Key To The Seagrasses Of The Great Barrier Reef

1. Leaves ligulate (i.e. a tongue-like structure at junction of the leaf blade and sheath, which attaches to the rhizome) 8

- Leaves without ligules 2

2. Leaves strap-shaped, neither compound nor petiolate (stalked) 7

- Leaves compound or petiolate (with a stalk) Halophila 3 (6 taxa)

3. Erect, lateral shoots bearing a number of compound leaves 4

- Erect lateral shoots bearing one pair of simple leaves 5

4. 10-20 pairs of opposite leaflets (serrate margins) on an erect shoot

Halophila spinulosa (Fig. 16.10)

- 2-3 leaflets (serrate margin, no cross-veins), 6-18 nodes per shoot

Halophila tricostata

5. Leaf margin finely serrulate, hairs on leaf surface 6

- Leaf margin entire, no hairs present 7

6. Leaf hairs throughout and on both sides, cross veins 9-14 Halophila decipiens

- Leaf hairs only at base on abaxial side, cross veins 6-8

Halophila capricorni (Fig. 16.10)

7. Leaf blade paddle shaped, <5 mm long, <10 cross-veins Halophila minor

- Leaf blade paddle shaped, >5 mm long, >10 cross-veins

Halophila ovalis (Fig. 16.10)

8. Rhizome of two forms, scale-bearing and leaf-bearing, short shoots. Root hairs abundant on roots Thalassia hemprichii (Fig. 16.10)

- Rhizome of only one form, covered with long, black bristles and bearing leaves all over. Root hairs inconspicuous Enhalus acoroides (Fig. 16.10)

9. Leaf blade terete (round) Syringodium isoetifolium

- Leaf blade flat 10

10. Erect stem long bearing clusters of leaves at the end. Leaf apex rounded and coarsely toothed. Rhizome woody Thalassodendron ciliatum (Fig. 16.10)

- Erect stem short. Rhizome monopodial and not woody 11

11. Leaf blade 2 mm wide or less with three lateral veins running down each leaf

Halodule 12

- Leaf blade more than 3 mm wide and with nine or more lateral veins

Cymodocea 13

12. Tip of leaf with three teeth, the middle one being blunt

Halodule uninervis (Fig. 16.10)

- Tip of leaf rounded; three teeth, but side teeth poorly developed

Halodule pinifolia

13. Tip of leaf rounded to blunt with dense teeth, leaf 4-9 mm wide

Cymodocea serrulata (Fig. 16.10)

- Tip of leaf blunt (or faintly heart-shaped), leaf 2-4 mm wide. Short, erect shoot with leaf scars right around shoot Cymodocea rotundata (Fig. 16.10)

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