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
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 apparently has a  woody basal stem suggesting that it is the
perennial glasswort Sarcocornia perennis. However, in annual forms when the leaves die and are shed near the older and more shaded bases of stems and branches the tough xylem core  and some secondary thickening can make the stems look woody and this could be an annual Salicornia. Glassworts are tricky! We shall have a closer look below and see if we can determine this specimen.

Sarcocornia perennis The prostrate (lying horizontally on the substrate) woody and branched main stems of perennial glasswort 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).

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.

glasswort up close
glasswort up close
Plant-Life in a Tidal Salt Marsh
Glasswort (Goosefoot family, Chenopodiaceae)
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 bracts have translucent margins which are often described as scarious (dry and papery) but are generally fleshy despite their papery appearance. The flowers appear from August to September and each consists of a disc (of 3 to 4 fused fleshy tepals) with a pore in the center 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, but see below). In some species the central flower of each group is bisexual, the two lateral flowers male. Each ovary, deep within the flower, contains a single ovule with a style and 2 to 3-lobed stigma, which may also emerge through the pore but usually at a different time to the stamen. The ovary 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 the 3 to 4 fleshy lobes of the perianth (non-reproductive parts, i.e. sepals/petals or tepals).
Above: Salicornia. 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. In contrast, the Perennial Glasswort, Sarcocornia perennis, is a perennial chamaephyte: a plant which produces dormant buds just above ground level. Note the groups of three disc-like flowers. In Salicornia these flowers are arranged in an obvious triangle with the two lateral flowers below the central flower. The specimen on the left is probably Salicornia ramosissima, Purple Glasswort. Purple Glasswort often has a reddish or purple tinge, but so can other species of glasswort so we have to consider other characters as discussed below.

Each pollinated flower may produce a single fruit. The fruit is compressed and membranous and enclosed in the closed calyx which is either wingless or with a small wing. 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 are glassworts 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
(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?


Above: this is early in the season for glassworts (late July) and the flowering shoots on this specimen have only just begun to develop making it hard to determine this specimen. The full colour also develops later with species variously turning yellowish, orange or reddish-purple according to the amount of anthocyanins produced.

Glasswort 'gone over'

Above: This is late in the season (late December) and this glasswort finished flowering. Click images for full size.


These glassworts have a beaded appearance (due to the convex segments) and short branches mostly less than 2 cm in length and are quite strongly tinged reddish/purple. This makes me suspect that this is Salicornia ramosissima, the Purple Glasswort, a very variable annual. However, Sarcocornia perennis (Perrenial Glasswort) is another possibility since this also has short branches and a beady appearance.


These plants are tending towards being prostrate, which is again compatible with either Purple or Perennial Glasswort. The base of the stem certainly looks woody and I would have previously considered this to suggest Perennial Glasswort. However, when the fleshy leaves whither and fall from the stems of annuals then they can appear woody at the base. The stem is not visibly rooting at the nodes as one would expect for Perennial Glasswort, which can also become yellowish to reddish. (The red pigment in glassworts generally develops as the plant matures). Perennial Glasswort also typically has some 'sterile shoots' not bearing flowers and so noticeably much narrower - all the shoots here look fertile. Also, there was little visible trace of the glassworts in winter suggesting they were annuals that had died away completely. Purple Glasswort has been recorded before in this area, but perennial glasswort has also been recorded within one kilometer of here. This area is completely submerged during spring high tides. Good external link with nice photographs of perennial glasswort:


The red-purple colouration of Purple Glasswort increases into the season and by late summer / early Autumn they are reddest, but some individuals remain green. Although some Purple Glassworts have prostrate stems, others are erect.



A more upright (erect) specimen. Salicornia ramosissima is recorded as varying from erect to procumbent (trailing along the ground, i.e. prostrate stems) or decumbent (stems prostrate but turing up to become erect or ascending at the tips). It has been recorded that prostrate growth in glassworts may disappear in cultivation and so may be an adaptation to local conditions rather than a fixed genetic trait.


