|Plant-Life in a Tidal Salt Marsh
Glasswort (Goosefoot family, Chenopodiaceae)
Glassworts are so-called because in 16th century England their ashes were used as a source of
sodium salts in making soda-based glass. Their high salt content derives from the fact that they
are halophytes - plants that grow in very salty conditions. The glasswort above is growing on a
tidal salt-marsh, which is part of an extensive river estuary.
Glassworts can be divided into two genera: Salicornia, the annual glassworts, and Sarcocornia,
the perennial glassworts. The one illustrated here clearly has woody basal stems and is the
perennial glasswort Sarcocornia perennis.
The prostrate (lying horizontally on the substrate) woody and branched main stems are no more
than about 3 mm wide. Some of the nodes give it adventitious roots which anchor in the substrate
and clones of the plant can spread asexually in this way. The woody stems thus form runners or
rhizomes. The aerial stems, which may erect or decumbent (lying down) are little branches and
consist of swollen cylindrical or club-shaped internodes and reach 8 to 22 cm in length
(occasionally up to 30 cm).
Each node of the aerial stems has a pair of cone-shaped and reduced leaves, whose swellings give the stems an
articulated (jointed) appearance. The leaves actually form the succulent outer covering of the stems. Each leaf is
fused at the edges to its partner in each opposite pair of leaves. Developmentally, this leaf sheaf is also fused with
the stem. Underneath this succulent coating the epidermis and an underlying endodermis of the stem persist as
the outermost layer of the true stem. When the leaves fall away, a woody stem is left behind. The wood is formed
by secondary growth. The aerial internodes contain a layer of photosynthetic parenchyma beneath the epidermis
and inside of this there is water-storing parenchyma, giving the plant its succulent appearance. Inside this is the
endodermis, a layer of thick-walled cells enclosing the vascular tissue, which consists of about half a dozen
(primary) vascular bundles (xylem and phloem) enclosed in parenchyma. (See: plant cell types.)
Secondary growth (development of wood and thickening) in older stems is anomolous (not showing the more
common pattern of secondary growth) as it is in the Goosefoot family generally. A layer of cambium beneath the
endodermis produces xylem to the inside and secondary cortex (parenchyma cells, presumably with phloem) to the
outside (beneath the endodemis). There may also be photosynthetic cells beneath the endodermis in some
populations. The woody horizontal stems contain a small, sometimes hollow, central pith enclosing the primary
vascular strands/bundles and some photosynthetic tissue. This is surrounded by the secondary xylem (lignified)
again with some photosynthetic parenchyma (i.e. chlorenchyma). Outside the cambium, green chlorenchyma is
produced in three layers: compact and thin inner and outer layers sandwiching a thicker middle layer of looser
cells with large air spaces (presumably primarily to supply carbon dioxide for photosynthesis). Outside this, a
second cambium produces dark brown cells which rupture, these are the bark cells, which push off the outer layers
of stem tissue.
Inflorescence and Flowers
The inflorescence (flower-bearing shoot) is a spike-like thryse. A thyrse is a main monopodial axis giving off
sympodial branches (see plant architecture) and each branch is a cyme (a sympodial inflorescence). The main
axis shows indeterminate growth, growing throughout the growing season, but the branches are determinate,
only growing so far before stopping. Each fertile segment produces 3 flowers (occasionally 4 or 5) each group of
three making up one cyme. Each such cyme is subtended by the tip of the bract-like leaf from the segment below.
The flowers appear in from August to September and each consists of a disc with a pore in the centre through
which the (usually single) stamen emerges. The flowers are usually bisexual and are protogynous (the female
parts ripen first followed by the male parts, hence reducing the risk of self-pollination). Each ovary, deep within the
flower, contains a single ovule which produces a single seed. The seed is enclosed in a thin testa and this is
surrounded by a thin fruit-wall (pericarp) which is surrounded by 3 to 4 fleshy lobes of the perianth
(non-reproductive parts, i.e. sepals/petals).
As we shall see, glasswort biology is at least as curious as the plant's name. They are clearly
adapted to dehydrating conditions. Although water is abundant here, the water is saline and that
makes it hard for plants to extract enough water from it. The stems are succulent and the leaves
are inconspicuous, so that less water is lost in the salty coastal winds. Stomatal density is low in
this species (about 30 stomata per square mm) to reduce water loss by transpiration (see water
transport in plants).
The green photosynthetic shoots turn yellowish, orange-brown or reddish with age. The main
stem and some of the branches end in flowering spikes (1 to 4 cm, or up to almost two inches in
length). The plant occurs in gravely or sandy soil about 1 to 2 m above the water-line.
The flowers sit in cavities in the stem which are exposed when the flowers are shed. The fruit ripen in October and
are shed as the inflorescence segments senesce and disintegrate. The aerial stems retain green segments
throughout the winter and buds produce new branch segments in spring. Sarcocornia is a chamaephyte: a plant
which produces dormant buds just above ground level. Note the groups of three disc-like flowers.
