Tropical Seagrass Identification (Seagrass-Watch)

This page outlines how to identify all the tropical seagrass species. This includes illustrations and links to additional resources. 

Cymodocea rotundata (CR)

  • Flat, strap-like leaves 2-4mm wide
  • Rounded, smooth leaf tip
  • Smooth rhizome
  • Scars from well developed leaf sheaths form a continuous ring around the stem
  • Found on shallow reef flats

Cymodocea serrulata (CS)

  • Linear strap-like leaves, 5-9mm wide
  • Serrated leaf tip
  • Leaf sheath is broadly triangular with a narrow base
  • Leaf scars do not form a continuous ring around the stem
  • Found on shallow subtidal reef flats and sand banks

Enhalus acoroides (EA)

  • Very long ribbon-like leaves 30-150 cm long
  • Leaves with inrolled leaf margins
  • Thick rhizome with long black bristles and cord-like roots
  • Found on shallow/intertidal sand/mud banks (often adjacent to mangrove forests)

Halodule pinifolia (HP)

  • Fine, delicate leaves up to 20cm long
  • 1 central vein
  • Black central vein splits into two at the rounded leaf tip
  • Usually pale rhizome, with clean black leaf scars
  • Found on intertidal sand banks

Halodule uninervis (HU)

  • Usually larger than Halodule pinifolia
  • Trident leaf tip
  • 1 central longitudinal vein
  • Rhizome usually pale ivory, with clean black leaf scars
  • Dugong preferred food
  • Found on shallow/intertidal sand or mud banks

Halophila capricorni (HC)

  • Small oval leaves that are hairy on one side
  • Central vein on leaf with 9-14 cross veins
  • Usually found deeper than 10m in coral environments proximal to coral reefs
  • Only found in subtidal Australian waters (>10m) proximal to coral reefs 

Halophila decipiens (HD)

  • Small oval leaf blade 1-2.5cm long
  • 6-8 cross veins
  • Leaf hairs on both sides
  • Leaves usually longer than wider
  • Found at subtidal depths (>10m)

Halophila ovalis (HO)

  • Oval shaped leaves in pairs
  • 8 or more cross veins
  • No hairs on leaf surface
  • Preferred dugong food
  • Common early colonising species
  • Found from intertidal to subtidal depths

Halophila minor (HM)

  • Less than 8 pairs of cross veins
  • Small oval leaves occurring in pairs
  • Wedge-shaped leaf sheath
  • Found on shallow/intertidal sand flats

Halophila spinulosa (HS)

  • Fern like
  • Leaves arranged in opposite pairs
  • Erect shoot up to 15cm long
  • Found at subtidal depths (>10m)

Halophila tricostata (HT)

  • Erect shoots 8-18cm long
  • Leaves with 3 veins
  • 2-3 leaves at each node
  • Leaves “whorl” around stem
  • Found at subtidal depths (>10m)
  • Endemic to Queensland, Australia 

Syringodium isoetifolium (SI)

  • Cylindrical in cross section (spaghetti like)
  • Leaf tip tapers to a point
  • Leaves 7-30cm long
  • Found on shallow subtidal reef flats and sand banks

Thalassia hemprichii (TH)

  • Short black bars of tannin cells in leaf blade 
  • Thick rhizome with scars between shoots
  • Hooked/curved shaped leaves
  • Leaves 10-40cm long
  • Common on shallow reef flats

Thalassodendron ciliatum (TC)

  • Cluster of ribbon-like curved leaves at the end of an erect stem
  • Round, serrated leaf tip
  • Tough, woody rhizomes with scars from successive shoots
  • Very coiled, branched roots
  • Typically found in rocky areas with strong reef crests

Zostera capricorni (ZC)

  • Long strap-shaped leaves