8
C. den Hartog and J. Kuo
(2000) did not regard Thalassocharis as a seagrass
anymore.
In spite of the great differences in the morphology
and the anatomy of their reproductive structures as
well as their modes of pollination, Les et al. (1997)
treated the families Cymodoceaceae, Posidoniaceae
and Ruppiaceae together as one phylogenetic unit,
the ‘Cymodoceaceae complex’, to distinguish it
from the other seagrass groups such as the Zosteraceae and the marine Hydrocharitaceae.
Within the family two groups of genera can be recognized. Halodule, Cymodocea, and Syringodium
have a monopodial rhizome, are herbaceous, and
have leaf-blades that are shed before the leaf-sheaths.
Thalassodendron and Amphibolis have a sympodial,
ligneous rhizome, and the leaf-blades are shed with
the sheaths as single units; further, these two genera show vivipary. There is, however, in our opinion
no reason to give these groups a formal taxonomic
status.
Key to the Genera
1a. Rhizome monopodial, herbaceous, with a short
erect stem at each node. Leaf-sheath persisting
longer than the leaf-blade. Anthers stalked. . . 2
1b. Rhizome sympodial, ligneous, with elongate,
more or less branched, erect stems at certain
nodes. Leaf-blade shed with its sheath. Anthers
subsessile. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
2a. Leaves flat. Flowers solitary. . . . . . . . . . . . . . . . 3
2b. Leaves subulate. ‘Flowers’ arranged into a cymose inflorescence. . . . . . . . . . . . . Syringodium
3a. Nerves 3. Anthers not attached at the same
height on the peduncle. Ovary with one undivided style . . . . . . . . . . . . . . . . . . . . . . . . Halodule
3b. Nerves 7–17. Anthers attached at the same
height on the peduncle. Style divided into two
stigmata. . . . . . . . . . . . . . . . . . . . . . . . Cymodocea
4a. Rhizome with two unbranched or little branched
stems at every fourth rhizome node; roots 1–
5 on the node preceding the stem-bearing one.
Leaves with parallel nerves and denticulate
apex. ‘Flowers’ enclosed by four leafy bracts.
Anthers connate over their entire length, each
crowned with one appendage. Style with two
stigmata. False fruit composed of 1 or 2 fertilized ovaries surrounded by the enlarged inner
bract . . . . . . . . . . . . . . . . . . . . . .Thalassodendron
4b. Rhizome with 1–2 branching roots at each node
and at a distance of (1-) 4–8 nodes one profusely
branched stem. Leaves entire, with pseudoparallel nerves, and a bidentate apex. ‘Flowers’ enclosed by normal leaves. Anthers connate with
their lower parts, each crowned with 2–3 appendages. Style with three stigmata. ‘Fruit’ consisting of one fertilized ovary with four pectinate, spreading lobes arising just above its base;
viviparous. . . . . . . . . . . . . . . . . . . . . . Amphibolis
Halodule Endl., Gen. Pl. suppl. 1 (1841) 1368.
Type species: Diplanthera tridentata Steinheil
(= H. uninervis (Forssk.) Ascherson).
The typification of Halodule has been complicate.
Du Petit Thouars (1806) was the first to describe
the genus from Madagascar under the name Diplanthera, but he unfortunately did not add a species
name to his material. Steinheil (1838) described the
material as D. tridentata. Steudel (1840) referred to
the same material and named it, without a description, D. madagascariensis. He recognized a second
species, D. indica that turned out to be Halophila
ovalis. From Steudel’s work it becomes also obvious, that the genus name Diplanthera has been
used also for other genera in very different families. Endlicher (1841) referred to the material of
Du Petit Thouars (1806) and the work of Steinheil
(1838) as he founded the genus Halodule, but regrettably he failed also to transfer the species name
to the new genus. Miquel (1855) was the first to
describe a species in the genus as H. australis,
for material from Indonesia, similar to Steinheil’s
species; therefore, the new epithet was superfluous.
It took till 1882, before this material was properly
named.
The genus consists of seven species. The main
characters used for the identification of the species
are the shape of the leaf tip and the width of the
leaves (den Hartog, 1970). There are too few data of
the generative structures, and the degree of variation
of these is not yet clear; at present they cannot be
used to identify the taxa. Moreover, they are not
known for several taxa.
H. uninervis commonly occurs in the tropical
Indo-West Pacific with a narrow- and a wide-leaved
form. It is possible that these two forms represent different taxa; in that case the name H. uninervis is linked to the wide-leaved form, while the
narrow-leaved form should be named H. tridentata
(Steinheil) F. von Mueller. In the West Pacific a
second species, H. pinifolia, occurs as well; in the
C. den Hartog and J. Kuo
(2000) did not regard Thalassocharis as a seagrass
anymore.
