70
J. Kuo and C. den Hartog
2. Hydrocharitaceae
In the Hydrocharitaceae, dioecious Enhalus has a
many-flowered male inflorescence on a short peduncle, enclosed by the leaf sheaths, usually referred to
as a spathe. Each mature flower is thinly pedicellate,
with six tepals and three stamens. At maturity they
break free and float in dense patches on the surface.
The female flower is solitary on a long peduncle and
is enclosed by two overlapping bracts, extending and
floating on the surface at maturity (Fig. 13A). Each
female flower has three tepals, three recurved sepals,
erect petals and six branched styles. The ovary is
compressed, with several anatropous ovules. In dioecious Thalassia, the inflorescence is usually single;
each has a separate spathe on short shoots. Each unit
can be interpreted as a one-flower inflorescence.
Most Halophila species are dioecious, the exceptions being H. decipiens, H. beccarii, H. capricorni and H. sp. allied to H. ovalis from Indonesia
(Kuo, unpublished), which are monoecious. However, the flower formation in the three monoecious
Halophila species is different. Both male and female floral shoots of H. decipiens are produced at the
same rhizome nodes (Kuo et al., 1995) (Fig. 11A),
while either male or female floral shoots of H. beccarii (Parthasarathy et al., 1988, Muta Harah et al.,
1999), H. capricorni (Larkum, 1995) and Halophila
sp. being formed on separate rhizome nodes of the
same plants (Fig. 13C). Regardless whether they are
monoecious or dioecious, flowers of Halophila are
unisexual, almost always solitary, and enclosed by
two overlapping spathes (bracts) (Fig. 11B). In the
species with erect stems, e.g. H. tricostata, H. spinulosa, H. engelmanni, etc., flowers are produced
at each distal node of an erect stem and flowers
and fruits mature acropetally along the erect shoot
during the reproductive season (Kuo et al., 1993).
For the species without erect stems, e.g. H. ovalis,
H. stipulacea, H. decipiens, etc., flowers develop
and mature progressively at each node along the
rhizome branches. This results in the oldest fruits
being furthest from the youngest shoot apex (Kuo
and Kirkman, 1995). The male flower has three imbricate tepals, which enclose three anthers. At anthesis, the pedicel extends upwards and the tepals
become distinctly swollen and bright yellow, sometimes with pigments (Figs. 11A and 12A), then
the tepals open to release pollen from the anthers
(Fig. 12B). The entire male flower detaches from the
plant immediately after anthesis. The female flower
consists of an ovary with three parietal placentae
containing several to numerous ovules and a hypanthium extending into 2–6 filiform styles. After
anthesis, styles detach, but the hypanthium persists
(Fig. 13C).
3. Zosteraceae
In the Zosteraceae, the inflorescent shoots (known
as generative shoots) initiate as terminal or lateral
branches at rhizome nodes in all species in Zostera
as well as two species in Heterozostera (H. tasmanica and H. polychlamys) (see Kuo, 2005). Thus,
the mature reproductive shoot-bearing node usually
appears a few rhizome nodes behind the vegetative shoot-bearing node of the extending rhizome.
The mature generative shoot has repeated branching
with a conspicuous basal membranous prophyll at
each branch and bears one to three inflorescences
on each branch. Each generative shoot is normally
terminated with a generative branch in all Zostera
and Heterozostera species except in Z. caulescens
and H. nigricaulis and possibly H. chilensis. In
Z. caulescens, the generative shoot is terminated
with a sterile branch with several vegetative leaves,
resulting in this species growing up to 7 m long (Aioi
et al., 1997). H. nigricaulis and H. chilensis produce
rigid black erect stems, which bear an inconspicuous spadix amongst a tuft of leaves at the top of H.
nigricaulis (Kuo, 2005). Phyllospadix torreyi has a
prolonged generative shoot with several nodes bearing several inflorescences at the upper nodes. In contrast, the other four Phyllospadix species have a short
generative shoot with mostly one node bearing only
one, occasionally two, inflorescences.
The inflorescence in the Zosteraceae is called the
spathe, consisting of flowers formed on the flattened, spike-like axis known as the spadix and enveloped by a modified open leaf sheath known as
the spathal sheath. In the monoecious Zostera and
Heterozostera, two male flowers and one female
flower are arranged alternately in two longitudinal rows (Fig. 12C and D), while in the dioecious
Phyllospadix, either male or female flowers are arranged in two longitudinal rows. The male flower
has one stamen with two bilocular anthers (theca).
