''Ralfsia verrucosa'' is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of crustose

brown seaweed Brown algae (singular: alga), comprising the class Phaeophyceae, are a large group of multicellular algae, including many seaweeds located in colder waters within the Northern Hemisphere. Brown algae are the major seaweeds of the temperate and po ...

in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Ralfsiaceae Ralfsiaceae is a family of brown algae in the order Ralfsiales Ralfsiales is an order of crustose brown algae Brown algae (singular: alga), comprising the class Phaeophyceae, are a large group of multicellular algae, including many seawee ...

. 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 that exhibit a conical shell shape (patelliform) and a strong, muscular foot. Limpets are members of the class Gastropoda, but are polyphyletic, meaning the various groups called "limpets" descended indep ...

Description

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

thallus Thallus (plural: 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. Many of these organisms wer ...

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, cosmopolitan distribution is the term for the range of a taxon that extends across all or most of the world in appropriate habitats. Such a taxon, usually a species, is said to exhibit cosmopolitanism or cosmopolitism. The extre ...

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, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species o ...

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 (, "yellow") and (, "l ...

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-green ...

which masks the other pigments that are present, namely chlorophyll a,

chlorophyll c Chlorophyll ''c'' is a form of chlorophyll found in certain marine algae, including the photosynthetic Chromista (e.g. diatoms and brown algae) and dinoflagellates. It has a blue-green color and is an accessory pigment, particularly significant ...

, beta-carotene and other xanthophylls. The tissues contain

polyphenol Polyphenols () are a large family of naturally occurring organic compounds characterized by multiples of phenol units. They are abundant in plants and structurally diverse. Polyphenols include flavonoids, tannic acid, and ellagitannin, some of ...

s which act as a deterrent to herbivores. Round the coasts of South Africa, ''Ralfsia verrucosa'' enjoys a

mutual relationship Mutualism describes the ecological interaction between two or more species where each species has a net benefit. Mutualism is a common type of ecological interaction. Prominent examples include most vascular plants engaged in mutualistic intera ...

with the limpet ''

Scutellastra longicosta ''Scutellastra longicosta'', the long-spined limpet or the duck's foot limpet, is a species of true limpet, a marine gastropod mollusk in the family Patellidae, one of the families of true limpets. It is native to the coasts of South Africa wh ...

''. 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, particularly belonging or connected to a country, person, or animal. In international politics, a territory is usually either the total area from which a state may extract power resources or a ...

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

John Ralfs John Ralfs (13 September 1807 – 14 July 1890) was an English botanist. Born in Millbrook, near Southampton, he was the second son of Samuel Ralfs, a yeoman of an old family in Hampshire. He has been commemorated in the names of many plant gro ...

References

{{Taxonbar, from=Q16988999 Ralfsiales