A close look at the size and number of flowers on the shoots of glassworts is informative. For these specimens:


Recall the each flower is a fleshy disc (of 3 to 4 fused tepals) with a central pore. The obviously smaller lateral flowers, almost completely covered by the bract, the convex bead-like segments and the strong reddish tinge are all compatible with Salicornia ramosissima. This plant occurs mostly in the middle and upper parts of salt marshes, as here. Note the small triangular scale leaf/bract with a papery (scarious) margin beneath the group of three flowers.

A distinctly different second type of glasswort also occurred in the vicinity, albeit in much smaller numbers. This plant was yellow-green with no obvious purple tinge in these specimens, the branches were longer (3 cm plus) and less beaded in appearance as the segments were more cylindrical and the plants were erect in habit.


The lateral flowers are not much smaller than the central one, being more than half its width. My conclusion is that this is Salicornia fragilis or Yellow Glasswort (which can sometimes be tinged red but usually turns yellow-green to yellow). Checking the distribution database for the local area, both these species: Salicornia ramosissima and Salicornia fragilis were recorded in this area recently and no others. Yellow Glasswort occurs mainly on the lower parts of saltmarshes, such as along runnels.



Above and below: Salicornia fragilis. Note the more-or-less cylindrical spikes. The terminal spike has 6-15 (occasionally up to 22) fertile segments. Actually the specimen above is a bit ambiguous and could be Salicornia dolichostachya (see below).



More Glasswort Species

Globally Salicornia glassworts are distributed in the North temperate zone, northern subtropical and subarctic boreal regions and in the southern hemisphere they are restricted to South Africa. Sarcocornia is distributed in warm temperate and subtropical regions. The following discussion concerns glassworts found in the British isles, particularly those on the south-east coast.

Glassworts are notoriously difficult to determine! I found it helpful to seek expert instruction from glasswort experts. However, there are always glasswort plants that defy classification, sometimes because they are immature and sometimes because their morphological features do not fall neatly into either species according to keys. First of all, separating Sarcocornia perennis (Perennial Glasswort) from Salicornia is relatively straightforward.


Above: Sarcocornia perennis is perennial and produces a long woody stem which is horizontal for the most part (prostrate). However, the annual Salicornia may also produce a stem with a woody base due to secondary growth, and the stem of Sarcocornia perennis, which may be up to 1 m in length, is largely beneath the soil surface as a thin rhizome and not readily visible. Thus, looking for a woody stem is likely to confuse, but Sarcocornia perennis is extremely hard to uproot whereas the annual forms are easily lifted out of the soil whole. However, the presence of sterile shoots (bearing no flowers) in Sarcocornia perennis is a clear distinguishing feature: they can be seen in the above photo as very slender shoots, whereas the fertile shoots are thicker and more knobbly. The flowers occur in opposite groups of three and in Sarcocornia perennis the three are arranged more-or-less in a straight line and are similar in size (the central flower may be slightly uppermost but the two laterals never touch each other beneath the central flower and the central flower is generally slightly larger) whereas in Salicornia the flowers form a distinct triangle with the central flower uppermost and with the two laterals sometimes touching. Click the photo above for full size and zoom in to see the flowers.


Above: Sarcocornia perennis; note the anthers visible protruding from the central pores of some of the flowers.

Sarcocornia perennis also tends to occur higher up towards the top of salt marshes, though its distribution overlaps with Salicornia. Salicornia species are annuals and can be split into two principal groups within a single geographical region: the diploid species (2n = 18 chromosomes) and the tetraploid species. The diploids consist of: Salicornia pusilla, also called Salicornia disarticulata (although it is not entirely certain that these two are in fact the same species) and the Salicornia europaea aggregate (agg.) of species. S. pulsilla is readily told apart from other Salicornia since its flowers occur singly and not in groups of three and forms narrow shoots.


