''Stigeoclonium'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

green algae The green algae (: green alga) are a group of chlorophyll-containing autotrophic eukaryotes consisting of the phylum Prasinodermophyta and its unnamed sister group that contains the Chlorophyta and Charophyta/ Streptophyta. The land plants ...

in the family

Chaetophoraceae Chaetophoraceae is a family (biology), family of green algae in the order Chaetophorales. Members of the family are variously semi-terrestrial to aquatic in habitat, and consist of branched filaments in two parts, a prostrate system of filaments ...

. It is a common

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include non-salty mi ...

genus, found growing attached to various substrates; it has a

cosmopolitan distribution 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 ...

. There are currently 53 accepted species within this group. However, recent phylogenetics have identified that this group is

polyphyletic A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, homoplasies ...

and will need reassessment. The

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

for this genus is ''S. tenue,'' described in 1843 by F.T. Kützing. It was first described in 1814 by Carl Agardh under the

basionym In the scientific name of organisms, basionym or basyonym means the original name on which a new name is based; the author citation of the new name should include the authors of the basionym in parentheses. The term "basionym" is used in both botan ...

''Draparnaldia tenuis.'' The name ''Stigeoclonium'' has been conserved against the genus ''Myxonema'' named by

Elias Magnus Fries Elias Magnus Fries (15 August 1794 – 8 February 1878) was a Swedish mycologist and botanist. He is sometimes called the Mycology, "Linnaeus of Mycology". In his works he described and assigned botanical names to hundreds of fungus and li ...

; ''Myxonema'' is a heterogeneous assemblage of various algae.

Description

''Stigeoclonium'' consists of two systems of filaments, prostrate and erect filaments. Prostrate filaments are attached to the substrate and are creeping or rhizoidal, occasionally forming a pseudoparenchymatous mass. Erect filaments emerge from the prostrate filaments, and are variously branched. The erect filaments terminate in an obtuse or acutely pointed tip, or a long multicellular hair. Under unfavorable conditions, a "stunted" form develops with predominantly prostrate filaments. Cells are uninucleate, cylindrical or swollen, with a single parietal

chloroplast A chloroplast () is a type of membrane-bound organelle, organelle known as a plastid that conducts photosynthesis mostly in plant cell, plant and algae, algal cells. Chloroplasts have a high concentration of chlorophyll pigments which captur ...

and one to several

pyrenoid Pyrenoids are sub-cellular phase-separated micro-compartments found in chloroplasts of many algae,Giordano, M., Beardall, J., & Raven, J. A. (2005). CO2 concentrating mechanisms in algae: mechanisms, environmental modulation, and evolution. ''An ...

s. The whole thallus is commonly surrounded by a layer of

mucilage Mucilage is a thick gluey substance produced by nearly all plants and some microorganisms. These microorganisms include protists which use it for their locomotion, with the direction of their movement always opposite to that of the secretion of ...

. Reproduction occurs asexually and

sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...

. Asexual reproduction occurs by zoospores of two sizes, large and small (macrozoospores and microzoospores), both of which have four

flagella A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...

. Sexual reproduction is

isogamous Isogamy is a form of sexual reproduction that involves gametes of the same morphology (indistinguishable in shape and size), and is found in most unicellular eukaryotes. Because both gametes look alike, they generally cannot be classified as ma ...

and involves biflagellate or quadriflagellate gametes. Both zoospores and gametes are termed "swarmers", and are formed mostly in the erect filaments. They escape through a lateral pore in the cell wall. Zoospores swim for some time, then attach to a substrate via their anterior (flagellar) end, withdraw their flagella, and germinate. Mature zygotes are orange to red in color.

Ecology

''Stigeoclonium'' is almost exclusively found in freshwater, although some species are also found in

brackish water Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuary ...

s. It is distributed worldwide and can be found in a variety of habitats, from under ice to in hot springs. Typically, they are found in streams, rivers, lakes, and other bodies of water where they are attached to various surfaces such as stones, wood, and leaves. Some forms are also epizoic on the surface of animals, such as

snail A snail is a shelled gastropod. The name is most often applied to land snails, terrestrial molluscs, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class Gas ...

shells,

kissing gourami Kissing gouramis, also known as kissing fish or kissers (''Helostoma temminckii''), are medium-sized tropical freshwater fish comprising the monotypic labyrinth fish family Helostomatidae (from the Greek ''elos'' tud, nail ''stoma'' outh. These ...

, and even toads. ''Stigeoclonium'' can be found in a wide pH range, but its

autecology Autecology is an approach in ecology that seeks to explain the distribution and abundance of species by studying interactions of individual organisms with their environments. An autecological approach differs from ecosystem ecology, community ecolo ...

is overall rather poorly known.

Taxonomy

The taxonomy of ''Stigeoclonium'' is currently poorly known. Traditionally, morphological characters used to delimit species include the cell dimensions, branching degree, presence/absence of hairs, thallus color and habitat. These characters have long been known to be variable; for example, hair presence is known to be affected by light and nutrient levels. Consequently, many authors have merged most of the species under just a few names. Studies based on

molecular phylogenetics Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

have shown that ''Stigeoclonium'' is

, and the clades are not characterized by traditional morphological characters, but instead the morphology of the germling after it germinates from the zoospore. ''Stigeoclonium helveticum'' was shown to be within the clade of

, and was reclassified into a new genus, '' Pseudostigeoclonium''.

Species list

As of 2025,

AlgaeBase AlgaeBase is a global species database of information on all groups of algae, both seaweed, marine and freshwater algae, freshwater, as well as sea-grass. History AlgaeBase began in March 1996, founded by Michael D. Guiry, Michael Guiry. Text ...

includes the following species: * '' S. aestivale'' * '' S. amoenum'' * '' S. attenuatum'' * '' S. australense'' * '' S. bertholdianum'' * '' S. biasolettianum'' * '' S. bifurcatum'' * '' S. carolinianum'' * '' S. chroolepiforme'' * '' S. condensatum'' * '' S. curvirostrum'' * '' S. elongatum'' * '' S. falklandicum'' * '' S. farctum'' * '' S. fasciculare'' * '' S. flagelliferum'' * '' S. fritschianum'' * '' S. gayanum'' * '' S. geraldii'' * '' S. gracile'' * '' S. islamii'' * '' S. klebsii'' * '' S. longipilum'' * '' S. lubricum'' * '' S. mejeri'' * '' S. nanum'' * '' S. nelsonii'' * '' S. nudiusculum'' * '' S. ovisporum'' * '' S. pachydermum'' * '' S. penicillatum'' * '' S. polymorphum'' * '' S. prolixum'' * '' S. pusillum'' * '' S. rivulare'' * '' S. sarmae'' * '' S. segarare'' * '' S. setigerum'' * '' S. stagnatile'' * '' S. subsecundum'' * '' S. subspinosum'' * '' S. subuligerum'' * '' S. tenue'' * '' S. thermale'' * '' S. tibeticum'' * '' S. variabile'' * '' S. westii''

References

{{Taxonbar, from=Q7616464 Chaetophorales genera Chaetophoraceae Freshwater algae