Illustrations and descriptions of the kelp species found in UK waters

Alaria esculenta

Laminaria digitata

Laminaria hyperborea

Laminaria ochroleuca

Laminaria saccharina

Saccorhiza polyschides

Undaria pinnatifida

Alaria esculenta

The holdfast is compact and haptera are usually short; the stipe is flexible and usually short; older plants may have flat, leaf-like sporophylls growing from the stipe at the base of the blade; the blade is a rich brown colour, simple (ribbon-like) in form and with a well defined conspicuous midrib; the blade tissue is remarkably supple to the touch and the entire blade is very flexible; the blade length varies both seasonally and with the location, but is commonly 30-90 cm; the blade becomes tattered distally during the summer due to abrasion of the tissue at the tip.

 

 

 

 

 

 

Laminaria digitata

The holdfast is formed of conspicuous root-like haptera, gripping the substratum, the holdfast of older plants may become conical; the stipe is cylindrical or may be slightly flattened and is flexible, smooth, and variable in length depending on location; the stipes are relatively rarely colonised by epiflora but this may depend on the age of the plant and its location; the blade is dark brown, large, tough, flat and usually split into 5-12 fingers or straps (digitate); the blade length varies with season, age of plant and location, reaching over 1 m under suitable conditions; the shape of the blade-stipe junction varies seasonally from cuneate (pen-nib shaped) in autumn & winter, to cordate (heart shaped) in early spring through the summer (Gayral & Cosson, 1973). This species is often difficult to distinguish from L. hyperborea, particularly when plants are young. The two species can be separated by the absence of mucilage ducts in the stipe (they are present in the stipes of L. hyperborea) and the benzidine test (Jensen & Haug, 1952) which slowly turns freshly cut tissue of L. digitata to a yellow-brown colour.

 

 

 

 

 

 

Laminaria hyperborea

The holdfast is formed of conspicuous haptera forming a conical attachment in mature plants; the stipe is cylindrical but thicker at the base of the plant, it is rough textured (except in very young plants) and is stiff rather than flexible; the length of the stipe varies depending on the depth and location; stipes are often heavily colonised by epiflora and epifauna; the blade is very dark brown, large, tough, flat and usually split into 5-20 fingers or straps (digitate); the blade length varies with season, age of plant and location, reaching over 2 m. under suitable conditions; each year the new blade grows below the old one (starting in November), leaving a distinct collar between the two and the old blade tissue is shed in the spring and early summer. This species is often difficult to distinguish from L. digitata, particularly when plants are young. However, mucilage ducts are present throughout the plant and the benzidine test (Jensen & Haug, 1952) immediately turns freshly cut tissue to a bright red colour.

 

 

 

 

 

 

 

Laminaria ochroleuca

In appearance this plant is very similar to L. hyperborea, but the stipe and the frond are a much lighter colour with a yellowish cast. The stipes are smooth and generally lack epiphytes and epifauna.

Laminaria saccharina

The holdfast is usually compact, the haptera usually short; the stipe is flexible and usually short; the blade is golden brown, a simple ribbon form, with a thicker ribbon of tissue forming a midrib; the blade tissue may be supple to the touch or feel substantial (depending on local wave conditions) but the entire blade is flexible; the blade may be 10-50 cm wide, smooth or bullate, and the wider plants from sheltered sites may develop luxuriant marginal undulations (not shown here); the plant length varies both seasonally and with location, commonly reaching 30 cm-1.5 m; blades become tattered distally especially during the late summer.

 

 

 

 

 

 

Saccorhiza polyschides

 

 

 

The holdfast is initially formed of haptera but these become obscured by the growth of a large bulbous hollow expansion of tissue, up to 30 cm. in diameter, covered by short protuberances and attached to the substratum by un-branched haptera; the stipe is flattened and is twisted towards the base and is very tough but not rigid; in older plants the base of the stipe bears tough, undulating lateral extensions or frills (sporophylls); the blade is dark brown, broad, flat, tough and divided into 3-30 fingers or straps (digitate); both blades and stipes are variable in length depending on depth, plant age and location, but plants can become more than 3 m in length; the distal portions of the blade become tattered late in the growing season.

 

 

 

 

 Undaria pinnatifida

The holdfast is formed of haptera, and at present in the UK this species is most often found attached to some man-made structure rather than to the local substratum; the stipe is usually short (10-30 cm) and in mature plants bears convoluted outgrowths or frills (sporophylls); the blade is brown and is initially simple and broad with a distinct midrib; older plants have thicker blade tissue which splits horizontally down to the midrib to form fingers or straps; the distal portion of the blade and the straps are tattered; at the end of the season the blade may become covered by colonial animals.

 

 

 

 

 

 

 Next section                 References