Chenopodiaceae
Above: Atriplex glabriuscula (Babington's Orache)
The Chenopodiaceae are an unusual and fascinating group of plants, but they are difficult to work with as they can be tricky to identify to species level, compounded by the occasional appearance of hybrids. Many occur along riverbanks, salt marshes and sea shores and may be unfamiliar to those who have not well explored these habitats.
The genus Atriplex (Oraches) includes a number of species that can be tricky to tell apart especially as many of them hybridize occasionally. The flower are monoecious, that is separate male and female flowers occur on the same plant. These flowers are clustered into glomerules, each glomerule containing male and female flowers, in some forms the flowers are densely packed together and distinct glomerules are not so apparent. The flowers are born on spikes (spike: a central axis bearing stalkless flowers) at the end of the main shoot and branch tips. The spikes may be isolated or organized into a panicle (branched inflorescence) depending on species. The male flowers have 5 sepals (or tepals) slightly united to one-another at their bases and 3 or 5 stamens and either fail to produce to a seed or produce an abortive seed oriented perpendicular to the stem. Female flowers have no petals or sepals and no stamens but have a pair of valves (interpreted as bracts or sepals) that enclose the 'seed' (true fruit) parallel to the stem.
Atriplex glabriuscula (Babington's Orache)
Shown above and below, Atriplex glabriuscula is an annual found on sandy, shingly seashores, salt marshes and waste land by the sea in northwestern Europe (including Iceland) and northeastern USA (and introduced in some other parts of the USA). Here it is shown on a shingle beach in the British Isles (southeastern coast). The stem of this plant is generally prostrate or ascending and branched, and striped green and white or green and red.
Atriplex prostrata (Spear-leaved Orache)
Atriplex prostrata (formerly Atriplex hastata; Spear-leaved or Triangular-leaved Orache) is an annual with erect or decumbent stems.
The lower leaves of Atriplex, including Atriplex prostrata, are typically in opposite pairs, but those further along the stem alternate. The leaves are triangular and hastate (shaped like an arrow-head with projecting basal lobes). The flowers of A. prostrata, as in many Atriplex, are monoecious, that is separate male and female flowers occur. The male flowers have 5 sepals/tepals, stamens and produce either no seed or an abortive seed in the horizontal position. The female flowers have no stamens, and no sepals or petals but do have two fleshy lobes, united at their base, enclosing the 'seed' (strictly the fruit proper) as two valves in fruit which are interpreted as bracts or sometimes sepals.
This specimen resembles both Atriplex prostrata and Atriplex patula in some respects, and both these species grow in the same habitats (here on the sandy bank of a river) and both are recorded from this location. There are no records of the two hybridizing so we can rule that out. Note that A. prostrata usually has an erect stem, as here, despite its name although prostrate forms do occur. The leaves of this specimen are not entirely typical for Atriplex prostrata, as in this species usually have leaf bases that are either at right-angles to the leaf stalk or are somewhat cordate (curving inwards near the leaf stalk) and the margins are often clearly and irregular serrated. In A. patula the lower leaves are more diamond shaped, with the base of the leaf gradually tapering into the stalk and are also hastate (spear-head shaped with projecting side-lobes at the base of the leaf blade) with the side lobes clearly projecting forwards and the margins more entire.
Above: leaf of Atriplex prostrata growing at the top of a slat
marsh.
In A. patula the leaf tips and basal lobes are acute (pointed)
whereas in A. prostrata they are more rounded. Examining the
notes of Bob Leaney who carried out an extensive study of Atriplex
species of the British Isles in Norfolk populations (Terminology and
identification in the annual native Atriplex species of the
British isles: part II identification and key, BSBI News 139: Sept 2018)
we notice several clues. The leaf base in A. prostrata can make
an angle between about 170 and 220o (180 degrees meaning the
leaf base is a straight line, i.e. perpendicular to the leaf stalk, and
an angle less than 180o meaning the base tapers - i.e. is
cuneate or 'cone'-shaped) as shown below:
Whereas the leaf bases of A. patula are much more tapered, with angles less than 160 degrees and the leaves are thus more diamond-shaped. The leaves of our specimen is within the range of leaf shapes given for Atriplex prostrata but not for Atriplex patula. Close examination of the valves on the fruit can also help: in Atriplex patula the fruit are also more diamond-shaped, but again there is considerable variation.