In spite of the great differences in the morphology
and the anatomy of their reproductive structures as
well as their modes of pollination, Les et al. (1997)
treated the families Cymodoceaceae, Posidoniaceae
and Ruppiaceae together as one phylogenetic unit,
the ‘Cymodoceaceae complex’, to distinguish it
from the other seagrass groups such as the Zosteraceae and the marine Hydrocharitaceae.
Within the family two groups of genera can be recognized. Halodule, Cymodocea, and Syringodium
have a monopodial rhizome, are herbaceous, and
have leaf-blades that are shed before the leaf-sheaths.
Thalassodendron and Amphibolis have a sympodial,
ligneous rhizome, and the leaf-blades are shed with
the sheaths as single units; further, these two genera show vivipary. There is, however, in our opinion
no reason to give these groups a formal taxonomic
status.
Key to the Genera
1a. Rhizome monopodial, herbaceous, with a short
erect stem at each node. Leaf-sheath persisting
longer than the leaf-blade. Anthers stalked. . . 2
1b. Rhizome sympodial, ligneous, with elongate,
more or less branched, erect stems at certain
nodes. Leaf-blade shed with its sheath. Anthers
subsessile. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
2a. Leaves flat. Flowers solitary. . . . . . . . . . . . . . . . 3
2b. Leaves subulate. ‘Flowers’ arranged into a cymose inflorescence. . . . . . . . . . . . . Syringodium
3a. Nerves 3. Anthers not attached at the same
height on the peduncle. Ovary with one undivided style . . . . . . . . . . . . . . . . . . . . . . . . Halodule
3b. Nerves 7–17. Anthers attached at the same
height on the peduncle. Style divided into two
stigmata. . . . . . . . . . . . . . . . . . . . . . . . Cymodocea
4a. Rhizome with two unbranched or little branched
stems at every fourth rhizome node; roots 1–
5 on the node preceding the stem-bearing one.
Leaves with parallel nerves and denticulate
apex. ‘Flowers’ enclosed by four leafy bracts.
Anthers connate over their entire length, each
crowned with one appendage. Style with two
stigmata. False fruit composed of 1 or 2 fertilized ovaries surrounded by the enlarged inner
bract . . . . . . . . . . . . . . . . . . . . . .Thalassodendron
4b. Rhizome with 1–2 branching roots at each node
and at a distance of (1-) 4–8 nodes one profusely
branched stem. Leaves entire, with pseudoparallel nerves, and a bidentate apex. ‘Flowers’ enclosed by normal leaves. Anthers connate with
their lower parts, each crowned with 2–3 appendages. Style with three stigmata. ‘Fruit’ consisting of one fertilized ovary with four pectinate, spreading lobes arising just above its base;
viviparous. . . . . . . . . . . . . . . . . . . . . . Amphibolis
Halodule Endl., Gen. Pl. suppl. 1 (1841) 1368.
Type species: Diplanthera tridentata Steinheil
(= H. uninervis (Forssk.) Ascherson).
The typification of Halodule has been complicate.
Du Petit Thouars (1806) was the first to describe
the genus from Madagascar under the name Diplanthera, but he unfortunately did not add a species
name to his material. Steinheil (1838) described the
material as D. tridentata. Steudel (1840) referred to
the same material and named it, without a description, D. madagascariensis. He recognized a second
species, D. indica that turned out to be Halophila
ovalis. From Steudel’s work it becomes also obvious, that the genus name Diplanthera has been
used also for other genera in very different families. Endlicher (1841) referred to the material of
Du Petit Thouars (1806) and the work of Steinheil
(1838) as he founded the genus Halodule, but regrettably he failed also to transfer the species name
to the new genus. Miquel (1855) was the first to
describe a species in the genus as H. australis,
for material from Indonesia, similar to Steinheil’s
species; therefore, the new epithet was superfluous.
It took till 1882, before this material was properly
named.
The genus consists of seven species. The main
characters used for the identification of the species
are the shape of the leaf tip and the width of the
leaves (den Hartog, 1970). There are too few data of
the generative structures, and the degree of variation
of these is not yet clear; at present they cannot be
used to identify the taxa. Moreover, they are not
known for several taxa.
H. uninervis commonly occurs in the tropical
Indo-West Pacific with a narrow- and a wide-leaved
form. It is possible that these two forms represent different taxa; in that case the name H. uninervis is linked to the wide-leaved form, while the
narrow-leaved form should be named H. tridentata
(Steinheil) F. von Mueller. In the West Pacific a
second species, H. pinifolia, occurs as well; in the