Chapter 1 Taxonomy of Seagrasses
3
without a perianth. Pollen boomerang-shaped,
free. . . . . . . . . . . . . . . . . . . . . . . . . . . . Ruppiaceae
3a. Inflorescence cymose, with the branches ending
in ‘spikes’. Flowers actinomorphous, bisexual,
consisting of three stamens with large connectives and one ovary with a sessile, disc-shaped
stigma. Tannin cells present . . . Posidoniaceae
3b. Flowers simple, unisexual, consisting of 1 or
2 ovaries or a single stamen, arranged within
a specialized inflorescence or just single or in
pairs. Stamens with reduced connectives. Ovary
bearing a style with 1, 2, or 3 stigmata. Tannin
cells present or absent. . . . . . . . . . . . . . . . . . . . . 4
4a. Flowers, unisexual or bisexual, arranged in two
rows on one side of a flattened spadix enclosed
in a spathe. Stamens consisting of two extrorsely
dehiscent thecae, connected by a ridge-like connective. Ovary horizontally placed, with a short
thick style and two stigmata shed after flowering. Tannin cells absent. . . . . . . . . . Zosteraceae
4b. Flowers unisexual, solitary, in pairs or as a cluster on a common pedicel, terminating a short
branch. Tannin cells present or absent. . . . . . . 5
5a. Leaves with 3-many nerves and numerous tannin cells. Flowers unisexual, without a perianth, solitary or in pairs, or arranged within
a cymose inflorescence. Male flowers sessile
or stalked consisting of two, dorsally connate anthers. Pollen filiform. Ovaries in pairs
with 1, 2, or 3 filiform styles. Tannin cells
present. . . . . . . . . . . . . . . . . . . . .Cymodoceaceae
5b. Leaves very narrow, with only one central nerve,
without tannin cells. Flowers terminal. Male
flower consisting of a stalked anther, often
with a small scaly perianth. Female flower consisting of 1–8 free carpels on a joint pedicel, surrounded by a scaly perianth. Styles
peltate or feathery. Pollen spherical. Tannin cells
absent . . . . . . . . . . . . . . . . . . . . Zannichelliaceae
III. Seagrasses: General Taxonomy
Zosteraceae
Zosteraceae Dumortier, Anal. Fam. Pl. (1829) 65,
66; nom. cons.
Typus: Zostera L.
Monoecious or dioecious marine plants. Rhizome
creeping, herbaceous, monopodial or sympodial;
when monopodial with two vascular bundles in
the cortical layer and at each node two or more
unbranched roots and a leaf or a prophyllum, with
in its axil a short lateral branch bearing a bunch of
distichously arranged leaves; roots and rhizomatic
leaves alternating; when sympodial (Heterozostera)
with 4–10 vascular bundles in the cortical layer and
at each node two unbranched roots and an erect
stem with distichously arranged leaves and without roots at its nodes. Leaves linear, differentiated
into a sheath and a blade with a ligule. Leaf sheath
compressed, amplexicaulous, ligulate, either membranous and tubular or open and then auriculate
with scarious flaps. Leaf blade linear, with 3–9(11) parallel nerves and with several accessory bundles between every two of these; nerves connected
by perpendicular cross-veins, margin entire, sometimes slightly denticulate or provided with a fringe
of uncolored, sclerenchymatic ‘fin cells’; tip variable in shape. Generative shoot terminal or lateral,
sympodial, erect, consisting of a panicle of rhipidia,
but often reduced to a single rhipidium; each rhipidium consisting of 2–5 spathes, but sometimes
reduced to a single one; peduncle of each spathe
partially coalescent with the axis from which it
springs or completely free. Spathe consisting of a
sheath and a blade; spathal sheath ligulate, open
with two more or less overlapping, auriculate flaps,
enclosing a sessile or stalked spadix on the dorsal side of which in Zostera and Heterozostera the
male flowers (stamens) and female flowers (gynoecia) are alternately arranged. Stamens consisting
of two free, bilocular, extrorsely length-wise dehiscent, deciduous thecae connected by a reduced
ridge-like connective, without a filament; pollen
confervoid. Retinacula intramarginal, one beside
each stamen, sometimes absent (Zostera subgen.
Zostera); on the female spadices of Phyllospadix
alternating with the gynoecia. Gynoecium consisting of a superior, horizontally placed, ellipsoid or
crescent-shaped ovary with a short thick style and
two stigmata of which the distal parts are shed after fertilization; ovule 1, orthotropous, pendulous.
