 | This article may be too technical for most readers to understand.(October 2014) |
| Hypnea | |
|---|---|
 | |
| Hypnea musciformis | |
Scientific classification  | |
| (unranked): | Archaeplastida |
| Division: | Rhodophyta |
| Class: | Florideophyceae |
| Order: | Gigartinales |
| Family: | Cystocloniaceae |
| Genus: | Hypnea J.V.Lamouroux, 1813 |
| Species | |
See text | |
Hypnea is a genus of red algae, and a well known carrageenophyte (plant producing polysaccharide carrageenan).
Hypnea is a genus of red seaweed under class Florideophyceae, order Gigartinales, and family Cystocloniaceae. There are 99 species listed on Algaebase with 78 being accepted taxonomically. [1] The genus was originally classified under family Hypneaceae, [2] which was considered distinct from Cystoclonoiaceae on the basis of differences in their carposporophyte structure, [3] [4] and the shape of the thalli and cortical cells. Differences in carrageenan chemistry, with Hypneaceae species producing kappa-carrageenan and Cystocloniaceae producing lambda-carrageenan, was another reason for their distinction. [5] However, these criteria were questioned and molecular analysis later showed that the two families had similar vegetative and reproductive characters. [6] [7] Furthermore, it was proven that lambda-carrageenan and kappa-carrageen coexist within the Gigartinales order. [7] This led to the two families being merged into simply Cystocloniaceae.
Phylogeography of Hypnea valentiae in India indicates that nuclear ribosomal DNA Internal transcribed spacer-1 (ITS1) sequences had 4.35 x 10-1 Tamura 3-parameter (T3P) pairwise distance between them, which indicate significant evolutionary differences accumulated over time. [8] In comparison, T3P distance between related genera Kappaphycus and Eucheuma was 1.85 x 10–1. In phylogeny reconstruction using Bayesian inference, both the isolates formed a well-supported clade along with the only available accession of this genus at ITS1 locus, indicating affiliation of both the isolates in this genus. The isolate from the west coast was more basal in the phylogram, which suggests phylogenetically primitive position of this population. Newly generated DNA barcodes of the geographic isolates of this native carrageenophyte in this study is expected to be a key in tracing its further dispersal routes, either natural or deliberate. This is the first report on the comparative morphological and molecular assessment of Hypnea from India.
Hypnea is characterized by membranous or cartilaginous thalli which can be either erect or prostrate. The thallus features a main axis with an apex of varying shapes (straight, curved, tendril or bifurcated). Various forms of branching occur, with the irregular type being most common, with dichotomous or lateral branching occurring in some species. Thallus color is highly variable, with yellow, green, pink, red, brown and black being observed. Habitat type can influence thallus length, which varies from 0.5 to 50 cm. [9] The habit of the thallus is used to divide species into two major groups: those with >10 cm thallus height, and those that measure between 2–3 cm. [9] Like many other algal species, Hypnea exhibits a high degree of phenotypic plasticity and cryptic diversity which makes species difficult to distinguish from each other morphologically since they share many characters. [10] [11]
The genus is found in the Atlantic, Pacific, and Indian Oceans, with the Atlantic having the most species. In terms of countries, China has the most number of species although none are endemic. Other countries with many endemic species of Hypnea include South Africa, Australia, Japan, Indonesia, Mauritius, the Philippines, India, and Brazil. Hypnea musciformis has the widest geographical distribution. [9]
Hypnea is commonly present in various habitats, from intertidal and subtidal zones, as well as in sites with varying degrees of exposure. They can also be found growing as epiphytes on other organisms such as the brown alga Sargassum. The genus exhibits seasonal abundance which is highly influenced by similarly seasonal variations in light, temperature, and tidal levels. [12]
Hypnea exhibits a dioecious thallus and a triphasic life cycle consisting of two diploid phases and a haploid phase. The diploid carposporophyte releases carpospores that develop into a diploid tetrasporophyte which undergoes meiosis to form four haploid tetraspores which will form 50/50 male and female gametophytes. After fertilization of gametes, the carposporophyte is formed and the cycle begins again. [13] [9]
Carrageenans are abundant in the cell walls of some red algae, where they provide the thallus with additional flexibility to protect it from the impacts of herbivory, wave action, and desiccation. Environmental variables such as temperature, amount of rainfall, and salinity likely influence the yield and viscosity of the carrageenan.
Hypnea is cultivated in many tropical countries such as the Philippines, Brazil, Bangladesh, India and Vietnam for food and for their kappa- carrageenan extracts. [14] After Eucheuma/Kappaphycus, it is the second most important source of carrageenan in the tropics, however it is only cultivated in experimental settings and not commercially. The technology needed to do this is still being developed and requires further investigation. [15] Most experimental cultivation activities have been done using Hypnea musciformis, and its highly variable morphology may be partly responsible for the inconsistency in the results of these experiments. [16] [17]
Carrageenan has a wide range of applications from food to pharmaceutical uses. The extracts of various Hypnea species have been investigated for their antiviral, antibacterial, antioxidant and antifungal properties. [18] [19] [20]
The sea lettuces comprise the genus Ulva, a group of edible green algae that is widely distributed along the coasts of the world's oceans. The type species within the genus Ulva is Ulva lactuca, lactuca being Latin for "lettuce". The genus also includes the species previously classified under the genus Enteromorpha, the former members of which are known under the common name green nori.
Gracilaria is a genus of red algae (Rhodophyta) notable for its economic importance as an agarophyte, as well as its use as a food for humans and various species of shellfish. Various species in the genus are cultivated among Asia, South America, Africa and Oceania.
Codium is a genus of edible green macroalgae under the order Bryopsidales. The genus name is derived from a Greek word that pertains to the soft texture of its thallus. One of the foremost experts on Codium taxonomy was Paul Claude Silva at the University of California, Berkeley. P.C. Silva was able to describe 36 species for the genus and in honor of his work on Codium, the species C. silvae was named after the late professor.
Chordariaceae is a family of brown algae. Members of this family are may be filamentous, crustose with fused cells at the base, or they may be terete and differentiated into a central medulla and an outer photosynthetic cortex. They have a sporphytic thallus usually aggregated to form a pseudo-parenchyma.
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Halymenia a genus of a macroscopic red algae that grows in oceans worldwide.
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Plocamium is a genus of red algae in the family Plocamiaceae. It contains around 40 species and has a cosmopolitan distribution in temperate seas, although it is most diverse in the southern hemisphere. It is widely distributed in tropical and also warm-temperate and cold-temperate seas, such as northern Europe, the northern Arabian Sea and western Australia. They are also found in the Antarctic regions of Admiralty Bay and Terra Nova Bay.
Laurencia is a genus of red algae that grow in temperate and tropical shore areas, in littoral to sublittoral habitats, at depths up to 65 m (213 ft).
Dumontiaceae is a red alga family in the order Gigartinales.
Chondria is a red alga genus in the family Rhodomelaceae.
Dictyota is a genus of brown seaweed in the family Dictyotaceae. Species are predominantly found in tropical and subtropical seas, and are known to contain numerous chemicals (diterpenes) which have potential medicinal value. As at the end of 2017, some 237 different diterpenes had been identified from across the genus.
Michael Dominic Richard Guiry, is an Irish botanist, who specialises in phycology (algae). See for example the articles. He is the founder and director of the algal database, AlgaeBase.
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