Eriogonum trichopes and E. inflatum
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| Fig. 1. Left: Eriogonum trichopes, a yellow-green annual that grows primarily in the Badlands. Pix taken by Tom Chester on 8 March 2011 on the West Butte of Borrego Mountain
Right: Eriogonum inflatum, a gray-green perennial that grows primarily outside the Badlands. Note the dead stems from a previous year, as well as the large number of new stems that a perennial can often produce. Pix taken by Dale Noonkester (@dale12) in the Coyote Mountains on 28 December 2022 (see his iNat observation). Click on the pictures for larger versions. | |
Table of Contents
Introduction
Normally, Eriogonum trichopes and E. inflatum are very easy to tell apart at a glance; see Fig. 1.
E. trichopes is an annual with yellow-green leaves and stems, which lives primarily in the Badlands. It is even often recognizable in its dead state by the large number of dead stems populating hillsides in the Badlands.
E. inflatum is a perennial with dark gray-green leaves and stems that primarily lives outside the Badlands, although it can be found in the Badlands as well.
However, E. inflatum readily grows from seed, and often flowers in its first year, appearing as an annual. Worse, new leaves and stems can often be green, so the plant as a whole appears close to those of E. trichopes.
This is such a well-known problem that Reveal comments, in his Flora of North America Eriogonum inflatum treatment:
The "annual" phase of Eriogonum inflatum is distinct from its truly annual relatives. Its flowering stems and inflorescence branches are distinctly grayish, whereas those of the true annuals are green or yellowish green.
However, I and others have had trouble determining rosettes of young plants that have greenish leaves, since it appears that E. inflatum can indeed have green leaves, and that the color of its leaves can vary depending on the illumination. Furthermore, it appears that young stems of E. inflatum can also be green.
Examples:
- A young plant of E. inflatum. with gray-green older leaves, but a dead green newer leaf.
- An older plant of E. inflatum with many dead green newer leaves, amidst many older gray-green leaves, from this observation.
- The same leaves can appear different in color depending on the photograph! Compare the same leaves in the two photographs of this observation, where they appear distinctly greener in the first photograph than in the second photo.
- (add example of leaf in sun with green in part of the leaf)
E. trichopes is also said to be "often glaucous" in the FNA, which imparts a grayish or bluish color to its stem and leaves.
Color variations, especially subtle ones, are often hard to discern by many people, including me.
Carla Hoegen and Fred Melgert noticed that the leaves of E. trichopes are generally flattish, and those of E. inflatum are generally quite wrinkled. This isn't mentioned in the floras, but appears to be a promising characteristic to help distinguish the two species. The difficulties with this characteristic in pix is that the perceived degree of wrinkling depends strongly on the lighting of the leaf, and assigning a given leaf to a category of wrinkling is somewhat subjective.
Since I have been having lots of trouble determining some young rosettes, I decided to go through a number of examples at iNat to assign a leaf color to them, and a stem color if a stem is present, and judge the degree of wrinkling, to see how well those characteristics can be used for determination.
The number of teeth on the involucre is often an excellent distinction between these two species, since E. trichopes usually has four teeth, rarely five, and E. inflatum always has five teeth. So a plant with four teeth is almost certainly E. trichopes, and a plant with five teeth is probably E. inflatum. Unfortunately, the number of teeth is rarely shown in photographs.
Analysis
In order to assign a numerical ranking to the leaf and stem color, as well as the degree of wrinkling, I made a preliminary estimate for those quantities so that I could make a reference image for each character state. Figs. 2 and 3 give those reference images.
| Leaf Flatness | Leaf Color | ||
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| Yellow-green (1) | Green (2) | Gray-green (3) | |
| Wrinkled (3) | 
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| Somewhat Wrinkled (2) |  | ||
| Flattish (1) |   | ||
| Fig. 2. Reference images for leaf color and wrinkling. The number in parentheses is used to score each plant in order to plot the results.
The analysis reported below showed that all examined plants with yellow-green leaves, the color shown in the first column of photos, are those of E. trichopes. That analysis also showed that all examined plants with green and gray-green leaves, the colors shown in the last two columns, are those of E. inflatum. | |||
| Stem Color | |||
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| Yellow-green (1) | Green (2) | Gray-green (3) | Blue-green (4) |
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| Fig. 3. Reference images for stem color. The number in parentheses is used to score each stem color in order to plot the results. Young stems of both species are often reddish, and those are not scored. | |||
Using the reference images in Fig. 2, I scored the most recent iNat images that had a good picture showing the leaves for the leaf color and the leaf flatness. In every observation, I used the darkest leaf to assign a leaf color score, since E. inflatum at least sometimes produces green new leaves, which turn gray-green with age. I assigned the score for the leaf flatness only for mature leaves, since immature leaves are more wrinkled than mature leaves. I occasionally assigned scores halfway between the integer reference scores, and in one case assigned a score of 3.5 for a very wrinkled leaf.
I also measured the leaf length and width for the longest mature leaves I could see in the pix.
The results are shown in Figs. 3 and 4.
Fig. 3. Scores for leaf flatness plotted vs. score for leaf color. See Fig. 2 for the interpretation of the scores. A dithering of a random number between -0.05 and 0.05 was used to separate the points that otherwise would have plotted on top of each other.
There is a very clear separation between the two species in Fig. 3 for leaf color, and a fairly good separation using the leaf flatness.
Fig. 4. Scores for leaf length / width plotted vs. score for leaf color. See Fig. 2 for the interpretation of the leaf color score. A dithering of a random number between -0.05 and 0.05 was used to separate the points that otherwise would have plotted on top of each other.
Fig. 4 shows that the leaves of E. trichopes are often a bit more round than the leaves of E. inflatum, but there is so much overlap between the two species that this is not a very useful separation.
Analysis of stem color to be added later.
Examples of leaves from the two species are shown side by side in Fig. 5, all from plants in Don Rideout's Borrego Springs yard near Christmas Circle. Although in the current version of Fig. 5 the color difference seemed to be pretty clear between the two species for most leaves, it appears that it might be more complicated. Don later posted an observation that seems to have the leaf color of E. inflatum, but the number of involucre lobes of E. trichopes. See the discussion for that species for possible interpretations, which are:
- there is overlap in the color of the leaves of the two species; or
- these non-Badland plants are an undescribed species, with leaves that range from yellow-green to gray-green; or
- these plants are hybrids between E. inflatum and E. trichopes. If so, it possibly might be an ancient stabilized hybrid, which now would be a different species.
More work is needed!
| E. inflatum | E. trichopes | |||
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Older leaf of same plant shown to right | 
Younger leaf of same plant shown to left. This leaf is also partially shown at lower right in the pix to left. | 
Leaf from same plant shown to the right | 
Leaf from same plant shown to the left | |
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Leaf from plant 1 of two plants in same iNat post | 
Leaf from plant 2 of two plants in same iNat post | |
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| Fig. 5. Leaves from plants in Don Rideout's yard. Click on each pix to go to the iNat observation showing each plant. | ||||
I thank Carla Hoegen and Fred Melgert for stimulating this page.