''Ralfsia verrucosa'' is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

of crustose brown seaweed in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Ralfsiaceae Ralfsiaceae is a family of brown algae in the order Ralfsiales Ralfsiales is an order of crustose brown algae Brown algae (: alga) are a large group of multicellular algae comprising the class (biology), class Phaeophyceae. They include ...

. It grows intertidally in temperate waters around the world. In South Africa it is part of a mutualistic relationship with a

limpet Limpets are a group of aquatic snails with a conical gastropod shell, shell shape (patelliform) and a strong, muscular foot. This general category of conical shell is known as "patelliform" (dish-shaped). Existing within the class Gastropoda, ...

Description

''Ralfsia verrucosa'' forms roughly circular patches that grow outwards from the centre with the central parts sometimes becoming detached from the

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (aquatic environment), the earthy material that exi ...

. The

thallus Thallus (: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. A thallus usually names the entir ...

is deep brown or blackish-brown and is about thick. It has a distinct, often pale-coloured, margin which is formed from erect filaments which are fused together and that curve upwards from other prostrate filaments. The patches of thalli are thick, some in diameter and often coalescing to form larger patches. The surface is smooth and hard.

Distribution and habitat

''Ralfsia verrucosa'' is a

cosmopolitan species In biogeography, a cosmopolitan distribution is the range of a taxon that extends across most or all of the surface of the Earth, in appropriate habitats; most cosmopolitan species are known to be highly adaptable to a range of climatic and en ...

and is found in temperate waters in northern and western Europe, Mediterranean Sea, Iceland, Greenland, Canada, New England, Argentina, round the coasts of Africa, India, Japan, Korea, China, Russia, Indonesia, Australia and New Zealand. It grows on rock in pools in the

intertidal zone The intertidal zone or foreshore is the area above water level at low tide and underwater at high tide; in other words, it is the part of the littoral zone within the tidal range. This area can include several types of habitats with various ...

Biology

The brown colour of this seaweed results from the dominance of the

xanthophyll Xanthophylls (originally phylloxanthins) are yellow pigments that occur widely in nature and form one of two major divisions of the carotenoid group; the other division is formed by the carotenes. The name is from Greek: (), meaning "yellow", an ...

fucoxanthin Fucoxanthin is a xanthophyll, with formula C42H58O6. It is found as an accessory pigment in the chloroplasts of brown algae and most other heterokonts, giving them a brown or olive-green color. Fucoxanthin absorbs light primarily in the blue-gree ...

which masks the other pigments that are present, namely

chlorophyll a } Chlorophyll ''a'' is a specific form of chlorophyll used in oxygenic photosynthesis. It absorbs most energy from wavelengths of violet-blue and orange-red light, and it is a poor absorber of green and near-green portions of the spectrum. Chlorop ...

chlorophyll c Chlorophyll ''c'' refers to forms of chlorophyll found in certain marine algae, including the photosynthetic Chromista (e.g. diatoms and brown algae) and dinoflagellates. These pigments are characterized by their unusual chemical structure, with ...

, beta-carotene and other xanthophylls. The tissues contain

polyphenol Polyphenols () are a large family of naturally occurring phenols. They are abundant in plants and structurally diverse. Polyphenols include phenolic acids, flavonoids, tannic acid, and ellagitannin, some of which have been used historically as ...

s which act as a deterrent to herbivores. Round the coasts of South Africa, ''Ralfsia verrucosa'' enjoys a mutual relationship with the limpet '' Scutellastra longicosta''. This limpet clears an area of rock by intensive grazing, and allows ''Ralfsia verrucosa'' to settle on it while excluding other species of algae. The limpet then cultivates its "garden", grazing the algal turf to a moderate level and fertilising it with faeces and mucus. A limpet can "farm" an area of about of algal turf and defend its

territory A territory is an area of land, sea, or space, belonging or connected to a particular country, person, or animal. In international politics, a territory is usually a geographic area which has not been granted the powers of self-government, ...

from intrusion by other limpets. The genus name commemorates the botanist John Ralfs.

References

{{Taxonbar, from=Q16988999 Ralfsiales