Agave palmeri Engelm. (Palmer's agave) is the large, panicle-flowering agave of the Sky Island country in southeastern Arizona, southwestern New Mexico, and adjacent Sonora and Chihuahua. It grows on rocky slopes, bajadas, and oak-grassland edges between 900 m and 2,100 m, and is ecologically important as the principal nectar source for the migratory lesser long-nosed bat (Leptonycteris yerbabuenae) along its spring flight corridor.
Within the genus it sits in the subgenus Agave, group Ditepalae, closely allied to A. chrysantha and A. murpheyi. The group is defined by large paniculate inflorescences, broad glaucous leaves, and a bat-pollination syndrome.
Part of the Complete Agave Guide.
Identification
- Leaves. Lanceolate, 60 cm to 120 cm long and 10 cm to 18 cm wide, glaucous grey-green to blue-green, with a pronounced concave upper surface in mature plants. Margins carry prominent recurved brown teeth 4 mm to 10 mm long, spaced irregularly. The terminal spine is dark brown to black, 3 cm to 5 cm long.
- Rosette. Solitary or sparsely offsetting, 1.2 m to 2 m across at maturity. Many plants remain genuinely solitary and die without pups, which limits clonal propagation from any given specimen.
- Inflorescence. Paniculate, 4 m to 7 m tall, with 8 to 14 lateral branches carrying yellow to greenish-yellow tubular flowers that open at dusk. The nocturnal opening and copious nectar production match the species to its bat pollinators.
Bat-pollinated agaves share a set of floral features, dusk anthesis, copious dilute nectar, musty scent, and sturdy panicle architecture that supports hovering animals, and A. palmeri shows these textbook. At the landscape scale, a population in full bloom is visibly active with bats at twilight in late May and June.
Cultivation
A. palmeri diverges modestly from the pillar defaults:
- Cold tolerance. Good. Survives to about −12 °C to −15 °C when dry, placing it in USDA zone 7b. The Sky Island habitat sees regular winter frost and occasional snow.
- Light and heat. Tolerates and requires full sun. Performance in hot-summer desert climates is excellent; performance in cool maritime climates is mediocre as flowering is rarely triggered.
- Summer dormancy. In extreme summer heat above 40 °C, growth pauses and watering should be reduced rather than increased. This is the inverse of what novice growers often assume.
Container cultivation is workable for the first decade but the eventual rosette size argues for in-ground planting where the climate allows.
Propagation
Seed is the primary route for this species, unusual in the genus. Many individuals are genuinely solitary and never offset, so a single plant yields no clonal material during its life. Seed germinates readily from fresh material at 22 °C to 28 °C on a pumice-based surface. Seedlings are vigorous but take 3 to 5 years to reach identifiable species character and 15 to 25 years to flowering.
Where offsets are produced they propagate as per the pillar. Bulbils do form on the post-flowering scape in some years but yield is erratic compared with A. vilmoriniana or A. murpheyi.
Notes
The ecological significance of A. palmeri has conservation implications for growers. In the US portion of its range, wild collection is restricted and the species is protected as a resource for the endangered lesser long-nosed bat. Nursery-propagated plants are the only legitimate source.
Field identification is sometimes confused with A. chrysantha, a close relative with yellower flowers and a narrower altitudinal range on the Mogollon Rim. Both species hybridise where ranges overlap. If the flowers are strictly yellow without any green tint, the plant is more likely A. chrysantha.
The roasted hearts were a food plant for Apache and Yavapai peoples in the US Southwest, and archaeological roasting pits are common features of ridge-top sites throughout the species range.
See also: Agave parryi, Agave murpheyi, Agave americana.