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Algae (UK: / ˈ æ l ɡ iː / AL-ghee, US: / ˈ æ l dʒ iː / AL-jee; [3] sg.: alga / ˈ æ l ɡ ə / AL-gə) is an informal term for any organisms of a large and diverse group of photosynthetic eukaryotes, which include species from multiple distinct clades.
Some unicellular species of green algae, many golden algae, euglenids, dinoflagellates, and other algae have become heterotrophs (also called colorless or apochlorotic algae), sometimes parasitic, relying entirely on external energy sources and have limited or no photosynthetic apparatus.
Streptophyte algae include all green algae, and are the only photosynthetic eukaryotes from which the macroscopic land flora evolved (red lines). That said, throughout the course of evolution, algae from various other lineages have colonized land (yellow lines) —but also streptophyte algae have continuously and independently made the wet to ...
Algae is an informal term for a widespread and diverse group of photosynthetic protists which are not necessarily closely related and are thus polyphyletic. Marine algae can be divided into six groups: green , red and brown algae , euglenophytes , dinoflagellates and diatoms .
Green algae are a group of photosynthetic, eukaryotic organisms that include species with haplobiontic and diplobiontic life cycles. The diplobiontic species, such as Ulva , follow a reproductive cycle called alternation of generations in which two multicellular forms, haploid and diploid, alternate, and these may or may not be isomorphic ...
The fertilization of egg cells varies between species of brown algae, and may be isogamous, oogamous, or anisogamous. Fertilization may take place in the water with eggs and motile sperm, or within the oogonium itself. Certain species of brown algae can also perform asexual reproduction through the production of motile diploid zoospores.
Cyanobacteria are globally widespread photosynthetic prokaryotes and are major contributors to global biogeochemical cycles. [25] They are the only oxygenic photosynthetic prokaryotes, and prosper in diverse and extreme habitats. [26] They are among the oldest organisms on Earth with fossil records dating back at least 2.1 billion years. [27]
Photosynthetic organisms with plastids of different origin (such as brown algae) do not belong to the Archaeplastida. The archaeplastidans fall into two main evolutionary lines. The red algae are pigmented with chlorophyll a and phycobiliproteins, like most cyanobacteria, and