GIANT SEAWEED

New Zealand Listener, Volume 29, Issue 737, 28 August 1953, Page 5

GIANT SEAWEED

Sir-Everyone laughs at the botanist’s cumbrous Latin names for even unimportant plants. The defence is that it is well to be accurate, and there are pitfalls for the user of popular names. The Listener gives us a neat example. "Sundowner" took for his text for July 23 a quotation about the giant kelp, Macrocystis pyrifera, and its claim to be the largest (in the sense of the longest) plant in the world. That was fair enough. But it was hardly fair to head the column with a photograph of a

giant kelp that is neither Macrocystis nor a particularly long plant. Durvillea antarctica, or bull kelp, shown growing on intertidal rocks at Preservation Inlet, has a solid trunk a couple of feet long: the broad leathery fronds, split down the middle, make the traditional containers for preserved muttonbirds, and one bag is big enough to hold dozens of corpses. This is sturdy for a seaweed, but small in every way compared with a large tree. Macrocystis is a different matter. Its main dimension is length, and a big plant consists chiefly of dozens of flexible stems, as thick as a heavy skipping rope, and often 50 to 100 feet long. There are authentic records up to 200 feet, but the older stories of plants 1000 to 1500 feet long are now discredited. In fact it is usually impossible to unsnarl the tangled plants to find the length of a single one. Each stem arises diggctly from the grapnel-like base on the seafloor, often five, sometimes 10, and occasionally 20 fathoms down. Pearshaped floats (hence the name pyrifera) buoy these stems up to the surface and each float carries a membranous leaf a foot or two long. The plants grow in extensive beds, and form the goldenbrown rafts, anchored just offshore, that are familiar in most of our harbours from Cook Strait southwards, Durvillea is a common New Zealand seaweed too, growing only on the,most exposed rocks, from the far north to the subentarctic islands, It is a pity not to distinguish clearly between these two spectacular ‘kelps. Perhaps Maori names would help. Rimurapa is the textbook word for Durvillea but I do not know if it is in common use. Macrocystis is probably just rimuroa, the long seaweed, the giant kelp, which takes us back to where we began!

LUCY B

MOORE

(Wellington).

Sir,-As I do not want your excellent journal to become a vehicle for misinformation, I hope you will permit me to point out an error which arose from "Sundowner’s" recent reference to seaweeds. The statement in the text that the -giant kelp Macrocystis pyrifera is the largest plant in- the world is quite correct, and it is found on New Zealand coasts; but the photograph accompanying the article was that. of quite another kelp, Durvillea antarctica. The macrocystis has a relatively thin stem from which run air bladders at regular intervals, each bladder terminating in a long, thin, ridged leaf or frond. Strangely enough, it is off the coast" of California, where the giant redwoods: grow, that this seaweed_has been found up to 1000 feet in length, In other parts of the world, including New Zealand, it hes grown only up to about 100 feet. This truly giant kelp is being utilised in the United States for the manufacture of sodium alginate, a product which has manifold industrial uses, besides being

™» A the stabilising ingredient of half the ice cream made in the U.S.A. The Durvillea which appeared in Dr, Falla’s photograph often has _ broad, leathery blades and stems as thick as a man’s wrist. This is the seaweed which the Maoris slit down the centre to form a waterproof bag for storing such things as muttonbirds.

E. W.

de ROO

(Christchurch).