Hypnea Chordacea

''Hypnea'' is a genus of red algae, and a well known carrageenophyte (plant producing polysaccharide carrageenan).

Taxonomy and Nomenclature

''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. The genus was originally classified under family Hypneaceae, which was considered distinct from Cystoclonoiaceae on the basis of differences in their carposporophyte structure, 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. However, these criteria were questioned and molecular analysis later showed that the two families had similar vegetative and reproductive characters. Furthermore, it was proven that lambda-carrageenan and kappa-carrageen coexist within the Gigartinales order. This led to the two families being merged into simply Cystocloniaceae.

Phylogenetics

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. 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.

Morphology

''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. 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. 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.

Distribution

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.

Ecology

''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.

Life History

''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.

Chemical Composition

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.

Cultivation and Utilization

''Hypnea'' is cultivated in many tropical countries such as the Philippines, Brazil, Bangladesh, India and Vietnam for food and for their kappa- carrageenan extracts. 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. 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.

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.Heidarizadeh L,Mollataghi A, Saadat A,Mostoufi A, Mouradzadegun A, Seyednejad AS (2019) Phytochemical studies and their bioactivities of various crude extracts of red alga (Hypnea boergesenii). Basic Res J Microbiol 6:23–33

Known species

*''Hypnea musciformis''
*'' Hypnea valentiae''
*''Hypnea adunca'' J.Agardh S
*''Hypnea alopecuroides'' Kützing C
*''Hypnea anastomosans'' Papenfuss, Lipkin & P.C.Silva C
*''Hypnea arborescens'' P.Crouan & H.Crouan S
*''Hypnea arbuscula'' P.J.L.Dangeard C
*''Hypnea arenaria'' Kylin C
*''Hypnea armata'' (C.Agardh) J.Agardh S
*''Hypnea asiatica'' P.J.L.Geraldino, E.C.Yang & S.M.Boo C
*''Hypnea aspera'' Kützing S
*''Hypnea boergesenii'' T.Tanaka S
*'' Hypnea brasiliensis'' P.B.Jesus, Nauer & J.M.C.Nunes C
*''Hypnea bryoides'' Børgesen C
*'' Hypnea bullata'' P.Kundu & F. Bast C
*'' Hypnea caespitosa'' P.J.L.Geraldino & S.M.Boo C
*'' Hypnea californica'' Kylin S
*'' Hypnea caraibica'' Nauer, Cassano & M.C.Oliveira C
*'' Hypnea cenomyce'' J.Agardh C
*'' Hypnea ceramioides'' Kützing C
*'' Hypnea cervicornis'' J.Agardh C
*'' Hypnea charoides'' J.V.Lamouroux C
*'' Hypnea chordacea'' Kützing C
*'' Hypnea coccinea'' (Clemente) Cremades C
*'' Hypnea compressa'' Papenfuss C
*'' Hypnea conferta'' (Schousboe ex Montagne) Kützing S
*'' Hypnea confervoides'' (C.Agardh) J.Agardh S
