Gracilaria verrucosa (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Gracilaria verrucosa (Huds.) Papenf.

Protologue: Hydrobiologia 2: 195 (1950).

Family: Gracilariaceae

Chromosome number: 2n= most probably 48, although for European "G. verrucosa" a diploid number of 64 has been recorded; however, this was probably material belonging to the separate genus Gracilariopsis E.Y. Dawson; for all other European and Japanese material of "G. verrucosa", a haploid number of about 24 was established and thus is probably real Gracilaria material.

See : Gracilariopsis.

Synonyms

In Europe, material identified as belonging to "Gracilaria verrucosa" is partly G. gracilis (Stackh.) Steentoft, L.M. Irvine & Farnham, which is, however, an illegitimate name for G. confervoides (L.) Grev. Another part of this material belongs to Gracilariopsis longissima (S.G. Gmelin) Steentoft, L.M. Irvine & Farnham, which is again most probably an illegitimate name for which the correct binominal (based on the Hudson epithet) has not yet been proposed.

Vernacular names

• Philippines: gulaman, caocaoyan, gargararao, lagot.

Origin and geographic distribution

Although records under this name appear in almost all countries of the world, G. verrucosa is most probably restricted to the North Atlantic Ocean. Nevertheless, it has been recorded recently in Burma (Myanmar), Vietnam, Malaysia, Indonesia and the Philippines.

Uses

Gracilaria spp., to which this name is applied, are usually cultivated as raw material for agar production. The name is also listed as being used in traditional Chinese medicine.

Production and international trade

A Gracilaria named as G. verrucosa, has been cultivated in South Sulawesi (Indonesia) since 1986 and produces monthly exports of 60-80 t dried Gracilaria seaweed.

Properties

The agar from G. "verrucosa" from Takalar, South Sulawesi (Indonesia) in a 2% agar solution and obtained without alkaline hydrolysis, is not very promising (gel strength 45 g/cm², gelling point 27-28 °C, viscosity 51 cP). However, agar prepared using the same methods, but from Gracilaria material obtained from a commercial agar producer and recorded as being produced in the same locality, gave better results (gel strength 1331 g/cm², gelling point 40-41 °C, viscosity 75 cP). This difference may be due to differences in post-harvest handling of the raw material.

The water content of dried material is about 23.5%, while the amount of impurities (especially fine mud) can be as high as 40%, due to the high turbidity of the water in the culture ponds.

Description

• Plant erect, attached by a small discoid holdfast; main axes percurrent, with many orders of irregular branching; base of branches slightly constricted, the lower order branches elongate.
• Fronds slender, cylindrical, pale to dark brown or brownish with some yellow-green.
• Medulla consisting of cells 166-365 μm in diameter, with cell walls 10-30(-40) μm thick; cell transition to cortex gradual to abrupt.
• Spermatangia in deep, oval conceptacles.
• Cystocarps semiglobose, slightly or not rostrate, slightly or not constricted at bases.

Other botanical information

The name G. verrucosa has been somewhat indiscriminately applied to terete, irregularly branched specimens of Gracilaria. G. verrucosa has been reported worldwide from temperate to tropical waters. Many records of G. verrucosa from outside the eastern Atlantic Ocean now are considered to be incorrect and G. verrucosa may be confined to the north-eastern Atlantic Ocean. Reports from outside this area require careful examination. It has often been suggested that the entity known as G. "verrucosa" in many parts of the world does not belong to the same taxonomic species. Specimens previously called G. verrucosa from several countries have been reexamined and some of them have undergone a change of name. For example, studies on Chinese species identified as G. verrucosa, when compared with specimens from Weymouth, Devon (England) and from Hokkaido (Japan) resulted in the conclusion that the Chinese and Japanese specimens are similar to each other and can now be referred to as G. vermiculophylla (Ohmi) Papenf., which is distinctly different to the British materials.

Material collected in the Philippines and previously identified as G. verrucosa, was described as the new species G. manilaensis H. Yamam. & Trono, while specimens of Gracilaria from Thailand previously reported as G. verrucosa were re-identified as G. fisheri (B.M. Xia & I.A. Abbott) I.A. Abbott, C.F. Zhang & B.M. Xia and G. tenuistipitata C.F. Chang & B.M. Xia. Therefore it seems that G. verrucosa is not a valid name for Asian Gracilaria.

Ecology

There are no data available for material of G. verrucosa from South-East Asia.

Propagation and planting

Propagation and planting for G. verrucosa is as for other pond-grown Gracilaria spp.

Harvesting

Harvesting of G. verrucosa is as for other pond-grown Gracilaria spp.

Yield

Agar content of G. verrucosa from Takalar, South Sulawesi (Indonesia) is fairly high (47.7% has been recorded).

Handling after harvest

Cultivated material of G. verrucosa has to be thoroughly washed in running water, while much of the attached fine silt and salt crystals can be removed by vigorous shaking and beating the dried fronds before packing and sorting.

Prospects

The name G. verrucosa should no longer be connected with Gracilaria spp. and their products from South-East Asia.

Literature

• Abbott, I.A., 1983. Some species of Gracilaria (Rhodophyta) from California. Taxon 32: 561-564.
• Abbott, I.A., 1995. A decade of species of Gracilaria (sensu latu). In: Abbott, I.A. (Editor): Taxonomy of economic seaweeds 5. pp. 185-195.
• Fredericq, S. & Hommersand, M.H., 1989. Proposal of the Gracilariales ord. nov. (Rhodophyta) based on an analysis of the reproductive development of Gracilaria verrucosa. Journal of Phycology 25: 213-227.
• Hatta, A.M., 1994. Physical properties of agarophyte Gracilaria sp. (Verrucosa type) from seaweed culture of Takalar, South Sulawesi. Indonesian Food and Nutrition Progress 1: 39-43.
• Trono Jr, G.C., Azanza-Corrales, R. & Manuel, D., 1983. The genus Gracilaria (Gigartinales, Rhodophyta) in the Philippines. Kalikasan 12: 15-41.
• Yamamoto, H. & Trono Jr, G.C., 1994. Two new species of Gracilaria from the Philippines. In: Abbott, I.A. (Editor): Taxonomy of economic seaweeds 4. p. 95-101.
• Zhang, J. & Xia, B., 1985. On Gracilaria asiatica sp. nov. and G. verrucosa (Huds.) Papenfuss. Oceanologia et Limnologia Sinica 16: 175-180.

Authors

• K. Lewmanomont, S.-M. Phang & W.F. Prud'homme van Reine