Height structure and reproductive characteristics of senita, Lophocereus schottii (Cactaceae), in southern Arizona

In Organ Pipe Cactus National Monument, Arizona, height-class distributions of senita (Lophocereus schottii) indicate that recent regeneration has not been widespread. The majority of small plants in six of seven study sites showed evidence of asexual reproduction. Only the lowest elevation site showed extensive recent reproduction from seed. The potential for sexual reproduction of senita populations in the monument during summer 1986 was high. Most plants >2 m bore flowers and fruits, with each mature senita producing >100 fruits on average. A sample of 38 fruits collected had a mean seed content of 203 seeds/fruit, with a mean laboratory germination percentage of 81.6 at 20 to 25°C and a 12-h photoperiod. The absence of small plants in most sites was attributed to high seedling mortality rates, most likely from frequent freeze damage. Most habitats in the monument that senita occupies are alluvial flats that are affected by cold air drainage and likely experience more freezes than surrounding hillsides at slightly higher elevations.