The female flower (gynoecium) has a single ovary
with one ovule, a short style and two fine stigmata (Fig. 12C), which protrude to the surface of
the spathal sheath along the overlapping wings at
J. Kuo and C. den Hartog
2. Hydrocharitaceae
In the Hydrocharitaceae, dioecious Enhalus has a
many-flowered male inflorescence on a short peduncle, enclosed by the leaf sheaths, usually referred to
as a spathe. Each mature flower is thinly pedicellate,
with six tepals and three stamens. At maturity they
break free and float in dense patches on the surface.
The female flower is solitary on a long peduncle and
is enclosed by two overlapping bracts, extending and
floating on the surface at maturity (Fig. 13A). Each
female flower has three tepals, three recurved sepals,
erect petals and six branched styles. The ovary is
compressed, with several anatropous ovules. In dioecious Thalassia, the inflorescence is usually single;
each has a separate spathe on short shoots. Each unit
can be interpreted as a one-flower inflorescence.
Most Halophila species are dioecious, the exceptions being H. decipiens, H. beccarii, H. capricorni and H. sp. allied to H. ovalis from Indonesia
(Kuo, unpublished), which are monoecious. However, the flower formation in the three monoecious
Halophila species is different. Both male and female floral shoots of H. decipiens are produced at the
same rhizome nodes (Kuo et al., 1995) (Fig. 11A),
while either male or female floral shoots of H. beccarii (Parthasarathy et al., 1988, Muta Harah et al.,
1999), H. capricorni (Larkum, 1995) and Halophila
sp. being formed on separate rhizome nodes of the
same plants (Fig. 13C). Regardless whether they are
monoecious or dioecious, flowers of Halophila are
unisexual, almost always solitary, and enclosed by
two overlapping spathes (bracts) (Fig. 11B). In the
species with erect stems, e.g. H. tricostata, H. spinulosa, H. engelmanni, etc., flowers are produced
at each distal node of an erect stem and flowers
and fruits mature acropetally along the erect shoot
during the reproductive season (Kuo et al., 1993).
For the species without erect stems, e.g. H. ovalis,
H. stipulacea, H. decipiens, etc., flowers develop
and mature progressively at each node along the
rhizome branches. This results in the oldest fruits
being furthest from the youngest shoot apex (Kuo
and Kirkman, 1995). The male flower has three imbricate tepals, which enclose three anthers. At anthesis, the pedicel extends upwards and the tepals
become distinctly swollen and bright yellow, sometimes with pigments (Figs. 11A and 12A), then
the tepals open to release pollen from the anthers
(Fig. 12B). The entire male flower detaches from the
plant immediately after anthesis. The female flower
consists of an ovary with three parietal placentae
containing several to numerous ovules and a hypanthium extending into 2–6 filiform styles. After
anthesis, styles detach, but the hypanthium persists
(Fig. 13C).
3. Zosteraceae
In the Zosteraceae, the inflorescent shoots (known
as generative shoots) initiate as terminal or lateral
branches at rhizome nodes in all species in Zostera
as well as two species in Heterozostera (H. tasmanica and H. polychlamys) (see Kuo, 2005). Thus,
the mature reproductive shoot-bearing node usually
appears a few rhizome nodes behind the vegetative shoot-bearing node of the extending rhizome.
The mature generative shoot has repeated branching
with a conspicuous basal membranous prophyll at
each branch and bears one to three inflorescences
on each branch. Each generative shoot is normally
terminated with a generative branch in all Zostera
and Heterozostera species except in Z. caulescens
and H. nigricaulis and possibly H. chilensis. In
Z. caulescens, the generative shoot is terminated
with a sterile branch with several vegetative leaves,
resulting in this species growing up to 7 m long (Aioi
et al., 1997). H. nigricaulis and H. chilensis produce
rigid black erect stems, which bear an inconspicuous spadix amongst a tuft of leaves at the top of H.
nigricaulis (Kuo, 2005). Phyllospadix torreyi has a
prolonged generative shoot with several nodes bearing several inflorescences at the upper nodes. In contrast, the other four Phyllospadix species have a short
generative shoot with mostly one node bearing only
one, occasionally two, inflorescences.
The inflorescence in the Zosteraceae is called the
spathe, consisting of flowers formed on the flattened, spike-like axis known as the spadix and enveloped by a modified open leaf sheath known as
the spathal sheath. In the monoecious Zostera and
Heterozostera, two male flowers and one female
flower are arranged alternately in two longitudinal rows (Fig. 12C and D), while in the dioecious
Phyllospadix, either male or female flowers are arranged in two longitudinal rows. The male flower
has one stamen with two bilocular anthers (theca).
The female flower (gynoecium) has a single ovary
with one ovule, a short style and two fine stigmata (Fig. 12C), which protrude to the surface of
the spathal sheath along the overlapping wings at