Oxybasis chenopodioides (syn. Chenopodium chenopodioides) is a species of flowering plant in the family Amaranthaceae known by the common name saltmarsh goosefoot (or low goosefoot in America). It is native to Europe, Asia and parts of Africa, where it grows on bare mud in brackish hollows in coastal grassland, inland salt steppes and salty deserts. It has spread to similar habitats in both North and South America. Its habitat is an uncommon one and is threatened by agricultural improvement in many areas, but overall its populations are stable. This species often grows with, and is easily confused with the closely related red goosefoot.
Description Saltmarsh Goosefoot is an annual herb, up about 30 cm (sometimes as much as 50 cm) tall, but often growing prostrate along the ground. Its roots are short and fibrous, and the whole plant is easily lifted out of the soil. The stem is angular and often branched towards the base, with the branches generally occurring in (subopposite) pairs. The whole plant is glabrous (hairless), albeit sometimes with mealy vesicular hairs on the leaves, and it can be either green or crimson in colour (often both). The leaves are alternate, with a short (ca. 0.8 cm) petiole and no stipules. The leaf blades can be up to 8 cm long by 6 cm wide, but are usually much smaller than this, typically 2–3 cm long. The lamina is quite thick and fleshy, triangular to ovate in outline, and will be either entire (untoothed) or just with a few obscure teeth on the margin.
Flowering occurs from July to September in northern Europe. The inflorescences are technically panicles, with a branched structure and clusters of glomerules (bunches of flowers on very short stalks) but they often look like spikes (sessile flowers on a single stem). The glomerules consist of 10-20 small, red flowers of two types: the terminal ones are bisexual, with 5 tepals, 5 stamens and 2 stigmas; the lateral ones can be bisexual or female with 3-5 tepals and 0-3 stamens. The fruit is an achene which falls while still contained within the perianth.
Taxonomy The original name (basionym) of this species was Blitum chenopodioides, as coined by Linnaeus in his work Mantissa plantarum in 1771. Under the Linnaean system, the genus Blitum was differentiated from Chenopodium by having just one (rather than five) stamens. This strict reliance on flower structure declined with time, however, and it has until recently been known as Chenopodium chenopodioides, the name assigned to it by Paul Aellen in 1933. However, in 2012, an analysis of the relationships of the many species in the Chenopodioideae by Susy Fuentes-Bazan and colleagues resulted in its reassignment to the new genus Oxybasis, along with red goosefoot and some related plants. A large number of other synonyms have been coined over the years, most notably Blitum botryoides (by Solomon Drejer in 1877) and B. crassifolium (by Heinrich Reichenbach in 1832). A full list is given in Plants of the World Online. Several subspecies and varieties have been named over the years but none is currently accepted, although Sell & Murrell recently described var. lengyleianum Aellen as an erect and richly branched plant, while var. degenianum Aellen is a prostrate form. They may be kept separate by self-pollination. Its chromosome number is 2n = 18, but it often exhibits endopolyploidy, where certain somatic cells have more than one set of chromosomes, often as an adaptation to stress. The generic name Oxybasis was coined by Grigorij Karelin and Ivan Kirilov in 1841, while chenopodioides means "like a goosefoot." In England it is known as saltmarsh goosefoot, while Americans call it low goosefoot or buttered goosefoot.
Identification Saltmarsh goosefoot can be very difficult to separate from red goosefoot. Under normal circumstances, saltmarsh goosefoot is a low-growing plant with almost entire leaves, whereas red goosefoot is a much larger, erect plant with very definite leaf lobes and teeth. However, both plants are variable in these regards and sometimes they are almost indistinguishable. Either species can be predominantly red or green in colour. The key difference is that the tepals of the lateral fruits are fused to nearly the tip in saltmarsh goosefoot (i.e. forming an almost complete ball), while those of red goosefoot are only fused half way, allowing more of the seed to be seen. This character should be used when the fruit are mature.
Distribution and status Saltmarsh goosefoot is native to southern Europe, Asia and parts of North Africa, and widely established throughout the Americas. In central to southern Africa it is known from Kenya, Burundi, Namibia and South Africa and it has recently been added to the flora of the Congo from a specimen collected in 1914. It is thought to have been carried to this region by migrating birds, which would make it a native species there, albeit on the edge of its range. In the United States, by contrast, it is usually considered to be a casual, presumably introduced by humans. It has occurred in New York since at least 1894, but it dies out quite quickly. In western North America it is well established in the Rocky Mountains, from British Columbia to California, where it grows in sagebrush desert vegetation, usually on roadsides. Some American publications state that "low goosefoot" is a native of South America, where it has been known since at least 1891, when it was collected at Soriano in Uruguay. It is sometimes considered to be a plant of the coast of Argentina, but there are few records of it there.
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