Seedlings have two fleshy cotyledons (embryonic leaves) which fuse together at their side margins to enclose the
hypocotyl (region of embryonic/seedling stem between radicle and cotyledons, consists of root and stem tissue) in
a fleshy sheath (pseudocortex). The radicle (embryonic root) germinates first and produces a ring of root hairs to
anchor it in the loose substrate.
Review Q. How is Sarcocorrnia perennis adapted to life in salt marshes?
Other members of the Goosefoot family found growing with the glassworts, all within the same area of a few
square meters, were: Atriplex littoralis (Grass-leaved Orache), Atriplex portulacoides (Sea-purslane), Sueda
maritima (Annual Sea-blite). Also found here was Spergularia media (Greater Sea-spurrey). As we look at these
other plants, ask yourself: how are they adapted as halophytes?
Bibliography and Further Reading
Davy, A.J., G.F. Bishop, H. Mossman, S. Redondo-Gomez, J.M. Castillo, E.M. Castellanos, T. Luque
and M.E. Figueroa, 2006. Biological Flora of the British Isles: Sarcocornia perennis (Miller) A.J. Scott.
Journal of Ecology 94: 1035-1048.
Telenius, A. 1992. Seed heteromorphism in a population of Spergularia media in relation to the
ambient vegetation density. plant Biology 41: 305-318.
Telenius, A. and P. Torstensson, 1989. The seed dimorphism of of Spergularia marina in relation to
dispersal by wind and wqater. Oceologia 80: 206-210.
Salt marshes are challenging habitats for plants and the plants that thrive their have unusual
adaptations, making them fascinating subjects of study. Here we review a few such species
growing together as a single community on a single salt marsh.
Greater Sea-spurrey (Campion Family, Caryophyllaceae)
Grass-leaved Orache (Atriplex littoralis)
Annual Sea-blite (Suaeda maritima)
Sea-purslane (Atriplex portulacoides)
Sea Beet (Beta vulgaris)
Above: Pairs of trianglar bracteoles, covered in protuberances and trichomes, enclosing the female flowers.
Under the microscope, much of the plant and the pair of triangular bracteoles in particular, are covered with many
trichomes which look like beautiful tiny stalked vases of crystal glass (the photograph does not fully capture the
spectacle as seen under the microscope by eye). These are salt bladders or salt glands. They accumulate excess
salt that the plant has absorbed from the salty soil and secreted. They swell with salty liquid before bursting to release
their salt to the outside. This presumably accounts for the mealy appearance of many Oraches (waxy secretions can
also account for mealyness in plants).
The genus Atriplex includes the Oraches and Sea-purslane. These plants have very reduced flowers which reveal
their secrets under the microscope! Oraches are often fleshy and somewhat succulent in appearance. In Oraches the
male and female flowers are separate. The female flowers lack sepals and are enclosed within a pair of triangular
bracteoles that enlarge in the fruit. Grass-leaved Orache is an erect annual up to 1 m tall with narrow 'lanceolate'
(narrow and pointed) leaves. It occurs on coasts, shores and salt-marsh edges, sea walls and spreads inland along
This plant has striking, though very small (8 to 12
mm across) pinkish-white flowers (the camera has
made them look whiter than in life but a pink tinge is
visible). In Greater Sea-spurrey, the stems are
creeping to ascending and up to 30 cm long. This
species is perennial. The leaves are fleshy and
Seed dispersal shows some fascinating adaptations!
The fruit ('seeds') shown left, are distinguishable
from other species of Sea-spurrey in usually having
a large membranous wing around the entire
circumference. This aids dispersal of the enclosed
seed in open habitats. However, some individual
flowers may produce wingless fruit and some may
produce both. It has been shown that these plants
will produce more winged seeds if they are growing
in open habitats, where wind can easily scatter the
seeds (Telenius, 1992). However, in crowded
habitats, winged seeds are more likely to be trapped
by vegetation while wingless seeds disperse more
easily (Telenius and Torrstensson, 1989) and so the
plants produce fewer winged seeds when crowded!
This plant is a perennial (unlike other Oraches) and is a low shrub with a mealy
appearance. The bracteoles enclose the female flowers and developing fruits and
have broad 3-lobed tips and are fused together over much of their length (protecting
the sexual parts from dehydration).
Suaeda maritima is an annual salt-marsh plant with succulent
leaves (like half cylinders) with pointed tips and slightly tapered
bases. (The related perennial Shrubby sea-blite, Suaeda vera
(Suaeda fruticosa) is larger and has more cylindrical leaves with
rounded tips and less tapered bases). The stems are either
green or flushed red and may be upright or prostrate.
Sea Beet is similar in superficial appearance to a
Goosefoot or an Orache, with spikes of fairly
inconspicuous and dull-coloured flowers. However,
The flowers are more conspicuous to the naked eye
with the 5 fleshy sepals quite distinct. The coastal
form is usually subspecies maritimum. The cultivated
form, which produces the swollen taproot that is eaten
as beetroot, is subspecies vulgaris, which can
sometimes also be found along coasts.
Left: a series of three close-up photomicrographs in different
focal planes. Note the 5 fleshy sepals on each flower.
Bottom: a red-tinged and all-green plant for comparison.
Article created: 13 Sep 2016