Parish’s Glasswort

Parish’s glasswort (Arthrocnemum subterminale) is one of three pickleweed species identified from San Elijo lagoon Ecological Reserve. Parish’s glasswort is not uncommon, but it is similar to pickleweed (Salicornia pacifica), and it may be overlooked.  Parish’s glasswort is a little bit shrubbier than pickleweed, its green color is a little bit more olive, and it is more often found along the upper edges of the marsh.  The distinguishing taxonomic characteristics derive from the minute flowers and seeds, which are very difficult to examine in the field.

All this is further confused by the fact that Parish’s glasswort is sometimes called pickleweed and pickleweed is sometimes known as glasswort.

Description

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Parish’s glasswort (Arthrocnemum subterminale) is closely related to the pickleweeds (Salicornia spp.), which it strongly resembles. All are common members of the salt marsh community. All consist of succulent stems that appear segmented and leafless. All have minute flowers that are largely obscured by the tissue at the joints and are easily overlooked.

In Parish’s glasswort, the succulent stems are erect to ascending, densely branched, forming a small shrub, usually less than 30 inches (85 cm) high. Outer segments are yellow green to olive green; older segments are woody. Paired leaves are reduced to a tiny collar that covers the internode.

Parish’s glasswort generally produces several vegetative segments beyond those that bear flowers, giving rise to the Latin species name, subterminale.

In the flowering segments, two to five bisexual flowers develop at each node, with the stamens maturing before the pistil. There are two stamens per flower. Anthers are pale yellow oblongs, 1-1.5 mm long, held on a filament 1-1.7 mm long. There is one pistil per flower. The style is absent, and the two colorless, linear stigmas are hairy. There is a single, tiny, dark, glabrous seed (which I have yet to find). Parish’s glasswort generally blooms between April and September. ⁷

Classification

Parish’s glasswort is a dicot angiosperm  For many years it was grouped with the other pickleweeds in the genus Salicornia in the goosefoot family, Chenopodiaceae.²   More recently, some taxonomists have moved it into the genus Arthroceras  in the Amaranth family.^41,562

We accept the taxonomy used by Jepson and CalFlora and place Parish’s glasswort in the Arthrocnemum genus in the goosefoot family, Chenopodiaceae.^2,7 Plants in this family are often succulent or scaly; many are salt tolerant. Typical flowers are tiny, greenish and lack petals.^11,34,44

Arthrocnemum is a small genus ⁵⁶² with only one species in the United States.  Taxonomically, Arthrocnemum is separated from Salicornia by the location of the flowers below the end of the spike, and by several morphological differences between the tiny flowers and seeds.²

Ecology ⁵⁶³

Marsh vegetation often occurs in bands and swirls, seemingly responding to the topography.  In San Elijo Lagoon, one often sees  pickleweed (Salicornia pacifica) in the mid-elevation flats, while a narrow band of Parish’s glasswort grows above, often adjacent to the trails. One study in Carpenteria Marsh used transplants and removal of individual plants to determine the physical, chemical and biological factors that result in this recurring pattern.

These experiments showed that the lower boundary of pickleweed is restricted by the plants inability to survive periods of prolonged flooding between lowest tides. On the other hand, the upper boundary of  pickleweed is restricted by its intolerance of high soil salinity, left as the shallow water repeatedly evaporates after high tides. In contrast, Parish’s glasswort has a much higher tolerance for salt and therefore is successful in the high-salt zone above the pickleweed.  However,  transplant  experiments indicate that glasswort is able to thrive in the higher zone of pickleweed if the pickleweed is removed. Thus the sharp  boundary between pickleweed and Parish’s glasswort seems to be caused by species interactions, with pickleweed emerging as the dominant competitor and restricting the glasswort to the highest, most saline areas.

Human Uses ⁵⁶⁴

The common name, glasswort, is applied to several salt marsh plants used for making glass in the 16^th– 18^th  centuries. Wikipedia estimates as many as 30 different species were used, most in the genus Salicornia, and many bearing the common names glasswort and pickleweed.

Glass making requires three substances: formers (silica, originally obtained from sand); fluxes (such as sodium carbonate, that lower the temperature needed to melt the silica) and stabilizers (often lime, that neutralize the flux and strengthen the glass ).

The glassworts and pickleweeds were an important source of flux. These plants sequester salt (sodium carbonate) in their tissues. The plants were burned and the sodium carbonate was leached from the ashes. When the liquid was evaporated, the sodium carbonate, called soda ash was left as a powder.

Modern glass making no longer obtains flux from salt marsh plants. These plants have been replaced with other natural and synthetic sources of fluxes. But the name glasswort lingers on as a reminder of the history.

Interesting Facts

Parish’s glasswort is one of the hosts of the saltmarsh dodder (Cuscuta pacifica), which parasitizes several salt marsh plants during the summer.⁴⁶⁸  Two other species of dodder have been reported from San Elijo; California dodder (Cuscuta californica), that parasitizes species in the sage scrub and Cuscuta salina of alkali marshes.

Saltmarsh dodder is native to our salt marshes and has evolved a long-term balance with its hosts. The dodder is an annual plant and the hosts, such as glasswort, are perennial. Thus, chances are good that a single host plant will be parasitized for a single year only, giving the host a chance to recover during the following year.