Florideophyceae is a class of exclusively multicellular red algae. They were once thought to be the only algae to bear pit connections, but these have since been found in the filamentous stage of the Bangiaceae. They were also thought only to exhibit apical growth, but there are genera known to grow by intercalary growth. When alive, the Florideophyceae appear bright red or even violet. However, when placed in cold freshwater, their red pigment dissolves, causing the algae to turn green.
Classification
thumb|240px|A [[Laurencia red alga from Hawaii]]
There are various classification schemes; see red algae. One option is to use the following:
Subclass Hildenbrandiophycidae
- Hildenbrandiales
Subclass Nemaliophycidae
- Acrochaetiales
- Balbianiales
- Balliales
- Batrachospermales
- Colaconematales
- Nemaliales
- Palmariales
- Entwisleiales
- Thoreales
Subclass Corallinophycidae
- Corallinales
- Corallinapetrales
- Rhodogorgonales
- Sporolithales
The subclass Corallinophycidae was introduced in 2007.
Subclass Ahnfeltiophycidae
- Ahnfeltiales
- Pihiellales
Subclass Rhodymeniophycidae
- Bonnemaisoniales
- Ceramiales
- Gelidiales
- Gigartinales
- Gracilariales
- Halymeniales
- Nemastomatales
- Peyssonneliales
- Plocamiales
- Rhodymeniales
- Acrosymphytales
- Atractophorales
- Catenellopsidales
- Sebdeniales
According to molecular clock analysis, Florideophyceae diverged from other red algae about 943 (817–1,049) million years ago. It split into Hildenbrandiophycidae ca. 781 (681–879) mya, Nemaliophycidae ca. 661 (597–736) mya and Corallinophycidae ca. 579 (543–617) mya, and ca. 508 (442–580) mya the split between Ahnfeltiophycidae and Rhodymeniophycidae occurred.