Fruit indehiscent, ovoid or ellipsoid with scarious
pericarp or else crescent-shaped with the pericarp
differentiated into a soft exocarp and a hard fibrous endocarp. Seed 1, ovoid or ellipsoid; embryo macropodous consisting for the larger part of
the hypocotyl, which is ventrally grooved; in this
groove the short, straight, tubular cotyledon which
serves as a sheath for the plumula; primary root
3
without a perianth. Pollen boomerang-shaped,
free. . . . . . . . . . . . . . . . . . . . . . . . . . . . Ruppiaceae
3a. Inflorescence cymose, with the branches ending
in ‘spikes’. Flowers actinomorphous, bisexual,
consisting of three stamens with large connectives and one ovary with a sessile, disc-shaped
stigma. Tannin cells present . . . Posidoniaceae
3b. Flowers simple, unisexual, consisting of 1 or
2 ovaries or a single stamen, arranged within
a specialized inflorescence or just single or in
pairs. Stamens with reduced connectives. Ovary
bearing a style with 1, 2, or 3 stigmata. Tannin
cells present or absent. . . . . . . . . . . . . . . . . . . . . 4
4a. Flowers, unisexual or bisexual, arranged in two
rows on one side of a flattened spadix enclosed
in a spathe. Stamens consisting of two extrorsely
dehiscent thecae, connected by a ridge-like connective. Ovary horizontally placed, with a short
thick style and two stigmata shed after flowering. Tannin cells absent. . . . . . . . . . Zosteraceae
4b. Flowers unisexual, solitary, in pairs or as a cluster on a common pedicel, terminating a short
branch. Tannin cells present or absent. . . . . . . 5
5a. Leaves with 3-many nerves and numerous tannin cells. Flowers unisexual, without a perianth, solitary or in pairs, or arranged within
a cymose inflorescence. Male flowers sessile
or stalked consisting of two, dorsally connate anthers. Pollen filiform. Ovaries in pairs
with 1, 2, or 3 filiform styles. Tannin cells
present. . . . . . . . . . . . . . . . . . . . .Cymodoceaceae
5b. Leaves very narrow, with only one central nerve,
without tannin cells. Flowers terminal. Male
flower consisting of a stalked anther, often
with a small scaly perianth. Female flower consisting of 1–8 free carpels on a joint pedicel, surrounded by a scaly perianth. Styles
peltate or feathery. Pollen spherical. Tannin cells
absent . . . . . . . . . . . . . . . . . . . . Zannichelliaceae
III. Seagrasses: General Taxonomy
Zosteraceae
Zosteraceae Dumortier, Anal. Fam. Pl. (1829) 65,
66; nom. cons.
Typus: Zostera L.
Monoecious or dioecious marine plants. Rhizome
creeping, herbaceous, monopodial or sympodial;
when monopodial with two vascular bundles in
the cortical layer and at each node two or more
unbranched roots and a leaf or a prophyllum, with
in its axil a short lateral branch bearing a bunch of
distichously arranged leaves; roots and rhizomatic
leaves alternating; when sympodial (Heterozostera)
with 4–10 vascular bundles in the cortical layer and
at each node two unbranched roots and an erect
stem with distichously arranged leaves and without roots at its nodes. Leaves linear, differentiated
into a sheath and a blade with a ligule. Leaf sheath
compressed, amplexicaulous, ligulate, either membranous and tubular or open and then auriculate
with scarious flaps. Leaf blade linear, with 3–9(11) parallel nerves and with several accessory bundles between every two of these; nerves connected
by perpendicular cross-veins, margin entire, sometimes slightly denticulate or provided with a fringe
of uncolored, sclerenchymatic ‘fin cells’; tip variable in shape. Generative shoot terminal or lateral,
sympodial, erect, consisting of a panicle of rhipidia,
but often reduced to a single rhipidium; each rhipidium consisting of 2–5 spathes, but sometimes
reduced to a single one; peduncle of each spathe
partially coalescent with the axis from which it
springs or completely free. Spathe consisting of a
sheath and a blade; spathal sheath ligulate, open
with two more or less overlapping, auriculate flaps,
enclosing a sessile or stalked spadix on the dorsal side of which in Zostera and Heterozostera the
male flowers (stamens) and female flowers (gynoecia) are alternately arranged. Stamens consisting
of two free, bilocular, extrorsely length-wise dehiscent, deciduous thecae connected by a reduced
ridge-like connective, without a filament; pollen
confervoid. Retinacula intramarginal, one beside
each stamen, sometimes absent (Zostera subgen.
Zostera); on the female spadices of Phyllospadix
alternating with the gynoecia. Gynoecium consisting of a superior, horizontally placed, ellipsoid or
crescent-shaped ovary with a short thick style and
two stigmata of which the distal parts are shed after fertilization; ovule 1, orthotropous, pendulous.
Fruit indehiscent, ovoid or ellipsoid with scarious
pericarp or else crescent-shaped with the pericarp
differentiated into a soft exocarp and a hard fibrous endocarp. Seed 1, ovoid or ellipsoid; embryo macropodous consisting for the larger part of
the hypocotyl, which is ventrally grooved; in this
groove the short, straight, tubular cotyledon which
serves as a sheath for the plumula; primary root