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Copyright 2002 by Creation Research Society. All rights reserved.

The Growth Rate of Muhlenbergia torreyi (Ring Muhly Grass) Colonies in Central Arizona

Van Andel Creation Research Field Study Note

George F. Howe and John R. Meyer

CRSQ Vol 38 No 3 pp 159-161 December 2001

Muhlenbergia torreyi (ring muhly) covers a large area of the Van Andel Creation Research Society property in Chino Valley, AZ. Several features of this fascinating grass have been discussed in a previous publication (Howe, Williams, and Meyer, 1999) such as ring muhly’s possible role in reducing soil erosion, its morphology, its circular growth habit, its ecology, and the position that grass family members in general may have within the creation origins model.

Growth Rate of Rings

That same paper contained the description of a growth rate experiment which was begun on June 23, 1998 in order to measure how rapidly a growing arc of M. torreyi moves across the soil. Rebar pegs were placed so that each peg was touching the front or outer growing edge of eight ring muhly colonies and one colony of the blue grama grass (Bouteloua gracilis). Measurements of colony growth progression were made on September 22, 2000, roughly two years after the stakes were positioned. The distance from the trailing edge of each stake to the new front edge of each colony was measured in the direction of growth. These experimental colonies were separated from each other by an average distance of 1.54 meters (m), with l.0 m being the shortest distance between any two and 3.0 m the longest. All experimental arcs were located on flat terrain that was gently sloping southward with the following coordinates (latitude and longitude): 34o50.82N and 112o27.85W

Table I. Growth distances for eight M. torreyi colonies measured after 2 growing seasons (June 23, 1998 to September 22, 2000).
Colony Number
Compass Direction of Growth
Growth Distance (cm)

Average growth per colony over 2 years = 5.4 cm
Average growth per colony per year = 2.7 cm


Figure 1. Colony number 8 of Muhlenbergia torreyi after two growing seasons. Note how the arc has grown 7 cm in what is a SSW direction (to the left and down), leaving the rebar peg behind. Small white dot to the left of the peg is an artifact.

The direction and amount of growth for each colony was noted: see Table I. The total period of growth for each arc was 2.25 years. Although the experiment thus actually ran a little longer than two years, the average growth of each colony per year (Table I) was calculated by dividing the total average growth by two (instead of 2.25), as will be explained later. Figure 1 is a photograph of one of the eight ring muhly colonies (colony number 8) on September 22, 2000. Figure 3 shows the one Bouteloua colony and its two stakes after two growing seasons. In June, 1998, two stakes were placed on opposite edges of the blue grama grass clump shown in Figure 3. Figures 4 and 5 are photographs of M. torreyi and B. gracilis respectively, showing their inflorescences.

Figure 2. One of the ring muhly colonies photographed in January, 2001. Note how the grass itself is brown, dry, and dormant during winter.


Figure 3. Colony of Bouteloua gracilis (blue grama grass).


Figure 4. Colony of M. torreyi at the end of its growing season (September 2000). Infloresences are seen arising from the plants below.


Figure 5. Colony of B. gracilis at the end of its growing season (September 2000) showing leaves below and infloresences above.


In the future growth of these colonies will be monitored more frequently throughout the year to determine if they undergo one or two growth spurts annually. We believe that there is only one and that it occurs in the spring and summer season. Support for this assumption lies in the fact that M. torreyi and B. gracilis colonies examined in the winter (January 2001; Figure 2) were in a completely dormant (non-green) condition. Repeat measurements made on January 11, 2001, showed no change from the data previously gathered on September 22, 2000. These ring muhly colonies had not expanded between September and January1.

In the years during which this experiment has run the average annual temperatures at the nearby Prescott, AZ. airport were close to the mean for the last 33 years (U.S. Weather Bureau, 2001). The average annual rainfall in 1998 for Chino Valley was 5.18 inches (“) and in 1999 was 10.19" where the 33-year mean is 11.79". It appears that “moisture stress” on these grass colonies was somewhat greater than average. The average lateral spread of 2.7 cm per year (a little more than one inch) may therefore be somewhat low for M. torreyi rings and the same is true for the one colony of B. gracilis studied here; 2.5 cm per year. Undoubtedly the expansion rate for such grass colonies varies from year to year and from site to site, but the growth of one inch per year seen here may be useful in making rough estimates of the age of large muhly rings when it is possible to see entire rings or enough of an arc to calculate the center from which the colony started.

Figure 6. Muhlenberia torreyi rings after a light snowfall, January 2001.


Figure 7. Small, newly-formed clumps of ring muhly (right of pen) bear resemblance to Mammillaria cacti (left of pen) which grow nearby. While we attach no significance to this curious phenomenon, it is one of the visual features that greet those who study vegetation at VACRC.

M. torreyi rings serve as points where snow accumulates and melts, as seen in Figure 6. There is a superficial visual resemblance between the young, mound-like muhly colonies and Mammillaria cacti, which grow near them (Figure 7). In the previous paper (Howe et al., 1999) it was suggested that aspects of God’s creation can be understood by observing Muhlenbergia torreyi and other grasses. The scene of snow melting into the ground as a moisture supply for ring muhly and other wild plants (Figure 6) can also bring the Creator’s providence into focus. In Chapter 38, verses 25–27 God asked Job this probing question:

Who hath divided a watercourse for the overflowing of waters, or a way for the lightning of thunder; to cause it to rain on the earth where no man is; on the wilderness wherein there is no man; to satisfy the desolate and waste ground; and to cause the bud of the tender herb to spring forth?

We will continue to observe the growth rate of this interesting grass and to assess its pattern of expansion at VACRC throughout the course of the year.


We thank the donors to the CRS research fund, interest from which has helped to support portions of this study. We are grateful to the Jay and Betty Van Andel Foundation for contributions which have enabled CRS to build a research center and other facilities which have aided this study. We appreciate the assistance of various people, including Emmett Williams and Eugene Chaffin, in helping us improve the manuscript. We are thankful to Bobbi Blade for computer typing and other aspects of manuscript preparation.


Howe, G.F., E.L. Williams, and J.R. Meyer. 1999. Ring muhly—a grass that grows in circles. Creation Research Society Quarterly 35:193–199.

United States Weather Bureau Database 2001.

1 - Late June 1998 until late September 2000, although actually 2.25 years, would thus have included only two annual growth periods corresponding to spring–summer 1999 and spring–summer 2000.

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