A final clue comes from plant coloration: A. patula is reported as having green stems with white stripes whereas red coloration has been reported in A. prostrata, with the stems having white or red stripes and the leaves also sometimes possessing red coloration. Our specimen clearly has red striped on the stem and red margins to the fruit valves. However, I would not be surprised if there are exceptions to this.
Above and below: Atriplex prostrata growing on the edge of a reed bed near to a salt marsh. Notice that the upper leaves, and bracts on the flower spike, may not be hastate.
Above: a more basal leaf on the same plant.
Above: A prostrate form of Atriplex prostrata (I use 'prostrate' in its loose sense, meaning growing parallel to the substrate - there is no rooting at the nodes). this is easily confused with Atriplex gabriuscula at first glance, but in prostrata the fruit valves are fused together only at their base, whilst in gabriuscula they are fused up to the angles of the diamond-shaped valves, i.e. to about half-way.
Above: the fruit of Atriplex generally develops in the vertical position in female flowers (a sterile 'fruit' may develop in male flowers in the horizontal position).
Above:the two valves enclosing the ovary are united only at the base in this species. Not the white mealiness, which is variable, and due to the presence of salt-secreting glands.
Atriplex littoralis (Grass-leaved Orache)
Above: Atriplex littoralis growing with erect forms of Atriplex prostrata.these plants were growing at the top of a salt-marsh along with Suadea maritima (Annual sea-blite) which can be seen in the background below and is another member of the Chenopodiaceae.
The leaf above could be confused with that of Atriplex patula, but the leaves behind confirms this is Atriplex littoralis.
Above: notice the open male flowers with their five tepals (a tepal is a leaf-like petals or sepal and often used when the sepals and petals are morphologically indistinguishable).
Above and below:fruiting female flowers. In Atriplex littoralis these occur in glomerules in spikes that terminate the stem/branch axis and only have leaves at the base. The lower glomerules are well spaced. The fruit all develop in the vertical position in this species. The stems may reach about 120 cm (4 feet) in height.
The stems of Atriplex littoralis are generally erect and branched (branches curve and ascend upwards). The leaves usually alternate, are not hastate, are attenuated at the base. The upper leaves are linear or strap-shaped, the lower leaves have more sinuous or serrated margins. The leaves have short stalks.
Note: the papery whitish-brown projecting structure was one of a pair of insect pupal cases. A number of insects often feed on Atriplex, eating through the valves to reach the nutlet within.
The mealiness of Atriplex littoralis is variable and as in all Atriplex is due to salt-secreting glands.
Above: a more prostrate form of Atriplex littoralis growing on a shingle beach near the sea.
The nutlet of Atriplex is the fruit proper and is covered in a translucent perithecium (fruit wall derived from the ovary wall) which rubs/sloughs off readily to expose the seed, as it has here. Note that the fruit is in a vertical position within the valves.
The seed itself is shiny and smooth. Below: a seed with the perithecium still enclosing it. This can be easily rubbed off to observe the texture of the seed.
Atriplex patula (common Orache)
The chief caharacteristic of Atriplex patula (Common Orache) are the leaves with their clearly cuneate bases where the leaf-blade gradually tapers into the leaf stalk and the pair of basal lobes that project forwards. This species is an annual with an erect or decumbent stem with ascending branches. The flower spikes have male and female flowers in dense leafless spikes which may be arranged in a branched panicle. The lower leaves are in opposite pairs and hastate with entire or serrated margins and forwardly directed side-lobes. The upper leaves are mostly alternate with more entire margins and are more strap-shaped, elliptical or oblong in contour. The stem is striped green and white. This plant is found on cultivated ground, waste places, roadsides and sometimes on sandy seashores. here it is growing near to a path at the top of a shingly/sandy beach near the sea. The two valves enclosing the fruit are united only at the base.