SEARCH AND WILDFLOWER HOME PAGE     BLUE/PURPLE FLOWERS      CONTACT US



   The richly-colored flowers and the abundance of plants, make Dieteria bigelovii and Dieteria canescens very conspicuous in late summer and fall.  In most years both Dieteria species put on magnificent, long-lasting flower displays in foothill fields and along roadsides.  It is not uncommon to find these species alone or in very small patches in the late spring and through the summer. 

The two species are quite similar and difficult to tell apart. Making identification even more difficult are the several varieties of D. bigelovii and the many varieties of D. canescens. Adding the final touch of difficulty, the two species hybridize.

Below we will first take a look at some characteristics of these two species which are generally agreed on by floras of the Four Corners region, and then we will look at how these floras attempt to separate the two species. 

Dieteria bigelovii

Both Dieteria bigelovii and Dieteria canescens have phyllaries in over-lapping rows and often with recurved tips (bending outward and downward). It is generally agreed that the tips of the phyllaries of D. bigelovii are more reflexed, longer, and more glandular hairy than those of D. canescens.

Leaves of both species are variable in shape, length, and the way they are attached to the stem. Generally the leaves of D. bigelovii are longer and wider. In both species leaf margins may be entire or slightly toothed and these teeth often have a minute, buff-colored, spine-like tip. Some leaves on a plant may be ciliate margined, some not. The early formed basal rosette of leaves is usually dead, dried, and inconspicuous by late summer and fall flowering time.

Dieteria bigelovii is usually a bit taller (but both plants can be over two feet tall), less branched, and has fewer flowers than D. canescens

Dieteria bigelovii flowers tend to be deep violet to blue-white; Dieteria canescens tend to be lavender-pink.

Floras for the Four Corners region do not agree on the characteristics that separate the two species.

According to Weber's Colorado Flora, Dieteria bigelovii's phyllaries and peduncles (the common stalk of the flower cluster) are very sticky due to the presence of glandular hairs; Dieteria canescens' phyllaries are not glandular.

Weber indicates that you can also distinguish between the two species by noting the color of the phyllaries: Dieteria bigelovii's phyllaries (left photograph below) are green at the tip and for at least half the length of the phyllary. Dieteria canescens' phyllaries are green only at the tip but the lower three-fourths of the phyllaries is tan/white (often with a very narrow green stripe in the center).  A hand lens will help you observe these characteristics.

The photographs immediately below illustrate Weber's points: the plant of the left (Dieteria bigelovii) has green phyllaries; the plant on the right (Dieteria canescens)has green tips phyllaries. Also notice that in these photographs the tips of D. bigelovii phyllaries are longer and more recurved than those of D. canescens.

Dieteria bigelovii Dieteria canescens

FNA makes no mention of the phyllary coloring in its key or in its complete descriptions of the two species. The FNA key separates the two species as follows

If the plant has phyllaries and peduncles variously hairy (sometimes stipitate-glandular), rarely both prominently stipitate-glandular, it is Dieteria canescens

If the plant has both the phyllaries and peduncles prominently stipitate-glandular it could be either Dieteria bigelovii or Dieteria canescens and to determine which species, one needs to look at the following:

Mid-leaf blades lanceolate to oblanceolate and 5-15 mm wide; or phyllary apices long-acuminate (2–6 mm), or both ....Dieteria bigelovii

Mid-leaf blades linear-lanceolate to linear or linear-oblanceolate (ovate to obovate in var. leucanthemifolia), 1.5–5 mm wide; phyllary apices acute to acuminate (1–3 mm).....Dieteria canescens

In the photograph below of Dieteria bigelovii, you can see the gleaming dots of the sticky, glandular hairs covering the phyllaries, peduncle, and small leaf-like structures.  You can also see small buff-colored sand particles stuck to these hairs.  (About half-way up the stem on the right side, a black ant is feeding on the sticky sweetness. Or is he caught in it?)

Ackerfield's Flora of Colorado and Allred's Flora Neomexicana III use the FNA characteristics.

Stanley Welsh, Utah flora expert, lists and describes D. canescens as a Utah species, but he includes D. bigelovii in what he calls Machaeranthera commixta (Dieteria commixta). He separates the two species with the same characteristics Weber uses.

