14
C. den Hartog and J. Kuo
which bear on the top a pseudo-whorl of 4–10 sheathing petiolate leaves. It contains one delicate species,
H. beccarii, which shows some slight morphological
variation. This species is widely distributed along
the southern shores of the South Chinese Sea, the
Gulf of Thailand, the Gulf of Bengal, and the Indian coast of the Arabian Sea. So far, it has not been
recorded from Indonesia and Australia. It reaches its
northern limit in south China and Taiwan. The
species is usually associated with mud flats and mangrove communities and often exposed at low tide.
The fourth section of the genus, sect. Americanae
Ostenfeld is characterized by having distinct erect
lateral shoots with two scales about half way up
and a pseudo-whorl of 4–8 leaves at the top. It contains two morphologically fairly distinct dioecious
species, H. engelmanni, which occurs in the Gulf of
Mexico and the northern Caribbean (Cuba), and H.
baillonii, which has been recorded from the southern Caribbean, the Pacific coast of Central America,
and from Brazil.
The fifth section of the genus, sect. Tricostatae
Greenway, consists of fragile plants with herbaceous, elongated erect lateral shoots bearing at each
node a rosette of (2-) 3 leaves. The section contains
only one annual, dioecious species, H. tricostata,
which is restricted in its occurrence to north-eastern
Australia.
Ruppiaceae
Ruppiaceae Horaninov, Prim. Lin. Syst. Nat. (1834)
46; nom. cons.
Typus: Ruppia L.
In earlier editions of the International Code of
Botanical Nomenclature the name of the family was
ascribed to ‘Horaninov ex Hutchinson, Fam. Fl. Pl.2
(1934) 48’.
Monoecious, annual or perennial submerged
aquatic herbs. Rhizomes creeping, monopodial, but
often also laterally branched; in annual species often
considerably reduced. Central cylinder with a vascular strand, with in the centre a xylem canal; cortex
consisting of parenchyma with a circle of air channels. From each node 1 or 2 unbranched roots with
numerous very fine root-hairs arise, as well as an
erect shoot. Shoots very short to up to more than
2.5 m high, in the latter case profusely branched. Internodes elongate, variable in length. Leaves linear,
distichous, with very many tannin cells; leaf-sheath
amplexicaulous, with on either side a slightly auriculate membranous flap; flaps overlapping; no ligule;
leaf-blade with only a midrib; margins smooth, but
near the leaf-tip irregularly serrulate; on either side
of the midrib a wide air lacuna. Uppermost leaves of
generative branches opposite.
Inflorescence terminal, consisting of a peduncle,
which has at its top a two-flowered spike. Peduncle
arising from between the inflated sheathing bases of
the two apical leaves; short, erect and sometimes
thickened after flowering, or thin and varying in
length from a few cm to more than a metre (often
still lengthening itself by cell stretching during the
flowering process), and in most of the species after
flowering coiled or spirally contracted, pulling the
ripening fruits down to the bottom. Flowering takes
place at the water surface, or submerged. Flowers
placed at opposite sides of the axis, but very closely
together, bisexual, without a perianth, consisting of
two opposite stamens and 4-numerous carpels. Stamens consisting of one (sub-)sessile, bilocular anther; connective broad with at each side a theca; thecae circular to broad-elliptic, extrorsely dehiscent,
shed after emission of pollen. Pollen boomerangshaped with reticulate exine. Pollination aerial, on
the water surface, or under water in an air bubble. Carpels free, sessile or subsessile; ovary ovoid;
no style, but a small peltate disc-like stigma. In
most species a podogyne develops at the base of
each carpel after fertilization, giving the infructescence an umbellate appearance. Ovule solitary, pendulous, campylotropous. Fruit an achene, sessile or
stalked (podogyne and fruit form a morphological
entity without abscission zone), symmetric to very
asymmetric; exocarp spongy, soon decomposing;
endocarp hard, persistent with beak and usually a
podogyne; at the apical part of the endocarp a small
foramen occurs, the shape of which has diagnostic
value at the species level.
The family contains only one genus, Ruppia.
Ruppia L. Sp. Pl. (1753) 127.
Type species: Ruppia maritima L.
