# Zosteraceae

Zosteraceae (one of the four seagrasses families, Kubitzki ed. 1998) is a family of marine perennial flowering plants found in temperate and subtropical coastal waters, with the highest diversity located around Korea and Japan. Most seagrasses complete their entire life cycle under water, having filamentous pollen especially adapted to dispersion in an aquatic environment and ribbon-like leaves that lack stomata. Seagrasses are herbaceous and have prominent creeping rhizomes. A distinctive characteristic of the family is the presence of characteristic retinacules, which are present in all species except members of Zostera subgenus Zostera.
Zosteraceae has long been accepted by taxonomists as monophyletic. The APG II system of 2003 recognizes this family and places it in the monocot order Alismatales. The family contains approximately twenty-two species divided between two genera, Phyllospadix and Zostera totalling 22 known species (Christenhusz & Byng 2016). Zostera contains three subgenera: Heterozostera (formerly considered a separate genus), Zostera and Zosterella. Zosteraceae is closely related to Potamogetonaceae, a family of freshwater aquatics.
Zosteraceae is a conserved name.

## Taxonomy

Marine grasses families: Zosteraceae, Cymodoceaceae, Ruppiaceae and Posidoniaceae. Related families: Potamogetonaceae and sometimes including Zannichelliaceae.
Families and Genera crosses (Sea grasses) :
| Kubitzki (ed. 1998) | Watson & Dallwitz (delta-intkey) | data.kew | APWeb (mobot.org) |
| Zosteraceae ||||
| 1. Zostera L. | Zostera | Zostera L. | Zostera L. (including Heterozostera den Hartog, Macrozostera Tomlinson & Posluzny, Nanozostera Tomlinson & Posluzny, Zosterella J. K. Small) |
| 2. Heterozostera den Hartog | Heterozostera | Heterozostera (Setch.) Hartog | (in Zostera) |
| 3. Phyllospadix Hook. | Phyllospadix | Phyllospadix Hook. | Phyllospadix J. D. Hooker |
| Cymodoceaceae ||||
| 1. Syringodium Kütz | Syringodium | Syringodium Kutz. | (in Cymodocea) |
| 2. Halodule Endl. | Halodule | Halodule Endl. | Halodule Endlicher |
| 3. Cymodocea König | Cymodocea | Cymodocea K.Koenig (including Phycoschoenus (Asch.) Nakai ) | Cymodocea König (including Amphibolis Agardh ?, Syringodium Kütz. ?, Thalassodendron den Hartog ?) |
| 4. Amphibolis Agardh | Amphibolis | Amphibolis C.Agardh (including Pectinella J.M.Black) | (in Cymodocea) |
| 5. Thalassodendron de Hartog | (name not found) | Thalassodendron Hartog | (in Cymodocea) |
| Ruppiaceae ||||
| Ruppia L. | Ruppia | (in Ruppia L. in Potamogetonaceae) | Ruppia L. |
| Posidoniaceae ||||
| Posidonia König | Posidonia | Posidonia K.Koenig | Posidonia König |
Families and Genera crosses (Potamogetonaceae) :
| Kubitzki (ed. 1998) | Watson & Dallwitz (delta-intkey) | data.kew | APWeb (mobot.org) |
| Potamogetonaceae ||||
| 1. Potamogeton L. | Potamogeton | Potamogeton L. | Potamogeton L. (including Coleogeton Les & Haynes, Stuckenia Börner) |
| 2. Groenlandia J. Gray | Groenlandia | Groenlandia J.Gay | Groenlandia J. Gay |
| (in Ruppia in Ruppiaceae) | (in Ruppia in Ruppiaceae) | Ruppia L. | (in Ruppia in Ruppiaceae) |
| (in Althenia: Zannichelliaceae and Lepilaena: Zannichelliaceae) | (in Althenia: Zannichelliaceae and Lepilaena: Zannichelliaceae) | (in Althenia F.Petit: Zannichelliaceae and Lepilaena J.L.Drumm. ex Harv.:Zannichelliaceae) | Althenia Petit (including Lepilaena Harvey) |
| (in Pseudalthenia including Vleisia: Zannichelliaceae) | (in Pseudalthenia: Zannichelliaceae and Vleisia: Zannichelliaceae) | (Pseudalthenia not found, Vleisia Toml. & Posl.: Zannichelliaceae) | Pseudalthenia Nakai (including Vleisia Tomlinson & Posluszny) |
| (in Zannichellia L.: Zannichelliaceae) | (in Zannichellia: Zannichelliaceae) | (in Zannichellia L.: Zannichelliaceae) | Zannichellia L. |
| Zannichelliaceae ||||
| 1. Zannichellia L. | Zannichellia | Zannichellia L. | (in Zannichellia L.: Potamogetonaceae) |
| 2. Pseudalthenia Nakai (including Vleisia) | Pseudalthenia (excluding Vleisia) | (name not found) | (in Pseudalthenia: Potamogetonaceae) |
| 3. Althenia Petit (excluding Lepilaena Drumm. ex. Harv.) | Althenia (excluding Lepilaena) | Althenia F.Petit (excluding Lepilaena J.L.Drumm. ex Harv.) | Althenia Petit (including Lepilaena Harvey) |
| 4. Lepilaena Drumm. ex. Harv. | Lepilaena | Lepilaena J.L.Drumm. ex Harv. | (in Althenia Petit) |
| (in Pseudalthenia) | Vleisia | Vleisia Toml. & Posl. | (in Pseudalthenia: Potamogetonaceae) |