Click to read about the Astragalus genus.

     Astragalus naturitensis, Astragalus deterior (both shown below), Astragalus monumentalis, Astragalus desperatus, and Astragalus nuttallianus are quite similar in many morphological characteristics, are found in very similar habitats, and the first four are found only in, or primarily in, the Four Corners region.

     Descriptions of at least the first four species by expert botanists often do not agree on numerous characteristics of the species and it is, therefore, very difficult to know which species one is looking at.  Take, for example, the confusion in the descriptions of Astragalus naturitensis and Astragalus monumentalis : Weber indicates that the seed pod of A. naturitensis is "essentially straight" and the pod of A. monumentalis is "strongly incurved" ; Welsh indicates that the pod of A. naturitensis is "incurved" and that of A. monumentalis is "straight or curved"; Cronquist indicates that A. naturitensis is "gently incurved" and A. monumentalis is "when relatively short only a trifle incurved, when longer often but not consistently falcately incurved [sickle-like]".

     Using the following four characteristics seems to be best for separating Astragalus naturitensis and Astragalus monumentalis:

1) Leaflets of both species are hairy on the lower side, but A. naturitensis is often also hairy on the upper side.
2) The banner petal of A. naturitensis is light-colored, contrasting with the much darker wing petals.  A. monumentalis' banner and wing petals are of a similar hue.
3) The flowers of A. naturitensis are 11.2-15.5 millimeters long, versus 7-10.5 millimeters for A. monumentalis.
4) The pods of A. naturitensis are compressed along the suture lines; those of A. monumentalis are somewhat cylindrical and triangular in cross-section.
5) The pods of A. naturitensis are one-chambered ("unilocular"); the pods of A. monumentalis are bilocular.

   Astragalus naturitensis and Astragalus desperatus are also very similar.  Compare their seed pods to see the clear difference. 

   Astragalus nuttallianus is similar enough to the other four Astragalus under consideration to cause confusion and warrant careful comparison.  When in flower or seed, A. nuttallianus can fairly easily be separated from the others, as a comparison of the photos on this page and those on the Astragalus nuttallianus page make evident.  When not in flower or seed, the various species are difficult to tell apart but can be best separated by looking at the leaves.  Click to see the leaves. Also note that Astragalus nuttallianus is an annual and all of the others are perennials. A. nuttallianus is also the most widely distributed of these five Astragalus.

   I think the most difficult problem among these five species is distinguishing Astragalus deterior from A. naturitensis. Astragalus deterior, found only in Mesa Verde National Park, is so similar to A. naturitensis that Astragalus expert Rupert Barneby first described it in 1948 as a variety of A. naturitensis.

    Barneby discovered the species near Mesa Verde's Cliff Palace May 21, 1943. Click to see the type specimen of Astragalus naturitensis variety deterior from the California Academy of Sciences herbarium.  Barneby named the plant Astragalus naturitensis variety deterior in 1947, but in 1953 Barneby changed his mind and gave the plant species status. It has since been accepted as a species, and is now a candidate for rare and endangered species classification.

   The descriptions of A. deterior in the few floras that mention it are inconsistent in details.

   Barneby's original description indicates that A. deterior is

"essentially quite similar to A. naturitensis proper, but it is a more delicate plant with subfiliform petioles and peduncles, the stipules are shorter and narrower, the pod is of thinner texture and less heavily reticulate, the calyx is campanulate as opposed to cylindric, and the corolla one half shorter.... [The corolla of A. naturitensis is] conspicuously bicolored, [banner] white... and [wings and keel] purple.... By contrast the petals of var. deterior are all of a drab straw-color [ochroleucous], faintly purple-veined".

Barneby continues with more specific details about A. naturitensis var. deterior:

"Calyx campanulate, 3.5-5 mm long, corolla (ochroleucous) smaller, the banner 10-11 mm, the keel 7-8 mm long; pod chartaceous, delicately reticulate; stipules smaller, 2-4 mm long, 1.5-2 mm wide".

   Since Barneby's 1948 description of Astragalus naturitensis var. deterior other botanists have published descriptions of the plant that modify Barneby's description, but these modifications are not in accord with one another. The following characteristics (listed in order of importance), summarized from Barneby, other botanists, and my experience (often while assisting Mesa Verde botanists), help separate the two species:

1) The most certain way of telling whether you are looking at Astragalus deterior or Astragalus naturitensis is to know your location: if you are in Mesa Verde National Park, your plant is A. deterior. If you are not in Mesa Verde, your plant is A. naturitensis!!

2) Overall, A. deterior is a more delicate plant with smaller leaflets and smaller flowers. Flowers of A. deterior are 9.5-11 mm long: those of A. naturitensis are 13-15.5 mm long.