Widely distributed in temperate and tropical regions
all over the world, in the northern hemisphere even
extending beyond the polar circle, and from sea
level up to 4000 m altitude. The greatest species
diversity seems to occur in mediterranean-type climates, in poikilohaline environments. It occurs in
brackish waters as well as in continental salt waters, but also in highly diluted fresh waters and in
C. den Hartog and J. Kuo
which bear on the top a pseudo-whorl of 4–10 sheathing petiolate leaves. It contains one delicate species,
H. beccarii, which shows some slight morphological
variation. This species is widely distributed along
the southern shores of the South Chinese Sea, the
Gulf of Thailand, the Gulf of Bengal, and the Indian coast of the Arabian Sea. So far, it has not been
recorded from Indonesia and Australia. It reaches its
northern limit in south China and Taiwan. The
species is usually associated with mud flats and mangrove communities and often exposed at low tide.
The fourth section of the genus, sect. Americanae
Ostenfeld is characterized by having distinct erect
lateral shoots with two scales about half way up
and a pseudo-whorl of 4–8 leaves at the top. It contains two morphologically fairly distinct dioecious
species, H. engelmanni, which occurs in the Gulf of
Mexico and the northern Caribbean (Cuba), and H.
baillonii, which has been recorded from the southern Caribbean, the Pacific coast of Central America,
and from Brazil.
The fifth section of the genus, sect. Tricostatae
Greenway, consists of fragile plants with herbaceous, elongated erect lateral shoots bearing at each
node a rosette of (2-) 3 leaves. The section contains
only one annual, dioecious species, H. tricostata,
which is restricted in its occurrence to north-eastern
Australia.
Ruppiaceae
Ruppiaceae Horaninov, Prim. Lin. Syst. Nat. (1834)
46; nom. cons.
Typus: Ruppia L.
In earlier editions of the International Code of
Botanical Nomenclature the name of the family was
ascribed to ‘Horaninov ex Hutchinson, Fam. Fl. Pl.2
(1934) 48’.
Monoecious, annual or perennial submerged
aquatic herbs. Rhizomes creeping, monopodial, but
often also laterally branched; in annual species often
considerably reduced. Central cylinder with a vascular strand, with in the centre a xylem canal; cortex
consisting of parenchyma with a circle of air channels. From each node 1 or 2 unbranched roots with
numerous very fine root-hairs arise, as well as an
erect shoot. Shoots very short to up to more than
2.5 m high, in the latter case profusely branched. Internodes elongate, variable in length. Leaves linear,
distichous, with very many tannin cells; leaf-sheath
amplexicaulous, with on either side a slightly auriculate membranous flap; flaps overlapping; no ligule;
leaf-blade with only a midrib; margins smooth, but
near the leaf-tip irregularly serrulate; on either side
of the midrib a wide air lacuna. Uppermost leaves of
generative branches opposite.
Inflorescence terminal, consisting of a peduncle,
which has at its top a two-flowered spike. Peduncle
arising from between the inflated sheathing bases of
the two apical leaves; short, erect and sometimes
thickened after flowering, or thin and varying in
length from a few cm to more than a metre (often
still lengthening itself by cell stretching during the
flowering process), and in most of the species after
flowering coiled or spirally contracted, pulling the
ripening fruits down to the bottom. Flowering takes
place at the water surface, or submerged. Flowers
placed at opposite sides of the axis, but very closely
together, bisexual, without a perianth, consisting of
two opposite stamens and 4-numerous carpels. Stamens consisting of one (sub-)sessile, bilocular anther; connective broad with at each side a theca; thecae circular to broad-elliptic, extrorsely dehiscent,
shed after emission of pollen. Pollen boomerangshaped with reticulate exine. Pollination aerial, on
the water surface, or under water in an air bubble. Carpels free, sessile or subsessile; ovary ovoid;
no style, but a small peltate disc-like stigma. In
most species a podogyne develops at the base of
each carpel after fertilization, giving the infructescence an umbellate appearance. Ovule solitary, pendulous, campylotropous. Fruit an achene, sessile or
stalked (podogyne and fruit form a morphological
entity without abscission zone), symmetric to very
asymmetric; exocarp spongy, soon decomposing;
endocarp hard, persistent with beak and usually a
podogyne; at the apical part of the endocarp a small
foramen occurs, the shape of which has diagnostic
value at the species level.
The family contains only one genus, Ruppia.
Ruppia L. Sp. Pl. (1753) 127.
Type species: Ruppia maritima L.
Widely distributed in temperate and tropical regions
all over the world, in the northern hemisphere even
extending beyond the polar circle, and from sea
level up to 4000 m altitude. The greatest species
diversity seems to occur in mediterranean-type climates, in poikilohaline environments. It occurs in
brackish waters as well as in continental salt waters, but also in highly diluted fresh waters and in