The Flora of the Four Corners Region steps out on its own and uses two new characteristics:

Distal cauline leaves conspicuously auriculate-clasping or subclasping; involucres 10-15 mm... D. bigelovii

Distal cauline leaves not conspicuously clasping or subclasping; involucres 5-10 mm. 

 

I find that many Dieteria in our area possess a mix of the characteristics mentioned above in the various floras. Hybrids may be quite common.

 

"Dieteria" is Greek for "two" and "year", apparently referring to the biennial nature of some species in this genus  --  or perhaps referring to the not uncommon twice-a-year blooming habit of some plants.

"Machaer" is Greek for "sword" and "anthera" is Greek for "anthers" from "anthos", "flower".  "Machaeranthera" thus refers to the sword shape of the anther tips.

Dieteria bigelovii

Dieteria bigelovii

Dieteria bigelovii
Dieteria bigeloviiSynonym: Machaeranthera bigelovii,  Machaeranthera mucronata. (Bigelow's Tansy Aster)
Asteraceae (Sunflower Family)

Foothills, montane, subalpine.  Disturbed areas, openings.  Spring, summer, fall.
Above: Five Springs Farm, September 16, 2014 and McPhee Campground, September 30, 2014.
Left: Bisti/De-Na-Zin Wilderness, October 8, 2007.

M. bigelovii is common in fields and along trails and roadsides in late summer and fall, sometimes occurring by the thousands in very attractive displays.  The plant begins growing in early summer and often grows to over two feet tall (as in the photograph at left) with a strong, almost woody, central stem.  Leaves are few, short, and slender and often only on the upper part of the stem by flowering time.  It is usually the magenta flowers, seemingly floating, that attract attention.  This species occurs almost exclusively in Colorado, New Mexico, and Arizona.  M. canescens (below) is widespread through all western states.

Dr. John Bigelow was a Professor of Botany who collected in the Pacific Railroad Survey of 1853-1854 in the West.  (More biographical information about Bigelow.)

Dieteria bigelovii

Dieteria bigelovii

Dieteria bigeloviiSynonym: Machaeranthera bigelovii,  Machaeranthera mucronata. (Bigelow's Tansy Aster)
Asteraceae (Sunflower Family)

Foothills, montane, subalpine.  Disturbed areas, openings.  Spring, summer, fall.
Bisti/De-Na-Zin Wilderness, October 8, 2007 &
Hunter Canyon Trail, near Moab, Utah, September 26, 2005.

Dieteria bigelovii
Dieteria bigeloviiSynonym: Machaeranthera bigelovii,  Machaeranthera mucronata. (Bigelow's Tansy Aster)
Asteraceae (Sunflower Family)

Foothills, montane, subalpine.  Disturbed areas, openings.  Spring, summer, fall.
Big Spring Trail, Canyonlands National Park, Utah, September 10, 2005.

 

Dieteria canescens
Dieteria canescens
Dieteria canescens
Dieteria canescens. Synonym: Machaeranthera canescens.  (Gray Tansy Aster)
Asteraceae (Sunflower Family)

Foothills, montane, subalpine.  Disturbed areas, openings.  Spring, summer, fall.
Above: Hawkins Preserve, Cortez, September 2, 2016.
Left: Near Canyons of the Ancients National Monument, August 28, 2005.

Dieteria canescens is a complex species with many variations.  This photo shows a typical plant at full height with numerous flowers.

Thomas Nuttall collected the first specimen of this plant for science on the banks of the Missouri in 1811 and it was first named Aster canescens by Frederick Pursh in 1814.  Nuttall renamed this plant Dieteria canescens in 1840. Asa Gray renamed it Machaeranthera canescens in 1852 and the plant has endured several dozen other name changes since then. From the 2003 publication by Morgan and Hartman, the plant is now again named Dieteria canescens. Let's hear it for Nuttall!

"Canescens" is Latin for "becoming gray", usually appearing so due to the presence of an abundance of hairs.

Dieteria canescens
Dieteria canescens. Synonym: Machaeranthera canescens.  (Gray Tansy Aster)
Asteraceae (Sunflower Family)

Foothills, montane, subalpine.  Disturbed areas, openings.  Spring, summer, fall.
Near Canyons of the Ancients National Monument, August 28, 2005.

 

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

Range map for Dieteria bigelovii

Range map for Dieteria canescens