๐ด๐๐๐๐๐๐กโ๐ข๐ × ๐ก๐ข๐๐๐๐๐๐ ๐๐ (๐ด. ๐๐๐ข๐๐๐ก๐ข๐ × ๐ด. ๐๐๐ก๐๐๐๐๐๐ฅ๐ข๐ ): observation and interpretation of hybrid morphotypes.
Since 2024, I had been noticing unusual amaranth plants in my gardens without paying much attention to them. During the summer of 2025, I decided to investigate them more closely.
These plants turned out to be spontaneous hybrids between Amaranthus cruentus, a cultivated species, and A. retroflexus, a wild species.
These two species share the same ploidy level (2n = 34) and belong to the same evolutionary complex, the so-called “hybridus group”, characterized by strong phylogenetic proximity and both historical and ongoing gene flow.
Amaranthus cruentus:
A cultivated species originating mainly from Mexico and Central America, A. cruentus is derived from the domesticated complex related to A. hybridus and is primarily outcrossing.
This species exhibits considerable phenotypic variability, particularly in leaf coloration, inflorescence color, and growth habit, with either erect or drooping panicles.
In this case, the observed form is an amaranth with red stems and erect, relatively dense red panicles. The foliage displays varying shades of red depending on environmental conditions.
This red coloration is due to the synthesis of betalains, specifically betacyanins, the same class of compounds found in red beet.
Plants exhibit a mesotonic growth habit, with branching axes terminating in panicles.
Amaranthus retroflexus :
Amaranthus retroflexus is a cosmopolitan and highly invasive weed species, likely originating from North America.
It is phylogenetically close to the wild amaranth complex (i.e., A. hybridus sensu lato).
Unlike A. cruentus, it reproduces primarily through self-pollination.
This species, or at least the observed population, displays a basitonic growth habit, with green stems and a red root.
Leaves are lanceolate in shape, and their axils bear both a lateral branch and a small sessile panicle.
Amaranthus × turicensis :
The observed hybrids are highly heterogeneous and show a phenotypic structuring into two distinct groups, with traits biased toward one parent or the other rather than forming a strictly intermediate continuum.
Although backcrossing may contribute to this pattern, it is more likely explained by the direction of the cross.
Indeed, cytoplasmic genomes (chloroplasts and mitochondria), which are maternally inherited, can influence phenotypic traits such as vigor, germination rate, and certain physiological characteristics.
As a result, reciprocal hybrids may display notable phenotypic differences despite having similar nuclear genetic compositions.
Such asymmetry has been reported in several studies on interspecific hybridization within the genus Amaranthus.
The two main phenotypic groups were designated based on the first letter of the species with which they show the closest morphological affinity.
Type C-1 :
Here, on the left: Amaranthus × turicensis type C-1; on the right: A. cruentus.
The C-1 hybrid has green leaves and red panicles that are less dense than those of A. cruentus.
These panicles are borne on green stems. As in A. cruentus, the growth habit is mesotonic, and there are no sessile panicles in the leaf axils. Leaves are green with a slight purple margin.
Type R-1:
The R-1 type is characterized by a finer, greener inflorescence structure, with softer, more flexible spiny bracts.
Growth habit is mesotonic, with red stems similar to those of A. cruentus.
Leaves are variable in shape, often elongated and lanceolate, resembling those of A. cruentus, but sometimes differing from both parental species.
Most individuals produce sessile panicles in the leaf axils, as in A. retroflexus.
The panicles, initially green, developed red pigmentation as temperatures decreased. This coloration first appeared on sun-exposed parts, while shaded areas remained green for a longer period.
Type R-2 :
This phenotype, similar to R-1, is distinguished by its ability to produce red panicles without cold induction.
It was much rarer than R-1: only three individuals were observed, and they themselves showed variation among each other.
Type R-3 :
On the left: A. retroflexus (reference); on the right: R-3, another variant represented by a single individual.
This plant had green stems and elongated, drooping panicles, and remained entirely green even under cold conditions.
Type R-4 :
A particularly unusual and likely the most interesting individual observed!
It displayed a highly branched, irregular growth habit and produced small, isolated green panicles similar to those of R-1.
Its leaves were remarkably thick and completely glabrous, with a slight purple margin.
This foliage is clearly distinct from both parental species and from all other hybrids observed, and may have strong potential as a leafy vegetable.
The progeny of this individual will be investigated during the 2026 growing season.
The R-1 type is characterized by a finer, greener inflorescence structure, with softer, more flexible spiny bracts.
Growth habit is mesotonic, with red stems similar to those of A. cruentus.
Leaves are variable in shape, often elongated and lanceolate, resembling those of A. cruentus, but sometimes differing from both parental species.
Most individuals produce sessile panicles in the leaf axils, as in A. retroflexus.
The panicles, initially green, developed red pigmentation as temperatures decreased. This coloration first appeared on sun-exposed parts, while shaded areas remained green for a longer period.
Type R-2 :
This phenotype, similar to R-1, is distinguished by its ability to produce red panicles without cold induction.
It was much rarer than R-1: only three individuals were observed, and they themselves showed variation among each other.
Type R-3 :
On the left: A. retroflexus (reference); on the right: R-3, another variant represented by a single individual.
This plant had green stems and elongated, drooping panicles, and remained entirely green even under cold conditions.
Type R-4 :
A particularly unusual and likely the most interesting individual observed!
It displayed a highly branched, irregular growth habit and produced small, isolated green panicles similar to those of R-1.
Its leaves were remarkably thick and completely glabrous, with a slight purple margin.
This foliage is clearly distinct from both parental species and from all other hybrids observed, and may have strong potential as a leafy vegetable.
The progeny of this individual will be investigated during the 2026 growing season.
