Haigh, A. (2009). Neotropical Zosteraceae.
Herbs perennial , rarely annual , usually submerged, a few species intertidal and periodically exposed to air; rhizomes with monopodial branching. Leaves alternate , distichous , simple , linear . Inflorescences borne on simple or branched, erect spadices, the flowers in two rows, enclosed by spathe . Flowers unisexual ( monoecious or dioecious ), highly reduced; perianth absent. Staminate flowers with one stamen ; anthers with two distinct, bilocular thecae, longitudinally dehiscent , the pollen shed in long, filamentous strands. Pistillate flowers with 1-locular ovary , the stigmas two, long; ovule one. Fruits achenes; seeds without endosperm ; hypocotyl enlarged.
Distribution in the Neotropics
A cosmopolitan family of three genera and c. 18 species. All three genera represented in Latin America with c. 3 species.
- Zostera L.: about 12 species in mainly northern hemisphere waters, but with one species (Z. marina L.) extending into the coast of Mexico and northern Central America.
- Heterozostera den Hartog: monospecific (H. tasmanica (Martens ex Aschers.) Hartog), native to the coastal waters of southern Australia and northern Chile.
- Phyllospadix Hook.: five species mainly found in the northern temperate coastal waters of the Pacific ocean, one species (P. torreyi S.Watson) extends to the Neotropics.
- General Description
Number of genera
Three Neotropical genera (see above)General notes
- The family generally occurs in shallow coastal waters of temperate to subtropical regions, all three genera just reaching into the Neotropics.
- Perennial plants can form extensive stands (often called submarine meadows) in shallow brackish and saltwater areas with clear water and minimal wave action.
- Zosteraceae play an important role in stabilization of shallow marine sediments.
Native.Notes on delimitation
- Zosteraceae is placed in the Alismatales, closest to Potamogetonaceae.
Useful tips for generic identification
Key to genera of Neotropical Zosteraceae
1. Rhizome thick with condensed internodes; rhizome cortical cells thick-walled, cortical fibre bundles absent; roots short, thick; leaf blade thick, flat to biconvex; normally growing on rock substrate; dioecious — Phyllospadix
1. Rhizome slender, usually with elongate internodes; rhizome cortical cells thin-walled, cortical fibre bundle present; roots long, thin; leaf blade thin, flat; normally growing on sand/mud substrate; monoecious — 2
2. Rhizome internodes with 4-12 vascular bundles, fibre bundles distributed throughout cortex, commonly associated with stele; erect shoots long, wiry, branched and often forming new rhizomes with plantlets; only in older plants erect shoots sometimes developing inflorescences ... HeterozosteraDistinguishing characters (always present)
2. Rhizome internodes with 2 cortical vascular bundles, fibre bundles restricted to outer cortex; erect shoots herbaceous not wiry, always developing inflorescences — Zostera
- Intertidal to marine aquatic herbs.
- Flowers unisexual, aggregated in spadices (spikes), enclosed by a spathe.
- Fruits achenes.
Kuo, J. & McComb, A.J., 1998. Zosteraceae. In: K. Kubitzki (ed.), The families and genera of vascular plants 4: 296-502. Springer Verlag, Berlin.
Stevenson, D.W. 2004. Zosteraceae. p. 496. In: Smith, N., Mori, S.A., Henderson, A., Stevenson, D.W. & Heald, S.V. (eds.). Flowering Plants of the Neotropics. New York Botanical Garden, Princeton University Press, Princeton.
Zosteraceae, H. J. Beentje, M.Sc., Ph.D., F.L.S.. Flora of Tropical East Africa. 1999
- Morphology General Habit
- Perennial herbs adapted to life in shallow sea water, with creeping rhizomes, monoecious or dioecious; rhizomes creeping or tuberous, nodes with intervaginal scales
- Morphology Leaves
- Leaves distichous, linear or filiform; leaf sheath open or closed, often with stipuloid flanges, with an auriculate ligule at the junction with the blade; blade parallel-veined, sometimes with midrib
- Morphology Reproductive morphology Inflorescences
- Inflorescence of 1 to several spadices, each enclosed in a spathe formed by the sheath of the next leaf; flowers small, sessile in two rows on a flattened axis; pollination by water; petals absent, stamen 1, sessile, dorsifixed, anther with longitudinal slits, the pollen filamentous, without exine, with the same density as sea water; pistillate flower protogynous, gynoecium 1, 1- locular with basally united styles and two stigmatic arms; ovule single, pendulous, orthotropous, bitegmic
- Morphology Reproductive morphology Fruits
- Fruit a small irregular drupe, or irregularly dehiscing; endosperm absent
Flora of Tropical East Africa
- Flora of Tropical East Africa
Kew Names and Taxonomic Backbone
- The International Plant Names Index and World Checklist of Vascular Plants 2023. Published on the Internet at http://www.ipni.org and https://powo.science.kew.org/
- © Copyright 2022 International Plant Names Index and World Checklist of Vascular Plants. http://creativecommons.org/licenses/by/3.0
- Milliken, W., Klitgard, B. and Baracat, A. (2009 onwards), Neotropikey - Interactive key and information resources for flowering plants of the Neotropics.