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   It is widely agreed that the Amaranthus genus is, in the words of the Intermountain Flora authors, "studied by many [but...] poorly understood". Welsh points out in his A Utah Flora that there are commonly misidentified collections in various herbaria and that several species are difficult to separate and do hybridize. Welsh further indicates that, at least in Utah, those specimens labeled S. powellii might be no "more than variations within... [A. retroflexus]". In Manual of the Plants of Colorado, Harrington comes to the same conclusion: "A. powellii... appears to be merely a more glabrous form of... [Amaranthus retroflexus]". However, the Flora of North America, BONAP, Flora Neomexicana III, Intermountain Flora (IMF), and various Colorado floras all accept A. powellii as a distinct species.

The Flora of North America indicates, "Distribution of Amaranthus hybridus in North America needs clarification because the name was misapplied to other species, notably A. powellii... Specimens of A. retroflexusA. powellii, and A. hybridus are frequently interchangeably misidentified.

A. powellii, A. retroflexus, and A. hybridus are all monoecious annuals growing with very similar morphological characteristics in similar habitats and elevations. They have minute, crowded flowers in terminal and axillary spikes dominated by pistillate flowers with scattered staminate flowers.

A. powellii and A. retroflexus are especially difficult to distinguish from one another and there are considerable differences in the characteristics that floras use to distinguish between these two species. Allred's Flora Neomexicana III states the most agreed upon distinguishing characteristics:
Tepals of pistillate flowers obtuse, rounded, or emarginate at the apex.... A. retroflexus
Tepals of pistillate flowers acute or acuminate to aristate at the apex....... A. powellii
Observing these differences in flowers of only a few millimeters is quite difficult and variation in tepal length and shape within any given plant is so wide that the tepal distinction is far, far easier written than observed!

Intermountain Flora indicates that "the cultivated grain amaranths (A. caudatus, A. cruentus, and A. hypochondriacus) resulted from domestication of the wild species A. hybridus, A. powellii, and to a lesser extent A. retroflexus". IMF also indicates that Amaranthus powellii hybridizes with A. hybridus and A. retroflexus and appears to be the wild progenitor of A. hypochondriacus.

The Flora of North America indicates, "Distribution of Amaranthus hybridus in North America needs clarification because the name was misapplied to other species, notably A. powellii, and specimens of A. retroflexusA. powellii, and A. hybridus are frequently interchangeably misidentified."

I have accepted the species shown below as A. powellii on the basis of the smooth, non-glabrous stems, the shape and length of its tepals, bracts, seed pods and seeds and the fact that A. powellii is far more commonly found in Montezuma County, Colorado (where the photographs were taken) than is A. retroflexus.

The Amaranthus genus was named by Linnaeus in 1753. Linnaeus utilized the Greek word "amarantos", "unfading", because of the long-lasting flower color of some members of this genus. The specific epithet, "powellii" is for John Wesley Powell, explorer and Director of the U.S. Geological Survey. (Click for more biographical information about Powell.) 

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Above is the Harvard Herbarium type specimen of Amaranthus powellii grown from seeds that Powell collected. Click it to view collection details and to enlarge the specimen.

Amaranthus powellii

Amaranthus powellii

Amaranthus powellii

Amaranthus powellii (Powell's Amaranth)
Amaranthaceae (Amaranth Family)

Foothills. Openings, disturbed areas. Summer, fall.
Above and left: Near Yellow Jacket Canyon, October 8, 2021.

In the photograph above, dog Pepper is exploring for Northern Pocket Gophers in an extensive patch of 1 1/2 to 3+ foot tall Amaranthus powellii. 

The repeated branching pattern shown at left and immediately below is characteristic of the plants in the area of the photographs, but no floras mention this branching pattern.

Amaranthus powellii was named and described by Sereno Watson in 1875 from plants grown in the Harvard Botanic Garden, and these, Watson indicates, were "from seeds brought from Arizona by Col. [J. W.] Powell" in 1874.

         Amaranthus powellii

Amaranthus powellii

Amaranthus powellii

Amaranthus powellii

Amaranthus powellii (Powell's Amaranth)
Amaranthaceae (Amaranth Family)

Foothills. Openings, disturbed areas. Summer, fall.
Near Yellow Jacket Canyon, October 8, 2021.

Each of the photographs at left and below illustrate a diagnostic characteristic of Amaranthus powellii:

In the top photograph at left, the long, sharply pointed bracts are evident.

The second photograph shows the characteristic leaf shape and the long petiole, which the arrow points to.

The third photograph shows the glabrous stem with red streaks and axillary flower clusters.

The photograph below shows the 1+ mm long shining black seed. The left arrow points to a tepal, the bottom arrow points to a long and pointed bract, and the final arrow points to a dotted line along which the circumscissile pod dehisces (splits opens) exposing the one seed. The tassel-like appendages at the top of the capsule are the remnants of the three styles.

                                 Amaranthus powellii

Range map © John Kartesz,
Floristic Synthesis of North America

State Color Key

Species present in state and native
Species present in state and exotic
Species not present in state

County Color Key

Species present and not rare
Species present and rare
Species extirpated (historic)
Species extinct
Species noxious
Species exotic and present
Native species, but adventive in state
Eradicated
Questionable presence

Amaranthus powellii

Range map for Amaranthus powellii