Arrowhead

Sagittaria sagittifolia

Water-Plantain Family [Alismataceae]  

month8jul month8july month8Aug

status
statusZnative
flower
flower8bicolour
flower
flower8white
inner
inner8purple
morph
morph8actino
petals
petalsZ3
stem
stem8triangular
sex
sexZmonoecious

2nd Aug 2005, Leeds and Liverpool Canal, Appley Bridge. Photo: © RWD
Very distinctive aerial leaves have three long prongs shaped line an arrowhead and several lighter-green veins running lengthways. The stems for these leaves are triangular in cross section in places. Many of the stalks here have been decapitated by canal weed-cutting machines or boats propellers.


23rd July 2006, Leeds and Liverpool Canal, Plank Lane.. Photo: © RWD
Grows with roots in water at up to a foot or two deep. The arrow-shaped leaves and flower spike are held above water-level.


2nd Aug 2005, Leeds and Liverpool Canal, Appley Bridge. Photo: © RWD
  The flowers are in triplets on short stalks up the flowering stalk. Arrowhead is monoecious where each plant has both male and female flowers. On Arrowhead the male flowers are the upper ones, female the lower ones. Here the female flowers have turned to fruit and start with the larger brown spheres.


2nd Aug 2005, Leeds and Liverpool Canal, Appley Bridge. Photo: © RWD
  Spent male flowers the top two whorls, the female flowers have turned to fruit: the almost spherical green spiky spheres which later turning brown. It seems to the Author that the male flowers are on longer stalks than the short stubby stalks of the female flowers.


2nd Aug 2005, Leeds and Liverpool Canal, Appley Bridge. Photo: © RWD
 The globular fruits have short stubby spikes.


7th Aug 2005, Leeds and Liverpool Canal, Plank Lane. Photo: © RWD
 Flowers occur in whorls of three on separate stems, Some flowers seem to have but a single-all-encircling petal. The now-square flowering stem eminently visible emerging after the whorl of male flowers. Flowers stalks are round. Many short stamens with purple anthers.

The spike of the flowering stem is square at the top despite the triangular arrangement of flowers, which are not attached to the square section. Other parts of the stem may have a triangular cross-section, or may have a few flats, hence the 'angular' description.



2nd Aug 2005, Leeds and Liverpool Canal, Appley Bridge. Photo: © RWD
 The three white petals have a purple splurge of colour near the centre, where lies a spiky spherical globe of stamens? The petals may have translucent spots.


4th Aug 2009, Rufford Branch, Leeds & L/pool Canal. Photo: © RWD
 The central part of the flower starts off with purple spikes. Purple tips of anthers at centre.


24th Aug 2014, Rufford branch L&L canal. Photo: © RWD
 Stems angular, sometimes square. One of the triplet of flower stalks has extended to become another triplet of flowers.


24th Aug 2014, Rufford branch L&L canal. Photo: © RWD
 It seems to the Author that many white aquatic flowers have reddish marks on. Petals kidney shaped with a wide attachment where the purple stains lurk.


24th Aug 2014, Rufford branch L&L canal. Photo: © RWD
 The globed centre of a female flower showing the tiny white stigmas protruding.


24th Aug 2014, Rufford branch L&L canal. Photo: © RWD
Sepals three in number are equilaterally triangular, and cupped.


2nd Aug 2005, Leeds and Liverpool Canal, Appley Bridge. Photo: © RWD
Above-water (aerial) leaf-shape is notoriously variable in all Arrowheads. Here some atypically narrow ones. The arrow-shaped leaves are perched atop a stalk at the nodal point.


24th Aug 2014, Rufford branch L&L canal. Photo: © RWD
Other leaves are more or less normal (left leaf) whilst a few others are wider than normal (right-most leaf).

From the node of the leaf several prominent light-green coloured veins radiate, curving like magnetic field lines, reaching to the three extremities of the leaf.



24th Aug 2014, Rufford branch L&L canal. Photo: © RWD
Arrowhead has two other kinds of leaves - floating leaves which are oval with a deep notch at one end (lower right). [and - not shown -submerged leaves which are linear and translucent].


Arrowhead is native to the UK, and has been introduced onto canals.

All the other Sagittarias listed below are non-native and were introduced from North America:

Some similarities to Narrow-leaved Arrowhead (Sagittaria subulata) but that has either submerged leaves or floating leaves, none are aerial (above water). Most of the leaves are submerged and linear, the fewer floating leaves are elliptical. Crucially, no leaves are arrow-shaped, so it is easily distinguished from Arrowhead by that characteristic alone.

Differs from : Broad-leaved Arrowhead [aka Duck-potato] (Sagittaria subulata) in that the petals lack a purple patch in the centre (as they also do with Canadian Arrowhead) and the anthers are yellow not purple. It has similar arrow-shaped leaves (which may be broader)

Differs from : Canadian Arrowhead (Sagittaria rigida) in that it (like Broad-leaved Arrowhead) lacks the purple splodge at the centre of the petals and both aerial and floating leaves are elliptic (not often with 2 short basal lobes) but the submerged leaves are the same: linear. It is introduced from North America and is naturalised in canals and in 2 places in Devon.

Leaf-shape is notoriously variable in all Arrowheads and must not be used as an identifier alone!

No relation to : The Sea Arrow-grass or Marsh Arrow-grass [plants of similar names belonging to differing families]

Has triangular stems.

Arrowhead has the ability to absorb (sequester) large amounts of the poisonous heavy metallic element, cadmium, but without detrimental effects to itself, it is thus a Hyperaccumulator and a metallophyte. Cadmium is toxic to both plant and animal kingdoms. It can also be used as in phytoremediation to mop up radioactive   caesium-137 (as can the non-native Polygonum puntatum), but obviously, only in fresh-water.


  Sagittaria sagittifolia  ⇐ Global Aspect ⇒ Alismataceae  

Distribution
family8water-plantain family8alismataceae

 BSBI maps
genus8sagittaria
Sagittaria
(Arrowheads)

Arrowhead

Sagittaria sagittifolia

Water-Plantain Family [Alismataceae]  

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