geoff Toone
The leaves are narrow and elliptic to oblanceolate and tapered to their base. The flowers yellow with an orange-yellow inner.


20th July 2015, a farm reservoir, way down south. Photo: (CC by 2.0) Geoff Toone
The flowers can have 5 to 6 petals (your Author has seen some with 4 petals on the internet, buy maybe someone had mistaken them for False Hampshire-purslane which do have but 4 petals?). The sepals are long and narrow (far right flower).


20th July 2015, a farm reservoir, way down south. Photo: (CC by 2.0) Geoff Toone
The petals are between 15 to 30mm long.


20th July 2015, a farm reservoir, way down south. Photo: (CC by 2.0) Geoff Toone
Both style and stamens are yellow, the stigma with a flat top. Stamens are 2.5 to 3.5mm long and number 10 to 12 - that is - double the number of the petals. The inner part of the petals are a shade of orange. Petals have sunken veins perhaps doubling as petal stiffeners. There are gaps between the petals near the centre where the long, narrow green sepals underneath can be seen. The gaps are shaped like tiny oblanceolate leaves.


20th July 2015, a farm reservoir, way down south. Photo: (CC by 2.0) Geoff Toone
The leaves have paler veins. The leaves are alternate on the stem but arranged in a gappy circle, between 4 and 8cm long and 1 to 2cm wide. The leaves vary considerably in form because there are two forms of this plant: emergent and floating forms. Floating leaves are round to egg-shaped; emergent as seen in the photos. The roots are adventitious above but thicker lower down where they anchor themselves in the mud. The fruit is a capsule about 25mm long and 3 to 4mm wide with the 5 sepals still attached. The long thin pod contains many small seeds 1.5mm across and ia to be found in June or July (sometimes as late as September).


By comparison, the quite rare Hampshire Purslane (Ludwigia peploids) is native and grows only in a few locations in Hampshire and Dorset, is only 15cm high with extremely small flowers just 0.2 to 0.5mm across, an inconspicuous greeny colour and which appear in June. Its seeds are less than 1mm across, so that part is not much different from those of Water-primrose.

It is an un-wanted non-native introduction which spreads rapidly in shallow(ish) waters and hails from America, both North and South. Luckily at the moment it seems to be contained south of Watford.


  Ludwigia grandiflora  ⇐ Global Aspect ⇒ Onagraceae  

Distribution
 family8Willowherb family8Onagraceae

 BSBI maps
genus8Ludwigia
Ludwigia
(Hampshire-Purslanes)

WATER PRIMROSE

Ludwigia grandiflora

Willowherb Family [Onagraceae]