C. Biology:
Plants of A. arizonica have historically been known from a single population located on the North Kaibab Trail. On July 9, 2001 a survey of the North Kaibab Trail population was conducted. Plants grew only on slopes facing south-southeast, receiving direct sun, at varying slopes (0-90%). Plants ranged in height from 10 cm to 1.2 m. About 150 plants were counted on and off the trail between the first tunnel and the first bridge, 8 plants were in bloom with between 1 and 2 flowers per plant. Many stems were broken on plants; broken segments were still attached to plants. Dry sap was black in color while fresh sap was white in color. Plants were growing in and amongst rocks and other plants; no litter was present on the ground under A. arizonica (M. Koopman, pers. obs.).
A second population was located in 2001 as suggested by Kearney et al. (Kearney et al. 1960, McDougal 1973). A survey in June on the South Bright Angel Trail resulted in the discovery of about 36 plants growing just off the trail. About 25% of the plants were blooming, 50% were already in fruit. The sap was clear upon cutting, and turned a milky white as the plant received more air. No off trail work was done (M. Koopman, pers. obs).
Prior to 1993, five plants grew from seeds purposely scattered adjacent to the park's Roaring Springs pump house operator's residence (B. Aiken, pers. comm., 1994). This site is located at 1,389m (4,560 feet) near the junction of Roaring Springs and Bright Angel Canyons within the Cambrian-aged Tapeats Sandstone. An estimated 300 plants were found there in June 1993 (K. Darrow, pers. comm. 1998). The plants did not persist and were absent in 1994. In late March 1998, only three plants were noted, but over 80 plants were found in late July. Differences in the population estimates may be due to landslides, a decline in the seed bank, differences in germination and seedling establishment in the past five years, or other unknown factors. About 80% of the plants were reproductive during late July, 1998. Of these, about 40% had one to four flowers, while another 40% had both capsules and flower buds, but no open flowers. The remaining 20% were non-reproductive seedlings or juveniles.
Traveling off trail to document the species is hazardous. The glaucous blue herbage, similar to Garrya flavescens, and showy, white flowers, make the species visible from a distance. It has been observed that large black bees and a few ants visit the flowers. The flowers have no discernable scent. Plants do not grow in adjacent areas that are stabilized by herbaceous and woody shrub vegetation.
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