Amaranths & Pigweeds
What are they?
These are rather uninspiring plants to the casual observer - which probably automatically makes them of interest to the keener botanist! Amaranths are closely related to the goosefoots and the two groups have quite recently been amalgamated into the same family - the Amaranthaceae. These plants have tiny flowers that are packed into tight clusters, the flowers themselves having greenish, bract-like 'petals' that are known as tepals (a word used where the petals and sepals are not clearly differentiated from each other). Each flower also has several bracts known as bracteoles along side it and these bracteoles are often long-pointed and spiny, giving the flowerhead a very bristly look.
Although Amaranths generally tend to be upright while pigweeds tend to be more prostrate, there is no clear distinction between the use of these two names for the Amaranthus species. There is still some disagreement amongst botanists as to the true allocation of species names to some amaranths. Most species originate from South America, but some seem to have originated in cultivation as either hybrids or varieties of existing species and are not known in the wild.
Where are they found?
Amaranths and pigweeds are plants that favour rich soils and they are most often found as weeds of arable field margins (especially beet fields), allotments and the rougher corners of gardens, such as around the compost heap. Although they are rather scattered in distribution, they can be common, even abundant where they occur.
Identification
There are few short cuts with this family and amaranths can be difficult plants to identify. Most species are rather similar in their leaves (though useful features in these are pointed out in the species descriptions below) and the presence or absence of leaf spots is rather variable. Paramount in the identification of these species is the detail of the flowers themselves and care should be taken to note the precise size and shape of the (usually five) tepals of each flower. It is also best to wait to confirm identification once ripe seed has started to be produced, since the way in which the capsule surrounding the seed splits is important, too. Ripe seed can usually be confirmed by rubbing a flower cluster between finger and thumb and seeing if black, shiny seed falls out. Note also whether the capsule tops come away cleanly with a horizontal break like a small lid or whether they remain solid and need a good rub to open them up, at which point they tear roughly and rather randomly.
Species recorded in the UK but not yet noted in East Anglia may be found on a separate page here .
Love-lies-bleeding Amaranthus caudatus
An ornamental species that is unknown in the wild and is thought to have originated from Amaranthus quitensis. Popular as a garden annual and occasionally occurring self-sown among garden waste. Flowers July to October. The flowers are typical of the genus in their structure, but they are bright red in colour and are clustered in long, pendulous spikes.
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Common Amaranth Amaranthus retroflexus
Introduced from South America. Widespread in cultivated ground, especially in lighter, sandy soils. Flowers July to October. An upright species to a metre in height, usually with a tight flowerhead and noticeably hairy leaves. Very similar to Green and Indehiscent Amaranths and best told by the tepals, which are clearly rounded, but with a mucronate tip - in other words, the tip of the petal is rounded, but has a hair-like extension of the mid-vein. The tepals also tend to exceed the length of the central ovary of the flower, causing the stigmas to be somewhat hidden within the centre. The seed capsule splits neatly, horizontally across the centre when the seeds are ripe.
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Green Amaranth Amaranthus hybridus
Introduced from South America. Scattered in cultivated ground, especially in lighter, sandy soils. Flowers July to October. An upright species to a metre in height, usually with a somewhat open flowerhead and noticeably hairy leaves. Very similar to Common and Indehiscent Amaranths and best told by the tepals, which are clearly tapered to points at the tip. The tepals are usually about the same length as the central ovary of the flower, causing the stigmas to be somewhat more obvious within the centre. The seed capsule splits neatly, horizontally across the centre when the seeds are ripe. Despite the name, some populations have distinctly reddish-tinged flower spikes.
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Indehiscent Amaranth Amaranthus bouchonii
(Factoryweed) A plant of uncertain origin, having no known native distribution and perhaps having occurred spontaneously in Europe from Amaranthus powellii. Very common - often abundant in root crops - in Breckland but rare (although possibly increasing) elsewhere. Flowers July to October. An upright species to two metres in height, usually with a somewhat open flowerhead and noticeably hairy leaves. Very similar to Common and Indehiscent Amaranths with tepals that are clearly tapered to points at the tip. The bracteoles surrounding the flowers are particularly long and sharply-pointed. The seed capsule remains as an entire case surrounding the seed. If rubbed, it breaks roughly and doesn't form a neat, horizontal split across the centre.
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Spiny Amaranth Amaranthus spinosus
Introduced from South America. Very rare and not persisting, but recorded once or twice in imported soil and compost component shipments. Flowers July to October. An upright species to a metre in height, usually with a slender flower spike. Easily identified by the paired spines that appear in the leaf axils.
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Slender Amaranth Amaranthus viridis
A species found throughout the Tropics, formerly introduced via various agricultural products but only noted once (in Cambridgeshire) in recent times. Flowers July to September. An upright species to a metre in height (though often much less), typically with a long, slender flower spike. Flowers with 2-3 tepals, which are about as long as the strongly wrinkled fruit (and thus concealing it).
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Perennial Pigweed Amaranthus deflexus
Introduced from South America. Very rare and currently only recorded from south-east Suffolk, but this species is very well established in mainland Europe as an urban weed and may turn up in new places in the future. Flowers July to October. A spreading, procumbent species but young plants can be quite upright initially. Unusual for an Amaranthus in being a perennial species. Quite distinctive in its narrowly diamond-shaped leaves and relatively short, non-spiny flower clusters.
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Purple Pigweed Amaranthus blitum
(Guernsey Pigweed) Introduced from Southern Europe. Very rare in East Anglia and currently only recorded from southeast Suffolk in the 1990s. Flowers July to October. A sprawling species, spreading horizontally but with more or less upright stems. Quite distinct in its leaves which are deeply notched at the tip and have long petioles. The flowers appear in relatively short spikes in the upper leaf axils and at the stem tip. There seems to be nothing particularly purple about this species!
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Prostrate Pigweed Amaranthus blitoides
Introduced from North America. A handful of reports from arable sites around the region and more or less established in a small area of the Suffolk Brecks around Icklingham. Flowers July to October. A prostrate annual that usually hugs the ground but may grow to 30cm in height among taller vegetation. Leaves usually well marked with a pale blotch. Flowers in small clusters in the leaf axils, often red-tinged. Bracteoles shorter than the tepals, with the four to five tepals being unequal in length.
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White Pigweed Amaranthus albus
Introduced from North America. A handful of reports from around the region, perhaps originating from bird seed and occasionally in game strips. Flowers July to October. A well branched, low-growing species to around 60cm in height. Leaves usually with clearly crinkled or undulate margins. Flowers in small clusters in the leaf axils.
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