How Does Our Agave Grow? Reproductive Biology of a Suspected Ancient Arizona Cultivar, Agave murpheyi Gibson

Abstract

More than one species of Agave may have been cultivated by ancient farmers in Arizona. The arguments for this include apparent range extensions, burned Agave parts in archaeological roasting features, archaeological sites with in situ agaves thought to be relics of past human management, and limited molecular evidence. The reproductive biology of a single Agave murpheyi Gibson, one of the suspected cultivated species, is documented here in detail. After nine years of growth in a residential backyard in Tucson, Arizona, a flowering stalk rapidly elongated to 4.73 m (15.5 ft) during both daytime and nighttime hours from January through May. Daily records kept for much of that time revealed the stalk averaged 4.69 cm (1.85 in) of growth per day. Maximum growth spurts correlated with both high daily temperature and mean daily temperature. Lateral branches, eventually totaling twenty-two, began developing during March in the upper portion of the flowering stalk. Over a period of five weeks from late May to late June, these lateral branches flowered with normal-looking flowers, attracted a variety of potential pollinators, but produced no mature fruit. Instead, by the summer monsoon season of July and August, the mother plant had produced 359 miniature agaves or bulbils in these upper side branches. The bulbils appeared to arise from enlargements of tissue in the vicinity of the former flowers. Without releasing on their own, these bulbils became water-stressed and had to be forcibly removed a year later. By this time they were quite variable in fresh weight and size. Once planted, they rehydrated and immediately began to grow. This single plant shares aspects of bulbil production with three Agave murpheyi plants observed by others.