About Algae - Natural History Museum, London · 2019-11-28 · About Algae 'Algae' is a term of...
Transcript of About Algae - Natural History Museum, London · 2019-11-28 · About Algae 'Algae' is a term of...
About Algae
'Algae' is a term of convenience used for many oxygen-producing organisms that belong to different evolutionary lineages but have similar ecological requirements. All contain chlorophyll a, although the green colour of the pigment is often masked by accessory pigments.
These organisms are extraordinarily diverse and range from solitary cells to complex multicellular forms reaching several metres in length. Those possessing internal membranes and therefore organelles (such as chloroplasts and nuclei) are the eukaryotic algae and are usually placed in four of five supergroups or kingdoms, including the Plantae. The evolutionary history of the plastids of these eukaryotic algae is exceedingly complex and involves several endosymbiotic events.
Another important group is the 'blue-green algae'. These are prokaryotic organisms because they lack membrane-bound organelles. The group is more commonly called the cyanobacteria because of their close relationship to bacteria, although they contain chlorophyll a, like eukaryotic algae and vascular plants.
Some of the most important identifying features of algae are frequently lost on preservation. Even microalgae mounted on glass slides may deteriorate in time and rarely possess any useful diagnostic features. The diatoms are one of the most notable exceptions since their silica walls normally provide all the features necessary for identification. Many permanently preserved samples of freshwater algae therefore provide little useful information. For this reason, the type of microscopic algae is frequently not a specimen but a line-drawing or photomicrograph ('iconotype') and any preserved voucher material has limited use for cross-checking identifications.
Classification The classification follows the 2011 edition of The Freshwater Algal Flora of the British Isles and therefore recognises 15 phyla (see below). It differs in part from AlgaeBase, which to a large extent follows the consensus classification presented in Ruggiero et al. (2015).
Phylum in AlgaeVision Common name AlgaeBase classification
Cyanophyta Blue-green algae Phylum Cyanobacteria
Rhodophyta Red algae Phylum Rhodophyta
Euglenophyta Euglenoids Phylum Euglenophyta/Euglenozoa
Cryptophyta Cryptomonads Phylum Cryptophyta/Cryptista
Dinophyta Dinoflagellates Phylum Miozoa, class Dinophyceae
Raphidophyta Raphidophytes Phylum Ochrophyta, class Raphidophyceae
Haptophyta Haptophytes Phylum Haptophyta
Chrysophyta Golden or golden-brown algae
Phylum Ochrophyta, class Chrysophyceae and class Synurophyceae
Xanthophyta Yellow-green algae Phylum Ochrophyta, class Xanthophyceae
Chlorophyta Green algae (includes stoneworts)
Phylum Chlorophyta, phylum Charophyta,
Eustigmatophyta Eustigmatophytes Phylum Ochrophyta, class Eustigmatophyceae
Phaeophyta Brown algae Phylum Ochrophyta, class Phaeophyceae
Prasinophyta 'Primitive' green algae Phylum Chlorophyta
Bacillariophyta (not included in AlgaeVision)
Diatoms Phylum Ochrophyta, class Bacillariophyceae
Glaucophyta Glaucophytes Phylum Glaucophyta
Phylum Cyanophyta (blue-green algae/cyanobacteria)
blue-green, grey-green, violet, brown, purplish or red dependent on relative proportions of chlorophyll, phycocyanin and phycoerythrin
sometimes a brown sheath pigment (scytonemin) present
unicellular, colonial or filamentous (simple or branched)
internal membranes absent and so no organelles
Phylum Rhodophyta (red algae)
commonly red due to predominance of phycocyanin and phycoerythrin in chloroplasts
unicellular, filamentous or pseudoparenchymatous (flagellated stages absent)
food storage material - various, including floridean starch
unique features associated with reproduction
Phylum Euglenophyta (euglenoids)
green
commonly unicellular
often exhibit squirming movements, sometimes surrounded by an envelope or lorica
chloroplasts variously shaped
one or two flagella arising in a flask-shaped invagination
eyespot red, usually evident
walls with longitudinal or spiral striations
food storage material - paramylon
Phylum Cryptophyta (cryptomonads)
brown, blue, blue-green, red, red-brown, olive green, or yellow-brown due to accessory pigments in one or two chloroplasts
unicellular (rarely colonial), often bean-shaped, frequently dorsiventrally flattened
two or more unequal subapical flagella arising in an anterior invagination
food storage material - starch or starch-like
Phylum Dinophyta (dinoflagellates)
usually brown due to presence of accessory pigments
unicellular, rarely coccoid or filamentous
walls firm or of regularly arranged polygonal plates
biflagellate - one flagellum transverse and encircling the cell, other directed posteriorly directed
food storage materials - starch and oil
Phylum Raphidophyta
yellow-green due to predominance of accessory pigment diatoxanthin in two or more chloroplasts
unicellular, dorsiventrally organised, with no outer wall (naked)
two flagella arising in an apical, funnel-shaped invagination, one flagellum directed forwards and other backwards
food storage material - oil
Phylum Haptophyta
cells are golden or yellow-brown due to presence of accessory pigments (principally fucoxanthin)
unicellular
flagellates have amoeboid, coccoid, palmelloid or filamentous stages
walls often possess calcified scales
two flagella, and between them an appendage known as a haptonema
food storage material - principally chrysolaminarin
Phylum Chrysophyta (golden-brown algae)
cells are golden to yellow-brown due to presence of accessory pigments
single coccoidal cells or palmelloid, filamentous or parenchymatous
mostly uniflagellate or with two flagella, one long and the other short
outer wall absent or cell(s) within an often urn-shaped envelope (lorica)
silica scales sometimes present
food storage material - oil or leucosin
Phylum Xanthophyta (yellow-green algae)
cells are typically yellow-green due to present of the accessory pigment diatoxanthin in two or more chloroplasts
unicellular, filamentous, colonial or coenocytic
motile forms have two subapical flagella
walls frequently of overlapping parts
food storage material - oil, fat or leucosin
Phylum Chlorophyta (green algae)
cells with one to several green chloroplasts
unicellular, colonial, filamentous, coenocytic or macrophytes with robust axes bearing whorls of branches and branchlets
motile or non-motile - if motile then normally have one, two or four usually apical flagella
food storage material - principally starch surrounding in one to several pyrenoids
sexual reproduction oogamous in some orders
Phylum Eustigmatophyta
cells are yellow-green, with main accessory pigment usually violaxanthin in one or more chloroplasts
unicellular and coccoidal
motile forms have one flagellum or two unequal flagella inserted near apex
eyespot unique, independent of chloroplast
pyrenoid unique
food storage material unknown
Phylum Phaeophyta (brown algae)
cells are brownish due to presence of carotenoids pigments (principally fucoxanthin) in one to several chloroplasts
freshwater species of microscopic branched filaments (often closely packed)
motile stages pear-shaped with two laterally inserted flagella
walls frequently contain alginic acid and fucinic acid
food storage materials - laminarin and mannitol
Phylum Prasinophyta (primitive green algae)
cells have green, rarely yellow-green, chloroplasts
unicellular flagellates, rarely non-motile, with one to eight lateral or apical flagella, usually arising at base of a depression
walls and flagella mostly covered with organic scales
food storage material - starch or mannitol
Phylum Glaucophyta
cells are bright blue-green due to presence of phycocyanin and other pigments in cyanelles (not equivalent to chloroplasts)
unicellular or colonial
food storage material – starch, produced outside the cyanelles