3) Leaflets of both species are very often folded inward, but
a) the distance between leaflets along the rachis (the internodes) is longer for A. deterior,
b) the terminal single leaflet of A. deterior has a clearly discernible stem joining it to the rachis. A. naturitensis has a minute fraction of a millimeter or no space at all joining it to the rachis,
c) the upper and lower leaflet surfaces of A. deterior are hairy; the lower leaf surface of A. naturitensis is hairy, but the upper surface may be almost devoid of hairs.

4) The calyx of A. deterior is generally campanulate in shape; the calyx of A. naturitensis is cylindrical.

5) Although calyx and flower measurements are omitted for both or one of the two species in various floras, it is generally agreed that the calyx tube of A. deterior is 3-3.5 mm, that of A. naturitensis is 3.5-6.5.

6) The color of the flower of A. deterior can be ochroleucous or it can be the same purple and white as that of A. naturitensis.

7) The pods of A. deterior are papery; those of A. naturitensis are leathery.

8) Welsh indicates that the gynophore is "distinctly developed" (but also indicates that the pod disjoints from "an obscure gynophore up to 1 mm long"). Of A. naturitensis Welsh says that the pod "is sessile on a gynophore up to .8 mm long".

9) The lower stipules of A. deterior are said by some floras to be connate; those of A. naturitensis are separate. Other floras do not agree or do not mentions the stipules. Even if stipule shape were a distinguishing characteristic, it really does not help most of us in identifying the plants, because one needs to tear out a branch of the plant and examine it under a microscope to see the stipules with any degree of clarity (see below).

Astragalus deterior (Cliff Palace Milkvetch)
Fabaceae (Pea Family)

Foothills.  Rim rock, openings. Spring, summer.
Above and left: Mesa Verde National Park, May 19, 2016.

One characteristic that may help separate A. deterior and A. naturitensis is their habit: A. deterior has recumbent leaf and flower stems whereas A. naturitensis has recumbent leaf stems but flower stems are usually erect or slightly reclining. Compare the photographs of A. deterior with the photographs below of A. naturitensis to see these characteristics.

As indicated above, Rupert Barneby named this plant Astragalus naturitensis var. deterior in 1948 and then renamed it A. deterior in 1953. Barneby gave the specific epithet "deterior" to indicate that this taxon was a "deteriorated", i.e., smaller version of A. naturitensis.

Astragalus deterior (Cliff Palace Milkvetch)
Fabaceae (Pea Family)

Foothills.  Rim rock, openings. Spring, summer.
Mesa Verde National Park, May 19, 2016.

The stipules, the triangular appendages that cover the base of leaves, are said in some modern floras to be connate, i.e., joined around the base of the leaf stem, but Barneby makes no such observation. The photograph at left shows the quite small stipules to be separate, not connate. If they were connate, you would see them completely joined and encircling the stem base. One triangular stipule shows plainly in the center of the photograph and if we could turn the plant over we would see another similar separate stipule on the other side of the stem.

Also notice the hairiness of the upper side of the leaflets, whereas almost all leaflets shown below for A. naturitensis have glabrous upper leaf surfaces.

Astragalus naturitensis (Naturita Milkvetch)
Fabaceae (Pea Family)

Semi-desert.  Woodlands, openings.  Spring.
Above: Canyons of the Ancients National Monument, May 10, 2023 and Mesa Verde National Park, May 19, 2016.
Left: Canyons of the Ancients National Monument, April 20, 2007 and April 8 and May 3, 2010.

This is a rare species found just in just a few counties of Colorado, New Mexico, and Utah.  The plant grows in sand islands on rock expanses and in other sandy areas.  Flowers have delicately lavender streaked banners and intensely purple wings.  In shady areas with normal moisture (top photograph at left), it is often sparsely leaved, but in sunny areas following winters of continual moisture, it can be robust to eight inches in diameter.

As the second photograph above indicates, the plant is lightly to moderately to very hairy in stem, leaf, bud, calyx, and fruit. Notice also in the photograph that some little creature loves to snip off the flowers. 

In 1892 Alice Eastwood collected this beautiful plant west of Cortez in McElmo Canyon (perhaps in the very area these photographs were taken 115 years later).  In 1895 Marcus Jones named the plant Astragalus arientinus and then Astragalus stipularis but the names were ruled "nomen nudum", i.e., they were ruled "naked names", not accompanied by proper descriptions of the plant and, therefore, not accepted.  In about 1915, Edwin Payson found the plant near Naturita, Colorado, and properly published a description with the name Astragalus naturitensis.

Semi-desert.  Woodlands, openings.  Spring.
Canyons of the Ancients National Monument, April 20, 2007.

Astragalus naturitensis faded flowers give no indication of past beauty. 

Astragalus naturitensis seed pods are compressed, mottled, short-haired, and straight-to-moderately curved.

Range maps © 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 Astragalus deterior

Range map for Astragalus naturitensis