*'' Hypnea congesta'' Papenfuss C
*'' Hypnea cornuta'' (Kützing) J.Agardh C
*'' Hypnea corona'' Huisman & Petrocelli C
*'' Hypnea coulteri'' Harvey S
*'' Hypnea cryptica'' P.B.Jesus & J.M.C.Nunes C
*'' Hypnea cystoclonioides'' Sonder S
*'' Hypnea divaricata'' (C.Agardh) Greville C
*'' Hypnea divergens'' (C.Agardh) J.Agardh S
*'' Hypnea ecklonii'' Suhr C
*'' Hypnea edeniana'' F.Nauer, V.Cassano & M.C.Oliveira C
*'' Hypnea episcopalis'' Hooker f. ''&'' Harvey S
*'' Hypnea esperi'' Bory U
*'' Hypnea evermannii'' Setchell & N.L.Gardner C
*'' Hypnea fastigiata'' Harvey S
*'' Hypnea filiformis'' (Harvey) Womersley C
*'' Hypnea flagelliformis'' Greville ex J.Agardh C
*'' Hypnea flava'' Nauer, Cassano & M.C.Oliveira C
*'' Hypnea flexicaulis'' Y.Yamagishi & M.Masuda S
*'' Hypnea flexuosa'' A.C.Brown & N.Jarman C
*'' Hypnea fruticulosa'' Kützing C
*'' Hypnea furcellata'' Hooker f. ''&'' Harvey S
*'' Hypnea furnariana'' Cormaci, Alongi and Dinaro C
*'' Hypnea hamulosa'' (Esper) J.V.Lamouroux C
*'' Hypnea harveyi'' Kützing S
*'' Hypnea hippuroides'' Kützing S
*'' Hypnea horrida'' (C.Agardh) J.Agardh S
*'' Hypnea indica'' P.Kundu & F.Bast C
*'' Hypnea intricata'' Kylin C
*'' Hypnea japonica'' Tanaka C
*'' Hypnea johnstonii'' Setchell & N.L.Gardner C
*'' Hypnea krugiana'' Hauck C
*'' Hypnea mamillosa'' Zanardini U
*'' Hypnea marchantiae'' Setchell & N.L.Gardner C
*'' Hypnea multicornis'' (Montagne) Montagne C
*''Hypnea musciformis'' (Wulfen) J.V.Lamouroux C
*'' Hypnea nidifica'' J.Agardh U ''Hypnea'' ''nidulans'' Setchell C
*'' Hypnea nigrescens'' Greville ex J.Agardh C
*'' Hypnea pannosa'' J.Agardh C
*'' Hypnea pectinella'' Børgesen C
*'' Hypnea planicaulis'' Harvey S
*'' Hypnea platyclada'' Barreto de Jesus & Castro Nunes C
*'' Hypnea pseudomusciformis'' Nauer, Cassano & M.C.Oliveira C
*'' Hypnea purpurascens'' (Hudson) Harvey S
*'' Hypnea ramentacea'' (C.Agardh) J.Agardh C
*'' Hypnea rangiferina'' (R.Brown ex Turner) Greville S
*'' Hypnea reptans'' Papenfuss C
*'' Hypnea rigens'' Sonder S
*'' Hypnea rissoana'' J.Agardh S
*'' Hypnea rosea'' Papenfuss C
*'' Hypnea rugulosa'' Montagne C
*'' Hypnea saidana'' Holmes S
*'' Hypnea schneideri'' Nauer, Cassano & M.C.Oliveira C
*'' Hypnea secundiramea'' Montagne S
*'' Hypnea seticulosa'' J.Agardh S
*'' Hypnea simpliciuscula'' Okamura ex De Toni S
*'' Hypnea spicifera'' (Suhr) Harvey C
*'' Hypnea spicigera'' Harvey S
*'' Hypnea spinella'' (C.Agardh) Kützing C
*'' Hypnea spongiiformis'' Zanardini U
*'' Hypnea stellulifera'' (J.Agardh) Yamagishi & Masuda C
*'' Hypnea tenuis'' Kylin C
*'' Hypnea unilateralis'' P.J.L.Dangeard C
*'' Hypnea ustulata'' (Turner) Montagne S
*''Hypnea vaga'' Kützing C
*'' Hypnea valentiae'' (Turner) Montagne C
*'' Hypnea valida'' J.Agardh S
*''Hypnea variabilis'' Okamura C
*''Hypnea viridis'' Papenfuss C
*'' Hypnea volubilis'' Searles C
*'' Hypnea wurdemannii'' Harvey S
*'' Hypnea wynnei'' Nauer, Cassano & M.C.Oliveira C
*'' Hypnea yamadae'' Tanaka C
*'' Hypnea yokoyana'' Nauer, Cassano & M.C.Oliveira C

References

{{Taxonbar, from=Q18350571

Red algae genera
Gigartinales