16 – Mangroves and Seagrasses
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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)
169
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)