RAY'S KNOTGRASS

Polygonum oxyspermum

Dock & Knotweed Family [Polygonaceae]

month8jun month8june month8jul month8july month8aug month8sep month8sept

status
statusZnative
flower
flower8white
inner
inner8pink
morph
morph8actino
petals
petalsZ5
stem
stem8round
stem
stem8fluted
rarity
rarityZuncommon

23rd July 2016, Ainsdale dunes, Sefton Coast. Photo: © RWD
Bird's-eye view, about a foot across.


23rd July 2016, Ainsdale dunes, Sefton Coast. Photo: © RWD
Small flowers in most leaf-axils.


24th July 2011, Booley Bay, Eire. Photo: © Paula O'Meara
Straggles up to a metre in length (often much shorter) on coastal sand and shingle.


24th July 2011, Booley Bay, Eire. Photo: © Paula O'Meara
Stems thicker and more robust than other Knotgrasses except for the much rarer Sea Knotgrass which also shares the same larger flowers and prominent fruit of Ray's Knotgrass.


24th July 2011, Booley Bay, Eire. Photo: © Paula O'Meara
Un-like Sea Knotgrass leaves not in-curled at the margins.


24th July 2011, Booley Bay, Eire. Photo: © Paula O'Meara
Flowers larger than other Knotgrasses except Sea Knotgrass. Between 2-6 flowers nestle in axis of each leaf. Leaves single on alternate sides of stems.


24th July 2011, Booley Bay, Eire. Photo: © Paula O'Meara
Flowers have five white 'petals' (actually tepals), sometimes pink-edged. Stems multi-angular or multi-ridged. The pink/white papery sheaths at each node are short. Fruits chestnut-brown and glossy, protruding from dead flowers.


23rd July 2016, Ainsdale dunes, Sefton Coast. Photo: © RWD


24th July 2011, Booley Bay, Eire. Photo: © Paula O'Meara
Leaves (and stems) have a fine grainy appearance typical of plants which are frequently exposed to sea salt-water; they have to have a mechanism for getting rid of the salt which they inevitably uptake when absorbing the moisture in the sand.


24th July 2011, Booley Bay, Eire. Photo: © Paula O'Meara
Flowers can be pink when in bud (leftmost).


23rd July 2016, Ainsdale dunes, Sefton Coast. Photo: © RWD
The flowers emerge from a pale-brown blending to white sheath at a leaf-node.


23rd July 2016, Ainsdale dunes, Sefton Coast. Photo: © RWD
Each flower has 5 tepals (they are not called petals because there are no sepals). The tepals are green with a wide white margin. The fruit is an achene, which is brown, shiny, tapers to a point with the remains of 3 short now brown stigmas atop. The fruit is widest near the base and has 3 noticeably indented sides.


23rd July 2016, Ainsdale dunes, Sefton Coast. Photo: © RWD
Within the corolla are 8 stamens with yellow anthers and three small, almost sessile stigma, which are also yellow.


23rd July 2016, Ainsdale dunes, Sefton Coast. Photo: © RWD
One of the 3 discoidal stigmas can be seen here, as well as several x-shaped anthers which are a deeper-yellow in colour.


Not to be semantically confused with : Knotweeds such as Himalayan Knotweed, Japanese Knotweed, Lesser Knotweed nor with Knotted Clover, Knotted Pearlwort, Knotted Crane's-bill or Knotted Hedge-parsley [plants with similar names]

The Genus name of Knotgrasses, Polygonum can easily be misinterpreted as Polygonatum which is the genus name of Solomon's-seals such as Angular Solomon's-Seal (Polygonatum odoratum).

No relation to : Knotted Clover, Knotted Pearlwort, Knotted Crane's-bill or Knotted Hedge-parsley [plants with similar names].

Easily mis-identified as : Sea Knotgrass but that is a much rarer [RRR], has woody stems near the base of the plant, has between 1-4 flowers in each node (Ray's Knotgrass has 2-6 - so if there is ever only 1 flower, then it must be Sea Knotgrass, but if 5-6 flowers can ever be found then it must be Ray's Knotgrass; the overlap region (2-4) tells nothing), has leaves with in-rolled or down-turned margins and has longer papery sheaths (up to 10mm long).

Some similarities to : Knotgrass but that is less compact and with less stout stems.

Slight resemblance to : Bistorts, such as Water-pepper and Tasteless Water-pepper.

A rare plant! Rays's Knotgrass is procumbent and usually an annual (only sometimes perennial),. It is branched and can grow to 1m in length, and is sometimes woody nearer the roots. It is native and grows near the sea on sandy beaches, sometimes close enough to get washed away by forceful spring tides.

It is found as one of two species:

  • Polygonum oxyspermum ssp. oxyspermum (which has totally disappeared from our shores now but had narrower leaves and achenes which are a paler brown)
  • Polygonum oxyspermum ssp. raii which is now our sole species.


  Polygonum oxyspermum  ⇐ Global Aspect ⇒ Polygonaceae  

Distribution
 family8Dock & Knotweed family8Polygonaceae

 BSBI maps
genus8Polygonum
Polygonum
(Knotgrasses)

RAY'S KNOTGRASS

Polygonum oxyspermum

Dock & Knotweed Family [Polygonaceae]

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