Above: Salicornia disarticulata (= S. pusilla) the One-flowered Glasswort - a population of small plants which characteristically turn orange-red or purplish-pink when mature and may be non-branched or much branched. Click image for full size and zoom to see the single flowers. Below: close-up of a short branch (typical of the population in this region) showing the single flowers in opposite pairs with one pair per segment. Where Salicornia ramosissima grows nearby some specimens resembling One-flowered Glasswort will have a variable 1, 2 or 3 flowers on each segment with segments bearing different numbers of flowers being found on the same plant. This is the hybrid Salicornia disarticulata x S. ramosissima (S. x marshallii). Occasionally single flowers may occur in other species, but in S. disarticulata this trait is genetic.


The Salicornia europaea agg. in this region consists of S. ramosissima (Purple Glasswort), S. europaea (Common Glasswort although not by any means as common as the Purple Glasswort, though some consider these two to be the same species) and S. obscura (Glaucous Glasswort) . Purple Glasswort occurs mainly in the middle and upper saltmarsh and are often (though not always) flushed reddish-purple by late summer / early autumn. In these forms the flowers occur in triangular arrangements of three, with two opposite pairs present on each segment (and alternating with pairs on adjacent segments). The scale leaves (bracts) form obvious triangular collars with relatively wide scarious (papery) margins. The segments are usually strongly convex, giving the shoots a beaded appearance.

The tetraploid species (4n = 36) in Britain consist (at least) of the Salicornia procumbens aggregate of species: S. emerici (Shiny Glasswort), S. fragilis and S. dolichostachya. Salicornia fragilis and S. dolichostachya occur typically in runnels and on the lower parts of saltmarshes. Also found in similar locations are forms that appear intermediate between S. fragilis and S. ramosissima, having the colour and branching habit of fragilis but the convex fertile segments and unequal flower size of ramosissima. These could be hybrids, though the difference in ploidy in the parental species (fragilis being tetraploid and ramosissima diploid) would create a barrier to interbreeding, this barrier may not be total. Otherwise I suspect these plants are a variety or form of S. ramosissima or one of the species with which I am less familiar, such as Salicornia emerici, S. europaea or S. obscura (Glaucous Glasswort). Glassworts are tricky!

Long-spiked Glasswort
Above and below: Salicornia dolichostachya (Long-spiked Glasswort).

Long-spiked Glasswort
Although superficially similar to Salicornia fragilis, the Long-spiked Glasswort has 12-30 fertile segments per terminal spike instead of the 6-15 (occasionally as many as 22) found in S. fragilis. Thus, if a specimen has more than 22 segments in its terminal spike, as in this case, then it can be determined as S. dolichostachya. The terminal spike is also usually tapering slightly in S. dolichostachya.

Long-spiked Glasswort
Above: Salicornia dolichostachya - close-up view of flowers.

Why are Salicornia such a 'taxonomic nightmare'?

In their 2007 paper, A taxonomic nightmare comes true: phylogeny and biogeography of glassworts (Salicornia L. Chenopodiaceae), Kadereit et al. (Taxon 56(4): 1143-1170) report on the difficulties of Glasswort taxonomy and utilise genetic analyses to group related species.  First of all, the reduction in stems, leaves and flowers to a similar cylindrical form reduces the range of characters that can be used to distinguish types. These characters include: the convexity of segments, color, number of flowers, size and shape of central flower and the size and form of the bracts. Characters like anther length have in some cases been questioned. Additionally, Glassworts do not preserve well as herbarium specimens, hampering the analysis of large collections.

Long-spiked Glasswort
Above, from left to right: Salicornia fragilis, S. disarticulata (S. pusilla) and S. dolichostachya.

Part 2: More salt marsh plants

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 water. Oceologia 80: 206-210.


Thanks to Liam Rooney for expert advice on determining glassworts and to Sue Buckingham and The Wild Flower Society, UK, along with the Kent Botanical Recording Group (KBRG) for a guided tour of glassworts in Oare Marshes, Kent.

Article created: 13 Sep 2016

Article updated: 15 Sep 2018
Article updated: 14 Sep 2019 (determinations of glassworts revised)
Article updated: 16 Sep 2019

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.